Replication of DNA
TEST CH. 17
Thursday April 21st
Section 17.3
p. 582-588
The first 13 slides of this
presentation correct the
32 questions on the
Guided reading lesson
about DNA Replication.
GUIDED Reading Lesson
Replication of DNA Section 17.3
INTRODUCTION p.582
1. How many base pairs are in the human genome?
•
6 billion
2. How long would it take a typist to type those one
letter codes if he could type at 60 words a
minute?
•
30years
3. How long does it take the cell to copy the human
genome?
•
A Few hours
4. Replication of DNA is very accurate. How
accurate is it?
•
1 error per 1 billion nucleotide pairs
Replication of DNA Section 17.3
THE PROCESS OF REPLICATION p.582
5. Replication of DNA is semi-conservative.
What does that mean?
• ½ is new and ½ is from the parent
DNA
6. What are the three main stages of DNA
replication?
• Initiation; elongation; Termination
Replication of DNA Section 17.3
Initation
7. What is a replication origin?
8. How many replication origins does prokaryotic
DNA have?
9. How many replication origins does eukaryotic DNA
have?
10. What is a replication bubble?
Replication of DNA
Section 17.3
Initation
11. What role does DNA
polymerase play in DNA
replication?
12. What is a replication
fork?
13. How many replication
forks does a replication
bubble have?
14. What is the role of
helicases?
Replication of DNA Section 17.3
Initation
15. Using fig. 17.21 as a guide draw a strand of
Eukaryotic DNA and label the following parts
a. Replication origin
b. Replication loop
c. Replication fork
d. Location where DNA polymerase operates
e. Location where Helicases operate
Replication of DNA Section 17.3
Initation
15. Using fig. 17.21 as a guide draw a
strand of Eukaryotic DNA and label the
following parts
a. Replication origin
b. Replication loop
c. Replication fork
d. Location where DNA polymerase
operates
e. Location where Helicases operate
Replication of DNA Section 17.3
Initation
16. How fast does the bacterium
E. coli unwind its DNA?
– 4500RPM
17. How fast does the
replication fork move in the
bacterium E. coli?
– 650 nucleotides per second
Replication
of DNA
Section 17.3
Elongation
18. What is the
function of the
primer?
19. How many
primers are
needed on the
lead strand?
20. How many
primers are
needed on the
lagging
strand?
21. What are
Okazaki
fragments?
Replication of DNA Section 17.3
Elongation
22. In which direction does DNA replication
occur on the leading strand?
23. In which direction does DNA replication
occur on the lagginging strand?
Replication of DNA Section 17.3
Elongation
24. What is the function of DNA ligase?
25. Which strand requires DNA Ligase?
26. What is Primase?
27. What is the role of the RNA Primer?
Replication of DNA Section 17.3
TERMINATION p.585
28. What are telomeres?
– Repeating TTAGGG nucleotides
found at the end of a chromosome
that are not replicated during DNA
replication. They do not direct cell
development so their loss does
not affect the cell.
29. How much DNA is lost with each
replication?
– 100 base pairs
30. What is telomerase?
– An enzyme the extends telomeres
(related to long life)
Replication of DNA Section 17.3
PROOFREADING AND CORRECTION p. 586
31. How does the DNA polymerase detect that the
wrong nucleotide was inserted?
– Absence of hydrogen bonds
32. Sketch a replication machine.
When does Replication of
DNA Occur?
Interphase of Meiosis & Mitosis
What are the three phases of
DNA Replication?
1 Initiation
2 Elongation
3 Termination
Watch the whole process at
http://www.johnkyrk.com/DNAreplication.html
Initiation of DNA Replication
Initiation:
• A portion of the double helix is unwound by a
helicase.
• Helicase is an enzyme that breaks the helix
apart at a region rich in A-T binds.
• Remember A-T bonds only have 2 hydrogen
bonds whereas C-G bonds have 3 hydrogen
bonds.
• Eukaryotic DNA often has several origins of
replication
Initiation of DNA Replication
• Remember A-T bonds only have 2 hydrogen
bonds whereas C-G bonds have 3 hydrogen
bonds.
Elongation of DNA Replication
• DNA polymerase uses the exposed Parental
DNA as a template for assembling 2
semiconserved strands of DNA.
• This action causes Replication bubbles
Elongation of the Leading strand in
DNA Replication
A molecule of a DNA
polymerase binds to
one strand of the DNA
and begins moving
along it in the 3' to 5'
direction, using it as a
template for
assembling a leading
strand of nucleotides
and reforming a double
helix. In eukaryotes,
this molecule is called
DNA polymerase delta
(δ).
Elongation of the
Lagging strand
Because DNA synthesis
can only occur 5' to 3', a
molecule of a second
type of DNA polymerase
(epsilon, ε, in
eukaryotes) binds to the
other template strand as
the double helix opens.
This molecule must
synthesize
discontinuous segments
of polynucleotides
(called Okazaki
fragments). Another
enzyme, DNA ligase I
then stitches these
together into the
lagging strand.
Termination
The beginning end of the lagging and leading
strand can not be replicated.
telomere –
specialized
nontranscribed
structure
typically rich in
G nucleotides,
at the end of
each
chromosome.
The use of
telomeres
protects us
against the
loss of genetic
material
during
replication
Proof Reading
DNA Polymerase check for unattached
hydrogen bonds. C-G must have 3 bonds
and A-T must have 2 bonds. Therefore the
wrong combination would leave a free H
bond. DNA Polymerase fixes MOST errors