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Molecular genetics > DNA replication > Flashcards

DNA replication Flashcards

1
Q

What type of replication does DNA undergo?

A

Semi Conservative

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2
Q

What is required to form a new DNA strand?

A

Template strand, free DNA nucleotides (dNTPs), enzymes

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3
Q

What is the pre-replication complex?

A

Protein complex that forms at the origin of replication

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4
Q

What is required to initiate replication?

A

Formation of the pre-RC

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5
Q

What enzymes promote DNA opening ?

A

DNA helicase

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6
Q

How does DNA helicase promote DNA opening?

A

Cleaving the inter-base hydrogen bonds using ATP hydrolysis energy.

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7
Q

What enzyme synthesises short RNA primers?

A

Primase

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8
Q

What do the RNA primers do?

A

Primers anneal to the strand of DNA to initiate replication and the action of DNA polymerase.

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9
Q

Which strand are RNA primers added to?

A

RNA primer added to both the leading and lagging strands.

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10
Q

Why is a primer used?

A

Provides a 3-OH’ (prime) terminus to initiate replication

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11
Q

How many primers are needed in the leading strand vs lagging strand?

A

1 in leading (at the start)

Several in lagging for each okazaki fragment

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12
Q

What about DNA means there is a lagging and a leading strand?

A

Anti-parallel

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13
Q

DNA polymerase can only add new dNTPs to the … end

A

3’

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14
Q

DNA polymerase can only add new dNTPs to the 3’ end in a ….. direction

A

5’ to 3’

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15
Q

Where does the DNA polymerase move in the leading strand?

A

5’ to 3’ (following new strand)

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16
Q

How does DNA polymerase move along the strand?

A

Sliding clamp - PCNA

17
Q

What direction does the template strand lie in leading strand?

A

3’-5’

18
Q

What direction does the template strand lie in lagging strand?

A

5’-3’

19
Q

Why cant DNA polymerase not add dNTPs on lagging strand in 3’-5’ direction?

A

DNA polymerase can only add to 3’ end

20
Q

What direction does the new strand lie in leading strand?

A

5’-3’

21
Q

What direction does the new strand lie in lagging strand?

A

3’-5’

22
Q

How can both strands be replicated in the same direction?

A

Okazaki fragments

Lagging strand replicated in ‘backstitch’ method

23
Q

Describe how the lagging strand is replicated

A

Primase inserts a primer onto the DNA in the direction the DNA needs to grow

Polymerase associates with the primer and will move 5’ to 3’ away from the primer in the opposite direction as the leading strand.

Then another primer is placed further back until the full strand is replicated in Okazaki fragments.

24
Q

What is the function of PCNA?

A

Clamp that tethers polymerase to the DNA and displaces the primase enzyme.

25
Q

What proteins loads clamp onto the DNA?

A

Protein RFC

26
Q

What does protein RFC require to attach PCNA to DNA?

A

ATP

27
Q

What unwinds the DNA further along to prevent coil strain and risk of breaking?

A

Topoisomerase

28
Q

What is the role of topoisomerase?

A

Topoisomerases unwind the DNA at fork to prevent tortional strain and risk of breaking.

29
Q

What removes and degrades the RNA primer flaps in the lagging strands?

A

FEN1

30
Q

What pushes the RNA primers out the way?

A

DNA polymerase

31
Q

What does FEN1 do?

A

Removes the RNA primer flap after it is pushed aside by DNA polymerase. It also degrades it.

32
Q

What joins together Okazaki fragments?

A

DNA ligase

33
Q

What do telomeres consist of?

A

Long tandem repeats, constitutive chromatin

34
Q

What do telomeres do?

A

Specific structures at the end of chromosomes that prevent chromosome shortening during cell division

35
Q

Why do telomeres shorten with each division?

A

There is no template for primase on the telomere so RNA primer can not form for the last Okazaki fragment. So with each round there is shortening and senescence.

36
Q

How is telomere shortening prevented?

A

Telomerase enzyme

Has an RNA component and is a reverse transcriptase so uses RNA template to make complimentary DNA.

37
Q

What is a proof-reading polymerase?

A

Polymerases with 3’ to 5’ exonuclease activity can correct mistakes.

38
Q

What can 3’-5’ exonuclease polymerases do?

A

Remove the wrong nucleotide when a mistake is made in replication

Molecular genetics (7 decks)

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