Metabolism And Growth Flashcards
When does the bacterial chromosome replicate in the binary fission process?
Before the formation of the FtsZ ring.
Define the term generation. What is meant by the term generation time?
Generation is the action of one cell generating two daughter cells. Generation time is how long this process takes.
How does FtsZ ring find the cell midpoint of a rod-shaped cell?
By the action of MinC and MindD that polymerize along the cell inhibiting the ring formation and then MinE put then aside leaving the centre of the cell free for ring formation.
What eukaryotic protein is related to MreB? What does this protein do in eukaryotic cells?
Actin. It forms microfilaments that scaffold the cell cytoskeleton and the cytokinesis.
What is crescentin and what does it do?
It is a protein present in a vibro-shaped bacteria. It forms filamentous structures that accumulate at the concave face of a curved cell and it’s responsible for its shape.
What are autolysis and why are they necessary?
They are enzymes localized at the periplasm which the same activity as lysozyme. They are necessary for cell wall construction during cell growth.
What is the function of bactoprenol?
This hydrophobic alcohol is a lipid carrier molecule responsible for the transport of M-G-pentapeptide to across the cell membrane.
What is transpeptidation and why is it important?
It promotes the crossed-links between the peptides and it strengths the peptidoglycan. The enzymes that catalyze this exergonic reaction have binding sites for penicillin.
Why does exponential growth lead to large cells populations in so short period of time?
Because at each generation cells are doubling cell mass and cell number.
What is a semilogarithmic plot and what information can we derive from that?
It is characterized by the cell number plotted in a logarithmic scale and time in a arithmetic scale. It is used to predict the generation time.
Distinguish between the terms specific growth rate and generation time.
Growth rate is how many new cells per unit of time and generation time is how long it takes for cells to double its number (and mass consequently).
In what phase of the growth curve are cells dividing in a regular and orderly process?
Exponential phase.
Under what conditions does a lag phase not occur?
When cells in exponential phase are transferred to an identical medium.
Why do cells enter stationary phase?
When there is depletion of a limiting nutrient or when a waste product of the bacteria’s metabolism accumulates and inhibits growth.
How do microorganisms in a chemostat differ from microorganisms in a batch culture?
They can be in exponential phase for longer so they may be more active, have more enzymes and higher metabolism rate.
What happens in a chemostat if the dilution rate exceeds the maximal growth rate of the organisms?
The cells are washed out.
What are some of the problems that can arise when unstained preparations are used to make total cell counts of samples from natural environments?
1) Debris can be mistaken for cells;
2) Small cells are hard to be seen and counted;
3) Dead cells cannot be distinguished from viable cells;
4) Precision is hard to achieve;
5) A phase-contrast microscope is needed when there is no staining;
6) Motile cells have to be immobilized;
7) Low density cultures might not show any cell.
Why is a viable count is more sensitive than a microscope count? What major assumption is made in relating plate count results to cell number?
Viable count only count cells that are able to generate offspring. The major assumption is that each colony arose from one single cell.
Describe how you would dilute a culture by 10 to the power of negative 7?
By 10-fold dilutions. 1mL of the culture is added to 9mL of water and 10 to the power of negative 1 is obtained and the procedure is repeated until 10 to the power of negative 7 is obtained.
