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Genetics > Chapter 11 - DNA Replication > Flashcards

Chapter 11 - DNA Replication Flashcards

1
Q

DNA replication is the process by (definition)

A

which genetic material is copied
15-20 minutes

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2
Q

In DNA replication, the original DNA strands are used as ___

A

templates for synthesis of new strands with identical sequences

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3
Q

Two original DNA strands =

A

parental strands

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4
Q

Two newly made DNA stands =

A

daughter strands

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5
Q

What do the strands of DNA do in the actual replication?

A

Two complementary DNA strands come apart and each strand serves as a template strand for synthesis of new complementary DNA strands

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6
Q

In the late 1950s, what three different mechanisms were proposed for the replication of DNA?

A
  1. Conservative Model
  2. Semi-conservative Model
  3. Dispersive Model
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7
Q

What is the correct mechanism out of the 3?

A

Semi-conservative Model

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8
Q

What is the conservative model?

A

Both parental strands stay together after DNA replication

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9
Q

What is the semi-conservative model?

A

The double stranded DNA contains one parental and one daughter strand following replication

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10
Q

What is the dispersive model?

A

Parental and daughter DNA segments are interspersed in both strands following replication.

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11
Q

In 1958, what scientists devised a method to investigate the 3 models?

A

Matthew Meselson
Franklin Stahl

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12
Q

What was the method and hypothesis Meselson and Stahl used?

A

Method : able to distinguish between parental and daughter strands using light and heavy nitrogen (n15 radioactive)
Hypothesis: proved that DNA replication was semi conservative

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13
Q

Where is nitrogen found in DNA?

A

the bases

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14
Q

Where is oriC found and what does it mean?

A
  • E.Coli
  • Origin of chromosomal replication
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15
Q

What are the 3 types of DNA sequences in oriC ?

A
  1. DnaA boxes
  2. AT-rich regions
  3. GATC methylation sites
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16
Q

What are DnaA boxes?

A

sites for the binding of DnaA protein

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17
Q

What are AT-rich regions?

A

sites where the DNA strands separate

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18
Q

What are GATC methylation sites?

A

sites that help regulate DNA replication to mark parental + template strands

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19
Q

What strand is methylated?

A

Only the original strand is methylated initially

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20
Q

Describe bacterial DNA replication

A

The formation of two replication forks at the origin of replication (only 1)

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21
Q

Where does DNA synthesis being in bacterial DNA replication?

A

the origin of replication
Only has 1!

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22
Q

How is DNA written?

A

5’ to 3’ prime!

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23
Q

What are the 7 enzymes that are important in bacterial DNA replication?

A
  1. DNA Helicase
  2. Topoisomerase II or DNA Gyrase
  3. Single-stranded binding proteins
  4. Primase
  5. DNA Polymerase II
  6. DNA Polymerase I
  7. DNA ligase
24
Q

What does DNA helicase do?

A

breaks the hydrogen bonds between the DNA strands

25
What does topoisomerase II or DNA Gyrase?
alleviates positive supercoiling (like a hairbrush getting the knots out)
26
what do single stranded binding proteins do?
keep parental strands apart
27
What does primase do?
synthesizes an RNA primer
28
What does DNA polymerase III do? another name for it?
- The Work Horse - synthesizes a daughter strand of DNA (adds 750 nucleotides per second)
29
What does DNA polymerase I do?
Excises (cuts) the RNA primers and fills in with DNA - fixes mutations
30
What does DNA ligase do?
covalently links the DNA backbones in the Okazaki fragments together
31
DNA polymerases are
Enzymes that catalyze the attachment of nucleotides to synthesize a new DNA strand
32
In E.Coli, how many proteins are their and what do they do?
- 5 proteins with polymerase activity - DNA pol 1-5 - Pol 1 and 3 are normal replication - Pol 2, 4,5 - DNA repair and replication of damaged DNA
33
DNA polymerase III is a ?
Processive Enzyme meaning it can catalyze multiple reactions
34
What does DNA polymerase III need to be a processive enzyme?
a "B" clamp - with the presence of this DNA pol III stays on the DNA template long enough to polymerize up to 500,000 nucleotides (750 per second) - without it? 20 nucleotides per second
35
What is an exonuclease?
- When a DNA polymerase identifies a mismatched nucleotide and needs to remove it from the daughter strand (uses this) - 3' to 5' exonuclease activity to digest the newly made strand until the mismatched nucleotide is removed - DNA synthesis then resumes in the 5' to 3' direction
36
Where are ozaki fragments found?
only on lagging strand
37
What is on the opposite side of the chromosome (opposite of the oriC)?
- a pair of termination sequences called Ter sequences - T1 and T2
38
Describe Ter sequences
- termination happens within 15 - 20 minutes - T1 counterclockwise forks - T2 stops clockwise forks
39
What does tus stand for and what does it do?
TUS = Termination Utilization substance - binds to ter sequences and stops the movement of the replication forks
40
Describe the termination of replication process (4 steps)
1. only one ter sequence is needed in each cell to stop one fork 2. the other fork ends its DNA synthesis when it reaches the stopped fork 3. DNA replication ends when oppositely advancing forms meet 4. DNA ligase covalently links the two daughter strands back together.
41
Compare vs Contrast Bacterial vs Eukaryote DNA replication
- the types of proteins involved in bacterial DNA replication is also in Eukaryotes - More complex bc eukaryotes have large linear chromosomes, chromatin is tightly packed within nucleosomes, and more complicated cell cycle regulation
42
Replication bubbles from ___ ___ merge into completely replicated chromosomes
Multiple Origins
43
In Eukaryote replication, what does it begin with?
Prereplication complex (PreRC) which includes Origin recognition complex (ORC) - MCM Helicase
44
What is the ORC?
- in eukaryotes - a six subunit complex that acts as the first initiator of eukaryotic DNA replication
45
What does MCM helicase do?
binding of this completes DNA replication licensing and able to begin DNA synthesis
46
ORC vs ORIC
ORC - Eukaryotes ORIC - found in E.Coli
47
Describe telomere
- the complex of telomeric DNA sequences and bound proteins - found at both ends of linear eukaryotic chromosomes
48
Describe telomeric DNA sequences
- moderately repetitive tandem arrays - 3' overhand that is 12 to 16 nucleotides long - Several guanine nucleotides - many thymine nucleotides
49
Why is replication a problem at the end of linear chromosomes?
The DNA polymerases have 2 unusual features 1. synthesize DNA only in 5' to 3' direction 2. cannot initiate DNA synthesis on a bare (unprimed) DNA strand - at the ends of 3' linear chromsomes - the end of the strand cannot be replicated
50
How do linear chromosomes solve the problem? (replication at the end problem)
- by adding DNA sequences to the ends of telomeres called Telomerase
51
What is Telomerase?
- contains protein and RNA - RNA is complementary to the DNA sequence found in the telomeric repeat - allows the telomerase to bind to the 3' overhang
52
List the 3 steps in order of Telomerase:
1. Binding 2. Polymerization 3. Translocation
53
RNA primase doesn't need a what?
a precursor can just put down nucleotides - 3OH'
54
Telomeres tend to __ and what happens when that occurs?
- shorten in actively dividing cells - become senescent (lose their ability to divide) - insertion of highly active telomerase can block senescence
55
Why are mutations of telomerase bad?
- cancer cells carry this mutations when prevents telomere shortening and senescence - may be a target for anti-cancer drug treatments
56
What is the code for Telomeres?
TTAGGG

Genetics (12 decks)

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