CAPE BIOLOGY
UNIT 1
SPEEDRUN
Water consists of two slightly
positive H atoms covalently
bonded to one slightly negative
O atom. Due to this, it is a
dipole molecule.
Water is electrically neutral.
Water molecules can easily
bond with each other
(cohesion) and can act as an
excellent solvent.
FUNCTIONS OF WATER
- Temperature regulation – due to high
specific heat capacity and ability to
evaporate easily
- Universal solvent – Tiny +ve and –ve
charges easily attract other molecules or
ions
- Allows mass flow – H-bonds produce
cohesion and surface tension
- Reactivity – Used in hydrolysis reactions,
e.g. during digestion
- Assists buffers – Has a neutral pH
Carbohydrates are organic molecules
that contain carbon, hydrogen and
oxygen. They consist of:
Monosaccharides (1 unit): Written as
CH2On -- e.g. C6H12O6 (glucose) or C5H10O5
(ribose)
Disaccharides (2 units), e.g. maltose and
lactose
Polysaccharides (more than 2 units), e.g.
starch, glyocogen, cellulose
Alpha glucose: HOH HOH OHH HOH
Beta glucose: OHH HOH OHH HOH
CONDENSATION REACTIONS (e.g. SUCROSE)
- When many molecules combine, a molecule of water is lost. This
is called a condensation reaction.
- Observe the linkage between alpha-glucose and beta-fructose
to form a sucrose molecule.
The molecule of water
will be lost and the two
molecules will be joined
by the O-molecule, seen
next.
CONDENSATION REACTIONS
(e.g. SUCROSE)
This is called a glycosidic bond,
which occurs between sugars.
• Sucrose is used for transport
instead of glucose because it is
much more complex, more
energy-efficient and not as
reactive as glucose.
• Sugars with disaccharide bonds
are termed ‘non-reducing sugars’.
HCl is needed to break the
glycosidic bond.
POLYSACCHARIDES
Can consist of thousands of sugar monomers and glycosidic linkages. They may
form long chains or compact spirals. They are mostly insoluble and must be
hydrolysed before being absorbed by the digestive system.
The main 3 examples are:
1. Starch
2. Glycogen
3. Cellulose
STARCH
• A high-energy polysaccharide consisting of amylose and amylopectin.
• Amylose forms a chain of many alpha-glucose molecules linked by
alpha 1,4 glycosidic bonds.
• Amylopectin consists of similar 1,4 glycosidic bonds but also branches
linked by alpha 1,6 glycosidic bonds.
GLYCOGEN
• Starch is found in plants. Glycogen is found in animals.
• Glycogen consists of much more branches than amylopectin and is
usually a larger molecule, thus acting as a powerful energy reserve.
CELLULOSE
• Cellulose comprises thousands of beta-glucose molecules linked by beta 1,4
glycosidic bonds. They form a linear structure called a fibre.
• Due to the many H-linkages, their bonds are extremely strong. Cellulose is
insoluble.
• Each alternating beta glucose molecule is inverted 180 degrees.
• The linear chains can be linked and ‘stacked’ by H bonds.
TRIGLYCERIDES
• Triglycerides consists of three fatty acids bonded to a glycerol.
• They are insoluble and are hydrophobic (not water-attracted).
• Contain a –COOH (carboxyl) group that reacts with –OH groups of
glycerol to form an ester bond.
TRIGLYCERIDES
• The diagram above shows the condensation reactions.
• In triglycerides, all the C atoms are bonded to H, which makes
them yield more energy upon breakdown than carbs.
AMINO ACIDS
• Amino acids are monomers of polypeptides and proteins.
• They are used for cellular growth and repair. They also form
molecules such as enzymes and hormones.
They consist of a central C-atom
bonded to:
•
•
•
•
An H atom
An amino group (NH2)
A carboxyl group (-COOH)
A side-chain or residue (“R”
group)
AMINO ACIDS
• There are 20 different
amino acids.
• They are differentiated by
their R-groups. Some are
very simple, e.g. glycine
(with just an H-atom).
• Others are quite complex
with aromatic rings, e.g.
tryptophan.
AMINO ACIDS
(peptide bonds)
• During
condensation
reactions, peptide
bonds form
between the C of
one amino acid
and the N of the
other.
PROTEIN STRUCTURES
Primary
- Sequence of a chain of amino acids
determined by a gene.
Secondary
- Amino acids are linked by weak H
bonds between the H of the amino
group and O in the carboxyl group.
- Alpha helix or beta-pleated sheet.
PROTEIN STRUCTURES
Tertiary
- Multiple linked secondary structures.
Involves multiple bonds: H, ionic,
disulphide, hydrophobic interactions
- 3D shape. May have prosthetic
groups, e.g. haem in haemoglobin
Quaternary
- Multiple secondary and tertiary
structures. In haemoglobin, there are
two alpha- and two beta-chains with
haem groups attached.
FIBROUS AND GLOBULAR PROTEINS
Fibrous proteins
- Are insoluble in water.
- Consist of repeating amino acid
sequences.
- Usually have a structural role.
- E.g. collagen, keratin, elastin
Globular proteins
- Are soluble in water
- Specific shapes and sequences.
- Partake in chemical reactions.
- E.g. Enzymes, insulin, haemoglobin
COLLAGEN
- Is a fibrous protein.
- Used for structural support.
- Found in areas such as
cartilage, bones and tendons.
- Consists of 3 polypeptide chains
that form a triple helix.
- Held together by H bonds.
- Forms cross-links to become
fibres.
FOOD TESTS
Reducing and non-reducing sugar
- Add Benedict’s solution to sample in
water bath.
- Brick-red precipitate forms if sugar is
present. Green in trace amounts.
- For non-reducing sugars, dilute HCl is
needed to break glycosidic bond, before
neutralizing with NaOH.
Starch
- Add iodine solution to sample.
- Blue-black colour in presence of starch.
FOOD TESTS
Proteins
- Add Biuret reagent to sample.
- Purple or lilac colour if protein
present.
Emulsion test for lipids
- Pour ethanol into sample. Lipids
dissolve in ethanol.
- Add water. Hydrophobic lipid
molecules disassociate with solution,
forming a milky white layer at top.
- If cloudy emulsion present, then
lipids are present.
DIFFERENCES BETWEEN LIGHT AND ELECTRON MICROSCOPES
ANIMAL CELLS
-
Cytoplasm – Site of chemical reactions.
Keeps shape.
Mitochondria – site of ATP production
Plasma membrane – regulates entry and exit
of materials.
Nucleus – Stores genetic material and
regulates organelle activity.
Rough ER – Protein synthesis.
Smooth ER – Lipid synthesis.
Golgi body – Receives proteins from ER and
transports them to cell membrane.
Lysosomes – Contains enzymes.
Centrioles – Prduces microtubules to pull
chromosomes to ends of cell during cell
division.
NUCLEUS
• The nucleus contains long molecules of
DNA called chromosomes, made up of
threads called chromatin.
• The nucleus is surrounded by a pair of
membranes known as nuclear envelope.
• The nuclear envelope has tiny openings
called nuclear pores, which allow
movement of ATP and RNA.
• The nucleolus contains ribosomal RNA
or rRNA, which helps with protein
synthesis.
TRY LABELLING THEM YOURSELF!
TRY LABELLING THEM YOURSELF!
TRY LABELLING THEM YOURSELF!
TRY LABELLING THEM YOURSELF!
DIFFERENCES BETWEEN PLANT AND ANIMAL CELLS
PROKARYOTIC CELLS
-
Have no nucleus, but contain a
nucleoid region and plasmids
(circular DNA).
-
Have small, 70S ribosomes.
-
No membrane-bound organelles,
e.g. no mitochondria, chloroplasts,
ER, etc.
-
Small. Usually between 5-10 µm.
-
Have cell walls made of
peptidoglycan, e.g. bacteria.
EUKARYOTIC CELLS
-
Have a nucleus. DNA in long helical
strands connected to histones.
-
Have larger, 80S ribosomes.
-
Plant cells have cellulose cell walls.
-
Larger, as much as 100 µm.
-
Some have flagella, e.g. sperm.
Many prokaryotes also have
flagella, e.g. E. coli bacteria
ENDOSYMBIOTIC THEORY
-
“Endosymbiotic” – One organism
that lives within another organism,
of which at least one organism
benefits.
-
The theory states that mitochondria
and chloroplasts in eukaryotic cells
were once prokaryotes.
-
A large host prokaryote engulfed a
mitochondria-like prokaryote and a
chloroplast-like prokaryote and
gained the ability to
photosynthesise and yield ATP
through respiration.
EVIDENCE FOR ENDOSYMBIOTIC THEORY
Mitochondria and chloroplasts:
1. Have their own circular DNA, like prokaryotes.
2. Have their own ribosomes, similar in size to those in prokaryotes.
3. Are similar in size to many prokaryotes.
4. Divide by binary fission, while eukaryotic cells divide by mitosis.
5. Inner membranes have prokaryotic structure, while outer has eukaryotic structure.
TRANSVERSE SECTION OF A PLANT ROOT
1.
2.
3.
4.
Epidermis – root hairs allow water absorption (large surface area)
Cortex – Move water to the centre of root through cells or cell walls.
Endodermis – Waterproof layer. Contains Casparian strips.
Vascular bundle – Contains xylem and phloem for water and sucrose transport.
TRANSVERSE SECTION OF A PLANT STEM
Cambium – Responsible for secondary growth of stems.
Sclerenchyma (dead) – Used for support.
Collenchyma (alive) – Also support.
PHOSPHOLIPIDS
• Each phospholipid consists of a hydrophilic phosphate head and two
hydrophobic fatty acid tails. They are amphipathic.
• The head is bonded to the tails via a glycerol molecule.
• They form phospholipid bilayers, which form cell membranes.
THE FLUID MOSAIC MODEL
The model shows a double layer of phospholipids, with the hydrophilic phosphate
heads facing outward and hydrophobic fatty acid tails inward. Within this are
intrinsic proteins (span the bilayer) and extrinsic proteins (do not span bilayer).
Think of the model as
“protein icebergs
floating in a sea of
phospholipids”.
THE FLUID MOSAIC MODEL
• Cholesterol is found between phospholipids to maintain fluidity of membrane.
• Glycolipids and glycoproteins on the surface help with cell-to-cell signalling.
• Water and polar molecules cannot diffuse through the phospholipids.
PROTEIN CHANNELS AND CARRIERS
• Protein channels allow facilitated diffusion of larger, polar molecules, e.g.
glucose, RNA.
• Specialized channels called aquaporins transport water.
• Protein carriers bind specific molecules for transmembrane movement, e.g.
ATP.
SIMPLE AND FACILITATED
DIFFUSION
• Diffusion is the net movement of
molecules from regions of higher to
lower concentration. It does not
require ATP.
• Simple diffusion allows molecules
(e.g. gases) to move in and out of
the cell via the phospholipid bilayer.
• Facilitated diffusion requires the use
of transmembrane proteins.
SIMPLE AND FACILITATED
DIFFUSION
• Simple diffusion allows a
directly proportional
relationship between substance
concentration and diffusion
rates.
• Facilitated diffusion requires
the use of protein channels, so
the rate of diffusion plateaus if
all of the channels are ‘in use’.
ACTIVE TRANSPORT
• Active transport moves
molecules against a
concentration gradient, using
ATP.
• An example of this occurring is
when maintaining the balance
K+ ions and Na+ ions in a cell.
The K+ ions are pumped into
the cell by the carrier protein
as it changes shape, and Na+
ions are pumped out.
ENDO- AND EXOCYTOSIS
• Endocytosis moves substances in,
absorbing them, e.g. engulfing pathogens.
• Exocytosis moves substances out, releasing
them from the cell, e.g. removing toxins
from the cell cytosol.
• Both methods of transport are used for
bulk movement of materials. ATP is
required to form vesicles (sacs), which form
from or fuse with the cell membrane.
OSMOSIS AND WATER POTENTIAL
• Think of water potential (ψ) as the pressure
that pushes water molecules across a
membrane.
• Hypotonic – high ψ, low solute conc.
• Hypertonic – low ψ, high solute conc.
• Water potential has a negative value. The
more solute there is, the more negative ψ
becomes. The highest ψ is for pure water,
which is zero.
HYPO- AND HYPERTONIC
• In hypotonic solutions (higher ψ),
water enters cell, causing it to
swell and undergo lysis. Plant
cells do not burst due to their
cell walls.
• In hypertonic solutions (lower
ψ), water exits cell, causing it to
shrivel (plasma membrane
retracts in plant cells).
• In isotonic solutions (same ψ), no
net flow of water occurs.
DETERMINING WATER POTENTIAL
Place potato strips in different molarities of solute. If there is no change in length, there was
no difference in water potential inside and outside of the cell (ψsolution = ψpotato).
ENZYMES
• Biological catalysts made of protein. They
lower activation energy needed for reaction.
• Globular proteins, tertiary structure, 3D
shape.
• Contains specific amino acid chains.
• Contains a cleft called an ‘active site’ that a
substrate would fit into.
• May be anabolic (combine small molecules
to larger).
• Or catabolic, breakdown large molecules
into smaller.
ENZYME MODE OF ACTION
• Enzymes bind substrate molecules to form
an enzyme-substrate complex and convert
them into products.
• The enzyme is unaltered by the end.
• It does this by fitting substrates into specific
active sites (lock and key mechanism).
• Sometimes the enzyme alters its shape
slightly to accommodate substrate. This is
called induced fit.
RATE OF ENZYME REACTION
• A – substrates rapidly bind to available enzyme.
• B – all of the enzymes are currently ‘occupied’, so substrates must now ‘wait’ for
an active site to be free. Rate of product formation decreases.
• C – very few substrate molecules left, so product formation rate is very low. It
plateaus when there is no more substrate left.
INCREASING SUBSTRATE
CONCENTRATION
• Same as before, if there
are limited enzymes, they
become ‘occupied’ with
substrate quickly.
• Reaction rate slows down
as substrates must ‘wait’
for active sites to be free.
• Vm refers to how fast the
enzyme can catalyze the
reaction.
INCREASING ENZYME
CONCENTRATION
• Think of increasing the amount of
enzymes as adding more tellers to
the bank. Customers can now access
multiple tellers and transactions
occur at a greater rate.
• There are more enzymes that are
able to interact with substrate.
• Enzyme concentration increases the
initial rate of reaction in a
proportionate manner.
ENZYME ACTIVITY VS
TEMPERATURE
• Kinetic energy in substrate molecules
allows them to rapidly move and
eventually bind with enzymes.
• Low energy causing slow movement,
making binding less likely. Rate of
reaction initially increases with
temperature.
• Until an optimum temp (40oC) in graph.
• In high temp, the tertiary protein
structure of enzyme breaks down,
H-bonds break and enzyme’s active site
deforms (denaturation).
ENZYME ACTIVITY VS pH
• Think of pH as suppression of H ions. The
lower the pH, the higher the number of
H ions.
• Differences in pH can break ionic bonds,
change the tertiary structure of the
enzyme protein, deform the active site
and cause denaturation.
• On the graph, pepsin has an optimum pH
of 2.5 (acidic) and trypsin’s optimum pH
is about 9 (alkaline).
ENZYME INHIBITORS
• Decrease the rate of an enzyme reaction.
• They prevent or limit the binding of
substrates to active sites of enzymes.
• Inhibitors may be similarly shaped to
substrates and bind to the active site
instead (competitive inhibition).
• They may bind to another attachment site
(allosteric site) and disrupt the shape of the
enzyme (non-competitive inhibition).
COMPETITIVE AND
NON-COMPETITIVE INHIBITION
• Competitive – Inhibitor temporarily binds
to active site, ‘blocking’ substrate from
entering. Usually, a reversible process, so
only slows down product formation.
• Non-competitive – Inhibitor binds to
allosteric site. Can be irreversible if it
permanently alters 3D shape of enzyme
and active site, stopping product formation
altogether.
COMPETITIVE AND
NON-COMPETITIVE INHIBITION
• Competitive – Think of it as someone
taking too long in the toilet,
preventing you from entering. You will
eventually get in there, though.
• Non-competitive – Someone has
destroyed the toilet, preventing
anybody else from using it!
COMPETITIVE AND
NON-COMPETITIVE
INHIBITION
•
No inhibitor – Typical reaction rate.
•
With competitive inhibitor –
Increasing substrate conc. can
combat effects of inhibitor. Still
attains the maximum velocity of
reaction (Vm).
•
With non-competitive inhibitor –
Substrate conc. has no effect.
Maximum rate (Vm) is lower.
Enzymes may be permanently
STRUCTURE OF DNA
• DNA has the shape of a
double helix.
• The strands are anti-parallel.
• Each chain of the helix is
made of nucleotides.
•
-
DNA nucleotides consist of:
Phosphate group
Pentose sugar (deoxyribose)
Nitrogenous base (adenine,
cytosine, guanine, thymine)
DNA BASES
• A and G are purines (2 rings).
• C and T are pyridimines (1 ring)
• Bases form complementary
pairs.
- A binds to T (apple in tree)
- C binds to G (car in garage)
• One strand is marked 3’ to 5’,
while the other is 5’ to 3’.
These refer to the numbered
carbon of the sugar.
SUGAR-PHOSPHATE BACKBONE
• The diagram shows the two strands running in opposite directions (anti-parallel).
• Each nucleotide is bonded via condensation reactions. Phosphates of one
nucleotide bond to the sugar of another. This forms a sugar-phosphate backbone.
• These linkages are called phosphodiester bonds.
DNA REPLICATION
When mitosis (cell division) occurs, DNA replicates to produce two copies, one for
each daughter cell. How does this happen?
1.
DNA helicase ‘unzips’ DNA into
two separate strands by
breaking H bonds.
2.
DNA polymerase pairs free
nucleotides with the ones
attached to the original
strands.
3.
H bonds form, linking the two,
creating two new identical
DNA molecules.
DNA REPLICATION
• Since there is one old strand (the original) and one new strand (the one built
by DNA polymerase), it is called semiconservative replication.
• Very few errors occur during this process. However, if one does occur, it may
result in a mutation or cancer.
DNA and RNA Differences
• DNA is double-stranded
• RNA is single-stranded.
• DNA’s sugar is deoxyribose.
• RNA’s sugar is ribose.
• DNA has thymine (T).
• RNA has uracil (U) instead of thymine.
• DNA is found in the nucleus.
• RNA is found in the nucleus and cytoplasm.
DNA TO PROTEIN
• A gene is a sequence of DNA that codes for a
polypeptide or protein.
• This occurs in the ribosomes in cytoplasm.
• First, the DNA sequence must be ‘transcribed’
onto a messenger RNA (mRNA) strand. This is
because mRNA is mobile and can exit the
nucleus to go to ribosomes.
• The mRNA sequence is read in 3-letter codons
and ‘translated’ into amino acid seqences.
TRANSCRIPTION
• Production of an mRNA molecule with complementary base sequences to a
DNA strand.
• In RNA, thymine (T) is replaced with uracil (U), so A binds with U.
• Example: TAC pairs with AUG. This is a triplet codon.
TRANSCRIPTION
• DNA helicase breaks H bonds,
thus ‘unwinding’ DNA into two
separate strands.
• RNA polymerase allows free
nucleotides to bind to the DNA
strand to build the mRNA
strand, which is in a 5’ to 3’
direction.
• The mRNA elongates as more
nucleotides keep linking. The
mRNA exits the nucleus.
TRANSLATION
• Each triplet codon is linked to a
particular amino acid.
• Transfer RNA (or tRNA) in the
cytoplasm each have a particular
amino acid binded to them.
• The ribosome ‘reads’ the mRNA
sequence and tRNA pairs with the
codon.
Each tRNA has an anticodon that attaches to the codon (e.g. CGC on mRNA will
pair with a GCG on tRNA).
TRANSLATION
• mRNA is read by ribosome.
tRNA anticodons pair with
complementary mRNA
codons.
• An amino acid is deposited.
Peptide bonds form a
polypeptide chain.
• This polypeptide will then
‘fold’ into a 3D shape, a
protein.
DNA AND PHENOTYPE
• DNA determines gene sequence and
thus, amino acid sequence and
proteins.
• Phenotype is the physical expression
of a gene, e.g. skin colour.
• DNA can determine production of
melanin proteins, which contribute to
darker skin colour.
• External factors, such as sunlight, can
stimulate melanin production.
CELL DIVISION
•
-
Mitosis
Daughter cells identical.
1 cell division.
2 daughter cells.
Diploid (2n) chromosome no.
•
-
Meiosis
Daughter cells are varied.
2 cell divisions.
4 daughter cells.
Haploid (n) chromosome no.
IMPORTANCE OF MITOSIS
1.
Asexual reproduction – one parent produces
identical offspring rapidly, e.g. Amoeba, Hydra
2.
Growth – e.g. a zygote’s cells keep dividing to form
an embryo. Or meristems of plants.
3.
Tissue repair – regenerates cells lost due to damage
or age.
4.
Immunity – When a foreign invader enters the body,
lymphocytes multiply to produce antibodies.
STAGES OF MITOSIS
• INTERPHASE
- DNA replication occurs here.
- Nucleolus still intact.
• PROPHASE
- Chromatin condenses to form
chromosomes.
- Nucleolus disappears and nuclear
membrane begins breakdown.
- Microtubules and spindles begin
to form at centrioles.
STAGES OF MITOSIS
•
-
METAPHASE
Nuclear membrane broken down.
Chromosomes align at equator.
Centrioles on polar ends of cell.
• ANAPHASE
- Chromosomes break at
centromeres.
- Sister chromatids move to poles
of cell.
STAGES OF MITOSIS
• TELOPHASE AND CYTOKINESIS
- Chromatids at poles unwind to
form chromatin threads.
- Spindle fibres break down.
- Nuclear membrane and nucleolus
reform.
- Cytoplasm divides and cell splits
in two (cytokinesis). Two identical
daughter cells are formed from
one parent cell.
STAGES OF MITOSIS
• A stained root tip
squash micrograph
of onion (Allium) is
shown.
• Label:
• Interphase,
Prophase,
Metaphase,
Anaphase,
Telophase.
STAGES OF MITOSIS
• A stained root tip
squash micrograph
of onion (Allium) is
shown. .
HOMOLOGOUS CHROMOSOMES
• The figure to the right shows the
visual appearance of all 23 pairs of
human chromosomes.
• The first 22 pairs are similar in shape
and carry the same genes on the
same positions (loci). These are
homologous.
• The 23rd pair are the sex
chromosomes (X or Y). They do not
have the same shape or loci. They
are not homologous.
DIPLOID AND HAPLOID
• Diploid cells have the full set of
chromosomes (46 in humans). These
are usually every cell in the body
(somatic cells) besides gametes.
• Haploid cells have half the number
of chromosomes (23 in humans).
These are found in gametes.
A NOTE ON CHROMOSOMES AND
CHROMATIDS
• When a chromosome is in its duplicated
state, it has 2 chromatids (sister
chromatids) but is still considered 1
chromosome.
• When the chromatids separate (during
anaphase), each unit is still referred to
as a chromosome.
• To make it less confusing, just count
each unit and not each chromatid.
MEIOSIS
• Occurs in organisms that must produce
gametes for sexual reproduction.
• Forms 4 haploid daughter cells that are all
genetically varied. This takes two cell
divisions, named Meiosis I and Meiosis II.
• When the chromosomes align, they pair
up and DNA ‘crosses over’ or mixes.
• These pairs are called bivalents. Where
the loci cross are called chiasmata.
MEIOSIS
MEIOSIS I AND II
Meiosis II’s events are
very similar to Mitosis.
Meiosis I
- Instead of
chromosomes aligning
independently in
equator, they pair up
into bivalents.
- The chromosome
number is halved during
Anaphase I.
MEIOSIS AND GENETIC VARIATION
• CROSSING OVER – During pairing up, they
cross loci at chiasmata and swap DNA.
• INDEPENDENT ASSORTMENT – When
chromosomes pair up, one comes from the
mother and one from the father. These pairs
are independent of each other, resulting in a
massive number of combinations.
• RANDOM FERTILIZATION – Each gamete
contains a random mix of DNA. The gametes
that fuse with each other are up to chance.
ADVANTAGES OF GENETIC VARIATION
• SLOWING DISEASE SPREAD – Each member of
a species can have varying levels of immunity
or adaptation against communicable diseases.
• ADAPTATION TO ENVIRONMENT CHANGES –
Ensures some individuals are able to overcome
selective pressures such as extremes in climate
or temperature and continue the species.
• LIMITING OVERCOMPETITION – Needs for
survival such as diet and habitat would differ,
thus preventing the need to fight for limited
resources. E.g. The Galapagos Island finches.
GENE MUTATIONS
• A mutation is a random error during copying DNA, usually during DNA replication.
There are three main types of gene mutations:
• SUBSTITUTION - A single base is replaced by another.
• DELETION – The loss of a base pair.
• INSERTION – The addition of a base pair.
FRAMESHIFT MUTATIONS
• Deletion and addition are considered frameshift mutations.
• Bases are ‘transcribed’ and ‘translated’ in triplet (3-letter) codons.
• So, after deletion, the first codon TGG changes to GGC. The next codon, which is
supposed to be CAG, would now begin with AG…
• In addition, the first codon TGG changes to ATG.
• This means the ribosomes may build entirely differently polypeptide sequences
based on this error.
SICKLE CELL ANAEMIA
• Sickle cell anaemia is a disease where
red blood cells have a sickle shape
instead of their biconcave shape. This
limits oxygen uptake and flexibility.
They can also create blockages.
• A single base pair has been substituted
for another.
• The incorrect triplet is transcribed onto
the mRNA molecule.
• A different amino acid is formed (VAL
instead of GLU).
• As a result, the haemoglobin protein
structure and function changes.
CHROMOSOME MUTATIONS
• Chromosome mutations are changes in the cell’s chromosome number or
structure. During meiosis, the chromosomes are unevenly pulled apart.
•
•
•
Down syndrome – an extra chromosome (47 chromosomes)
Klinefelter’s syndrome – XXY chromosomes
Turner syndrome – one X chromosome in women
INHERITANCE COMMON TERMS AND DEFINITIONS
• Gene – a nucleotide sequence which determines formation of a protein.
• Allele – A variant of a gene.
• Dominant – describes an allele that will express its trait if a different allele is
present.
• Recessive – describes an allele that will only express its trait if a dominant allele is
absent
• Codominance – Describes alleles that produce a combined effect when expressed
together
• Genotype – A gene combination that will express a trait (e.g. FF, Ff, ff)
• Phenotype – The observable characteristics expressed by a gene.
• Homozygous – A genotype where both alleles are the same (e.g. FF or ff)
• Heterozygous – A genotype where both alleles are different. (e.g. Ff)
MONOHYBRID INHERITANCE
(Punnett Square)
• Using Cystic Fibrosis (CF) as an
example. It is inheritable. Causes the
body to produce large amounts of
thick mucus in the lungs. The mucus
leads to bacterial overgrowth and
infection.
• CF is caused by a faulty allele ‘f’. The
normal allele, ‘F’, is dominant. A
patient suffering from CF will have the
genotype ‘ff’.
• How can two parents who don’t
suffer from CF have a child with CF?
MONOHYBRID INHERITANCE
(Blood Types)
• In inheritance of ABO blood type
alleles, A and B are both codominant.
If together, they will express the blood
type AB.
• The A and B alleles are dominant to
the O alleles (which are recessive).
• How can a Type A father and a Type
B mother have a child with Type O?
SEX-LINKED ALLELES
• The Y chromosome has less available positions (loci) for alleles than the X
chromosome. Some alleles cannot be present on the Y chromosome.
• Haemophilia occurs due to the inheritance of a faulty ‘h’ allele on an X
chromosome.
• Since it cannot be inherited via a Y chromosome, a father cannot pass on a
faulty allele to his son (since his son receives the Y chromosome from him)
SEX-LINKED ALLELES
• How can two parents who do not suffer from haemophilia have a child who
suffers from haemophilia?
DIHYBRID INHERITANCE
• Occurs when TWO alleles are
inherited at the same time.
• Let’s look at traits of peas where:
- Round (R) is dominant to wrinkled (r)
- Yellow (Y) is dominant to green (y).
DIHYBRID INHERITANCE
DIHYBRID INHERITANCE (try one yourself!)
DIHYBRID INHERITANCE (try one yourself!)
EPISTASIS
• Epistasis occurs if one pair of alleles
directly influences the expression of
another pair.
• For example, imagine ‘B’ is black
coat and ‘b’ is brown coat.
• But ‘C’ represents melanin
production and ‘c’ represents albino
(no melanin).
• Every mouse with ‘cc’ (albino)
cannot have a brown or black coat,
despite the ‘B’ or ‘b’ alleles.
EPISTASIS (try it yourself!)
B – Black, b – brown
C – Melanin, c – albino
Write in the genotypes of the
mice in the boxes that match
their colour coats.
Then write the phenotypic
ratio.
EPISTASIS (try it
yourself!)
B – Black, b – brown
C – Melanin, c – albino
Remember: Any mouse with
‘cc’ cannot produce melanin,
so will not have a black or
brown coat.
Phenotypic ratio:
9 black : 3 brown : 4 albino
CHI-SQUARE TESTS
• A chi-square test is a statistical test used to compare observed results with
expected results for significant differences.
• Sometimes external variables such as environmental factors, mutations or
human intervention may be affecting an experiment. The chi-square test is
used to determine if those variables exist.
• To perform a statistical test, a null hypothesis (H0) is set up. It would read as:
There is no significant difference between the observed and expected results.
An alternative hypothesis (H1) would read the opposite:
There is a significant difference between the observed and expected results.
CHI-SQUARE TESTS
CHI-SQUARE TESTS
CHI-SQUARE TESTS
CHI-SQUARE TESTS (example)
•
In the Punnett square to the right, 75% of peas are
round and 25% are wrinkled.
•
Let’s say 7324 plants were observed. Out of that, 5474
had round peas and 1850 had wrinkled. Let’s now
determine what was expected:
Round = 75% x 7324 = 5493
Wrinkled = 25% x 7324 = 1831
CHI-SQUARE TESTS (example)
•
•
•
Next, determine the degrees of freedom (df).
This is easy – just take the no. of phenotypes
and minus one.
In this case, there are 2 phenotypes, so there
is 1 d.f.
Now, determine the ‘p value’. We look at a
critical value of 0.05.
CHI-SQUARE TESTS (example)
•
•
•
•
At 0.05, we can see the p value is 3.84.
We now compare that value (3.84) to the
chi-square value (0.263).
Since our chi-square value is MUCH lower, we
can accept the null hypothesis…
…and conclude that there was no significant
difference between our observed and
expected results.
CHI-SQUARE TESTS (2nd example)
•
•
Try this one yourself! Complete the top row and Chi-square (X2) value.
How many degrees of freedom would be there?
(Remember d.f. = No. of phenotypes – 1)
CHI-SQUARE TESTS (2nd example)
•
•
These are your answers!
There would be 3 degrees of freedom (4 phenotypes – 1).
CHI-SQUARE TESTS (2nd example)
•
•
Now look at the probability table. Remember the chi-square value was 5.8.
With 3 d.f., what is the p value?
CHI-SQUARE TESTS (2nd example)
•
•
We look at the critical value (0.05) column at 3 d.f.
The p value is 7.82. Our Chi-square value is 5.8. Is it a significant difference or not?
CHI-SQUARE TESTS (2nd example)
•
•
Chi square value of 5.8 is less than the critical value of 7.82…
…therefore we accept the null hypothesis! (There is no significant difference between
observed and expected results.
GENETIC ENGINEERING
• Definition: The altering of an
organism’s DNA, either by inserting
DNA from another species or
changing the organism’s genome.
• Altered DNA is called recombinant
DNA. An organism with recombinant
DNA is called a genetically modified
organism, or GMO.
• A common example are GloFish,
which are zebrafish fused with
bioluminescent jellyfish DNA.
GENETIC ENGINEERING – how?
1.
2.
3.
Make copies of the target DNA using an enzyme, reverse transcriptase and
DNA polymerase.
Restriction enzymes are like DNA scissors. They cut similar-shaped lengths of
DNA from both human and the bacteria.
DNA ligase is like DNA glue. It combines both segments of DNA. This is now
recombinant DNA.
4. The recombinant DNA
is then re-inserted into
the bacteria, and the
bacteria will now express
that trait.
GENETIC ENGINEERING – making multiple copies
•
•
•
•
Reverse transcriptase allows mRNA to form DNA (the reverse of ‘transcription’).
It builds one strand of DNA. This DNA copied from mRNA is called cDNA.
DNA polymerase attaches free nucleotides to form the other strand.
This process is called gene isolation.
GENETIC ENGINEERING – cutting the DNA
• As said, restriction enzymes are like DNA scissors.
• Are used by bacteria to ‘cut’ viral DNA out of
them, thus ‘restricting’ the virus from infecting
them.
• They cut specific base sequences of DNA, e.g.
EcoRI cuts a GAATTC sequence (as well as its
complementary DNA).
• These are often asymmetrical and so leave
“sticky ends”, which can easily form H bonds with
complementary base pairs and be rejoined.
GENETIC ENGINEERING –
rejoining the DNA
• DNA ligase is like DNA glue.
• Both segments of cut DNA are
mixed with the ligase enzyme.
• It allows ‘sticky ends’ of cut DNA
to join, linking the
sugar-phosphate backbones of
both cut segments.
• When joined, the DNA is now
called recombinant DNA.
GENETIC ENGINEERING –
inserting the recombinant DNA
• The recombinant DNA plasmids are
mixed in a solution containing
bacterial culture. Some of the
bacteria will take up the plasmid.
• The new DNA (seen in red) is
located in an area where there used
to be a tetracycline-resistant gene.
• We can expose all of the plasmids
to tetracycline. The ones that die
are the ones with that took up the
target DNA.
• By applying the same samples in
plates without tetracycline, these
colonies can be easily identified and
isolated, and the desired product
can be made in a fermenter.
Let’s recap with insulin!
1.
2.
3.
4.
Genes are isolated from human
pancreatic beta cells and E. coli
bacteria using reverse transcriptase.
cDNA is formed.
cDNA is cut with restriction enzymes
to form sticky ends.
DNA ligase rejoins the segments. H
bonds form at sticky ends.
Recombinant DNA is taken up by E.
coli bacteria when mixed. The E. coli
can now produce insulin.
Recombinant bacteria is fermented
with sugar and oxygen. Insulin is
produced.
GENE THERAPY
• Gene therapy is the process of
treating or preventing disease by
altering the genes in a person’s
cells.
• We will use the example of Cystic
Fibrosis treatment, caused by a
defective allele that affects a
protein called CFTR in the lungs.
Because of this, mucus builds up.
• The ‘repaired’ DNA is inserted into
a virus and transported into the
patient.
GENE THERAPY – can it go wrong?
• If the repaired DNA is delivered to
the target cells to fix the CFTR
protein, all is well for now. But…
1.
2.
3.
4.
Viruses may mutate in patient.
They may cause infection in
immunocompromised patients.
The repaired DNA may not be
taken up by enough target cells,
or any at all!
White blood cells may destroy
the viral vector before it reaches
the target cells.
GERMLINE VS. SOMATIC
• Somatic gene therapy targets
certain body cells (such as the
CFTR proteins for CF). It has risks,
but also many advantages. The
altered DNA does not enter the
gametes.
• Germline gene therapy is very
controversial. It allows gametes to
pass on the recombinant DNA.
Therefore, offspring will inherit
this DNA and the entire gene pool
can be altered as a result.
ADVANTAGES and DISADVANTAGES
• Environmental
- Crops can produce their own pesticides.
They can also be made frost-resistant.
- If a GMO species of plant is able to pollinate
with wild plants, it can cause an ecological
and food web imbalance.
- Golden Rice containing beta-carotene for
Vitamin A helps those suffering from night
blindness.
ADVANTAGES and DISADVANTAGES
• Ethical and Social
- Can be seen as playing God.
- The possibility of cloning humans raises
social issues.
- Producing designer babies for cosmetic
desirable traits.
- Production of biological weaponry is
possible, especially if germline gene
therapy technology is used.
ADVANTAGES and DISADVANTAGES
• Medical
- Gene therapy is continuously being
researched and improved to treat
diseases such as CF, SCID and lymphoma.
- CRISPR-Cas9 is a major scientific
breakthrough in gene editing that can
possibly treat even more diseases.
- GMO’s may lead to diseases not yet
known, due to viral mutations and
allergens.
- They may also reduce genetic diversity
over time, giving rise to new diseases.
NATURAL SELECTION
• Natural selection occurs when offspring
that are well-adapted to their
environments can survive and
reproduce.
• They pass on those advantageous traits
to offspring, which can also survive.
A species has a better chance of survival if there is high genetic variation in its
members.
Example: Galapagos finches were able to adapt to many different diets due to their
varied beak size, thus preventing competition with each other.
NATURAL SELECTION
• These finches grouped themselves
together in niches, e.g. thick beaked
seed-eaters, thin-beaked insect-eaters.
• These characteristics were amplified as
they reproduced. Eventually, the groups
differed so much from each other that
their members became new distinct
species.
• This is called speciation.
SPECIES CONCEPTS
• Biological species concept
- Two members of the same species are
able to interbreed and produce fertile
offspring.
- Cannot apply to organisms that
reproduce asexually, e.g. Amoeba
• Phylogenetic species concept
- Organisms can be classified according to
defining traits or morphology.
- Can include all organisms.
- But polymorphism makes it error-prone,
e.g. peacocks and peahens.
DARWIN’S DEDUCTIONS
Observations:
1. Members of a species vary between each other.
2. All organisms produce excess offspring.
3. Population numbers remain fairly constant over long periods of time.
Deductions:
1. If traits can be inherited, organisms pass them on to their offspring.
2. There is a struggle for existence among members of each species.
3. Members that are best adapted to their environment are the ones
most likely to survive, reproduce and pass on their advantageous traits.
ANTIBIOTIC RESISTANCE
• Penicillin is an antibiotic that prevents formation of bacterial cell walls.
• Some bacteria have mutated to produce an enzyme that inactivates penicillin.
They have developed antibiotic resistance.
• These resistant bacteria survive and reproduce, rapidly increasing the
population of penicillin-resistant strains of bacteria.
TYPES OF SELECTION
• There are three types of selection:
1.
2.
3.
Directional selection
Stabilizing selection
Disruptive selection
DIRECTIONAL SELECTION
• One variant that has an extreme
form of the trait is selected over
the average and other extreme.
• Example: Peppered moths
(Biston betularia). Black moths
will survive in dark, sooty
environments by camouflaging.
White and grey moths will be
more visible to predators.
STABILIZING SELECTION
• Only the variant of average form
is selected. The extremes are
selected against.
• Example: Robins that lay eggs in
fours have the highest chance of
survival. Too few means lower
chance of survival. Too many
leads to overcompetition.
DISRUPTIVE SELECTION
• Both extremes of the trait are
selected over the average form.
• Example: Male Chinook salmon
compete to fertilize eggs. Large
fish are competitive fighters
while smaller fish are more
stealthy. The average-sized
salmon has neither advantage.
ISOLATION MECHANISMS
• Isolation mechanisms are barriers that prevent members of a species from
interacting. These barriers can be geographical, behavioural, mechanical,
ecological or temporal.
• When isolation occurs, various groups of the same species may be subjected to
different selective pressures (e.g. predators, harsh climates) and would have to
adapt in different ways.
• No gene flow may occur between the splintered populations.
• These populations change over time and speciation may occur.
ISOLATION MECHANISMS
• Geographical barrier – Two species are
physically separated by a landmass.
• Ecological barrier – Two species live in the
same area but rarely or never meet.
• Behavioural barrier – Two species have
different courtship behaviours and will not
mate.
ISOLATION MECHANISMS
• Mechanical barrier – Two species are
physically incompatible, in terms of size,
genitalia or gametes.
• Temporal barrier – Two species live in the
same area but experience different times of
sexual maturity.
ALLOPATRIC SPECIATION
• Same as geographical isolation.
• Species will form splinter groups due to a
separation by a land mass, such as a mountain or
ocean.
•
The presence of this land mass means that the
groups will not meet and thus, will not mate.
• On either side of the mountain, there may be
different selective pressures, such as different
coloured trees, terrain, predators. Each member
must now adapt to these pressures.
SYMPATRIC SPECIATION
• Occurs when there is no geographical separation.
• Example: A species of fruit fly in North America named R. pomonella usually fed
and laid their eggs on hawthorn berries. However, after apples were introduced
in the 1800’s, some began laying eggs in apples. These populations are becoming
increasingly distinct from each other and will one day undergo speciation.
REPRODUCTION IN FLOWERING PLANTS
• Male gametes are formed within pollen,
found in anthers, in stamens.
• Female gametes are found within embryo
sacs found inside of the ovule, in the ovary.
• Pollination occurs when pollen from an
anther is deposited onto the stigma.
• Fertilization occurs when the male gametes
from the pollen fuse with the female gametes
in the ovule.
MALE PARTS OF FLOWER
• Pollen grains are formed from
microsporangial cells within four
pollen sacs in the anther.
• Fibrous layer – Thickened cellulose
walls.
• Tapetum – Provides nutrition to
developing grains in pollen sac.
• Stomium – Point of dehiscence
(splitting) to release pollen.
• Pollen mother cell – Undergoes
meiosis to form gamete nuclei.
FORMATION OF POLLEN
• Formation of pollen grains occur when a pollen mother cell undergoes meiosis.
• A tetrad of haploid cells called microspores are formed.
• These then undergo mitosis to form two types of nuclei within each.
FORMATION OF POLLEN
• Pollen grains contain:
- Exine – Outer waterproof wall
- Intine – Inner wall with enzymes
- Generative nucleus – Undergoes
mitosis to form two male gamete
nuclei
- Tube nucleus – Forms pollen tube to
deliver gamete nuclei to embryo sac.
FEMALE PARTS OF FLOWER
• Egg cell – Becomes zygote after
fertilization. Haploid cell.
• Funicle – Stalk-like connection between
ovule to ovary.
• Integuments – Develop into seed coat.
• Micropyle – Allows passage of pollen
tube during fertilization.
• Antipodal cells – Nourishes embryo sac.
• Synergids – Directs pollen tube growth
to egg cell.
• Polar nuclei – Becomes endosperm
nucleus after fertilization.
FORMATION OF
EMBRYO SAC
• A diploid megaspore
mother cell undergoes
meiosis to produce a
tetrad of haploid
megaspores.
• Only one is functional.
• This undergoes mitosis
until it forms an embryo
sac of 8 haploid nuclei.
FORMATION OF EMBRYO
SAC
• All of the 8 cells in the embryo
sac are haploid (n).
•
-
There are:
3 antipodal cells
2 synergids
2 polar nuclei
1 egg cell
POLLINATION
• Pollination is the transfer of pollen
from anther to stigma.
• This can be done by insects or
wind.
• Self-pollination occurs within the
same flower or between two
flowers of the same plant.
• Cross-pollination occurs between
two flowers of different plants.
POLLINATION
• Each pollen grain has two nuclei:
generative and tube nucleus.
• Generative nucleus divides by mitosis
to form two haploid male gametes.
• The tube nucleus uses digestive
enzymes to elongate and grow down
the style to the ovary.
• The two male gametes follow the
pollen tube to the embryo sac.
DOUBLE FERTILIZATION
• One male nucleus (n) fuses with the
egg cell (n) to form the zygote (2n). This
will eventually develop into an embryo.
• One male nucleus (n) fuses with the
polar nuclei (2n) to form the
endosperm nucleus (3n).
• This forms the endosperm, which
provides nutrition for the developing
embryo.
POST-FERTILIZATION STRUCTURES
• After fertilization occurs, many changes occur in the flower:
-
Egg cell – becomes a zygote and then an embryo.
Ovary – becomes the fruit.
Ovary wall – becomes the fruit pericarp, storing many sugars.
Ovule – becomes a seed, still attached to parent plant.
Integuments – becomes seed coat.
Endosperm nucleus – becomes endosperm, which nourishes embryo.
Petals – wither and fall off.
EMBRYONIC
DEVELOPMENT
1.
Zygote undergoes mitosis. A
terminal cell forms from a
parent basal cell.
2.
Mitosis continues. A ‘belt’ of
terminal cells form called a
suspensor.
3. The first terminal cell keeps dividing to form a globular embryo. Early
root (radicle) and shoot (plumule) develops, as well as early leaves
(cotyledons).
OUTBREEDING MECHANISMS
• These are characteristics that ensure
cross-fertilization occurs in plants.
• Ensures genetic variation and diversity
of the species. Maintains vigour in
species, and aids in speciation.
• These include:
1. Self-incompatibility and sterility
2. Dioecious plants
3. Protandry and protogyny
4. Heterostyly
OUTBREEDING MECHANISMS
• Self-incompatibility ensures
pollen of the same alleles of a
plant do not germinate.
• Example: S1S2 plant will not allow
pollen grains of S1 and S2 alleles
to sprout pollen tubes. Only those
that are S3 and S4.
• Male sterility ensures pollen
grains are not produced or are not
viable.
OUTBREEDING MECHANISMS
• Dioecious plants – have male and female flowers
on separate plants, making self-pollination
impossible.
• Monoecious means the plant has both male and
female flowers, making self-pollination possible.
• Protandry – Stamens mature before stigmas.
• Protogyny – Stigmas are receptive to pollen
before stamens mature.
OUTBREEDING MECHANISMS
• Heterostyly – The various forms of
the flowers makes it difficult for
self-pollination to occur due to
stigma and anther position.
• It is difficult for pin flowers to
self-pollinate due to the stigmas
being higher than the anthers.
PLANT ASEXUAL REPRODUCTION
• No gametes are produced. No fertilization
occurs and so, there is no genetic variation.
• Can occur via budding or fragmentation.
• Vegetative propagation can be done with
cuttings, e.g. sugarcane.
• Tissue culture can produce large numbers of
clone plants from a single ex-plant tissue in
sterile settings.
ADVANTAGES AND DISADVANTAGES OF ASEXUAL REPRODUCTION
SPERMATOGENESIS
• Occurs in the lumens of the seminiferous
tubules in the testes.
• Large Sertoli cells nourish the cells and
regulate the process.
• Germinal epithelium gives rise to
spermatogonia cells, which then become
primary and secondary spermatocytes
after mitosis and meiosis.
• Spermatids are then formed, which grow
a flagellum to become spermatozoa.
FEMALE REPRODUCTIVE SYSTEM
• A secondary oocyte (not ovum) is released during ovulation from ovaries.
• If fertilization occurs, the zygote is implanted on endometrium.
• The endometrium allows growth of structures that exchange materials
between the foetal and maternal bloodstream during pregnancy.
OOGENESIS
• Before birth, oogonia divide to
form primary oocytes. Meiosis
begins but ‘arrests’.
• At puberty, meiosis continues and
produces a secondary oocyte
(gamete) and a polar body.
Meiosis stops again.
• The polar body is not viable, so it
degenerates.
• Meiosis finishes upon fertilization
to form the ovum and another
polar body, which degenerates.
OOGENESIS
Structures called follicles
are formed within the
ovary, which gradually
mature.
When ovulation occurs,
the follicle ruptures
leaving behind a corpus
luteum, which secretes
progesterone, allowing
the endometrium to
thicken.
COMPARING SPERMATOGENESIS AND OOGENESIS
SPERM CELL STRUCTURE
• Its role is to transport male genetic
material to the female gamete.
• Head – Contains nucleus, and acrosome
loaded with hydrolytic enzymes to digest
a path into female gamete.
• Neck – Contains centrioles that help form
flagellum.
• Body – Contains mitochondria that
provide ATP for motility.
• Flagellum – Comprises microtubules that
allow movement in whip-like motions.
SECONDARY OOCYTE STRUCTURE
• Its role is to accept genetic material from
the sperm cell during fertilization.
• It is significantly larger than spermatozoa.
They are non-motile.
• Its nucleus contains half of the maternal
DNA (the other half is in the polar body).
• Much more cytoplasm than sperm cells.
Has food storage (lipids) and many
mitochondria.
• Its plasma membrane has microvilli,
which assist in attaching incoming sperm.
COMPARING SPERMATOZOA AND SECONDARY OOCYTES
FERTILIZATION OF OOCYTE
• The fusion of male and female gamete
nuclei. Takes place in the oviduct.
• Uterine enzymes digest sperm cell plasma
membranes. Sperm become capacitated,
allowing them to swim faster towards
egg.
• Upon contact with zona pellucida, an
impermeable fertilization membrane
forms, preventing entry of other sperm.
• Meiosis completes in oocyte, forming
ovum and second polar body.
IMPLANTATION
• Zygote divides by mitosis to form a
blastocyst.
• Blastocyst moves from oviduct to
endometrium, where it is implanted.
• Trophoblast cells on blastocyst surface
secrete enzymes to digest a ‘pocket’ in
the endometrium.
• Trophoblast cells undergo mitosis and
specialize into chorionic villi, which
connect foetal and maternal
bloodstreams (the placenta).
PLACENTAL FUNCTIONS
• Gas exchange – Chorionic villi help
oxygen flow from maternal to foetal
blood in intervillous spaces.
• Nutrient and antibody intake – Chorion
facilitates diffusion of glucose and amino
acids.
• Waste transfer – Allantois allows removal
of waste from foetal kidneys.
• Blood pressure regulation – Reduces
maternal blood pressure.
AMNION FUNCTIONS
•
Shock absorber – Protects foetus from
external injury.
•
Temperature regulator – Amniotic fluid
absorbs excess heat, has high specific heat
capacity.
•
Limb development – Movement in fluid
facilitates limb growth and development.
•
Support – Fluid keeps foetus supported
against gravity.
•
Blood barrier – Prevents intermingling of
foetal and maternal blood and pathogens.
HORMONAL REGULATION
• GnRH – Stimulates release of LH and FSH. Secreted by hypothalamus.
PITUITARY HORMONES (Gonadotropins)
• FSH – Stimulates growth of eggs; regulates sperm production.
• LH – Stimulates ovulation; release of gonadal hormones.
GONADAL HORMONES
• Oestrogen – Stimulates LH production; endometrium thickness.
• Progesterone – Maintains endometrium thickness.
• Testosterone – Stimulates sperm production.
• Inhibin – Inhibits release of GnRH, and thus FSH and LH.
GAMETOGENESIS HORMONES
• GnRH released from
hypothalamus. Stimulates
release of FSH and LH.
• LH binds to Leydig cells to
secrete testerone. FSH binds to
Sertoli cells, making them more
receptive to testosterone.
• FSH and testosterone both
inhibit the release of GnRH, FSH
and LH. Prevents testosterone
levels from rising too high.
OOGENESIS HORMONES
• GnRH released from hypothalamus.
Stimulates release of FSH and LH.
• LH and FSH develop ovarian follicle,
stimulating release of oestrogen and
progesterone.
• Oestrogen and progesterone inhibit
GnRH, LH and FSH.
• But when ovulation occurs, they allow
increased secretion of GnRH, FSH and
LH to allow follicle to rupture and
release secondary oocyte.
MENSTRUAL CYCLE
• Follicular phase – FSH and LH
triggers release of oestrogen from
ovarian follicle, causing a surge in LH.
• Ovulation – The LH surge triggers
ovulation, causing secondary oocyte
to be released from follicle. Follicle
becomes a corpus luteum.
• Luteal phase – Corpus luteum
secretes progesterone to maintain
endometrium thickness for
implantation.
OOGENESIS HORMONES
• Menses – If no implantation occurs,
progesterone levels drop and uterine
lining sheds. This drop causes a slight
increase in FSH and LH.
• If a woman does become pregnant,
the endometrium remains thickened.
This is because the blastocyst
secretes hCG, a hormone that
ensures menses does not take place.
• Only pregnant women produce hCG.
BIRTH CONTROL
• Birth control methods prevent pregnancy. They can be:
- Contraception – prevention of fertilization
- Anti-implantation – fertilization occurs, but not implantation of fertilized egg
•
-
Contraceptive methods include:
Barriers, e.g. condoms and diaphragms
Sterilization, e.g. vasectomy or tubal ligation
Oral contraceptives, which suppress ovulation
Depo-Provera injections, which inhibit ovulation.
• Anti-implantation methods include:
- Morning after pill, which changes endometrium to limit implantation.
- IUD’s, which stimulate immune responses to attack sperm.
PRE-NATAL CARE
• These are behaviours that a mother adopts to reduce ill health of foetus.
- Proper diet – Folic acid to prevent spina bifida; iron for formation of
haemoglobin; calcium for bones; avoiding foods that are unpasteurized.
- Avoiding alcohol – May lead to reduced development, cleft palate and foetal
alcohol syndrome (FAS).
- Avoiding smoking – Nicotine constricts foetal blood vessels. Carbon monoxide
and tar limit oxygen intake by build-up of mucus and destroying alveoli.
- Rubella vaccine – Rubella can be fatal to foetuses.
- Monitoring programs – Ultrasound probes monitor foetal heat rate and organ
development.