DNA, Cell Cycles
and Genetics!
Mrs. Stahl
Biology
Let’s Think!!!!
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What does DNA stand for?
Where is DNA located in the cell?
What is DNA to you?
Where do we find DNA?
1928- Fredrick Griffith’s Experiment
• Looked into the bacterium that
causes pneumonia.
• One form is coated by
carbohydrates and is smooth (S
form) while the other form is
rough.
• He injected the mice and the
smooth ones died, when the S
bacteria was killed with heat
first, the mice lived.
• Combo- R and heat treated S=
mice died. Found S bacteria in
the blood. Some of the S
bacteria must have transferred
into the R. The R became
harmful.
• Conclusion: Transforming
Principle
Why did this happen?
• Heating bacteria to 60 C (140 F) can kill the
bacteria without denaturing (falling apart)
their DNA. DNA can remain unchanged up to
90 C (194 F). Therefore, the S bacteria in
Griffith’s experiment died, but their DNA
remained intact.
Oswald Avery- 1944
• Figured out what the transforming principle was by
observing it in a Petri dish.
• Conducted three tests:
– 1. Qualitative- chemical tests showed that there weren’t
any proteins, but DNA was present.
– 2. Chemical Analysis- Elements in the extract (sample)
closely matched those found in DNA.
– 3. Enzyme Tests- tested the reaction to certain enzymes.
Added to the extract enzymes that breakdown proteins, the
extract still transformed the R bacteria to the S form.
Transformation did not occur when they added an enzyme
to destroy the DNA .
– Conclusion- DNA is the transforming principle.
Hershey and Chase 1952
• Studied bacteriophages-> a type
of virus that takes over a
bacterium’s genetic machinery
and directs it to make more
viruses.
• They are ones responsible for
confirming that DNA is the
genetic material.
• They used radioactive sulfur
(found in proteins ) and
radioactive phosphorus (found in
DNA)
Hershey / Chase Experiment
• Experiment 1:
– Infected bacteria with
bacteriophages grown
in radioactive sulfur;
separated bacteria from
the phages, found no
activity in the bacteria.
• Experiment 2:
– Infected bacteria with
bacteriophage grown in
radioactive phosphorus;
separated bacteria from
bacteriophages; found
significant radioactivity
inside the bacteria,
which showed that DNA
from the
bacteriophage had
entered the bacteria.
Final Result
• DNA is the genetic material.
Watson and Crick determined the threedimensional structure of DNA by building
models.
• They realized that
DNA is a double
helix that is made
up of a sugarphosphate
backbone on the
outside with bases
on the inside.
The Structure of DNA
• Deoxyribonucleic Acid
• Very long polymer or chain of repeating units
• Monomers are called nucleotides
– Each nucleotide is made up of a sugar, phosphate, and
nitrogenous base (ATGC)
– A= Adenine
– T= Thymine
– C= Cytosine
– G= Guanine
Structure Continues
• Double helix / twisted ladder
• Backbone= sugars and
phosphates
• Strands are complementary they fit together and are
opposite each other.
• Base pairs are held together by
hydrogen bonds.
• Sugars and phosphates are held
together by covalent bonds.
• http://www.youtube.com/watc
h?v=p835L4HWH68
Why would the middle /
nitrogenous bases be held
together by hydrogen bonds and
the “backbone” or sides be made
up of covalent bonds?
Answer
• Base pairs are held together by weak,
hydrogen bonds because the strands need to
be able to break apart so that they can
replicate. The sides of the latter need to be
strong to keep the strand in tact when it
splits a part to replicate.
Label the DNA Molecule
Hydrogen
Bonds
Phosphates
T
A
C
Sugars
G
A
T
C
G
Covalent Bonds
Chargaff’s Rule
• Base pairs match up
– A always binds with T (held
together by 2 hydrogen bonds)
– C always binds with G (held
together by 3 hydrogen bonds)
• The bonds that hold them
together are hydrogen bonds
• Example- ACACAC, what is the
complementary strand?
G
C
A
T
Phosphates
Sugars
hydrogen bond
covalent bond
Let’s Practice- Find the
Complementary Strand
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1. TGCATTGC
2. ATATAGCTAG
3. ATA
4. CAT
5. TATGC
How do Forensic Scientists determine
if someone commits a crime? What
do they look at?
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Fingerprints
Blood
Saliva
Cheek Cells
Straws, cigarettes
Hair sample
Do they all have the
same DNA?
If so how?
Why do you always have to cut your
hair, fingernails, and the lawn?
• Growth caused by new cells being made.
Cells divide at different rates.
• The rate of cell division varies with the need for
those types of cells.
•
Some cells are unlikely to divide (G0).
Cells divide at different rates- cont.
• Prokaryotic cells divide faster than eukaryotic
cells.
• Go= cells that rarely divide but still function
– Ex- neurons and muscle cells
– Ex- lymphocytes= part of your immune system ->
B cells and T cells. They don’t divide until they
recognize an invader and then they rapidly divide
to fight that antigen.
Cell Size
• Cells are limited in size by their surface
area to volume ratio
– Cells can get so large that they can no
longer obtain enough oxygen and nutrients
at which point they divide.
• Surface area must allow for
adequate exchange of
materials.
– Cell growth is coordinated with division.
– Cells that must be large have unique
shapes.
Cell cycle
• A regular pattern of growth, DNA replication, and
cell division that occurs in eukaryotic cells.
• 5 main stages:
– 1. Gap 1
– 2. Synthesis
– 3. Gap 2
– 4. Mitosis
– 5. Cytokinesis
Interphase
First Stop- Interphase
Gap 1 or G1
• Cell growth
•Cells increase in size and
organelles increase in
number
• Critical checkpoint to
make sure that the DNA is
perfect and that there are
no imperfections.
Synthesis or S Phase
• Copies the DNA- DNA
Replication, Transcription
and Translation occur here.
• By the end the cells
nucleus contains two
complete sets of DNA.
Gap 2 or G2
• Additional growth
• Critical checkpoint to
make sure that the DNA is
not damaged and that the
cell is adequate size.
Let’s Look at Synthesis a little closer
• DNA Replication, Transcription, and
Translation
DNA Replication
• The process by which DNA is copied during the cell
cycle and occurs in the nucleus.
• A single DNA strand can serve as a template or
pattern for a new strand.
• Assures that every cell has a complete set of
identical genetic information.
• Your DNA is divided into 46 chromosomes that are
replicated during the S phase of the cell cycle. Your
DNA is copied once in each round of the cell cycle
= complete set of DNA for each cell.
DNA Replication Continues
• The enzyme helicase unzips the double helix
in both directions to separate the strands of
DNA. Breaking the hydrogen bonds holding
them together.
• Nucleotides are free floating in the nucleus
and can pair up with the nucleotides from
the existing DNA strands.
• DNA polymerase (enzyme) bonds the new
nucleotides together, creating a new strand.
Step 1
The DNA molecule unzips in
both directions.
Step 2
new strand
nucleotide
DNA polymerase
new strand
original strand
Two molecules of DNA
Stage 3
DNA Transcription
• Now that we have
replicated or
duplicated our DNA
we now need to
transcribe it. The
ultimate goal is to
make proteins so now
we need to break the
DNA down into RNARibonucleic Acid.
replication
transcription
translation
Transcription Continues
• Defined as : The process of making RNA from DNA
and occurs in the nucleus.
• RNA= Ribonucleic Acid
• The nitrogenous bases change a bit. Instead of T or
Thymine, RNA has U or Uracil.
• A-U and C-G are paired up together.
• Example of a DNA Strand: TACGGAC
• Example of an RNA Strand: AUGCCUG
• Do the examples in your notes!
Facts about RNA
• Sugar is ribose
• It’s single stranded and not double stranded.
This allows them to catalyze reactions much
like enzymes do. Speed things up.
• It has Uracil instead of Thymine.
Transcription Cont….
• Only a gene is transferred not a chromosome.
• Catalyzed by RNA polymerase (enzyme)
• Created three types of RNA
• Messenger RNA (mRNA) carries the message
that will be translated to form a protein.
• Ribosomal RNA (rRNA) forms part of ribosomes
where proteins are made.
• Transfer RNA (tRNA) brings amino acids from
the cytoplasm to a ribosome.
Next Step- Translation
• Now lets take the RNA and turn it into a protein /
amino acid.
• Occurs in the cytoplasm and uses mRNA
• We have 20 amino acids. Now we will string
together nucleotides to make amino acids that the
body can use.
• The sequences are called codons and they are
made up of three letters each. Each codon codes
for an amino acid.
• AUG = start codon-> start of translation
• UAA, UAG, and UGA= stop codons-> signal the end
of amino acid chain.
codon for
methionine (Met)
codon for
leucine (Leu)
The genetic code matches each RNA codon with its amino acid or function.
mRNA Recap
• Short lived
• Carries instructions from DNA in the nucleus
to the cytoplasm
• Read in a set of three nucleotides or codons
• HOW DOES IT TRANSLATE A CODON INTO AN
AMINO ACID????
Ribosomes and tRNA molecules!!
Ribosomes consist of two subunits.
– The large subunit has three binding sites for
tRNA. Holds the growing protein.
– The small subunit binds to mRNA.
tRNA
• Adaptor – just like a plug in an outlet. One
end is the amino acid and the other is the
anticodon (a set of three nucleotides that are
complementary to a mRNA codon.
• Example- Codon= GGG, the anticodon would
be CCC
End Result
• New proteins for the cells to use.
• The whole process is continual
Videos
• www.cellsalive.com/mitosis.htm
• http://www.youtube.com/watch?v=C6hn3sA0
ip0&feature=related
• http://www.youtube.com/watch?v=lf9rcqifx3
4
• http://www.youtube.com/watch?v=efyVYxV0P0&feature=related
Next Stop- Mitosis & Cytokinesis
• Mitosis is defined as the division of the cells
nucleus and its contents.
• Cytokinesis is the division of the cytoplasm
• Results in 2 identical daughter cells.
• In this process the nuclear membrane dissolves
and the duplicated DNA condenses around
proteins and separates, resulting in two nuclei
formed.
Terminology First
• Chromosomes- long continuous strand of DNA
• Histones- A group of proteins that your chromosomes
are associated with.
• Chromatin- loose combination of DNA and proteins,
looks like spaghetti
• Chromatid- one half of the duplicated chromosome.
• Centromere- the center where sister chromatids are
held together.
• Telomere- the ends of DNA molecules and they
prevent the chromosomes from accidently attaching
to one another as well as gene loss.
Chromosomes
• Long continuous thread of DNA with lots
of genes that regulate your entire body
• Body= 46 chromosomes / 23 pair
• In just one cell it is about 3ft long
• DNA wraps around proteins called
histones
• DNA and histones form chromatin (looks
like spaghetti- interphase)
• Chromosomes condense tightly for
mitosis-> duplicated looking like an X.

DNA wraps around proteins (histones) that condense it.
DNA double
helix
DNA and
histones
Chromatin
Supercoiled
DNA
• DNA plus proteins is called chromatin.
• One half of a duplicated
chromosome is a
chromatid.
• Sister chromatids are
held together at the
centromere.
• Telomeres protect DNA
and do not include
genes.
Mitosis
• The nucleus and
chromosomes go
through dramatic
changes to create two
identical daughter cells.
• 4 Stages- PMAT
(Prophase, Metaphase,
Anaphase, and
Telophase)
Parent cell
centrioles
Spindle
fibers
centrosome
nucleus with
DNA
Interphase
• Copies DNA, grows, and duplicates
organelles.
Remember- the cell has
already gone through
Interphase and everything
is perfect with the DNA
therefore it can continue
on.
Prophase= DNA and proteins condense into
tightly coiled chromosomes, nuclear envelope
breaks down, centrioles begin to move to
opposite sides, and spindle fibers form.
Metaphase- spindle fibers attach and align
chromosomes along the cells equator.
Anaphase- chromatids separate and
move to opposite sides of the cell.
Telophase- nuclear membrane starts
to form, chromosomes begin to uncoil,
and spindle fibers fall apart.
Cytokinesis- divides the cytoplasm
into two identical daughter cells.
– In animal cells, the
membrane pinches
closed.
– In plant cells, a cell
plate forms.
Fill it
out!
Videos
• http://www.youtube.com/watch?v=VlN7K19QB0
• http://www.pinterest.com/pin/320882160698
18262/
Regulation of the cell cycle
• External
– Outside the cell
– 1. cell to cell contact.
When one cell touches
another it stops growingunknown.
– 2. Some cells send
chemical messages telling
others to grow.
– Cancer cells
– Hemophilia
– Growth hormones
• Internal
– Inside the cell
– A lot of times they are
triggered by external
factors
– Kinase and cyclin
– Kinase is an enzyme that
transfers phosphates- all
over your body but the
ones that trigger the cell
cycle are called cyclinsproteins involved in the
cell cycle.
Apoptosis is programmed cell death.
– a normal feature of healthy organisms
– caused by a cell’s production of self-destructive
enzymes
– occurs in
development
of infants
webbed fingers
Cell division is uncontrolled in cancer.
• Cancer cells form disorganized clumps called tumors.
– Benign tumors remain clustered and can be removed.
– Malignant tumors metastasize, or break away, and can form
more tumors.
normal cell
cancer cell
bloodstream
Carcinogens are substances known to promote
cancer.
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Standard cancer treatments typically kill both cancerous and healthy cells.
http://www.pinterest.com/pin/320882160696
39864/
Sexual Reproduction
• Sexual reproduction- the joining of
two specialized cells called gametes
– Gametes= sperm and eggs
Asexual Reproduction
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Creation of offspring from one parent.
No gamete exchange!
Offspring are genetically identical to parent.
Examples include
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Amoebas
Hydras
Fungi
Bacteria
Archaea
Protists
Sea anemones
Coral
Starfish
Some non-flowering plants
– Strawberry
– Onion
– Potato
Example 1- Mushrooms (FUNGI)
Hydras
http://www.youtube.com/watch?v=a5oHMjGq
jyo&feature=related
Amoeba
Bacteria
• http://www.youtube.com/watch?v=DY9DNWc
qxI4
Sea Anemones
http://www.youtube.com/watch?v=sPwi2QcLK
ao
Sea Star
Binary fission
• Most prokaryotes
• Results in 2
identical daughter
cells just like
mitosis.
parent cell
DNA
duplicates
cell begins
to divide
daughter
cells
Budding- eukaryotes through mitosis
Examples
– A new plant growing from
cutting the stem.
– Hydra
Hydra
bud
Yeast
Defined As
• Small projection grows on
the surface of the parent
organism, forming a new
organism.
Fragmentation
Examples
• Sea Star- parent splits into
pieces.
• Flatworms
Defined As:
• The splitting of the parent
into pieces that each grow
into a new organism.
Vegetative Reproduction
Examples
• Strawberries
• Potatoes
Defined as:
• Forms a new plant from the
modification of a stem or
underground structure on
the parent plant.
Advantages of Asexual reproduction
• 1. They all can reproduce a lot.
• 2. More efficient in favorable environments
• 3. They don’t have to worry about attracting
a mate.
Disadvantage of Asexual
Reproduction
• 1. Mutation in a population could cause the
entire population to die.
2. So many at one time can cause
competition in food and space.
3. Extreme temperatures can wipe out entire
colonies.
Your body has 2 types of cells….
Somatic Cells / Body Cells
• Makes up most of your
body and tissues.
• Ex- heart, kidneys, eyeballs,
etc.
• DNA in your body cell is not
passed on to your children.
Sex Cells / Germ Cells
• Cells in your reproductive
organs.
• Ovaries and testes that
develop into sperm and
eggs= your gametes.
• DNA is spread to your child.
Your Cells have Autosomes and
Sex Chromosomes.
• 23 pairs of chromosomes = 46 total in humans
• Get 23 from mom and 23 from dad
• Each pair = homologous chromosome = means
having the same structure.
• Homologous Chromosomes- two chromosomes,
one from mom and one from dad, that have the
same length and general appearance.
• The chromosomes have copies of the same
genes but they may differ.
Autosomes
• Chromosome pairs 1-22
• Not related to the sex of the organism.
Sex Chromosomes
• Pair number 23
• In Humans- XY= male,
and XX= female
• They are not
homologous
• X chromosome is larger
and carries more genes
than the Y, which is
smaller and carries
fewer genes.
Karyotype – a picture of your
chromosomes.
Homologous
Chromosomes
Autosomes
Sex Chromosomes
Questions????????????
• What is pair 23 called?
• Is it a male or female?
• How many total chromosomes are there
total?
• Which sex chromosome is always larger?
Find the Homolog……
Answers!!!!
• Chromosome #5
• Chromosome # 12
Sexual Reproduction
• The fusion of gametes,
resulting in the genetic
mixture of both parents!
Fertilization
• The actual fusion of the sperm and the
egg.
• When it occurs the nucleus of the egg
and the sperm become one.
Diploid and Haploid Cells
Diploid
• Cells have two
copies of each
chromosome. One
from mom and one
from dad.
• Body cells
• 2n
• Diploid number in
humans = 46
because 2 X 23 = 46
Each human egg
or sperm has 22
autosomes and
only 1 sex
chromosome.
Haploid
• Cells have only
one copy of
each
chromosome.
• Gametes /
germ cells
• N
• Haploid
number in
humans = 23
Process of Meiosis
• Results in 4 genetically different Haploid Cells
• Two rounds: Meiosis 1 and Meiosis 2
– Meiosis 1- divides the homologous chromosomes
– Meiosis 2- divides the sister chromatids
• Reduces chromosome number and increases
genetic diversity
• Sex Cells or gametes that are dividing.
Homologous Chromosomes and
Sister ChromatidsHow do I tell them apart?
• Homologous Chromosomes– Two separate chromosomes, one from your mom and
one from your dad.
– They are the same length and carry the same genes,
but they are not copies of each other.
– Each half of a duplicated chromosome is called a
chromatid and together they are called sister
chromatids  and are held together at the centromere.
Homologous
chromosomes
Sister
chromatids
Sister
chromatids
• Meiosis I occurs after DNA has been replicated.
• Meiosis I divides homologous chromosomes in four
phases.
• Meiosis II divides sister chromatids in four phases.
• DNA is not replicated between meiosis I and
meiosis II.
Prophase 1 of Meiosis
-Homologous pairs
form
-Chromosomes trade
genes
-Nuclear membrane
breaks down
-Centrioles move to
opposite sides
--Spindle fibers
assemble
--Longest phase
-CROSSING -OVER
Why is crossing over important?
• Gives rise to
genetic
recombination.
Genetic material
between mom and
dad is being
exchanged.
Metaphase 1
• Homologous chromosomes are aligned in the middle by
spindle fibers.
• 23 chromosomes line up along each side of the equatorsome from mom and some from dad.
• Each side of the equator has chromosomes from both
parents.
• Results in 8,388,608 possible chromosome combinations.
Anaphase 1
• Homologous chromosomes separate to
opposite sides of the cell.
• Sister chromatids remain attached together.
Telophase 1
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Spindle fibers fall apart
Nuclear membrane may reform
Cell undergoes cytokinesis
End result= 23 unique duplicated
chromosomes from both parents
Prophase II
• Nuclear envelope breaks down
• Centrosomes and centrioles move to
opposite sides of the cell.
• Spindle fibers form
Metaphase II
• Spindle fibers align chromosomes along the
cells equator.
Anaphase II
• Sister Chromatids are pulled apart from each
other to opposite sides of the cell.
Telophase II
• Nuclear Membranes
form around
chromosomes
• Spindle fibers fall apart
• Cell undergoes
cytokinesis
• Results in 4 genetically
different haploid cells.
Review……………..
Mitosis
• Produces 2 genetically
identical diploid daughter
cells
• Takes place throughout an
organisms lifetime
• Involved in asexual
reproduction.
• Occurs only in body cells.
• Responsible for the growth,
repair, and development in
all types of organisms.
Meiosis
• Produces 4 genetically different
haploid cells
• Takes place only at certain times
in an organisms life cycle.
• Involved in sexual reproductionDNA is copied once but divided
2X’s.
• Occurs only in sex cells / germ
cells to produce gametes.
• Sometimes called “reduction
division” because it divides the
cells chromosomes by half.
• https://docs.google.com/present/view?id=dfh
23k67_2220hsfjcdf3