T3 L15: Lipid metabolism and pathways Flashcards
What are the 3 steps for oxidation of triglycerides?
- Glycerol is removed and the fatty acid chain is oxidised into 2-carbon fragments in the form of acetyl CoA
- Acetyl-CoA is oxidised to CO2 in the citric acid cycle
- e- are transferred in the e- transport chain
What is Beta-oxidation?
The removal of glycerol and oxidation of long fatty acids into acetyl CoA from a triglyceride
Where does Beta-oxidation occur?
In the mitochondria and peroxisomes
What is acetyl-CoA made of?
An acetyl group from the fatty acid and CoA that bond together during beta-oxidation
What does each cycle of beta-oxidation produce?
1 acetyl CoA, 1 FADH2, and 1 NADH
Where does fatty acid synthesis occur?
In the cytosol of hepatocytes and adipocytes
Where is acetyl CoA found in a cell?
In the mitochondria
Which process makes acetyl CoA leave the mitochondria?
The citrate malate cycle
What is the rate-limiting step of the citrate malate cycle?
Carboxylation
What is the rate limiting step of beta-oxidation?
The transfer of acetyl-CoA into mitochondria
What is formed during fatty acid synthesis?
Malonyl-CoA from acetyl-CoA, catalysed by acetyl-CoA carboxylase. This is subject to control by insulin and glucagon
What are the physiological roles of cholesterol?
For membranes, precursor of steroid hormones, source of bile acid
What are the physiological roles bile acids?
Lipid digestion, lipid absorption, cholesterol excretion
What is an amphipathic lipid and what is it made from?
It has both hydrophobic and hydrophilic portions and is synthesised from acetyl-CoA and bile acids. It’s the storage form of cholesterol in most tissues
What is the rate determining step of cholesterol biosynthesis?
2nd bit where HMG-CoA is made into Mevalonate using HMG-CoA reductase
Which hormones control the activity of HMG-CoA reductase?
Insulin and glucagon
What is the function of albumin?
Its a transporter protein that circulates in the blood
What is the function of lipoproteins?
They carry insoluble proteins
Describe the structure of a lipoprotein
The insoluble lipids will be carried in the centre, and the out layer is made of amphipathic phospholipids and cholesterol
What is IDL?
Intermediate density lipoprotein
Order these from least dense to most dense: VLDL, LDL, HDL, and IDL
VLDL, IDL, LDL, and HDL
What is the function of chylomicrons?
They deliver dietary triglycerides to muscles and adipose tissue and they carry dietary cholesterol to the liver
What does VLDL carry?
transports endogenous triglycerides and cholesterol
What does LDL carry?
Transports cholesterol from the liver to tissues
What does HDL carry?
transports cholesterol from tissues to liver (removes cholesterol from tissues), AKA reverse cholesterol transport
How does IDL form?
When VLDL becomes depleted of lipids
What does lipoprotein lipase do?
Releases triglycerides from chylomicrons and VLDL at tissues (they are bound to tissues)
How does the liver recognise remnants of lipids?
Using their ApoE (Apolipoprotein E) content found on all but LDL
How is LDL recognised?
By cell surface LDL receptors (LDLR’s) because LDL has ApoB-100 so it can’t be recognised like other lipoproteins
How are LDL receptors regulated?
By SREMP transcription factors and PCSK9 which causes degradation of LDL receptors
What is the function of ABCA1 and ABCA8?
They allow cholesterol excretion from cells
