Cell growth kinetics Flashcards
What does a typical growth curve show?
Changes in cell concentration with time.
The different phases of growth are more readily distinguished when the logarithm of viable cell concentration is plotted against time.
What is the rate of cell growth dependent on?
Growth phase
What happens in the lag phase of a cell?
Cells adapt to their new environment: new enzymes or structural components may be synthesised but the concentration of cells does not increase
What happens in the acceleration phase of a cell?
Growth starts
What happens in the growth phase of a cell?
Growth continues at an exponential rate. This appears as a straight line on a typical cell growth curve as cell concentration is a log plot
What happens in the decline phase of the cell?
Cell growth still occurs but at a decreasing rate
What happens in the stationary phase of the cell?
No further cell growth occurs
What happens in the death phase of the cell?
Cells lose viability or are destroyed by lysis
During the cell growth and decline phases, what’s the equation for cell growth rate?
How do we calculate a specific growth rate from the rate of cell growth equation if it’s constant?
How are cell growth rates usually expressed?
In terms of doubling time, td
For the biomass composition to stay constant during cell growth, what has to happen? Give an equation for this
The specific rate of production of each component in the culture must be equal to the cell-specific growth rate μ
What is the growth rate limiting substrate?
The single substrate exerts a dominant influence on the rate of growth
Give the monod equation - Showing how the specific growth rate is related to the concentration of the growth-limiting substrate
Only applicable for balanced growth
If μ is dependent on substrate concentration as indicated in the Monod equation, how can the monod equation be consistent with the observation of exponential growth with constant μ that is typical of so many cell cultures?
The answer lies in that typically Ks «_space;s. As a result, m is effectively independent of substrate concentration until s reaches very low values
Therefore, μ ~ μmax and growth follows exponential kinetics as long as s remains greater than about 10 Ks, which is usually for most of the culture period. This explains why μ remains constant and equal to μmax until the medium is virtually exhausted of substrate. When s finally falls below 10 Ks, the transition from growth to stationary phase can be very abrupt as the very small quantity of remaining substrate is consumed rapidly by the large number of cells present.
