Fatty acids and Membrane phospholipids biosynthesis

Question 1

seeing as the carbons from an acetyl-coA are the ones used to elongate a fatty acid, what brings the acetyl into the cytosol?

Answer 1

the tricarboxylate transport system

Question 2

the initiation of fatty acid synthesis takes place by?

Answer 2

the carboxylation of acetyl-coA to generate malonyl-coA

Question 3

fatty acid synthesis carries out ? rxns at a time. It lengthens a fatty acid ? carbons at a time

Answer 3

7, 2

Question 4

elongation and desaturation of Free fatty acids requires which enzymes?

Answer 4

elongases and desaturases

Question 5

triacylglycerol are synthesized from ?

Answer 5

glycerol and fatty acids

Question 6

fatty acid oxidation occurs where? Has which carrier group? Has what as an electron acceptor?

Answer 6

in the mitochondria. CoA as a carrier. FAD, NAD+ as acceptors.

Question 7

what is the tricarboxylate transport system?

Answer 7

is it a citrate-malate-pyruvate shuttle. That provides cytosolic Acetyl -CoA and NADPH for fatty acid synthesis

Question 8

what at the 3 sources of acetyl-coA

Answer 8

amino acid degradation (makes cytosolic). Fatty acid oxidation (makes mitochondrial). Glycolysis (cytosolic pyruvate) which is converted to acetyl-coA in mitochondria

Question 9

how does the mitochondrial acetyl-coA enter the cytosol?

Answer 9

as citrate

Question 10

How is citrate converted into pyruvate?

Answer 10

citrate + ATP citrate lyase = Oxaloacetate. +malate dehydrogenase = malate. + Malic enzyme = pyruvate

Question 11

what is the Acetyl- carboxylase reaction?

Answer 11

It needs an ATP, a bicoarbonate ion, a Biotin enzyme
ATP is hydrolysed, the energy released form here is used to transfer the CO2 from bicarbonate to biotin.
This CO2 is then moved to acetyl-coA .
and this has formed malonyl-coA

Question 12

acetyl-coA carboxylase, is inhibited by, and is activated by?

Answer 12

it is activated by citrate.

it is inhibited from long chain fatty acid

Question 13

malonyl-coA inhibits

Answer 13

carnitine palmitoyl transferase I, which is a mitochondrial enzyme

Question 14

explain the ACC hormones control. PKA

Answer 14

PKA senses CMP levels (controlled by glucagon levels). It can phosphorylate the carboxylase making it less sensitive to allosteric control

Question 15

explain the ACC hormones control. AMP dependant kinase?

Answer 15

senses ATP/ADP levels in cells. Can phosphorylate carboxylate making it less sensitive

Question 16

explain the ACC hormones control. protein phosphate 2A

Answer 16

dephosphorylation carboxylate making it more active

Question 17

what’s are the steps of biosynthesis of fatty acids

Answer 17

loading, condensation, reduction and dehydration, elongation, unload

Question 18

what is the loading step

Answer 18

has a malonyl/acetyl-transferase MAT. We load the acetyl group from acetyl-coA from the ACP. Then we load a malonate group from the malonyl-coA enzyme to the ACP. IN the end we have an acetyl group on the cysteine residue of FAS , and a malonate group on the ACP site of FAS. A coA is released

Question 19

explain the condensation reactive

Answer 19

The decarboxylation of the malonate group, that allows the nucleophilic attack on the thioester bond between the acetyl group on the cysteine residue on FAS .it is done by beta-ketoacyl-ACP synthase. It generates acetoacetyl-ACP . CO2 is released

Question 20

explain the reduction and dehydration steps

Answer 20

3: we reduce the ketone function of acetoacetyl-ACP by ACP reductase, and form hydroxybutyryl-ACP .
4: we have a dehydration reaction done by hydroxyacyl-ACP dehydrogenase, to form butenoyl-ACP
5: we have to make the double bond a single bond this is done by enoyl-ACP reductase, this forms butyryl ACP

Question 21

butyryl-ACP becomes?

Answer 21

palmitoyl-ACP after 7 rxns cycles. Then it gets hydrolysed by palmitoyl-thioesterase. Then forms palmitate

Question 22

list the domains of fatty acid synthase

Answer 22

ketoacyl synthase, malonyl synthase, dehydrase, enoyl reductase, ketoacyl reductase, thioesterase

Question 23

what are desaturases?

Answer 23

are enzyme that form a double bond. Mammals only have C9/6/4/5 fatty acyl-coA desaturases. This means that a C9,12 acid is obtained by the diet and not by the body. They need the energy of NADHP. go to slide 26

Question 24

how are dietary triacylglyerols turned into triacylglycerols for the body

Answer 24

they are acted upon by lipases, monoacylglycerol acyltransferase, diacylglycerol acyltransferase, and 2 coA groups are released (from the enzymes)

Question 25

sphingolipids are synthesized from?

Answer 25

palmitoyl-coA and serine

Question 26

prostaglandin synthesis from arachidonate is blocked by?

Answer 26

drugs

Question 27

what forms the myelin sheath?

Answer 27

sphingomyelin

Question 28

gangliosides are used for

Answer 28

brain neuron transmission

Question 29

tay sachs disease is caused by?

Answer 29

malfunction in hexoaminidase A