Bacterial Replication

Question 1

3 characteristics of bacterial replication?

Answer 1

Bidirectional
Single site of origin
Replisome (synthesis by a single complex)

Question 2

What are the two main recognition components in bacterial replication initiation?

Answer 2

DnaA (initiator protein)

oriC (250bp replicator sequence)

Question 3

What is the initial step in bacterial replication initiation?

Answer 3

5 monomers of DnaA bind 9 bp repeats in the OriC

Question 4

How many monomers of DnaA bind the oriC initially ?

Answer 4

5

Question 5

What is the consensus sequence of the 9bp repeats in the oriC

Answer 5

5’- TTATCCACA-3’

Question 6

What proteins facilitate the initiation of bacterial replication (binding of DnaA monomers)??

Answer 6

IHC

HU

Question 7

What does the binding on the DnaA monomers do?

Answer 7

Melts 3 tandemly repeated 13bp AT rich segments left of the oriC

Question 8

What is the consensus seq of the 13 bp rich segments ??

Answer 8

5’-GATCTNTTNTTTT-3’

Question 9

Formation of the open complex allows for what?

Answer 9

The 45 bp segment to be p1 nuclease sensitive (cut by p1 nuclear)

Question 10

What is required for the open complex?

Answer 10

DnaA

ATP (binding on DnaA is atp dependent)

Question 11

What is recruited to the melted region?

Answer 11

DnaB6:DnaC6 complex

Question 12

When dnab6:dnac6 is recruited to the melted region what is formed?

Answer 12

Prepriming complex

Question 13

Formation of the prepriming complex allows for what to occur?

Answer 13

Addition 5 monomers of DnaA to bind to the blind DnaA to form dimers

Question 14

What is the role of dnaC6 ?

Answer 14

An atpase that promotes loading of the dnaB6

Question 15

DnaB6 function?

Answer 15

Helicase- unwinds the DNA in the prepriming complex in both directions either side of the bubble

Question 16

What 2 proteins are necessary for dnaB6 function?

Answer 16

SSB’s

Gyrase

Question 17

What is the function of gyrase?

Answer 17

Relieves strain when DNA is being unwound

Question 18

Function of ssbs?

Answer 18

Prevent reannealing

Question 19

After dnaB6 unwinds the DNA, what enters the unwound DNA?

Answer 19

RNA polymerase

Question 20

RNA polymerase binding activates what?

Answer 20

RNA polymerases promise activity

Question 21

Function of primase?

Answer 21

RNA primer synthesis (10-12 nt long)

Question 22

Why is an RNA primer necessary?

Answer 22

Primer has a 3’ OH that provides a starting point for DNA pol 3 to add nucleotides

Question 23

In 40 mins how much bacterial DNA can be replicated?

Answer 23

4.7x106 bp

Time for each polymerase to transverse half the chromosome

Question 24

Cells with doubling times of less than 60 mins must what?

Answer 24

Start replication before the end of the previous cycle - resulting in multiforked chromosomes
Allows the double all the DNA before division

Question 25

On the lagging strand, when DNA B is unwinding the DNA what proteins join it?

Answer 25

Primosome (helicase and primase) | SSB's

Question 26

What protein is responsible for strand synthesis in bacterial elongation?

Answer 26

DNA pol 3

Question 27

Describe the structure of DNA pol 3

Answer 27

A holoenzyme

Question 28

Describe the structure of the replisome

Answer 28

Single multi protein complex that contains the two pol 3 cores

Question 29

What subunits are the DNA pol 3 cores made up of | ?

Answer 29

Alpha E O circle

Question 30

What are the2 DNA pol cores linked by?

Answer 30

Tau protein

Question 31

How does lagging strand synthesis occur?

Answer 31

Holoenzyme dissociates from lagging strand and relocated to an upstream primer that has previously been synthesised by primosome

Question 32

What happens the the RNA primers after they've been used to synthesise the new DNA ?

Answer 32

Excised by DNA pol 1

Question 33

How many termination sequences are there?

Answer 33

6 (non palindromic)

Question 34

What are the termination sequences for replication forks travelling anti-clockwise?

Answer 34

Ter E, D AND A

Question 35

What are the terminator sequences for replication forks travelling clockwise?

Answer 35

Ter B, C AND F

Question 36

What gene encodes tus protein?

Answer 36

Termination utilisation substance gene

Question 37

What does tus protein do?

Answer 37

Binds to the ter site and prevents strand displacement by DNA helicase