Lipid synthesis and degradation (revised version) Flashcards
What are triglycerides broken down into? [2 marks]
- Fatty acids
- Glycerol
What can one of the components of triglycerides be fed into? [2 marks]
GLYCEROL
- Glycolysis
- Gluconeogenesis
Structure of fatty acids [3 marks]
- Chains of methyl groups
- Terminal carboxyl group
- Cis configuration for double bonds
Where does fatty acid synthesis and degradation occur? [2 marks]
- Synthesis occurs in the cytosol
- Degradation occurs in the mitochondria
What are the intermediates for fatty acid synthesis and degradation linked to? [2 marks]
- Intermediates are linked to acyl carrier proteins (ACPs) in synthesis
- Intermediates are linked to CoA in degradation
What are added and removed in fatty acid synthesis and degradation? [2 marks]
- Sequential addition of 2 carbons in synthesis
- Sequential removal of 2 carbons in degradation
What is the reductant in fatty acid synthesis? [1 mark]
NADPH
What are the oxidants in fatty acid degradation? [2 marks]
- FAD
- NAD
Where does NADPH for fatty acid synthesis come from? [2 marks]
- 60% from pentose phosphate pathway
- 40% from acetyl CoA transfer
What is the preferred energy source for cardiac muscle? [1 mark]
Fats
What is involved in acetyl CoA transfer? [4 marks]
- Acetyl CoA
- Oxaloacetate
- Citrate
- Malate
What are the products of acetyl CoA transfer? [3 marks]
- Pyruvate
- CO2
- NADPH
First step in fatty acid synthesis [3 marks]
Acetyl-CoA + ATP + HCO3- → malonyl-CoA + ADP + Pi
- acetyl-CoA carboxylase
- irreversible
What is involved in fatty acid elongation? [4 marks]
- Acetyl CoA
- Malonyl CoA
- Acetoactyl-ACP
- Butyryl-ACP
What enzyme is used in fatty acid synthesis and what is its structure? [4 marks]
- Fatty acid synthase
- Large and multi-enzyme
- Lots of active sites
- Dimer (makes synthesis more efficient)
What is the first step of fatty acid synthesis activated by? [1 mark]
Citrate (via positive feed back)
What is the first step of fatty acid synthesis inhibited by?
Palmitic acid (via negative feed back)
Where is cholesterol synthesised? [1 mark]
Endoplasmic reticulum
What is the first step of cholesterol synthesis?
Activation of acetate
What is the regulatory step of cholesterol synthesis? [1 mark]
HMGCoA → mevalonate
What enzyme does cholesterol inhibit? [3 marks]
- HMGCoA reductase
- Involved in cholesterol synthesis
- Target for statins
Does cholesterol provide energy? [1 mark]
NO
Where does fatty acid mobilisation occur and how is it mediated? [2 marks]
- Happens in the adipocyte
- cAMP mediated (beta 3 adrenoceptor)
What enzyme does protein kinase activate in fatty acd mobilisation and what does this enzyme do? [2 marks]
- Triacylglycerol lipase
- Breaks down triglycerides into glycerol and free fatty acids
Where does fatty acid activation (for degradation) occur? [1 mark]
In the liver cytosol
What is involved in fatty acid activation (for degradation)? [3 marks]
- Acyl CoA
- Carnitine
- Acyl carnitine
What inhibits transport of acetyl CoA from cytosol to matrix? [1 mark]
Malonyl-CoA (made in fatty acid synthesis)
Where does fatty acid degradation/β-oxidation occur? [1 mark]
In the liver mitochondria
What is made form the removal of 2 carbon atoms in acyl-CoA in degradation? [3 marks]
- FADH2
- NADH
- acetyl CoA
In what conditions does acetyl-CoA enter the citric acid cycle?
- Under glycolysis only
- Only in non hepatic cells
What can acetyl-CoA form in hepatic cells? [1 mark]
Ketone bodies (then enter bloodstream)
How many ATP molecules are ade from the oxidation of palmitate? [1 mark]
106
What happens if the chain length of the fatty acid is odd? [2 marks]
- Propionyl-CoA is made
- Double bonds removed by isomerase
Which enzymes remove even numbered double bonds? [2 marks]
- Reductase
- Isomerase
What enzyme is inhibited by a low insulin/glucagon ratio? [1 mark]
Acetyl-CoA carboxylase
Ketogenesis process [4 marks]
Acetyl-CoA → acetoacetyl-CoA → HMG-CoA → acetoacetate
Which organs are ketone bodies a major energy source? [2 marks]
- Cardiac muscle
- Renal cortex
What is insulin’s negative effects on fat metabolism? [2 marks]
- Negative effect on breakdown
- Negative effect on β-oxidation
What is insulin’s positive effect on fat metabolism? [1 mark]
Fatty acid synthesis
