Atoms
• Chemistry will help you learn
about biology because
organisms are chemical
machines!
• Atom: smallest unit of matter
that cannot be broken down
by chemical means. Made of:
– Protons: positive, in nucleus
– Neutrons: neutral, in nucleus
– Electrons: negative, in electron
cloud
Elements and Chemical Bonding
• Atoms can join with other atoms to
form sable substances. The force that
joins atoms is a chemical bond.
• Element: a pure substance made of
only one type of atom
– Differ in the number of protons in the
nucleus
• Compound: a substance made of the
joined atoms of two or more different
elements in known proportions
– Represented by chemical formulas
Atomic Bonds
• Covalent Bonds: form when two or more
atoms share electrons to form a molecule
• Molecule: A group of atoms held together
by covalent bonds
• Hydrogen Bonds: Bonds based on polarity
of molecules which causes chemical
attraction.
– Bonds with an unequal distribution of
electrical charge are called polar
molecules.
– Water molecules are polar and often
forms hydrogen bonds
– The different charges in each molecule
makes the molecules attract each other.
• Sometimes atoms or molecules gain or lose
electrons.
– Ion: An atom/molecule that has gained
or lost an electron
• Ionic Bonds: a bond formed when ions of
opposite charges are attracted
– Found in table salt (Sodium Chloride,
NaCl)
Dehydration Synthesis and
Hydrolysis
• Dehydration Synthesis: A
chemical reaction that builds
up molecules by losing water
molecules.
• Hydrolysis: The process of
splitting a compound into
fragments with the addition
of water; a kind of reaction
that is used to break down
polymers into simpler units,
e.g. starch into glucose.
• So, Dehydration Synthesis LOSES
water, while Hydrolysis ADDS water!
http://bioweb.wku.edu/courses/biol115/
wyatt/biochem/macromolecules.htm
http://en.wikipedia.org/wiki/Hydrolysis
Information From:
http://www.biology-online.org/dictionary
Polarity
• The polarity of water enables many substances to
dissolve in water.
• Ionic compounds and polar molecules dissolve best
in water, because they are charged like the water.
• When ionic compounds are dissolved in water, the
ions become surrounded by polar water molecules.
Acids and Bases
• While the bonds in water molecules are strong,
sometimes these bonds break, forming a hydrogen ion
(H+) and a hydroxide ion (OH-).
H2O  H+ + OH• Acids: compounds that form hydrogen ions when
dissolved in water
• Bases: compounds that reduce the concentration of
hydrogen ions in a solution
Carbohydrates
• Organic compounds made of carbon, hydrogen and oxygen
atoms in the proportion of 1:2:1
• Carbohydrates are basically made of carbon and water!
• Carbohydrates are built from single sugars called
monosaccharides
• Polysaccharides are chains or three or more
monosaccharides.
• Polysaccharides are macromolecules
Lipids
•Lipids are nonpolar
molecules that are not soluble
or are mostly insoluble in
water
•Include fats,
phospholipids, steroids,
and waxes.
•Important in cell membranes
•Fats store energy
Proteins
• A large molecule formed by
linked smaller molecules called
amino acids
• Amino acids are the building
blocks or proteins.
• 20 different amino acids are
found in proteins
• Some proteins are enzymes and
promote chemical reactions
Nucleic Acids
• All of your cells contain nucleic acids
– DNA and RNA are two common nucleic acids
• Nucleic acids are long chains of smaller molecules called
nucleotides
• A nucleotide as three parts: a sugar, a base, and a phosphate
group
ATP
• ATP Stands for Adenosine triphosphate
• A single nucleotide with two extra energy storing
phosphate groups
• Cells need a steady supply of ATP to function
http://biochemisms.com/tag/atp/
Activation Energy
• Activation energy: the energy needed to start a chemical reaction
– Example: a big rock rolling down the hill—to make it roll, you must first
push it. The activation energy is a “push” for chemical reactions!
• Enzymes are substances (mostly proteins) that increase the speed
of chemical reactions (catalysts)
• Most biochemical reactions (reactions that occur in cells) require
activation energy to begin.
• Chemical reactions can occur quickly and at the low temperature
of our body because of enzymes.
• Enzymes: substances that increase the speed of chemical
reactions. Most enzymes are proteins.
• Enzymes help organisms maintain homeostasis.
Enzyme Specificity
• Substrate: a substance on which an enzyme acts
during a chemical reaction.
– Enzymes act ONLY on specific substrates.
– For example, amylase, an enzyme in your saliva, assists
in the breakdown of starch to glucose in your food.
• An enzyme’s activity is determined by the shape of
the enzyme.
Protein Function
• The function of a protein depends
on its confirmation which forms
due to R groups and bonding.
• R groups have different
properties, some are polar, some
are non-polar. This causes
particular bonds to form between
R groups and makes the protein
shape in a particular way. When a
protein is heated, these bonds
between R groups can break,
causing the protein to denature.
• Enzymes are proteins and can
also break down in this way.
When enzymes denature, they do
not speed up reactions properly!
• Before your body can use the
nutrients in food you eat, the
large food molecules must be
broken down.
• Digestion: the process of
breaking down food into
molecules the body can use.
• Digestion of food begins in
your mouth.
• Teeth rip and chew food and
mix food in with saliva.
• Saliva contains amylases.
• Amylases: enzymes that begin
•
the breakdown of
carbohydrates such as starch,
into monosaccharides (single
sugars).
•
• Food then passes through the
pharynx into the esophagus.
Breaking Down Food
Esophagus: a long tube that connects
the mouth to the stomach.
– No digestion takes place in the esophagus.
Food is moved through the esophagus
through peristalsis.
– Peristalsis: successive rhythmic waves of
smooth muscle contractions in the esophagus
that moves the food toward the stomach.
The Stomach
• The stomach is a saclike
organ that stores food
temporarily and mechanically
breaking down food and
chemically breaking down
proteins.
• When food enters the
stomach, it secretes gastric
juice, a mixture of
hydrochloric acid and pepsin.
– Pepsin: a digestive enzyme that
breaks protein strands into
chains of amino acids.
•
•
•
•
•
•
•
The Intestines
Food passes into the small intestine is where carbohydrates are
broken down into monosaccharides, proteins into amino acids,
and lipids into fatty acids and glycerol.
Fats are digested by pancreatic enzymes called lipases, but are
first treated with bile which emulsifies the fats (turns them into
little drops).
Absorption of nutrients occurs in the small intestine through the
lining of the small intestine on projections called villi.
Components of food that are not for energy production are
considered wastes.
Wastes move into the large intestine, also called the Colon.
No digestion takes place in the colon.
Most of colon’s contents are dead cells, mucus, digestive
secretions, bacteria, and yeast.
Balancing water absorption is an important function of the
colon.
The Liver’s Role in Digestion and Metabolism
• The liver plays several roles in human digestion and metabolism.
• The Liver’s Role in Digestion
– Secretes bile, which aids in the emulsification of fat and promotes the
absorption of fatty acids and fat soluble vitamins A, D, E, and K.
• The Liver’s Role in Metabolism
– The liver stabilizes blood sugar by converting extra sugar to glycogen for
storage. The liver then breaks down the glycogen when needed.
– The liver also modifies amino acids.
– Fat-soluble vitamins and iron are stored in the liver.
– The liver monitors the production of cholesterol and detoxifies poisons.
If the liver cannot make something non-toxic, it stores it.
Cell Size
• Small cells function more efficiently than large cells.
• This is because they have a high surface area to volume
ratio.
• We have lots of small cells so that all the substances
that leave and enter cells have a large surface area to
do it. If the surface area-to-volume ratio is too low,
substances do not have enough space to move across.
Common Cell Features
• Cell Membrane: outer boundary of the cell,
regulates what enters and leaves a cell
• Cytoplasm: the cell interior, which contains many
structures
• Cytoskeleton: a system of microscopic fibers that
suspend structures inside the cell
• Ribosomes: cellular structures on which proteins
are made
• Additionally, all cells contain DNA (unless they lose
their DNA later).
Characteristics of Prokaryotes
• Prokaryote: the smallest and simplest cells, single-celled organisms that lack a
nucleus and other internal compartments (organelles).
– Because they have no organelles, they cannot carry out many specialized
functions.
• The familiar prokaryotes that cause infection belong to a type of prokaryotes
called bacteria.
• Exist in a broad range of environmental conditions.
• A prokaryote’s enzymes and ribosomes are free to move around in the
cytoplasm because there are no internal compartments.
• Prokaryotes have a cell wall surrounding the membrane for structure and
support.
– Prokaryotes lack a strong internal support system.
– Prokaryotes have a cell wall made of polysaccharides connected to amino
acids.
– Some cell walls are surrounded by a capsule which allows prokaryotes to
stick to things!
• Many prokaryotes also have flagella—long, threadlike structures for
movement.
Eukaryotic Cells
• Eukaryotes: an organism with a cell nucleus
– Some eukaryote cells use flagella, others have hairlike cilia for
movement.
• Nucleus: an internal compartment that houses the cell’s DNA.
• Organelles: an internal compartment that carries out specific
activities in the cell.
– A complex system of internal membranes connects some organelles
inside the cytoplasm.
The Cell Membrane
• The inside of the cell (cytoplasm) is contained by the cell membrane.
• The cell membrane is fluid and selectively permeable, allowing only certain
substances in the environment to pass through.
• The selective permeability of the membrane is caused by the way
phospholipids interact with water.
– A phospholipid has a polar “head” and two nonpolar “tails”
• Lipid Bilayer: the arrangement of phospholipids in the cell membrane.
Nonpolar tails make up the interior of the bilayer because water in and out
of the cell repels the nonpolar tails.
– Ions and most polar molecules are repelled. Lipids are allowed to pass through.
Membrane Proteins
• Various proteins are located in the lipid bilayer.
• Proteins are made of amino acids. Some amino acids are polar,
others are nonpolar.
– The nonpolar part of a membrane protein is attracted to the interior of
the lipid bilayer but repelled by the water on either side. This holds the
protein in place.
• Membranes contain different proteins.
–
–
–
–
Marker Proteins: attached to a carbohydrate advertise cell type.
Receptor Proteins: bind signal molecules outside the cell.
Enzymes: involved in biochemical reactions in the cell.
Transport: aid in the movement of substances into and out of the cell.
The Nucleus, ribosomes, and the ER
• Controls most functions of the cell.
• Surrounded by a double membrane known as the nuclear envelope, made
of two lipid bilayers.
• Nuclear pores, small channels, are scattered over the surface of the nuclear
envelope so substances made in the nucleus can move into the cytoplasm.
• The hereditary information of a cell is coded in the DNA, which is stored in
the nucleus.
• Eukaryotic cells have a system of internal membranes that play a role in the
processing of proteins.
• Cells make proteins on ribosomes. Each ribosomes is made of proteins and
RNA. Some ribosomes are found “free” in the cytoplasm (cytosol) while
others are on the surface of the endoplasmic reticulum.
Production of Proteins
• Proteins that are exported from the cell are made on ribosomes on
the surface of the endoplasmic reticulum.
– Endoplasmic Reticulum: a system of internal membranes that move
proteins and other substances through the cell. Made of a lipid bilayer.
• The ER with ribosomes is called rough ER.
– The rough ER helps transport the proteins made by the ribosomes.
– Each protein crosses the membrane and enters the ER. The portion of
the ER with the protein pinches off to form a vesicle.
• Vesicle: a small, membrane-bound sac that transports substances in cells.
• The rest of the ER with no ribosomes is the smooth ER.
– Makes lipids and breaks down toxic substances.
Mitochondria
• Mitochondria: an organelle that harvests energy from organic
compounds (biomolecules) such as such as to make ATP.
• Cells like muscle cells that use a lot of energy can have thousands
of mitochondria.
• The outer membrane is smooth, the inner membrane is folded.
These membranes are where the chemical reactions take place.
• Mitochondrial DNA: independent of nuclear DNA, similar to
bacterial DNA
Plant Cells
• Plant cells have there
additional structures not found
in animal cells.
1. Cell Wall: a thick wall of
proteins and carbohydrates
including cellulose. Supports
and maintains cell shape.
2. Chloroplasts: Organelles that
use light energy to make
sugar. Have DNA like
mitochondria.
3. Central Vacuole: a large
membrane-bound space that
stores water and helps to
make the cell rigid so plants
can stand upright.
Bacteria: A Prokaryote
Bacteria Differ from Eukaryotes in at least seven ways:
1. Internal Compartmentalization
2. Cell Size
3. Multicellularity
4. Chromosomes
5. Reproduction
6. Flagella
7. Metabolic Diversity
Bacterial Cell Shapes
• Cell Walls: Eubacteria have two types of cell walls,
distinguished by a dye called Gram stain (Gram
negative, Gram positive). This is important because it
helps determine the type of antibiotics needed to fight
the bacteria.
• Endospores: Some bacteria form thick-walled
endospores around their chromosomes with a bit of
cytoplasm when the bacteria are exposed to harsh
conditions. This allows the bacteria to remain dormant
and survive the environmental stress.
• Pili: Allow bacteria to adhere to the surface of sources
of nutrition. Also allow bacteria to connect and
exchange genetic material.
– Conjugation: a process in which two organisms exchange
genetic material. In prokaryotes, pili from on bacterium
connects to a second and genetic material is exchanged.
Diffusion and Random Motion and Concentration
• Your body responds constantly to external conditions to maintain a
stable internal environment.
• Homeostasis: the maintenance of constant internal conditions in
spite of changing external conditions.
– Homeostasis can be conducted in many ways including moving
substances across the cell membrane with or without energy from
the cell.
• Passive Transport: Movement across the cell membrane that does not require
energy.
• Concentration Gradient: a difference in the concentration of a substance across a
space
• Equilibrium: a condition in which the concentration of a substance is equal through
Movement of Substances
• Particles of substances of a solution move around randomly.
• Concentration gradients cause substances to move from an
area of high concentration to an area of low concentration.
• Diffusion: the movement of a substances from an area of
high concentration to an area of lower concentration caused
by the random motion of particles
• The cell membrane is selectively permeable to substances;
the nonpolar interior of the lipid bilayer repels ions and most
polar molecules.
– Many substances such as molecules and ions enter or leave the
cells by diffusing across the membrane.
– Concentrations are different inside the cell than they are outside,
so substances move “down” the concentration gradient (high to
low!).
• Diffusion Video
Osmosis
• Osmosis: the diffusion of water
through a selectively permeable
membrane
• Because water molecules are so
small, they can diffuse through the
membrane even though they are
polar.
– Osmosis is caused because some water
molecules are attracted to ions on one
side or the other of the membrane. If
the different sides of the cell has
different concentrations of dissolved
particles, they will have different
concentrations of “free” water.
Osmosis occurs as free water moves
into the solution with the lower
concentration of free water.
•
Hypertonic,
Hypotonic,
Isotonic
Three directions water can move in a cell:
1. Water moves out: hypertonic solutions cause a cell to shrink; the
solution outside has a higher concentration of dissolved particles
than cytosol.
2. Water moves in: hypotonic solutions cause a cell to swell; the
solution outside has a lower concentration of dissolved particles
than cytosol. Could cause a cell to burst.
3. No net water movement: isotonic solutions cause no change in cell
volumes; the cytosol and outside solution have the same
concentration of free water molecules.
Movement Against a Concentration
Gradient
• Facilitated diffusion can only transport substances
down their concentration gradient.
• Active Transport: the transport of a substance
across the cell membrane against its concentration
gradient
– Active transport requires the cell to use energy because
the substance is being moved against its concentration
gradient.
– Usually this energy comes from ATP.
– Some active-transport processes involve carrier proteins
which require energy and act as pumps to move
substances against their concentration gradient.
Sodium-Potassium Pump and Vesicles
• Extremely important in animal cells.
• In a complete cycle, it transports three sodium ions (Na+) and two potassium
ions (K+) into the cell because sodium cells are usually more concentrated
outside the cell than inside, while potassium are usually more concentrated
inside the cell.
•
– The energy for this pump is provided by ATP.
– This prevents sodium from accumulating in the cell (what would happen if there were
too many).
– Helps maintain the concentration gradient because this is used to transport other
substances.
Some substances (proteins, polysaccharides) are too large to be transported by carrier
proteins and instead use vesicles.
– Vesicle: a small cavity or sac in a eukaryotic cell made of cell membrane; part of the membrane surrounds
the materials to be taken into the cell.
– Endocytosis: the movement of a substance into a cell by a vesicle.
– Exocytosis: the movement of a substance by a vesicle to the outside of the cell.
Building Molecules That Store Energy
• Metabolism involves either using energy to build
molecules or breaking down molecules in which energy
is stored.
• Photosynthesis: process by which light energy is
converted to chemical energy.
• Autotrophs: organisms that use energy from sunlight
of from chemical bonds in inorganic substances to
make organic compounds.
– Most Autotrophs are photosynthetic organisms.
Breaking Down Food For Energy
• Chemical energy in organic compounds can be
transferred to other organic compounds or to
organisms that consume food.
• Heterotrophs: organisms that must get energy from
food instead of directly from sunlight or inorganic
substances. Heterotrophs get energy from food
using cellular respiration.
• Cellular respiration: a metabolic process that
releases energy in food to make ATP which can
provide the cell with the energy it needs.
ATP
• ATP or Adenosine triphosphate is a nucleotide with two extra
energy-storing phosphate groups.
• The phosphate groups store energy like a compressed
spring—the energy is released when the bonds holding the
phosphate groups together is broken.
• The removal of a phosphate group from ATP makes ADP, or
Adenosine diphosphate in the following reaction:
H20 + ATP  ADP + P + ENERGY!!!
Photosynthesis: Using the Energy in Sunlight
• There are three stages in Photosynthesis:
– Stage 1: Absorption of Light Energy—Energy is captured
from sunlight.
– Stage 2: Conversion of Light Energy—Light energy is
converted to chemical energy, which is temporarily
stored in ATP and the energy carrier molecule NADPH.
– Stage 3: Storage of Energy—The chemical energy
stored in ATP and NADPH powers the formation of
organic compounds, using carbon dioxide.
• Stages 1 and 2 of photosynthesis are light-dependent
reactions.
6 CO2 + 6H2O  C6H12O6 + 6O2
Carbon
dioxide
Sunlight
Water
Glucose
(sugar)
Oxygen
gas
Stage 1: Absorption of
Light Energy—Energy
is captured from
sunlight.
Stage 2: Conversion of
Light Energy—Light
energy is converted
to chemical energy,
which is temporarily
stored in ATP and the
energy carrier
molecule NADPH.
Stage 3: Storage of
Energy—The
chemical energy
stored in ATP and
NADPH powers the
formation of organic
compounds, using
carbon dioxide.
The Stages of
Photosynthesis
Stage One: Absorption of Light Energy
• Stage one is LIGHT DEPENDENT!
• Pigments: structures that absorb light in
certain wavelengths and reflect all others.
• Chlorophyll: primary pigment involved in
photosynthesis; absorbs blue and red light
and reflects green and yellow light. Two
types: chlorophyll a and chlorophyll b
• Cartenoids: pigments that produce fall
colors.
Factors that Affect Photosynthesis
• Photosynthesis is directly affected by various
environmental factors.
– The rate of photosynthesis increases as light
intensity increases until all pigments are being
used, when the Calvin cycle cannot proceed any
faster
– The carbon dioxide concentration affects the
rate of photosynthesis.
– Photosynthesis is also more efficient within a
certain range of temperatures (enzymes are
involved!)
Cellular Energy
• Your cells transfer the energy in organic
compounds, like glucose, to ATP through a process
called cellular respiration.
• Oxygen you breath in air makes the production of
ATP more efficient, although some ATP is made
without oxygen.
• Aerobic: metabolic processes that require oxygen
• Anaerobic: metabolic process that do not require
oxygen.
The Stages of Cellular Respiration
• Stage 1: Glucose is converted
to pyruvate, producing a small
amount of ATP and NADH.
• Stage 2: Pyruvate an NADH are
used to make a large amount
of ATP in a process called
aerobic respiration, occurring
in mitochondria.
– Krebs cycle and electron
transport chain take place,
making more ATP.
Glucose
(sugar)
Oxygen
Gas
Carbon
Dioxide
Water
C6H12O6 + 6O2  6CO2 + 6H2O + ATP energy
Respiration in the
Absence of Oxygen
• If there is not enough
oxygen for aerobic
respiration to occur, there is
no electron transport chain
• Under anaerobic
conditions, fermentation
occurs.
– Lactic Acid Fermentation
– Alcoholic Fermentation
Production of ATP
Total ATP Production
• Glycolysis: 2 ATP
• Krebs Cycle: 2 ATP
• Electron Transport Chain: Up to 34 ATP
The Path of Air
Alveoli: tiny air sacs in the
lungs where oxygen and
carbon dioxide gases are
exchanged.
• Air enters the respiratory
system through the nose
or mouth. About 21% is
oxygen gas.
• Air passes through the
pharynx and continues to
the larynx, or voice box.
• Air then passes into the
trachea, or windpipe
which divides into two
smaller tubes called
Bronchi, which branch
into the lungs.
• Within the lungs, smaller
tubes called bronchioles
divide off.
• Finally, the smallest
bronchioles reach air sacs
called alveoli where
gasses are actually
exchanged.
1. Oxygen reaches lungs.
2. Oxygen diffuses from alveoli
to capillaries (tiny blood
vessels surrounding alveoli).
3. Oxygen rich blood travels to
the heart.
4. Oxygen diffuses from the
blood into the cells for
aerobic respiration.
5. Carbon dioxide diffuses to
the blood from cells.
6. Most carbon dioxide travels
to the heart.
7. The heart pumps blood to
lungs. Carbon dioxide is
released to the alveoli.
8. Carbon dioxide is expelled in
exhalation.
Gas Transport:
Oxygen Transport
• Carbon dioxide is also
taken in by blood in
three forms.
– 7% is dissolved in
blood plasma.
– 23% is attached to
hemoglobin
molecules inside red
blood cells.
– 70% is carried in the
blood as bicarbonate
ions (H2CO3).
Gas Transport: Carbon
Dioxide Transport
Primary Tissue Layers
• There are three primary tissue layers, described in
the table below.
• The cells of all animals except sponges are
organized into units called tissues, which are cells
with a common structure that work together to
perform a function.
Buck 2011
The Cell Cycle
• Cell Cycle: a repeating sequence of cellular growth
and division during the life of an organism. A cell
spends ninety percent of its time in the first three
phases, known together as interphase.
• The cell will enter the last phases
of interphase only if the cell is about
to divide. There are five phases of
the cell cycle, listed below and
summarized on the next slide:
1. First growth 2. Synthesis, 3. Second
growth 4. Mitosis 5. Cytokinesis.
Buck 2011
When Control is Lost: Cancer
• Certain genes contain the information to make
proteins that regulate cell growth and division.
• If one of these genes is mutation, the protein may
not function, and regulation of cell growth and
division can be disrupted.
• Cancer: the uncontrolled growth and division of
cells.
– A disorder of cell division; cancer cells do not respond
normally to the body’s control mechanisms.
– Some mutations cause cancer by over-producing
growth-promoting molecules, speeding up the cell cycle.
Buck
– Others cause cancer by inactivating control proteins. 2011
Mitosis
Buck 2011
Mitosis
1. Prophase: Chromosomes coil up and become visible
during prophase. The nuclear envelope dissolves and a
spindle forms.
2. Metaphase: Chromosomes move to the center of the
cell and line up along the equator. Spindle fibers link
the chromatids of each chromosome to opposite poles.
3. Anaphase: Centromeres divide during anaphase. The
two chromatids (now called chromosomes) move
toward opposite poles as spindle fibers shorten.
4. Telophase: A nuclear envelope forms around the
chromosomes at each pole—chromosomes are now at
opposite poles.
Buck 2011
A Winding Staircase
• Watson and Crick determined that DNA is a double
helix. Each strand is made of linked nucleotides,
the subunits that made up DNA—made of a sugar
(deoxyribose), a nitrogen base, and a phosphate
group.
Buck 2011
Purines and
Pyrimidines
• The sugar and the phosphate
group are the same for each
nucleotide. However, there
are four different nitrogen
bases: adenine, guanine,
thymine, and cytosine.
• Adenine and guanine are
Purines.
• Thymine and Cytosine are
Pyrimidines.
• Nitrogen bases of nucleotides
face each other in the double
helix and are held together by
weak hydrogen bonds. Buck 2011
Pairing Between Bases
• A Purine on each strand (A or G) is always paired with a
pyrimidine on the other strand (C or T)
• A pairs with T
• G pairs with C
• Two strands contain complementary base pairs—the
sequence of bases on one strand determines the
sequence on the other strand.
Determine the complementary
strand for the following
sequences:
TCGAACT
CCAGATTG
Buck 2011
Roles of Enzymes in DNA Replication
• DNA Replication: The process of making a copy of
DNA
• DNA Helicases: open the double helix by breaking the
hydrogen bonds that link the complementary nitrogen
bases between the two strands
• Replication Fork: The area where the double helix
separates
• DNA Polymerase: enzymes that move along the strands
of DNA and add new nucleotides to the new nitrogen
bases
• When replication is complete, there are two
identical DNA molecules, each made of a new
strand and an old strand.
Buck 2011
Steps of DNA Replication
Buck 2011
Crossing-Over and Random
Fertilization
• DNA exchange during crossing over in Prophase I adds even more
recombination to the independent assortment of chromosomes,
making even MORE genetic combinations!
 Crossing-Over: a type of genetic recombination that occurs when
portions of a chromatid on one homologous chromosome are
broken and exchanged with the corresponding chromatid, increasing
genetic diversity.
•Meiosis, gamete-joining, and
crossing-over are essential to
evolution because these processes
generate genetic variation very
quickly.
•The pace of evolution is accelerated
by genetic recombination!
Buck Salinas 2012
Decoding the Information in DNA
• Gene: A segment of DNA in a chromosome that
codes for a particular protein.
– ALLELES are different VERSIONS of genes!
• Traits such as eye color are determined by proteins
built according to instructions coded in genes in the
DNA.
Buck Salinas 2012
Decoding the Information in DNA
• A gene’s instructions for making a protein are coded in the sequence
of nucleotides in the gene. The instructions for making a protein are
transferred from a gene to RNA in a process called transcription.
• Transcription: Making RNA using one strand of DNA as a template.
• Translation: in ribosomes, when mRNA (messenger RNA)
molecules are used to specify the sequence of amino acids in
polypeptide chains
(precursors of proteins)
Gene Expression: The
manifestation of the
genetic material of an
organism in the form of
specific traits.
Buck Salinas 2012
Transfer of Information from DNA to RNA
• The first step in making a protein is transcription. In
transcription, the information found in a gene in DNA is
transferred to a molecule of RNA by RNA polymerase.
• RNA Polymerase: an enzyme that adds and links
complementary RNA nucleotides during transcription.
1.
Transcription begins: RNA Polymerase binds to the gene’s promoter.
–
2.
Promoter: A specific sequence of DNA that acts as a “start” signal for
transcription
RNA Polymerase then unwinds and separates the two strands of the
double helix, exposing the DNA nucleotides on each strand.
RNA Polymerase adds and links complementary RNA nucleotides based
on the gene.
3.
–
–
Transcription follows the base-pairing rules for DNA replication except that Uracil
(U) pairs with Adenine (A) rather than Thymine (T).
Eventually, RNA polymerase eventually reaches a “stop” signal, which is the end
of the gene.
Buck Salinas 2012
The Genetic Code: Three-Nucleotide
“Words”
• Different types of RNA are made during transcription, depending
on the gene being expressed.
• When a cell needs a particular protein, mRNA (messenger RNA) is
made.
• Messenger RNA (mRNA): a form of RNA that carries the
instructions for making a protein from a gene and delivers it
to the site of translation.
• The information from mRNA is translated from the language of
RNA (nucleotides) to the language of proteins (amino acids).
• The RNA instructions are written as a series of three-nucleotide
sequences on the mRNA called codons.
• Each codon (set of three nucleotides) along the mRNA strand
corresponds to an amino acid or signifies a start of stop signal for
translation.
Buck Salinas 2012
The Genetic Code: Three-Nucleotide
“Words”
• Genetic
Code: the
amino
acids and
“start” and
“stop”
signals that
are coded
for by each
of the
possible 64
mRNA
codons.
Buck
Salinas
2012
RNA’s Roles in Translation
• Transfer RNA (tRNA) molecules and ribosomes help in the synthesis of
proteins.
• Transfer RNA (tRNA): single strands of RNA that can carry a specific amino
acid on one end, folds into a compact shape and has an anticodon.
– Anticodon: a three-nucelotide sequence on a tRNA that is complementary to
an mRNA codon.
• Ribosomal RNA (rRNA): RNA molecules that are part of the structure of
ribosomes, which perform translation, making proteins.
Buck Salinas 2012