Cell Growth And Kinetics

Question 1

How do bacteria grow (specifics)

Answer 1

• Asexually
• Binary fission
• Increase cell size
• Replicate DNA
• Divide

Question 2

What is doubling time?

Answer 2

-The time taken for microbial population to double in number

Question 3

What is generation time?

Answer 3

-Time taken for a single cell to divide

Question 4

What are the 4 stages of cell growth?

Answer 4

• Lag phase
• Exponential (log) phase
• Stationary phase
• Death phase

Question 5

What happens in the lag phase of growth?

Answer 5

• Little increase in cell conc.

- Cells are adjusting to environment, synthensizing enzymes and getting ready to reproduce

Question 6

What is the lag phase affected by?

Answer 6

• nutrient requirements
• media/extent of change of growth environment
• phase and size of innoculation bacteria

Question 7

What happens in exponential growth phase?

Answer 7

• Cells growth rate is proportional to cell conc.
• Dividing at maximum rate, all enzyme pathways for metabolizing substrate are in place from lag phase
• Can use nutrients most effectively

Question 8

What happens in the stationary phase?

Answer 8

• Cells reach minimum biological space,limited cell growth
• Lack one or more nutrients and depletion of essential metabolites
• Build up of organic acids and toxic materials also slow growth
• Net growth is zero
• Many important fermentation products e.g antibiotics are produced in this phase

Question 9

What happens in death phase?

Answer 9

• Decrease in live cell conc.

- Due to toxic by-prodcuts, harsh environment, depletion of nutrient supply or substrate

Question 10

What is the rate of change of Cc in a batch system?

Answer 10

dCc/dt = rG = μ*Cc

Integrated between Cc=Cc0 at t=0 and Cc=Cc at t=t gives:

ln(C/C0)= μt
Or
C=Cc0exp(μ*t)

Question 11

What is the equation for specific growth rate?

Answer 11

μ=(μmax*Cs)/(Ks+Cs)

μ, specific growth rate
μmax, max specifc growth rate
Ks, Monod constant, g/dm^3 (1/2 μmax)
Cs, substrate (nutrient) conc. g/dm^3

Question 12

What is the Monod equation in terms of μmax?

Answer 12

rG= (μmaxCcCs)/(Ks+Cs)

rG, growth rate g/dm^3.s

Question 13

What is the equation for doubling time?

Answer 13

td= ln(2)/μ

Question 14

What is the equation for rG in terms of μmax when a product inhibits the rate of growth?

Answer 14

rG=Kobs(μmaxCc*Cs)/(Ks+Cs)

Kobs=observed rate constant

Question 15

What is the equation for Kobs?

Answer 15

Kobs=(1-(Cp/Cp*))^n

Cp*, product conc. at which metabolism ceases
n, empiral constant

(Will be given)

Question 16

What is the equation for yield coefficient Yc/s?

Answer 16

Yc/s = -dCc/dCs=mass of new cells/mass of substrate consumed

Question 17

What is the equation for yield coefficient Yp/s?

Answer 17

Yp/s= -dCp/dCs =mass of product formed/mass of substrate consumed

Question 18

What factors influence biomass yield?

Answer 18

• Medium composition (complex/simple nutrients)
• Nature of carbon and nitrogen
• pH
• Temperature
• Biomass yield is greater in aerobic than anaerobic cultures as it is a higher energy reaction