Bacterial growth Flashcards
Define growth.
○Growth is when cell constituents are increased, causing cell to become larger and undergo cell division (Willey, et al , 2011, pp.163).
○It also means when the population size increases (Willey, et al., 2011, pp.163).
References: Willey, J.M., Sherwood, L.M., Woolverton, C.J. (2011) Prescott’s Microbiology. 8th edn. New York: McGraw-Hill.
Why would cells that are vigorously growing when inoculated into fresh culture medium have a shorter lag phase than those that have been stored in a refrigerator?
○Lag phase is when cells are synthesising new components like ribosomes, ATP and essential cofactors and don’t immediately divide and increase in number (Willey, et al., 2011, pp.164).
○Eventually, cells will undergo DNA replication and divide (Willey, et al., 2011, pp.164).
○Cells in fresh culture medium have shorter lag phase as they have a lot of nutrients available and start dividing quickly (Willey, et al., 2011, pp.164).
○Cells stored in refrigerator have longer lag phase as they are inactive and it takes time for them to activate their enzymes and get used to the fresh culture medium (Willey, et al., 2011, pp.164).
References: Willey, J.M., Sherwood, L.M., Woolverton, C.J. (2011) Prescott’s Microbiology. 8th edn. New York: McGraw-Hill.
Define balanced growth and unbalanced growth.
○Balanced growth is when cell components are synthesised at a constant rate relative to each other (Willey, et al., 2011, pp.164).
○Unbalanced growth is when the cell components rate of synthesis differs relative to each other, due to changes in nutrient levels or environmental conditions (Willey, et al., 2011, pp.164).
References: Willey, J.M., Sherwood, L.M., Woolverton, C.J. (2011) Prescott’s Microbiology. 8th edn. New York: McGraw-Hill.
Describe the difference between shift-up experiments and shift-down experiments.
○Shift-up experiments are when cultures are transferred from a medium which is poor in nutrients to a medium which is rich in nutrients (Willey, Sherwood, Woolverton, 2011, pp.164).
○A shift-down experiment is when cultures are transferred from medium which is rich in nutrients to a medium which is poor in nutrients (Willey, Sherwood, Woolverton, 2011, pp.164).
References: Willey, J.M., Sherwood, L.M., Woolverton, C.J. (2011) Prescott’s Microbiology. 8th edn. New York: McGraw-Hill.
Why do shift-up and shift-down experiments cause cells to enter unbalanced growth?
○Cells enter unbalanced growth in shift-up experiments as cells need to increase protein synthesis by synthesising more ribosomes, causing a lag in growth (Willey, Sherwood, Woolverton, 2011, pp.164).
○Cells enter unbalanced growth in shift-down experiments as some nutrients may be unavailable, so cells synthesise the enzymes which synthesise the unavailable nutrients, causing a lag in growth (Willey, Sherwood, Woolverton, 2011, pp.164).
References: Willey, J.M., Sherwood, L.M., Woolverton, C.J. (2011) Prescott’s Microbiology. 8th edn. New York: McGraw-Hill.
What effect does increasing a limiting nutrient have on the yield of cells and the growth rate?
○As concentration of limiting nutrient increases, yield of cells and growth rate also increases, due to increased cell division (Willey, et al., 2011, pp.164).
○Growth rate increases in a hyperbolic way (Willey, et al., 2011, pp.164).
○When nutrient levels get high, growth rate won’t increase even if nutrient concentration continues to increase, because transport proteins are saturated at high concentrations of nutrients (Willey, et al., 2011, pp.164).
References: Willey, J.M., Sherwood, L.M., Woolverton, C.J. (2011) Prescott’s Microbiology. 8th edn. New York: McGraw-Hill.
Describe the first phase of the growth curve.
○The first phase is lag phase (Willey, et al., 2011, pp.164).
○Cells are synthesising new components, like ribosomes, ATP and essential cofactors, and don’t immediately divide and increase in number (Willey, et al., 2011, pp.164).
○Eventually, cells undergo DNA replication and divide (Willey, et al., 2011, pp.164).
○Importance: allows cells to synthesise components it may not have, allows synthesis of new enzymes, gives injured cells time to recover (Willey, et al., 2011, pp.164).
References: Willey, J.M., Sherwood, L.M., Woolverton, C.J. (2011) Prescott’s Microbiology. 8th edn. New York: McGraw-Hill.
Describe the second phase of the growth curve.
○The second phase is exponential phase (Willey, et al., 2011, pp.164).
Cells grow and divide at maximum rate and growth rate is constant (Willey, et al., 2011, pp.164).
○Cells are in balanced growth, where cell components are synthesised at constant rate relative to each other, but it may become unbalanced if cell components rate of synthesis differs due to changes in nutrient levels or environmental conditions (Willey, et al., 2011, pp.164).
References: Willey, J.M., Sherwood, L.M., Woolverton, C.J. (2011) Prescott’s Microbiology. 8th edn. New York: McGraw-Hill.
Describe the third phase of the growth curve.
○The fourth phase is stationary phase (Willey, et al., 2011, pp.164-165).
○Population growth stops as number of active cells remain constant (Willey, et al., 2011, pp.164-165).
○This could be due to cell division and cell death being in balance, or cells are still metabolically active but don’t divide (Willey, et al., 2011, pp.164-165).
○A result of nutrient limitation and toxic waste build up (Willey, et al., 2011, pp.164-165).
References: Willey, J.M., Sherwood, L.M., Woolverton, C.J. (2011) Prescott’s Microbiology. 8th edn. New York: McGraw-Hill.
Describe the fourth phase of the growth curve.
○The fourth phase is senescence and death (Willey, et al., 2011, pp.165-166).
○This is characterised by a decrease in viable cells (Willey, et al., 2011, 165-166).
○Cells are temporarily unable to grow and become VBNC, viable but nonculturable cells (Willey, et al., 2011, pp.165-166).
○Another cause is programmed cell death, where cells are genetically programmed to die after growth stops (Willey, et al., 2011, pp.165-166).
○The leakage of nutrients after they die allows other to survive (Willey, et al., 2011, pp.165-166).
References: Willey, J.M., Sherwood, L.M., Woolverton, C.J. (2011) Prescott’s Microbiology. 8th edn. New York: McGraw-Hill.
Describe the bacterial cell cycle.
Cell elongates and DNA is replicated.
Cell wall and membrane begin to divide.
Cross-wall forms completely around both DNA.
Cells separate.
References: Willey, J.M., Sherwood, L.M., Woolverton, C.J. (2011) Prescott’s Microbiology. 8th edn. New York: McGraw-Hill.
