Bacterial Metabolism Flashcards
1
Q
Overview
A
2
Q
What is constitutive enzyme?
A
- enzymes necessary for maintenance and growth.
- always synthesised irrespective of the environment.
3
Q
What is inducible enzyme?
why have different enzymes?
A
- enzymes synthesised in response to the presence of specific compounds (induces) in the environment, e.g., induced enzyme formation.
- different enzymes are caused by cell economy - no waste of energy.
4
Q
what are regulated enzymes?
A
- exist in metabolic pathways (e.g., glycolysis) so that the activity of the enzymes can be increased or reduced.
- this will affect the end result of the entire pathway.
5
Q
what is a property of metabolic enzymes?
A
- nearly all metabolic enzymes are intracellular.
- exception is hydrolytic enzymes exported to break down high molecular weight compounds, e.g., invertases.
6
Q
Sugar transport and acid production
A
in oral bacteria, glucose uptake is mediated by:
1. PEP-PTS transport
2. Multi sugar metabolism
3. Glucose permease
7
Q
Phosphoenolpyruvate-mediated phospho-transferase (PEP-PTS) Transport system properties
A
- high affinity transport system (teaspoon) for mono- & di-saccharides.
- Occurs in acidogenic (acid producing) oral bacteria, Streptococcus Lactobacillus, and actinomyces
- Constitutive for Glucose & Sucrose
- Inducible for Lactose, Mannitol & Sorbitol (represesed by glucose).
- The glycolytic intermediate Phosphoenolpyruvate (PEP) provides the phosphate group (NOT ATP) which is cleaved to release energy for sugar uptake.
- activitty is modulated by environmental conditions - optimal under conditions of CHO limitation neutral pH and slow rates of bacterial growth (famine environment).
- repressed under conditions of excess sugar, low pH and high Growth rates (Feast environment).
- Oral Streptococci often exposed to transitory conditions of low pH and high sugar concentration.
8
Q
Glucose Permease Transport
A
- ATP dependent as ATP provides energy for uptake.
- Functions at High growth rates and Low pH (shovel)
- sugar is transported into the cell where it is also phosphorylated on the inner surface of the membrane.
9
Q
Compare the differences between respiration and fermentation of CHO metabolism
A
10
Q
Describe the process of glycolysis.
A
11
Q
Describe the process of CHO metabolism.
A
12
Q
What are pyruvate?
A
- most oral bacteria metabolise pyruvate to organic acids such as acetic acid, formic acid, & lactic acid.
13
Q
What is Pyruvate Formate Lyase?
A
- lactate production does not lead to more ATP.
- 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.
14
Q
Controlling the fate of pyruvate
A
- regulation of PFL and LDH enzymes controls the type of fermentation of pyruvate.
- Regulation of Pyruvate Kinase (PK) plays an important role in the regulation of the glycolytic cycle.
- Glucose Excess - increased intracellular concentration of glycolytic intermediates causing, inhibition of the PFL pathway.
- Glucose-6-P abundant which activates Pyruvate Kinase allowing conversion of PEP to pyruvate and then lactate = (homo-fermentation).
- FDP activates LDH causing increased conversion of pyruvate to Lactic acid generating ATP.
- Glucose permease operating as low affinity high volume uptake of glucose.
15
Q
Describe the regulation of glucose metabolism in S. Mutans
A
16
Q
Controlling the fate of glucose
A
- 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.
- Relevance into vivo situation - Studies on Human plaque have shown different profiles of acids at different times of the day.
