DNA Replication
In Eukaryotes and Prokaryotes
BOCA
• What are the nucleotide bases for
DNA?
• Which bases bond together?
DNA replication involves making
_____ from DNA.
1.
2.
3.
4.
Protein
DNA
RNA
rRNA
The Replication Process
– Before a cell divides, it duplicates its
DNA in a copying process called
replication.
– This process ensures that each
resulting cell has the same complete set
of DNA molecules.
Ultimately the information in
DNA is used to make:
1. Proteins
2. Lipids
3. Carbohydrates
How is DNA Copied
How do you make exact copies?
Each strand of the double helix of
DNA serves as a template, or model,
for the new strand
What does the structure of DNA
tell you about how to copy it?
How is DNA Copied
Semi-Conservative
DNA Replication
Eukaryotes
Begins at many origins
Strands must separate and unwind
Helicase, Topoisomerases, and SSB
proteins
Add Primer
Primase
Chromosome Structure
Eukaryotic chromosome
structure
DNA (linear molecule)
Histone proteins
Chromosome Structure
Prokaryotic chromosome
structure
DNA (Circular Molecule)
The Role Of Enzymes
– The principal enzyme involved in DNA replication is
called DNA polymerase.
–
DNA polymerase is an enzyme that joins individual
nucleotides to produce a new strand of DNA.
–
DNA polymerase also “proofreads” each new DNA
strand, ensuring that each molecule is a perfect copy of
the original.
DNA Replication
Replication
DNA polymerase
Fuse sections
DNA ligase
DNA Replication
Strands separate and unwind
(Helicase)
Add Primer (Primase)
Replication (DNA polymerase)
Fuse sections/fragments (DNA ligase)
New sections built 5’-3’ and anti-parallel
Telomeres
–
The tips of chromosomes are known as telomeres.
–
The ends of DNA molecules, located at the telomeres,
are particularly difficult to copy.
–
Over time, DNA may actually be lost from telomeres
each time a chromosome is replicated.
–
An enzyme called telomerase compensates for this
problem by adding short, repeated DNA sequences to
telomeres, lengthening the chromosomes slightly and
making it less likely that important gene sequences will
be lost from the telomeres during replication.
“Leading Strand” DNA synthesis would
occur in locations?
I
III
II
IV
3’
Origin
1.
2.
3.
4.
5.
I and II
I and III
I and IV
II and III
II and IV
20
How does DNA replication
differ in prokaryotic cells and
eukaryotic cells?
• Replication in most prokaryotic cells starts
from a single point and proceeds in two
directions until the entire chromosome is
copied.
• In eukaryotic cells, replication may begin
at dozens or even hundreds of places on
the DNA molecule, proceeding in both
directions until each chromosome is
completely copied.
Replication Quiz
1. Why is replication necessary?
2. When does replication occur?
3. Describe how replication works.
4. Use the complementary rule to
create the complementary strand:
A---?
G---?
C---?
T---?
A---?
G---?
A---?
G---?
C---?
A---?
G---?
T---?
Replication Quiz
A---T
1. Why is replication necessary?
G---C
So both new cells will have the correct DNA C---G
2. When does replication occur?
T---A
During interphase (S phase).
A---T
3. Describe how replication works.
G---C
Enzymes unzip DNA and complementary A---T
nucleotides join each original strand.
G---C
4. Use the complementary rule to
C---G
create the complementary strand:
A---T
G---C
T---A