Bacterial Cell Division

Question 1

What is microbial growth?

Answer 1

 Does NOT refer to cell size

 Refers to the increase in number of cells in a population

Question 2

What is binary fission?

Answer 2

cell dividing into two new cells

Question 3

What is the process of binary fission?

Answer 3

 Cell increases in size (about twice the size); genome is duplicating
 Septum forms: a partition that constricts the cell into two daughter cells (about half-way)
–> Results from the inward growth of the cytoplasmic membrane and cell wall
 Septum pinches off

Question 4

How does the septum form?

Answer 4

Results from the inward growth of the cytoplasmic membrane and cell wall

Question 5

What is the generation time?

Answer 5

time required for binary fission; time for a single cell to double

Question 6

What is a generation?

Answer 6

occurs as one cell separates to form 2 cells; period between 1 cell and 2 cells

Question 7

How variable is generation time?

Answer 7

Varies between organisms; within a single organism it can vary according to conditions (e.g. ideal/lab vs. normal growth conditions)

Question 8

How is a populations size measured?

Answer 8

2^n where n=#generations

Question 9

What are Fts proteins?

Answer 9

filamentous temperature sensitive

 Essential for cell division

Question 10

What happens in the case of mutations of Fts protein?

Answer 10

• Mutations on genes that encode for Fts proteins cause impaired cell division. Instead of normal division, the cells form long filamentous cells that fail to divide (septum doesn’t form)
   Multiple copies of genome in the filamentous cells

Question 11

When do the filamentous cells occur?

Answer 11

• Mutations of Fts

- Non-permissive temperatures for binary fission

Question 12

What is the major Fts protein?

Answer 12

FtsZ: homologous to eukaryotic tubulin

Question 13

What is the divisome?

Answer 13

• cell-division apparatus formed by Fts proteins
   Forms between the duplicated nucleoids
   Formation starts with the attachment of FtsZ molecules in a ring around the center of the cell

Question 14

What triggers the formation of the divisome?

Answer 14

completion of DNA replication

Question 15

How does the divisome disappear?

Answer 15

 Cell wall and cytoplasmic membrane forms along the plane, breaking down the divisome
–> Formation of the septum

Question 16

What are the limiting factors of microbial growth?

Answer 16

• Nutrient availability

- Formation of toxic metabolic wastes

Question 17

What “shape” describes the microbial growth cycle?

Answer 17

Growth curve

Question 18

What are the phases of the microbial growth cycle?

Answer 18

• lag phase
• log phase
• stationary phase
• death phase

Question 19

Describe the 1st phase of the microbial growth cycle.

Answer 19

 Time that immediately follows inoculation
 Little to no growth
 Time needed for nutrient replenishment
 Cells are metabolically active at this time

Question 20

Describe the 2nd phase of the microbial growth cycle.

Answer 20

 Maximum growth rate: due to maximum metabolic rate

 Cells are most sensitive to metabolic inhibition

Question 21

Describe the 3rd phase of the microbial growth cycle.

Answer 21

 No net increase or decrease of cells
 This stage is due to either
o Depletion of essential nutrient (used up)
o Waste product accumulates in the medium and inhibits growth
 Cells switch to a lower level of metabolism (less energy usage)
 Switch in metabolic pathways
–> Produce secondary metabolites: pigments or antibiotics
 Decreased sensitivity to metabolic inhibition

Question 22

Describe the 4th phase of the microbial growth cycle.

Answer 22

 Cell death is greater than cell division

Question 23

What are the environmental conditions for microbial growths?

Answer 23

1) Temperature (most important!)
2) pH
3) Osmotic pressure
4) Oxygen availability