lipid synthesis

Question 1

in lipid synth, high insulin to glucagon ratio induces synth of?

Answer 1

pyruvate DH
malic enzyme
citrate lysase

Question 2

key regulated enzyme in lipid synth, and what regulates it

Answer 2

acetyl coa carboxylase in conversion of acetyl coA to malonyl coA. inactive when phosphorylated by amp-activated protein kinase, dephosphorylated by phosphatase. Insulin activates (the phosphatase) Citrate activates, palmitoyl coA inhibits

Question 3

5 steps of fatty acid synth (repeated how many times?)

Answer 3

1. malonyl transacylase (scoot over/transacylation)
2. beta ketoacyl synthase (condensation; -CO2)
3. ketoacyl reductase (reduction; NADPH + H+ > NADP+)
4. dehydratase (dehydration; -H2O)
5. enoyl reductase (reduction; NADPH + H+ > NADP+)

repeated till have 16 C palmitate (7x)

Question 4

binding groups on FA synthase

Answer 4

phosphopantetheinyl residue (p residue) on acyl carrier protein (ACP)–acyl groups are transferred as thioesters on this

or -SH of a Cysteine residue

Question 5

regulation of fatty acid synthase

Answer 5

high insulin/glucagon ratio stimulates fatty acid synthase gene expression (and acetyl coA carboxylase).

- upstream stimulatory factors
- sterol response element binding proteins
- carbohydrate responsive element binding proteins

Question 6

fatty acid modifications (5)

Answer 6

1. elongation
2. desaturation (addition of double bonds)
3. formation of triacylglycerol
4. formation of phospholipids and sphingolipids
5. formation of prostaglandrins from linoleic acid (essential FA)

Question 7

steric acid

Answer 7

18C saturated fatty acid

created by adding to malonyl coA to palmitatewith FA chain attached to Coenzyme A instead of ACP (still uses NADPH)

Question 8

type of FA the brain makes

Answer 8

very long 22-24C FA

Question 9

Stargardt-like macular degeneration

Answer 9

mutations in elongation of very long chain fatty acids-4 gene (ELOVL4)

Question 10

where does FA desaturation occur?

Answer 10

endoplasmic reticulum–molecular oxygen is required

Question 11

Palmitoleic acid

Answer 11

16:1, desaturation at C-9

Question 12

Oleic acid

Answer 12

18:1, desaturation at C-9

Question 13

enzyme that breaks down TG in adipose cells in times of fasting (activated by PKA)

Answer 13

hormone-sensitive lipase (phosphorylated)

low insulin/glucagon ratio converts ATP to cAMP, activates PKA, phosphorylates hormone-sensitive lipase

Question 14

phospholipid synth basic steps

Answer 14

start with glycerol 3-phosphate, add two acylglycerols, reach phosphatidate same way as in triacylglyceride synth.

phosphatidate reacts with CTP, CDP intermediate is KEY, CDP-diacyglycerol reacts with inositol to get Phosphatidyl inositol

Question 15

Respitory distress syndrom cause by

Answer 15

failure to produce enough phosphotidylcholine in lung surfactant

Question 16

arachidonate

Answer 16

20:4 FA, saturated at 5, 8, 11, and 14-C

Question 17

Prostaglandin formed by

Answer 17

C2 fatty acid cleaved from phosphatidate in membrane by phospholipase A2

Question 18

sphingolipids

Answer 18

(e.g. sphingomyelin) important for myelin sheath on nerve cells.
antigenic determinants for the ABO blood groups

Question 19

cerebrosides

Answer 19

like sphingomyelin, but instead of phosphowhatever on the ceramide, there is a sugar head group

Question 20

ganglioside

Answer 20

like cerebrosides, but instead of one sugar on head group, there are numerous and they have sialic acids on the sugar

Question 21

gut hormone cholecystokinin causes what?

Answer 21

secretion of pancreatic enzymes (pancreatic lipase, colipase, bile salts)

Question 22

what is cholic acid and how does it differ from cholesterol

Answer 22

a bile acid synthesized in the liver with more hydroxyls, a polar tail, and no 5-6 double bond

Question 23

Cholybar and Questran are types of?

Answer 23

cholestyramines. bind to bile and prevent reabsorption (used to treat hypercholesterolemia and itching from liver disease)

Question 24

difference between LDL in heart/skeletal mm. isoenzyme and adipose isoenzyme

Answer 24

km lower in heart/skeletal muscle so can always get TGs, km higher in adipose so mainly only get after fatty meals.

Question 25

how does orlistat (xenical, alli) work

Answer 25

reversible inhibitor of lipase (pancreatic), which prevents triglycerides from being broken up, so less TG enters body. additionally, it can remove some fat soluble vitamins (A, K, E, D), so multivitamin recommended.