De Novo Fatty Acid Synthesis
| A | Increasing acetyl CoA carboxylase activity | |
| B |
Increasing the transport of glucose into the cell |
|
| C |
Inhibits PDH |
|
| D |
Decreased intracellular cAMP level |
Insulin causes lipogenesis by all, EXCEPT:
| A |
Increasing acetyl CoA carboxylase activity |
|
| B |
Increasing the transport of glucose into the cell |
|
| C |
Inhibits PDH |
|
| D |
Decreased intracellular cAMP level |
Insulin increases the activity of PDH (Pyruvate dehydrogenase). Insulin increases the recruitment of GLUT to the surface of various cells and thus increases the uptake of insulin via various cells. Insulin has got inhibitory effect on adenylyl cyclase activity and so cause dephosphorylation.
Insulin increases the activity of acetyl CoA carboxylase activity and thus has got stimulatory effect on lipogenesis.
Fatty acid oxidation produces:
| A |
Acetyl CoA |
|
| B |
Succinyl CoA |
|
| C |
Propionyl CoA |
|
| D |
All of the above |
In synthesis of fatty acids energy is supplied by:
| A |
NAD |
|
| B |
FAD |
|
| C |
GTP |
|
| D |
NADPH |
D i.e. NADPH
The most important source of reducing equivalents for fatty acid synthesis in the liver is:
| A |
Glycolysis |
|
| B |
TCA cycle |
|
| C |
Uronic acid pathway |
|
| D |
HMP pathway |
D i.e. HMP pathway
The reducing agent used in lipogenesis is derived from:
| A |
Pentose phosphate pathway |
|
| B |
Glycolysis |
|
| C |
TCA cycle |
|
| D |
Gluconeogenesis |
NADPH is involved as donor of reducing equivalents in both the reduction of the 3-ketoacyl and of the 2, 3-unsaturated acyl derivatives.
The oxidative reactions of the pentose phosphate are the chief source of the hydrogen required for the reductive synthesis of fatty acids.
| A |
NADH |
|
| B |
Acetyl-CoA |
|
| C |
Acyl-CoA |
|
| D |
Acetate |
Fatty acid biosynthesis in the cytosol requires a sufficient concentration of NADPH and acetyl CoA.
NADPH is generated in the cytosol by the pentose phosphate pathway, and by the malic enzyme which oxidizes malate into pyruvate and CO2, generating NADPH.
Which of the following enzyme is not a component of fatty acid synthase complex?
| A |
Acetyl Co-A carboxylase |
|
| B |
Ketoacyl synthase |
|
| C |
Enoyl reductase |
|
| D |
Acetoacetyl |
The Fatty Acid Synthase Complex Is a Homodimer of Two Polypeptide Chains Containing Six Enzyme Activities and the Acyl Carrier Protein.
The 6 enzymes are-
- Ketoacyl synthase
- Ketoacyl reductase
- Malonyl transacylase
- Dehydratase
- Enoyl reductase
- Thioesterase
Acetyl Co-A carboxylase is the rate-limiting enzyme of fatty acid synthesis and is an enzyme, which is not a component of fatty acid synthase complex.
Rate limiting step in fatty acid synthesis is ‑
| A |
Production of acetyl CoA |
|
| B |
Production of oxalocetate |
|
| C |
Production of malonyl-CoA |
|
| D |
Production of citrate |
Rate limiting enzyme in fatty acid synthesis ‑
| A |
PDH dehydrogenase |
|
| B |
Malonyl reductase |
|
| C |
Acetyl CoA carboxylase |
|
| D |
Transacetylase |
Ans. is ‘c’ i.e., Acetyl CoA carboxylase
The major source of NADPH for fatty acidsynthesis ‑
| A |
PPP |
|
| B |
TCA cycle |
|
| C |
Glycolysis |
|
| D |
Glycogenolysis |
Ans. is ‘a’ i.e., PPP
Source of NADPH for lipogenesis
- NADPH is involved as donor of reducing equivalentse in both the reduction of 3-ketoacyl by 3 ketoacyl reductase and of 2,3- unsasturated acyl by enoyl reductase. The main source of NADPH for lipogenesis is the pentose phosphate pathway: PPP (Hexose monophosphate shunt: HMP shunt)°.
- Other sources of NADPH include:-
- The reaction that converts malate to pyruvate catalyzed by malic enzyme.
- Exramitrochondrial isocitrate dehydrogenase.
