DNA replication Flashcards

1
Q

What does it mean bidirectional and semiconservative replication?

A

semiconservative - each parental strand ends up in one of the daughter moleculeds
bidirectional - progress in 2 directions from the origin of replication

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2
Q

Describe the process of initiation of replication.

A
  • Replication is initiated at oriC origin of replication
  • Initiator protein DnaA melts the DNA at the origin of replication
  • DNA helicase DnaB is recruited to the melted DNA and starts unwinding process with the use of ATP
  • In Eukaryotes ORC functions in a similar way to DnaA, DnaB and DnaC
  • Initiation of DNA synthesis requires a template and a primer
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3
Q

In what direction the new strand is synthesised in replication? What is the consequence of this?

A

DNA is synthesised in 5’-3’ direction. As a result the replication on the leading strand is continuous, while on the lagging strand it is episodal.

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4
Q

Describe the DNA synthesis on the lagging strand.

A
  • Okazaki fragments are synthesised by elongation from primers.
  • There are nicks between the 3’ ends of okazaki fragments and the preceeding RNA primers
  • Nick translation - DNA polymerase I extends the Okazaki fragments (5’-3’ polymerisation) and removes the RNA primer (5’-3’ exonuclease)
  • DNA ligase binds after polymerase dissociation and seals the nick between the fragments
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5
Q

What is replisome? What are the functions of Beta-Clamps, Primerosome and SSB tetramer?

A

Replisome is the molecular machinery for DNA replication.

  • Primosome – contains Primase which synthetises the RNA primase necessary for DNA replication
  • β-clamps keep the polymerase complex loaded on DNA
  • SSB tetramer – protect the single stranded DNA from damage and improper DNA formation
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6
Q

How many polymerases have E.coli? Which one has the highest processivity?

A

E. coli has >5 DNA polymerases - Pol I-V

DNA Pol III is the subunit of Pol III holoenzyme with the highest processivity

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7
Q

How many polymerases do Eukaryotes typically have?

A

> 15

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8
Q

What are the important features of Polymerases?

A

o Multisubunit enzymes
o Require templates
o Have proofreading activity (3’-5’ exonuclease)
o Replicative polymerases remain bound to the replication fork
o Coordinate synthesis of leading and lagging strands

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9
Q

What is the 3D shape of DNA polymerases?

A

right hand-shaped

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