Lecture 35: RECEPTORS AND CELL SIGNALLING Flashcards
Why do we need fuel stores?
Because the body cannot store ATP
What must happen because the body cannot store ATP?
ATP must be made in the cell at the time it is needed, at the rate it is needed by oxidising fuels
What are the reasons for storing fuel?
to maintain a supply of glucose between meals, to provide immediate fuel for increased activity and for long periods of time when food intake may be inadequate
What is fat stored as?
Triacylclycerols as fat droplets
Where is fat stored?
In adipose tissue
What can be done with excess fat and carbohydrate from the diet?
It can be converted to stored fat
What is there an unlimited amount of?
Fat stores
Where do the fatty acids for synthesis of TAG’s come from?
Chylomicrons
Where does the glycerol backbone fro synthesis of TAG’s come from?
Glucose
What are fatty acids activated to?
Fatty acyl-CoA
What happens after of activation of fatty acids to acyl-CoA?
Esterification of acyl groups to glycerol-3-phosphate (FA’s attached)
What is synthesis of TAG’s stimulated by?
Insulin
What does lipoprotein lipase do?
Releases fatty acids from VLDL’s (glucose) and chylomicrons (fat) and is stimulated by insulin
What is the pathway for fat to TAG’s?
Fat> chylomicrons> fatty acids > TAG
What is the pathway for glucose to TAG?
Glucose > glucose > Glucose > acetyl-CoA> FA > TAG > VLDL > VLDL > FA > TAG
What happens in fatty acid activation?
Fatty acid (R-COOH) + CoA-SH + ATP > Fatty acyl CoA (R-CO.SCoA) + AMP + PPi catalysed by fatty acylCoA synthetase
What molecule begins conversion to glycogen?
dihydroxyacetone phosphate
What is dihydroxyacetone phosphate converted to?
Glycerol phosphate by glycerol-3-phosphate dehydrogenase
What is glycerol-phosphate converted to?
glycerol to triacylglycerol which requires several steps
What are the enzymes involved in formation of glycerol from glycolysis?
Glycerol-3-phosphate acyltransferase and phosphatidate phosphatase followed by diacylglycerol acyltransferase
What happens in mobilisation of TAG’s?
Hydrolysis of TAG’s
What is hydrolysis of TAG’s catalysed by?
Hormone-sensitive lipase
What is hormone sensitive lipase stimulated by?
Adrenaline and glucagon
What is the result of hydrolysis of TAG’s ?
Release of free fatty acids and glycerol
What is glycogen?
A branched polysaccharide of alpha-1,4 and alpha-1,6 glycosidic bonds
Where is glycogen stored?
In the liver and as granules in the cytoplasm
Where does glycogen synthesis occur?
Mainly in the liver and muscle immediately after a meal
What does glycogen synthesis require?
Energy inputs (ATP and UTP)
What is the activated high energy precursor for glycogen synthesis?
UDP-glucose
What enzymes are required for glycogen synthesis?
Glycogen synthase and branching enzyme
What is glycogen synthesis stimulated by?
Insulin
What is the steps of glycogen synthesis?
- Glucose + ATP > ADP + glucose-6-phosphate
- Glucose-6-phosphate > glucose-1-phosphate
- Glucose-1-phosphate + UTP > UPD-glucose + PPi
- UPD-glucose + glycogen(n) > UPD + glycogen (n+1)
What catalyses the first step of glycogen synthesis?
hexokinase
What happens in the first step of glycogen synthesis?
Trapping in cell
What catalyses the second step of glycogen synthesis?
Mutase
What happens in the second step of glycogen synthesis?
A phosphate is transferred to commit to glycogen synthesis and diverge from glycolysis
What is the last step of glycogen synthesis catalysed by?
Glycogen synthase which is stimulated by insulin
What is there only so much space for?
Glycogen; excess glucose is converted to acetyl-CoA and then to fatty acids by the fatty acid synthase complex in liver cytosol
How is glycogen degraded?
By glycogenolysis
What happens with liver glycogen?
It is released into the blood for the brain
What happens with muscle glycogen?
It releases fuel for glycolysis within muscle cells
What can happen with excess glucose carbon?
It can be converted to fatty acids
Where does glucose > fatty acids occur?
Mainly in the liver
How is the glucose > fatty acids process described?
Complex, energy requiring
How are the fatty acids from glucose exported?
As TAG’s in VLDL
What is glucose > fatty acids stimulated by?
Insulin
What is the enzyme which converts glucose to fatty acids?
Fatty acid synthase complex
What are the features of fatty acid synthase complex?
7 activities (catalytic sites)
What does the fatty acid synthase complex need?
NADPH
What does the fatty acid synthase complex make?
Palmitic acid
What is the main fuel for the brain?
Glucose (can’t use fatty acids)
What is the main fuel for RBC’s?
Glucose
What is the main fuel for the liver?
Mostly fatty acids
What is the main fuel for the heart?
mostly fatty acids
What is the main fuel for resting muscle?
Mostly fatty acids
What is the main fuel for marathon muscle?
Mix of fatty acids and glucose
