LIPID METABOLISM

Question 1

what enzymes help the breakdown of triglycerides and where does it occur?

Answer 1

• occurs in the intestines

- pancreatic lipase helps to breakdown triglycerides to fatty acids and monoglycerols

Question 2

what helps to solubilize the lipids?

Answer 2

BILE SALT :

• made in the liver, amphipathic and its structure looks like cholesterol
• bile salts wrap around the lipid with the hydrophobic four-ring side facing the lipid

Question 3

how do you transport lipids throughout intestine?

Answer 3

• cannot pass through intestines w/o bile salts
• lipoprotein takes over the job of bile salt, allowing hte lipid to stay solubilize hence can go to other parts of the body

Question 4

how to transport lipids in the blood?

Answer 4

• lipids go to the tissue through the bloodstream after being absorbed by the intestine
• escorted by apolipoproteins which bind to the lipids and keep them soluble in the bloodstream

Question 5

what are the five classes of lipoprotein and what are their significance?

Answer 5

• chylomicrons
• very low density lipoprotein
• intermediate density lipoprotein
• low density lipoprotein
• high density lipoprotein
  1-4 : transport cholesterol and lipids to tissue from intestine and liver
  5 : transport cholesterol and lipids back to the liver from tissues
  1 to 5 : increasing % protein, % of phospholipid, % of cholesteryl ester, decreasing size and weight
• requires diff apolipoprotein to work with

Question 6

how is cholesterol transported intracellularly?

Answer 6

1 ) cholesterol is packaged into LDL complex in which cholesterol, phospholipid and apolipoprotein will wrap around LDL
2 ) LDL molecules are bound by LDL receptors on cell surface through the apolipoprotein B-100 component
3 ) LDL receptor and molecule is internalized by cell membrane pits forming through recruitment of clathrin proteins into clathrin-coated vesicles which then fuses with endosomes and clathrin molecules go back to the cell surface
4 ) lower pH causes release of LDL from LDL receptor
5 ) endosome containing LDL fuses with lysosome and apolipoprotein B-100 is degraded by the proteases inside the lysosome and cholesterol is released within the lysosome
6 ) cholesterol can either go to the ER or be converted to cholesteryl ester by acyl-coa cholesterol transferase
7 ) increased levels of cholesterol in the ER signals the cells to make more ACAT and less LDL receptor

Question 7

what is the rule of lipid catabolism?

Answer 7

• longer fatty acids yield more energy as it can go through more cycles of oxidation providing more energy
• CH16 can produce 8 acetyl-coa and 7 FADH2 and NADH

Question 8

how is fatty acid prepared for oxidation?

Answer 8

• fatty acid + ATP causes release of double phosphate bonds and AMP attaches itself to the O2 while H-S-CoA binds itslef to C-O bond
• forms Acyl-CoA by releasing AMP while S-CoA replace the O-AMP group
• reaction occurs in the cytoplasm and makes uses of acyl-CoA synthetase

Question 9

how is fatty acyl-CoA transported into the mitochondria?

Answer 9

• fatty acyl CoA removes the H-S-CoA w the help of carnitine palmitoyl transferase and replaces them with carnitine (I) and is brought into the mitochondrial mixture with the help of carnitine carrier protein
• carnitine is then removed and replaced by H-S-CoA in which carnitine is removed through the carnitine carrier protein w the help of palmitoyl transferase (II)

Question 10

what are the 4 reactions of beta oxidation?

Answer 10

1 ) Fatty acyl-coa is converted to trans-enoyl coa with the help of acyl-coa dehydrogenase, in which hydrogen is removed and will carry electron to FADH, converting it to FADH2 ; generating a double bond ~ 1 ATP
2 ) Trans-enoyl coa is converted to 3-hydroxyacyl-coa with the help of enoyl-coa hydrotase in which a water molecule is added
3 ) 3-hydroxyacyl-coa is converted to B-ketoacyl-coa with the help of 3-hydroxyacyl-coa dehydrogenase in which a hydrogen is removed and will carry electron to NAD+, converting it to NADH ~ 2 ATP
4 ) B-ketoacyl-coa is split into fatty acyl-coa (2 carbons shorter) and acetyl-coa with the help of B-ketoacyl-coa thiolase by cutting at after the 1st carbon and transfer another coa group at C=O group
- acetyl coa is oxidise via citric acid cycle to generate more FADH2 and NADH
- fatty acyl-coa return to the beginning of oxidation cycle to run through reactions again until all hydrocarbon is used up

Question 11

what is phosphatidate?

Answer 11

precursor of storage and membrane lipids formed by two acylation (adding of fatty acids) reactions starting from glycerol-3-phosphate to lysophosphate to phosphatidate
- glycerol-3-phosphate is primarily formed by the reduction of dihydroxy acetone phosphate, an intermediate of the glycolysis pathway

Question 12

how to synthesize triglyceride?

Answer 12

phosphatidate is hydrolysed by a phosphatase to yield diacylglycerol which is then acylated to form triglyceride by a diacylglycerol acyltransferase
- diacylglycerol kinase can be used in the reverse reaction to form phosphatidate from diacylglycerol