BIO 1AO3 > replication > Flashcards

replication Flashcards

(60 cards)

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1
Q

What did Watson and Crick propose about DNA replication?

A

DNA consists of a pair of template chains that are complementary to each other

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2
Q

What happens before DNA replication begins?

A

Hydrogen bonds between complementary strands are broken, allowing unwinding and separation

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3
Q

What does each DNA strand contain?

A

The information necessary to reconstruct the other strand

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4
Q

How is a new DNA strand formed?

A

Each strand serves as a template for ordering new nucleotides according to base-pairing rules

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5
Q

What is the result of DNA replication?

A

Two new helices identical to the parental DNA molecule

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6
Q

What is the semiconservative model?

A

Each daughter DNA molecule has one parental strand and one newly synthesized strand

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7
Q

What alternative models were proposed for DNA replication?

A

Conservative and dispersive models

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8
Q

What does the conservative model propose?

A

Parental strands remain together after replication

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9
Q

What does the dispersive model propose?

A

DNA strands are mixtures of old and new DNA

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10
Q

Who demonstrated semiconservative replication?

A

Matthew Meselson and Franklin Stahl

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11
Q

Matthew Meselson and Franklin Stahl: what organism and isotope did they use

A

E. coli; initially, 15N (heavy nitrogen)

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12
Q

Matthew Meselson and Franklin Stahl: what happened after transferring to 14N

A

New DNA strands incorporated 14N

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13
Q

Matthew Meselson and Franklin Stahl: what determined the DNA position in centrifugation

A

Density (15N heavier than 14N)

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14
Q

Matthew Meselson and Franklin Stahl: What was observed in 15N medium?

A

One distinct heavy DNA band

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15
Q

Matthew Meselson and Franklin Stahl: What was observed after one replication in 14N?

A

One band of intermediate density (hybrid DNA)

  • rejected the conservative model
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16
Q

Matthew Meselson and Franklin Stahl: What happened after many generations in 14N?

A

Two bands appeared (light and hybrid DNA)

  • confirmed the semiconservative model
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17
Q

Why were fluorescent nucleotides used?

A

Genome size made isotope experiments difficult

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18
Q

What did fluorescent labeling allow?

A

Visualization of DNA replication in eukaryotes

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19
Q

fluorscent labelling: What was observed in eukaryotic chromosomes?

A

Hybrid and fully labeled DNA strands

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20
Q

What did fluorescence patterns show?

A

Faintly and darkly labeled DNA within one chromosome

  • showed that replication is similar in prokaryotes and eukaryotes
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21
Q

Where does replication begin?

A

Origins of replication

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22
Q

How does replication occur in prokaryotes?

A

From a single origin around circular DNA

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23
Q

In what direction is the template strand read?

A

3’ to 5’

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24
Q

In what direction does the daughter strand grow?

A

5’ to 3’

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25
What bonds form between nucleotides?
Hydrogen bonds (between bases) and phosphodiester bonds (backbone)
26
What are replication forks?
Regions where DNA strands separate
27
What is required to initiate replication?
RNA primer (5–10 nucleotides long)
28
Why is a primer required?
DNA polymerase can only extend from existing DNA/RNA
29
What enzyme synthesizes DNA? What direction does it work in
DNA polymerase; 5' to 3'
30
What is the leading strand?
Continuously synthesized strand
31
How many primers does the leading strand require?
1
32
What is the lagging strand?
Discontinuously synthesized strand
33
What are Okazaki fragments?
DNA fragments on the lagging strand; separate primers form each okazaki fragments
34
What replaces RNA primers?
DNA nucleotides
35
Why is lagging strand replication discontinuous?
DNA polymerase can only synthesize 5’ to 3’
36
What is the replication complex?
Large complex of proteins involved in replication
37
What does DNA helicase do?
Unwinds DNA by breaking hydrogen bonds
38
What do single-stranded binding proteins do?
Stabilize unwound DNA so they don't join back
39
What do topoisomerases do?
Relieve torsional strain due to the unwinding at replication form - located upstream of the replication fork - also serve as initiator proteins that trigger the process of unwinding at the origin of replication
40
what is RNA primase
synthesizes the short RNA stretches of nucleotides which are complementary to the parental strands from which DNA polymerase can then elongate from
41
what does RNA polymerase III do
Elongation in prokaryotes
42
what does DNA polymerase I do
the enzyme that is responsible for removing the RNA primer after DNA replication and replacing those short sequences with DNA nucleotides in prokaryotes
43
Why must lagging strand wait?
Template must be exposed at the replication fork
44
What issue occurs after primer removal in eukaryotes?
Leaves a gap with free phosphate backbone
45
what does DNA ligase do
is able to join the 3’ end of a fragment to an adjacent DNA nucleotide by catalyzing the phosphodiester bond formation along this region of the DNA backbone and as a result, joining adjacent replicated Okazaki fragments together - Joins Okazaki fragments via phosphodiester bonds
46
how are errors in replication corrected
DNA polymerase proofreading
47
What happens during proofreading?
Incorrect nucleotide is removed and replaced
48
What do prokaryotes and eukaryotes both require?
primers
49
What direction is elongation in both prokaryotes and eukaryotes?
5’ to 3’
50
What structures do both prokaryotes and eukaryotes have?
Leading and lagging strands
51
Why can’t DNA replication complete 5’ ends?
No 3’ end available after primer removal
52
what is the result of the end replication problem
Shorter DNA after each replication
53
What are telomeres?
Repetitive DNA sequences at chromosome ends ex. TTAGGG
54
what is the function of telomeres
Protect coding regions
55
What happens to telomeres over time?
they shorten
56
Where is telomerase active?
Gametes and stem cells
57
What type of enzyme is telomerase?
- Reverse transcriptase - synthesizes DNA from an RNA template - a ribonucleoprotein that contains the RNA template as part of the complex itself
58
What does telomerase do?
Extends telomeres
59
how does telomerase work
Adds repeats to the template strand
60
telomerase: What happens after extension?
Primase, DNA polymerase, and ligase complete replication
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