Bacterial Metabolism

Question 1

Overview

Answer 1

Question 2

What is constitutive enzyme?

Answer 2

1. enzymes necessary for maintenance and growth.
2. always synthesised irrespective of the environment.

Question 3

What is inducible enzyme?
why have different enzymes?

Answer 3

1. enzymes synthesised in response to the presence of specific compounds (induces) in the environment, e.g., induced enzyme formation.
2. different enzymes are caused by cell economy - no waste of energy.

Question 4

what are regulated enzymes?

Answer 4

1. exist in metabolic pathways (e.g., glycolysis) so that the activity of the enzymes can be increased or reduced.
2. this will affect the end result of the entire pathway.

Question 5

what is a property of metabolic enzymes?

Answer 5

1. nearly all metabolic enzymes are intracellular.
2. exception is hydrolytic enzymes exported to break down high molecular weight compounds, e.g., invertases.

Question 6

Sugar transport and acid production

Answer 6

in oral bacteria, glucose uptake is mediated by:
1. PEP-PTS transport
2. Multi sugar metabolism
3. Glucose permease

Question 7

Phosphoenolpyruvate-mediated phospho-transferase (PEP-PTS) Transport system properties

Answer 7

1. high affinity transport system (teaspoon) for mono- & di-saccharides.
2. Occurs in acidogenic (acid producing) oral bacteria, Streptococcus Lactobacillus, and actinomyces
3. Constitutive for Glucose & Sucrose
4. Inducible for Lactose, Mannitol & Sorbitol (represesed by glucose).
5. The glycolytic intermediate Phosphoenolpyruvate (PEP) provides the phosphate group (NOT ATP) which is cleaved to release energy for sugar uptake.
6. activitty is modulated by environmental conditions - optimal under conditions of CHO limitation neutral pH and slow rates of bacterial growth (famine environment).
7. repressed under conditions of excess sugar, low pH and high Growth rates (Feast environment).
8. Oral Streptococci often exposed to transitory conditions of low pH and high sugar concentration.

Question 8

Glucose Permease Transport

Answer 8

1. ATP dependent as ATP provides energy for uptake.
2. Functions at High growth rates and Low pH (shovel)
3. sugar is transported into the cell where it is also phosphorylated on the inner surface of the membrane.

Question 9

Compare the differences between respiration and fermentation of CHO metabolism

Answer 9

Question 10

Describe the process of glycolysis.

Answer 10

Question 11

Describe the process of CHO metabolism.

Answer 11

Question 12

What are pyruvate?

Answer 12

1. most oral bacteria metabolise pyruvate to organic acids such as acetic acid, formic acid, & lactic acid.

Question 13

What is Pyruvate Formate Lyase?

Answer 13

1. lactate production does not lead to more ATP.
2. Pyruvate formate lyase makes acetyl CoA which can yield an ATP and acetate. Ethanol production is linked with re-oxidising NADH. The reaction has two steps.

Question 14

Controlling the fate of pyruvate

Answer 14

1. regulation of PFL and LDH enzymes controls the type of fermentation of pyruvate.
2. Regulation of Pyruvate Kinase (PK) plays an important role in the regulation of the glycolytic cycle.
3. Glucose Excess - increased intracellular concentration of glycolytic intermediates causing, inhibition of the PFL pathway.
4. Glucose-6-P abundant which activates Pyruvate Kinase allowing conversion of PEP to pyruvate and then lactate = (homo-fermentation).
5. FDP activates LDH causing increased conversion of pyruvate to Lactic acid generating ATP.
6. Glucose permease operating as low affinity high volume uptake of glucose.

Question 15

Describe the regulation of glucose metabolism in S. Mutans

Answer 15

Question 16

Controlling the fate of glucose

Answer 16

1. Glucose limitation - decreased availability of glucose leads to a decreased intracellular concentration of G-6-P. This restricts the activation of Pyruvate kinase and produces an accumulation of PEP, needed for the high affinity uptake of glucose via the PEP-PTS uptake system.
2. Relevance into vivo situation - Studies on Human plaque have shown different profiles of acids at different times of the day.

Question 17

Metabolic effect of fluoride

Answer 17

1. inhibits enolase and therefore reduces production of PEP. Thus under glucose limiting conditions the low levels of PEP will directly effect the PEP-PTS transport system reducing the organism ability to grow.
2. Glucose excess conditions reduces fluorides effect on bacteria as the PEP-PTS system in repressed. Glucose uptake is not dependent upon PEP (Permease operates).