Energy Release From Fat Flashcards
What are the main functions of lipids? (3)
Components of cell membranes (phospholipids and cholesterol)
Hormone precursors
Long-term fuel stores (triglycerides)
What type of hormones are formed from cholesterol?
Steroid hormones
What type of hormones are formed from arachidonic acid?
Prostaglandins
How much fat does the average adult have?
11-15kg
How much energy does 1g of fat store?
38kJ
Order the following in ascending amount of energy stored:
Protein, carbohydrate, fat
Carbohydrate
Protein
Fat
What is another name for triglycerides?
Triacylglycerols
What is the structure of a triglyceride?
3 fatty acids with ester bonds to glycerol
Give three examples of saturated fatty acids and state their C:C=C ratio
Stearic acid 18:0
Palmitic acid 16:0
Myristic acid 14:0
Give four examples of unsaturated fatty acids and state their C:C=C ratio
Oleic acid 18:1
Linoleic acid 18:2
Linolenic acid 18:3
Arachidonic acid 20:4
What type of enzyme breaks down lipids?
Lipases
Describe how triglycerides are broken down into their components
Removal of one fatty acid at a time
What enzymes are used in the breakdown of triacylglycerol?
Triacylglycerol lipase
Diacylglycerol lipase
Monoacylglycerol lipase
How do fatty acids travel in the blood stream?
Bound to albumin (as water-insoluble)
How does glycerol travel in the blood stream?
Diffusion/free in plasma
How many carbons are in glycerol?
3
What activates triacylglycerol lipase?
Glucagon
Adrenaline
What happens to glycerol in most tissues?
Enters glycolysis as dihydroxyacetone phosphate
What happens to glycerol in the liver/during starvation?
Enters glycolysis as dihydroxyacetone phosphate
Converted to glucose by gluconeogenesis
What is the name of the process of fatty acid breakdown?
Beta oxidation
Where do the reactions of beta oxidation occur?
Mitochondrial matrix
How is the biological energy of fatty acids conserved?
Transfer of 2 hydrogen atoms to NAD+ or FAD
How many steps are there in beta oxidation?
4
What is the result of one cycle of beta oxidation?
Removal of one 2C unit (acetyl CoA)
One NADH and one FADH2 formed
What must occur before the fatty acid is transported into the mitochondrion?
Activation using ATP
Where does fatty acid activation occur?
Cytosol
What is the reaction of fatty acid activation?
Fatty acid –> fatty acyl CoA
Catalysed by fatty acyl CoA synthetase/synthase
ATP –> AMP + PPi
Describe how fatty acyl CoA is moved into the mitochondrial matrix
Diffuses through permeable outer mitochondrial membrane into intermembrane space
CoA swapped for carnitine by carnitine palmitoyl transferase I
Fatty acyl carnitine moved into matrix by translocase
Carnitine swapped for another CoA by carnitine palmitoyl transferase II
What are the four steps of beta oxidation?
- Removal of 2H atoms
- Addition of water across C=C
- Removal of 2H atoms
- Removal of 2C/acetyl unit
What is the first reaction of beta oxidation?
Fatty acyl CoA –> enoyl CoA
Acyl CoA dehydrogenase
FAD –> FADH2
What is the second reaction of beta oxidation?
Enoyl CoA –> hydroxyacyl CoA
Enoyl CoA hydratase
What is the third reaction of beta oxidation?
Hydroxyacyl CoA –> b-ketoacyl CoA
Hydroxyacyl CoA dehydrogenase
NAD+ –> NADH + H+
What is the fourth reaction of beta oxidation?
b-ketoacyl CoA –> fatty acyl CoA + acetyl CoA
b-ketoacyl CoA thiolase
What happens to the products of beta oxidation?
Fatty acyl CoA re-enters cycle
Acetyl CoA goes into TCA cycle
How many cycles of beta oxidation would a 16C fatty acid go through for complete breakdown?
7
How many NADH, FADH2 and acetyl CoA does a cycle of beta oxidation produce?
1 of each
How much ATP is formed from the use of one acetyl CoA molecule (TCA and oxidative phosphorylation)?
10
Where are odd-numbered carbon fatty acids often found?
Shellfish
How would a three carbon fatty acid be metabolised?
Propionyl CoA carboxylase adds carbon dioxide using ATP hydrolysis
Methyl malonyl CoA mutase converts methyl malonyl CoA to succinyl CoA
Succinyl CoA enters TCA cycle
What is the name for ketone body formation?
Ketogenesis
When does ketogenesis occur?
When fat metabolism is the main source of energy in starvation and type I diabetes
Why does ketogenesis occur?
Beta oxidation in hepatocytes leads to high concentrations of acetyl CoA which exceeds capacity of TCA cycle
So excess acetyl CoA converted to ketone bodies in liver
What are two examples of ketone bodies?
Acetoacetate
b-hydroxybutyrate
Why can the liver not use ketone bodies?
Lacks enzymes to convert them into TCA cycle intermediates to prevent a futile cycle
Why can the brain not use fatty acids?
Cannot pass blood-brain barrier
Why can red blood cells not use fatty acids or ketone bodies?
No mitochondria
