8.3 DNA Replication
First Five 2/10
1.Without using your lab,
who were the people,
in order, that
discovered the
structure of DNA?
2.Turn in your lab
notebook to the bin
behind Kringle’s
computer.
Schedule
1.First Five
2.DNA notes
HW:
1.Discovering DNA Lab
– Due Today
2.DNA
Molecule/Replication
wkst – due Friday
GQ2: How does DNA’s
structure relate to its
function?
8.3 DNA Replication
First Five 2/4
1. Who do you think
contributed the most to the
discovery of DNA’s
structure and Why?
- Watson/Crick
Franklin
- Wilkins
- Pauling
- Chargaff
2. Turn in your lab notebook
to the bin behind
Kringle’s computer.
Schedule
1.First Five
2.Finish Movie
3.Letter Assignment
HW: Letter Due Friday
GQ: How does DNA’s
structure relate to its function?
8.3 DNA Replication
Choose one of the following letters to write.
1. Write a letter to James Watson as Rosalind Franklin,
detailing your disappointment for not receiving credit for
providing pertinent information for DNA’s structure.
2. Write a letter to Rosalind Franklin as Maurice Wilkins,
detailing why Franklin should have received credit for
DNA’s structure.
3. Write a letter to the Nobel Prize committee as Rosalind
Franklin, detailing your contributions to Watson and
Crick’s discovery of DNA structure.
8.3 DNA Replication
First Five 2/4
1. Without your movie notes;
what did the following
people discover about
DNA’s Structure?
- Watson/Crick
Franklin
- Wilkins
- Pauling
- Chargaff
Schedule
1.First Five
2.Quiz – Cell Cycle
3.Replication Notes
4.Replication Lab
HW: DNA Molecule – Due
Thurs
DNA Replication – Due Thurs
GQ: How is DNA replicated?
8.3 DNA Replication
DNA is composed of four types of nucleotides.
• DNA is made up of a long chain of nucleotides.
• Each nucleotide has three parts.
– a phosphate group
– a deoxyribose sugar
– a nitrogen-containing base
phosphate group
deoxyribose (sugar)
nitrogen-containing
base
8.3 DNA Replication
• The nitrogen containing bases are the only difference in
the four nucleotides.
8.3 DNA Replication
Watson and Crick determined the three-dimensional
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.
8.3 DNA Replication
• Watson and Crick’s discovery built on the work of Rosalind
Franklin and Erwin Chargaff.
– Franklin’s x-ray images suggested that DNA was a
double helix of even width.
– Chargaff’s rules stated that A=T and C=G.
8.3 DNA Replication
KEY CONCEPT
DNA replication copies the genetic information of a
cell.
8.3 DNA Replication
Remember that a cell’s DNA needs to replicate (duplicate)
before the cell can divide. Write a hypothesis proposing
how DNA replicates.
8.3 DNA Replication
Nucleotides always pair in the same way.
• Chargaffs Rules:
– #A = #T
– #G = #C
• The base-pairing rules show
how nucleotides always pair
up in DNA.
– A pairs with T
– C pairs with G
• Because a pyrimidine
(single ring) pairs with a
purine (double ring), the
helix has a uniform width.
G
C
A T
8.3 DNA Replication
• The backbone is connected by covalent bonds.
• The bases are connected by hydrogen bonds.
hydrogen bond
covalent bond
8.3 DNA Replication
Replication copies the genetic information.
• A single strand of DNA serves as a template for a new
strand.
• The rules of base pairing direct
replication.
• DNA is replicated during the
S (synthesis) stage of the
cell cycle.
• Each body cell gets a
complete set of
identical DNA.
8.3 DNA Replication
First Five 2/5
1. What is the monomer of
DNA?
2. Write a hypothesis as to
how DNA is replicated.
Schedule
1.First Five
2.Replication Notes
3.Replication Lab
HW: DNA Molecule – Due
Tomorrow
DNA Replication – Due
Tomorrow
Cell Cycle Quiz Make up –
Due Friday
GQ: How is DNA replicated?
8.3 DNA Replication
Proteins carry out the process of replication.
• DNA serves only as a template.
• Enzymes and other proteins do the actual work of
replication.
1. Enzymes unzip the double helix. (Helicase)
2. Free-floating nucleotides form hydrogen bonds
with the template strand.
nucleotide
The DNA molecule unzips
in both directions.
8.3 DNA Replication
3. DNA polymerase enzymes bond the nucleotides
together in the new strand (covalent bonds between
sugars and phosphates) to form the double helix.
– DNA Polymerase fixes misplaced nucleotides in the new
strand.
new strand
nucleotide
DNA polymerase
8.3 DNA Replication
• Two new molecules of DNA are formed, each with an
original strand and a newly formed strand.
• DNA replication is semiconservative.
original strand
Two molecules of DNA
new strand
8.3 DNA Replication
Replication is fast and accurate.
• DNA replication starts at many points in eukaryotic
chromosomes.
There are many origins of replication in eukaryotic chromosomes.
• DNA polymerases can find and correct errors.
8.3 DNA Replication
First Five 2/6
1. What two enzymes are
involved in replication?
2. Take out your DNA
molecule and DNA
Replication wksts.
Schedule
1.First Five
2.Replication Lab/ Oral
Quizzes
3.Clean Up
HW: DNA Molecule – Due
Today
DNA Replication – Due Today
Cell Cycle Quiz Make up –
Due Friday
Test/Test Packet – Due Thurs
2/13
Review – Due Wednesday
2/12
GQ: How is DNA replicated?
8.3 DNA Replication
Questions
1. In step 1 of replication, how does the DNA unzip?
2. In step 2 of replication, how do the new strands compare
with the template strands?
3. What enzyme is important in step 2?
4. What is the result of DNA replication?
5. Why is it important for the cell to correct any errors that
occur during replication?
8.3 DNA Replication
Oral Quiz
• What do we mean when we say that DNA replication
is semiconservative?
• What are the three steps of DNA replication? What
happens in each step?
• What type of molecule creates the bonds between the
sugars and the phosphates of the new nucleotides?
What type of bond is formed?
• What do we call the location where DNA replication
begins?
• Where do the free-floating nucleotides come from?
8.3 DNA Replication
Why do cells need to divide?
1. Replace old and damaged cells
2. Big cells begin to starve and lack Oxygen
3. Big cells cannot get rid of waste or CO2 fast enough
8.3 DNA Replication
Chromosomes condense at the start of mitosis.
• DNA wraps around proteins (histones) that condense it.
DNA double
helix
DNA and
histones
Chromatin
Supercoiled
DNA
8.3 DNA Replication
• DNA plus proteins is called chromatin.
chromatid
• 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.
telomere
centromere
telomere
Condensed, duplicated chromosome
8.3 DNA Replication
• Human Cells have 23 pairs
of chromosomes (total 46)
• Homologous chromosomes
– Two chromosomes that
have copies of the same
genes
8.3 DNA Replication
Duplicated vs. Unduplicated
Homologous Chromosomes
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