LECTURE 4 (Lipid synthesis) Flashcards
What are the properties of Fatty acids & triglycerides?
- Most lipids degraded to FREE FATTY ACIDS in intestine
- Enterocytes convert fatty acids into TRIACYLGLYCEROL
- When triacyglycerols reach the tissues to be used/stored, they are degraded back to free fatty acids
What is the form that fatty acids are transported through the plasma in?
Chylomicrons
Where is Lipoprotein lipase found?
- On endothelial surfaces of capillaries
- Abundant in adipocytes and muscle tissue
Where does Fatty acid synthesis take place?
- Liver
- Mammary glands
- Adipose tissue (small amount)
[excess carbohydrates and proteins -> fatty acids]
Where is fatty acid stored?
Adipose tissue
[where it’s stored as triglycerides]
How are fatty acids broken down?
Fatty acids are OXIDISED through fatty acid/β-oxidation into TWO-CARBON ACETYL CoA molecules, which can then enter the KREBS CYCLE to generate ATP.
Which two enzymes are used in Fatty acid synthesis?
- Acetyl-CoA carboxylase (ACC)
- Fatty acid synthase (FASN)
What are the properties of Fatty acid synthesis?
- Occurs in high energy states (fed state)
- Lots of acetyl-CoA -> lots of ATP
- Inhibition of ISOCITRATE DEHYDROGENASE ->. high CITRATE level inside the cell
Describe what happens in Fatty acid synthesis
1) Citrate moves from MITOCHONDRIA to CYTOSOL via CITRATE SHUTTLE
[since Acetyl-CoA cannot cross membrane]
2) Citrate is converted into acetyl-CoA via ATP-CITRATE LYASE which causes excess acetyl-CoA to move to the cytosol
3) Acetyl-CoA is converted to MALONYL-CoA via ACETYL-CoA CARBOXYLASE [RATE LIMITING STEP!]
4) Synthesis of PALMITATE which requires FATTY ACID SYNTHASE and NADPH -> uses carbons from ACETYL-CoA and MALONYL-CoA to create a 16-carbon fatty acid (PALMITATE)
Which co-factors are required to convert Acetyl-CoA into Malonyl-CoA?
- Citrate
- Insulin
- Glucagon
- Epinephrine
- Biotin
What is Biotin?
A co-factor for carboxylation enzymes that add 1-carbon group via CO2
Which Carboxylation enzymes require Biotin?
- Pyruvate carboxylase
- Acetyl-CoA carboxylase
- Proprionyl-CoA carboxylase
What are the major sources of NADPH required for fatty acid synthesis?
- Conversion of MALATE to PYRUVATE
- Conversion of GLUCOSE-6-PHOSPHATE to RIBULOSE-5-PHOSPHATE
How can fatty acid chains be further elongated?
- Addition of 2-carbon units in the SMOOTH ENDOPLASMIC RETICULUM (SER) where MALONYL-CoA is the 2-carbon donor and NADPH supplies the electrons
- BRAIN has elongation capabilities allowing it to produce the very-long-chain fatty acids (over 22 carbons) required for synthesis of lipids
Glucose transporter in adipocytes (GLUT-4) is _________-_________
Insulin dependent
