Energy Production - Lipids Flashcards
Why do lipids release more energy than carbohydrates when oxidised?
They are more reduced than carbohydrates
What 3 classes of lipids are there?
- Fatty acid derivatives (eg triacylglycerols)
- Hydroxy-methyl-glutaric acid derivatives (eg ketone bodies)
- Vitamins (A D E and K)
What are some hydroxy-metyl-glutaric acid derivatives?
Ketone bodies (C4)
Cholesterol (C27)
Cholesterol esters
Bile acids and salts (C24)
What are some fatty acid derivatives?
Fatty acids, triacylglycerols, phospholipids and eicosanoids
In what form are triacylglycerols stored?
Anhydrous form (lipid droplets) as they are hydrophobic - so stored in adipose tissue
Where are fatty acids converted back to triglycerides?
GI Tract
What are chylomicrons?
Chylomicrons are lipoprotein particles that consist of triglycerides, phospholipids, cholesterol, and proteins. They transport dietary lipids from the intestines to other locations in the body.
What is meant by an unsaturated fatty acid?
Fatty acid with one or more double bonds
What is an example of an essential fatty acid?
Linolenic acid
Where does stage 2 of fatty acid metabolism occur?
Mitochondria
In fatty acid catabolism, how is the fatty acid activated?
By linking to coenzyme A outside the mitochondrion by the action of fatty acyl CoA synthase
How is the activated fatty acid transported across the inner mitochondrial membrane?
Using a carnitine shuttle
How are fatty acids catabolised?
FA cycles through sequence of oxidative reactions with 2 carbons removed each cycle
What is the carnitine shuttle inhibited by?
Malonyl~CoA
For a C6 fatty acid, how many moles of ATP are generated?
41
Where does b-oxidation of fatty acids not occur?
Brain, RBC and WBC
Where is glycerol metabolised?
Liver
Which enzyme converts glycerol into glycerol phosphate?
Glycerol kinase
What 3 ketone bodies are produced in the body?
Acetoacetate, acetone and b-hydroxybutyrate
What is the normal plasma ketone body concentration?
< 1 mM
What is the range of ketone body concentration in starvation (physiological ketosis)?
2-10 mM
What can be the ketone body concentration in a patient with untreated type 1 diabetes?
> 10 mM (pathological ketosis)
- reduced insulin, reduced glucose uptake
What are ketone bodies synthesised by?
Liver mitochondria
What do station drugs ultimately inhibit?
Production of cholesterol
Inhibits HMG-CoA Reductase
What does CoA contain?
Vitamin B5
When the insulin/glucagon ratio is high, what is the state of lyase and reductase?
Lyase is inhibited, reductase activated -> cholesterol synthesis
When the insulin/glucagon ratio is low, what is the state of lyase and reducatase?
Lyase activated, reductase inhibited -> ketone body synthesis
True or False:
By using alternative substrate eg ketone bodies for muscles, glucose is conserved for the brain
True
Are ketone bodies hydrophobic or hydrophilic?
Hydrophilic
What can be made from HMG-CoA?
Mevalonate which can go on to make cholesterol
Or ketone bodies (acetoacetate, actone, b-hydroxybutyrate)
What is HMG and what can it go on to synthesise?
Hydroxymethyl glutaric acid (3 acetyl coAs condensed together)
Ketone bodies, cholesterol (and therefore steroid hormones)
What can fatty acids go on to synthesise?
Triaceylglycerols and phospholipids
What are the 3 pathways that acetyl-CoA can go on to?
Fatty acids, TCA cycle, HMG
What is the main convergence point for catabolic pathways?
Acetyl-CoA
What is the CH3CO group linked to coenzyme A by?
Via S-atom - high energy of hydrolysis
What can glycerol phosphate go on to do?
Triacylglycerol synthesis or DHAP in glycolysis
What are the products of b-oxidation of fatty acid catabolism?
Acetyl-CoA, AMP, 2Pi, FADH2, NADH and H+
Acetyl CoA goes to TCA cycle
FADH2, NADH + H+ goes to ETC
True or False:
B-oxidation stops in the absence of O2
True
True or False:
No ATP is synthesised in b-oxidation
True
Explain how acetyl-CoA can be diverted from the TCA cycle to synthesise ketone bodies
An increase in b-oxidation of fatty acids leads to increased production of NADH, meaning a low NAD+ substrate
NADH builds up and inhibits the actions of isocitrate dehydrogenase and a-ketoglutarate dehydrogenase in TCA cycle (product inhibition)
TCA therefore stops and acetyl-coA is diverted away to synthesise ketone bodies
