Topic 4-L1 - Cell division

Question 1

Most microbial cells divide by

Answer 1

binary fission

Question 2

binary fission:

Answer 2

DNA replicated, cell grows, cytoplasm evenly divided, producing two (essentially) identical daughter cells

Question 3

After replication, DNA must be

Answer 3

segregated to opposite sides of the cell so that each daughter gets one copy

Question 4

In BF, Cells elongate and a septum begins to form to

Answer 4

separate the cell into two, division site contracts and cells pinched off

Question 5

Cell division is a highly regulate process?

Answer 5

Yes

Question 6

Things about cell division that need to be coordinated

Answer 6

• Division at appropriate times only
• Chromosome is faithfully replicated & each daughter gets one copy of genetic material
• septum forms at right location
• cell wall remains intact to prevent bursting

Question 7

Nutritional status coordinated with

Answer 7

• DNA synthesis
• cell envelope synthesis
• division processes

Question 8

DNA replication is first step in cell cycle. Starts at specific site on chromosome –

Answer 8

oriC. Protein called DnaA binds oriC to initiate DNA replication

Question 9

Each strand of double-stranded chromosome acts as a

Answer 9

template to produce a new strand (DNA is fully replicated)

Question 10

What does the z-ring form in cell cycle

Answer 10

Divisome, promotes formation of septum at center of cell. Septum’s forms then cells detach

Question 11

DNA replication is controlled by binding of protein

Answer 11

DnaA to oriC.

Question 12

One important mechanism (there are multiple) for controlling DnaA binding to oriC is via a protein called

Answer 12

SeqA – competes with DnaA for oriC binding site.

Question 13

oriC DNA is

Answer 13

methylated by enzymes in
the cell. New DNA takes a while to get
methylated. Methylated DNA bound to SeqA, preventing DnaA form binding to oriC.

Question 14

Bacteria can undergo multiple rounds of DNA replication at once?

Answer 14

Yes

Question 15

For some bacteria, generation time (time to double your population) can be shorter than the amount of time it takes to

Answer 15

replicate the chromosome

Question 16

In certain bacteria (but not all), such as the model bacteria E. coli and
Bacillus subtilis,

Answer 16

multiple DNA replication forks can be active at once

Question 17

How can generation time be shorter then replication of DNA?

Answer 17

Multiple DNA replication forks

Question 18

In multiple replication forks, OriC region starts getting replicated

Answer 18

again before the first fork is finished.

Daughter cells receive a complete chromosome, as well as a second one whose production is in progress

Question 19

Bacteria build multi-protein complexes called divisomes to help identify the

Answer 19

center of the cell, building a septum, and separate the cell into two daughter cells

Question 20

A central protein for divisome is FtsZ – polymerizes to from a

Answer 20

ring (FtsZ ring) around circumference of cell at the midcell where division will occur, ring constricts and help division.

Question 21

Divisome helps build cell septum, including by

Answer 21

recruiting proteins to build cell envelope that separates the newly dividing cells

Question 22

For finding the mid cell,

Answer 22

• nucleoid occlusion

- inhibitors of FtsZ ring formation

Question 23

nucleoid occlusion

Answer 23

presence of the chromosome at midcell prevents divisome from forming there

Question 24

During cell division, Cell wall must be

Answer 24

remodeled but remain intact to prevent bursting

Question 25

How does the cell wall remain intact during division

Answer 25

• Peptidoglycan precursors brought across cytoplasmic membrane by
  Bactoprenol (hydrophobic molecule – lipid)
• Autolysin
• Transglycosylases enzymes

Question 26

Autolysin:

Answer 26

breaks glycolytic bonds for insertion of new monomers

Question 27

Transglycosylases enzymes form new

Answer 27

bonds in sugar backbone &

transpeptidase enzymes form new peptide crosslinks

Question 28

How the new cell wall is built as cell grows largely dictates

Answer 28

cell shape

Question 29

In rod-shaped cells, actin-like cytoskeleton protein

Answer 29

MreB ensures that new cell wall is added along its long axis – rod elongates

Question 30

Spherical cells lack MreB – new cell wall added only at

Answer 30

midcell. Spherical shape is essentially the default

Question 31

Alternative to binary fusion

Answer 31

Budding division

Question 32

Budding division is an alternative to binary fission seen in a number
of microbes. How’s it work?

Answer 32

New cell grows from old by budding off from a particular site on mother cell.

Question 33

multiple fission

Answer 33

For some species, new cells bud off from long extensions called hyphae. In some instances, long hyphal filaments will form multiple septa at once and break off into
many new cells