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Molecular Biology > DNA Replication, Repair And Recombination 1 > Flashcards

DNA Replication, Repair And Recombination 1 Flashcards

1
Q

What can result from high mutation rates in somatic cells?

A

Uncontrolled proliferation/cancer

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2
Q

What is the reaction that DNA polymerase catalyzes?

A

DNA(n) + dNTP -> DNA(n +1) + P2O7

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3
Q

In order for DNA polymerase to begin replication, what does it require?

A

A free 3’ -OH

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4
Q

What is the only direction that DNA polymerase can syntesize DNA in?

A

5’ to 3’ direction

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5
Q

What is the difference between the leading strand and lagging strand?

A

The leading strand is synthesized continuously, whereas the lagging strand is synthesized in segments.

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6
Q

What takes place immediately after incorrect bases are added?

A

Exonucleolytic proofreading.

A 3’ to 5’ exonuclease clips off unpaired residues at 3’ primer terminus.

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7
Q

In order to synthesize the lagging strand, what is initially needed?

A

An RNA primer. This allows DNA polymerase to make an Okazaki fragment.

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8
Q

Once an Okazaki fragment is made, how is the RNA primer removed?

A

By RNAseH. It replaces the RNA primer with DNA.

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9
Q

What enzyme unwinds DNA at the replication fork?

A

DNA helicase.

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10
Q

What is the function of single-stranded DNA binding proteins?

A

They bind tightly and cooperatively to exposed SS DNA.

They help stabilize unwound DNA and prevent the formation of hairpins. The DNA bases also remain exposed.

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11
Q

What is the function of a sliding clamp?

A

It keeps DNA polymerase on DNA when moving; it releases when double stranded DNA is encountered.

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12
Q

What does the assembly of a sliding clamp require?

A

A clamp loader. It hydrolyzes ATP as it loads the clap onto a primer-template junction.

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13
Q

As DNA polymerase moves along the leading strand, what other structure remains with the DNA polymerase?

A

A clamp

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14
Q

Why is a clamp loader needed at the lagging strand?

A

So it can assemble a new clamp at the start of each Okazaki fragment.

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15
Q

What is mismatch repair?

A

Repair that removes almost all errors missed by proofreading by detecting distortion caused by mispairing.

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16
Q

In mismatch repair, does MutS or MutL bind to the mismatch?

A

MutS;

MutL scans for the nick and triggers degradation of nicked strand.

17
Q

When occurs when there is a mutation in the mismatch repair gene?

A

Cells accumulate mutations at a high rate.

18
Q

What enzyme breaks a phosphodiester bond to change superhelicity and thereby relieving supercoiling?

A

Topoisomerases

19
Q

What is the mechanism of type I topoisomerases?

A

They create a single strand break in DNA.

This allows the DNA on either side of the break to rotate freely relative to each other.

Resealing then rapidly occurs.

20
Q

What is the mechanism of type II topoisomerase?

A

They make a double stranded break in the DNA.

A second strand passes through.

The break is resealed and dissociates.

21
Q

What is the replication origin?

A

A-T rich regions where sequence attacts initiator proteins to pry open DNA.

22
Q

What is involved in the initiation of DNA replication in bacteria?

A

Initiation proteins bind to specific sites in ORI and form a complex.

DNA helicase goes to the complex and binds to SS DNA.

Helicase unwinds DNA. A primarse makes RNA primer on the leading strand and the other proteins create 2 replication forks.

23
Q

When does eukaryotic DNA replication occur?

A

During DNA synthesis phase (S) which lasts eight hours for mammalian cells.

24
Q

Regions of gemone with ___ condensed chromatin replicate first.

A

Less

25
Q

What are the minimum requirements for sequence to be ORI?

A

Must have a binding site for ORC (origin recognition complex)

Must have an A-T rich stretch for easy unwinding

Must have binding site for proteins that help attact ORC

26
Q

In the S phase, activated Cdks lead to

A

Dissociation of helicase loading proteins

Activation of helicase

Unwinding of DNA

Loading of DNA polymerase

27
Q

When are histone proteins synthesized?

A

Mainly in S phase

28
Q

For efficient replication, what type of proteins are needed to destabilize the DNA-histone interface?

A

Chromatin-remodeling proteins.

29
Q

As the replicationf ork passes through chromatin, histone octamer breaks into:

A

An H3 - H4 tetramer, distributed randomly to daughter duplexes.

2 H2A - H2B dimers which are released from the DNA.

30
Q

Reassembly of DNA requires what type of chaperones?

A

Histone chaperones. THey are directed to DNA with sliding clamp called PCNA.

31
Q

Daughter nucleosomes generally contain what type of histones?

A

Old and new histones.

32
Q

What is a problem for replication on the lagging strand?

A

There is no place for an RNA primer.

33
Q

What special sequence is repeated thousands of times at the end of each chromosomes?

A

GGGTTA.

An enzyme called telomerase replenishes these sequences by elongating parental strand in 5’ to 3’ direction using an RNA template on the enzyme.

34
Q

What is the function of telomerase?

A

It extends the parental strand, which allow completion of replication of the lagging strand by DNA polymerase. It uses the extension as a template.

It ensures that the 3’ end is longer, leaving a protruding SS end that loops back and tucks into the repeat.

35
Q

What are T loops?

A

Structures that protect ends and distinguishes them from broken ones that need to be repaired.

36
Q

True or false: each chromosome end in a given cell contains variable numbers of telomere repeats depending on age.

A

True

37
Q

Why is it risky for an organism to control cell proliferation via telomeres?

A

Not all cells will stop dividing, and some cells may give rise to variant cells that lead to cancer.

38
Q

How are errors in the DNA sequence corrected?

A

Proofreading, DNA repair, and post-replication repair mechanisms.

Molecular Biology (12 decks)

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