Flashcards in MEH - Energy Production (Lipids) Deck (41):
Which are more reduced, carbohydrates or lipids?
Lipids, meaning that they release more energy when oxidised but complete oxidation requires more O2.
What are the three general classes of lipids?
1) fatty acid derivatives
2) hydroxy-methyl-glutaric acid derivatives
What are the different types of fatty acid derivatives?
- fatty acids
- triacylglycerols (triglycerides)
What are the different types of HMG acid derivatives?
- ketone bodies
- cholesterol esters
- bile acids and salts
What are the different types of fat soluble vitamins?
A, D, E and K
How are triacylglycerols structured?
Three fatty acid side chains with a glycerol backbone
When would triacylglycerols be used as an energy source?
During prolonged exercise, when in starvation, during pregnancy
What does a triacylglycerol form when it undergoes lipolysis?
A glycerol molecule and three fatty acids
Why are triacylglycerols stored in an anhydrous form?
They are hydrophobic
What controls the storage and mobilisation of triacylglycerols?
In the first stage of metabolism of triacylglycerol, it is hydrolysed by which enzymes, and where?
Pancreatic lipases in the small intestine
Once fatty acids and glycerol are broken down in the SI, how are they transported to consumer tissues or adipose tissue?
They are recombined in the small intestine and transported as TAG by lipoproteins (chylomicrons) via lymphatics
Which tissues cannot use fatty acids?
Cells without mitochondria, eg. red blood cells, and the brain as fatty acids do not easily pass the blood-brain barrier
What happens when there is low extracellular [glucose] in adipose tissue?
Fatty acids are released as an alternative fuel
What is the general formula for fatty acids?
CH3(CH2)nCOOH where n = 13-17
True or false - fatty acids are amphipathic?
Why are certain fatty acids required in diet?
Because mammals cannot introduce a double bond beyond C9, so we cannot synthesise them
Where does stage two of fatty acid metabolism take place?
In the mitochondria
The first step of the second stage of fatty acid catabolism actually occurs outside the mitochondria. What is this bit?
The fatty acid is activated by linking to coenzyme A outside the mitochondrion. This uses the enzyme fatty acyl CoA synthase.
How are activated fatty acids transported across the mitochondrial membrane?
Fatty acyl-CoA donates acrylic group to carnitine. The carnitine shuttle transporter then moves the acyl carnitine through the membrane. The acyl group is donated back to a coenzyme A within the membrane.
What inhibits the carnitine shuttle?
What happens to the activated fatty acids once they have been transported through the membrane?
They cycle through a sequence of oxidative reactions, with 2 carbons removed each cycle. They reduce FAD and NAD+
Where do the end products of fatty acid catabolism go?
The acetyl CoA goes to the Krebs cycle, and the reduced electron carriers go to oxidative phosphorylation
Which has a higher yield of ATP when broken down, fatty acids or glucose?
Is ATP synthesised during fatty acid metabolism?
Technically no, as is is produced during oxidative phosphorylation which is part of another process
Where is glycerol metabolised?
The liver - it is transported here in the blood
How is glycerol metabolised?
- changed into glycerol phosphate by glycerol kinase (using ATP)
- glycerol phosphate is either used for triacylglycerol synthesis or converted to dihydroxyacetone phosphate (reducing a NAD+ on the way) which goes to glycolysis
Why does acetyl CoA have a high energy of hydrolysis?
The acetyl group is joined to coenzyme A by the S atom, which has a high energy of hydrolysis
True or false - acetyl CoA is an intermediate in both catabolic and anabolic pathways?
True, it really is an EXCITING molecule (I hate MEH so much)
What are the three ketone bodies synthesised by the body?
What is the normal plasma ketone body concentration?
Less than one mM
What is the plasma ketone conc. in starvation?
2-10 mM (physiological ketosis)
What is the plasma ketone conc. in untested type 1 diabetics?
Over 10 mM (pathological ketosis)
What are ketone bodies synthesised by?
What are ketone bodies synthesised from?
What does HMG CoA-reductase do?
Causes HMG-CoA to become mevalonate, then cholesterol. Statin drugs inhibit this
How is ketone body production controlled?
If there is low NAD+ substrate availability, then there will be NADH product inhibition. This causes two enzymes to be inhibited, stopping the Krebs cycle. Acetyl-CoA is diverted away and used for ketone body formation instead.
Why is cholesterol sometimes formed instead of ketone bodies?
When insulin is high (in 'fed state') then lyase is inhibited and reductase activated, meaning that cholesterol is synthesised.
When insulin is low (starvation, diabetes) lyase is activated and reductase inhibited so ketone bodies are formed
What is the point of ketone body formation?
It spares glucose when the body is undergoing starvation, meaning glucose can still be used for cells that require it eg. The brain
What is ketonuria?
This is when ketones are excreted in the urine because they are above the renal threshold