Lecture 23 Flashcards
How are lipids transported in circulation?
As lipoproteins
What are the components of lipoproteins?
Triglycerides, phospholipids, cholesterol, cholesterol ester, apolipoproteins.
What are some functions of apolipoproteins?
Solubilize the proteins, enzyme activation and receptor binding
What makes up a triglyceride?
1 Glycerol and 3 Fatty acids chains
What is a fatty acid?
Unbranched hydrocarbon chains with a carboxyl group at one end.
How are fatty acids stored?
Stored in adipose tissue s triglyceride, used as a source of energy and converted to ketone bodies in liver
What is more energy efficient fat or glucose?
Fat
How are fatty acids used as energy?
They enter the Beta-oxidation pathway to provide energy.
Why is it called Beta-oxidation?
Because it is the Beta carbon atom that is oxidised.
What does the Beta-oxidation of fatty acyl CoA produce?
One molecule of Acetyl CoA and reduced nucleotides.
What then happens to the acetyl CoA?
It enters the TCA cycle
What is the net product of ATP from the complete oxidation of a C16 fatty acid?
129ATPs
What can happen if excess Acetyl CoA is present?
It can be converted into ketone bodies - this is known as ketogenesis. It occurs in liver mitochondria.
What happens to the ketone bodies?
They enter the blood and travel to other tissues where they can be oxidised to provide energy
Can ketone bodies be converted back to acetyl CoA
Yes
What can carbohydrates be metabolised to?
They can be metabolised to acetyl CoA - which then undergo lipogenesis, this is the process by which acetyl CoA is converted to fatty acids and subsequently triglycerides
How many steps is lipogenesis?
3 steps:
- Activation
- Elongation
- Termination
How do you supply acetyl CoA for lipogenesis?
It combines with oxaloacetate to form citrate and CoA
What is the next stage?
Citrate is then transported into the cytoplasm via a membrane transporter and cleaved to form acetyl CoA
What is step 1 of the process?
Activation:
In the cytoplasm, Acetyl CoA is carboxylated to malonyl-CoA which is catalysed by acetyl-CoA carboxylase
What is the rate limiting step of lipogenesis?
Step 1: Activation
What is stage 2 of lipogenesis?
Step 2: Elongation
The next stage is catalysed by the fatty acid synthase complex
What is fatty acid synthase?
Homodimer - two identical polypeptides with 7 different enzymes attached.
What does fatty acid synthase do?
It adds two carbons atoms at a time from malonyl-CoA to the growing fatty acid carbon chain wit the los of CO2. This repeats 6 times.
