cholesterol, TG & PL

Question 1

,,this is an essential component of cell membranes. needed for the formation of steroid hormones and bile. mammals do not need this in their diet, as all cells have the capability to synthesize it

Answer 1

cholesterol

Question 2

what is the starting material to make cholesterol?

Answer 2

acetate

Question 3

formation of cholesterol: three acetates come together to form ____________

Answer 3

mevalonate

Question 4

formation of cholesterol: mevalonate converts to phosphorylated ____________

Answer 4

5-C isoprene

Question 5

formation of cholesterol: qhow many isoprenes polymerize to form the 30-C linear squalene?

Answer 5

6

Question 6

formation of cholesterol: squalene cyclizes to form the four rings that are modified to produce ___________

Answer 6

cholesterol

Question 7

the enzymes and reactions are identical for the formation of HMG-CoA between cholesterol synthesis and ketone body synthesis. what is a difference?

Answer 7

ketone bodies are formed in the mitochondria using acetyl-CoA derived from beta-oxidation. whereas cholesterol Is formed in the cytosol using acetyl-CoA derived from citrate

Question 8

three acetyl-CoA are condensed to form ________ which is then reduced to form mevalonate

Answer 8

HMG-CoA

Question 9

formation of mevalonate from acetyl-CoA: what enzyme is used to make acetoacetyl-CoA from acetyl-CoA?

Answer 9

thiolase (aka acetyl-CoA acetyl transferase)

Question 10

formation of mevalonate from acetyl-CoA: is the conversion of acetyl-CoA to acetoacetyl-CoA reversible or irreversible?

Answer 10

reversible

Question 11

formation of mevalonate from acetyl-CoA: what enzyme is used to form HMG-CoA from acetoacetyl-CoA?

Answer 11

HMG-CoA synthase

Question 12

formation of mevalonate from acetyl-CoA: is the conversion of acetoacetyl-CoA to HMG-CoA reversible or irreversible?

Answer 12

irreversible

Question 13

formation of mevalonate from acetyl-CoA: what enzyme is used to from mevalonate from HMG-CoA?

Answer 13

HMG-CoA reductase

Question 14

formation of mevalonate from acetyl-CoA: is the conversion of mevalonate from HMG-CoA reversible or irreversible?

Answer 14

irreversible

Question 15

is the rate-controlling enzyme of the mevalonate pathway, the metabolic pathway that produces cholesterol; remember: uses 2 NADPH

Answer 15

HMG-CoA reductase

Question 16

true/fasle: HMG-CoA reductase is a common target of cholesterol lowering drugs (statins)

Answer 16

true

Question 17

three phosphates are transferred stepwise from ___ to mevalonate.

Answer 17

ATP

Question 18

once the three phosphates are transferred to mevanolate, what two processes occur to create a diphosphoryated 5-C product (isoprene) with a double bond?

Answer 18

decarboxylation and hydrolysis

Question 19

two _______ join head to tail, displacing one set of diphoshpates, forming 10-carbon geranyl pyrophosphate (GPP)

Answer 19

isoprenes

Question 20

GPP joins to another isopentenyl pyrophosphate to from 15-C farnesyl pyrophosphate. two farnesyl pyrophosphates join head to head to form phosphate free __________

Answer 20

squalene

Question 21

what enzyme is used to make squalene from two farnesyl pyrophosphates?

Answer 21

squalene synthase

Question 22

squalene gets converted to ______ by the cyclase enzyme, which then gets converted to cholesterol (through a few steps)

Answer 22

lanosterol

Question 23

does insulin inhibit or stimulate cholesterol synthesis

Answer 23

stimulates

Question 24

does glucagon inhibit or stimulate cholesterol synthesis

Answer 24

inhibits

Question 25

does a DROP in ATP supply inhibit or stimulate cholesterol synthesis

Answer 25

inhibit

Question 26

short term regulation of the activity of existing HMG-CoA reductase is regulated by phosphorylation by _______

Answer 26

AMP-dependant protein kinase (AMPK)

Question 27

glucagon _______ phosphorylation (inactivation) of HMG_CoA reductase, while insulin ______ dephosphorylation of the the enzyme

Answer 27

stimulates

Question 28

statins _______ (stimulate/inhibit) HMG-CoA reductase

Answer 28

inhibit

Question 29

acts as storage molecules for fatty acids; can be stored in lipid droplets within cells, and they can be carried through circulation in lipoproteins; structure is a glycerol with 3 esterified fatty acids

Answer 29

triacylglycerols (aka triglycerides or triacylglycerides)

Question 30

TG synthesis from glycerol and fatty acids: the addition of 3 different fatty acids onto a glycerol to generate at TG is essentially a ___________ reaction where a water is generated with the addition of each fatty acid

Answer 30

dehydration

Question 31

the synthesis of TG's requires glycerol OR dihydroxyacetone phosphate (DHAP), NADH, "activate" fatty acids, ATP and 5 enzymes. How is DHAP formed?

Answer 31

glycolysis and gluconeogenesis

Question 32

most glycerol 3-phosphate (backbone of TG) comes from DHAP from glycolysis/gluconeogenesis via what enzyme?

Answer 32

glycerol 3-phosphate dehydrogenase

Question 33

some glycerol 3-phosphate is made from glycerol which is a minor pathway in the liver in kidney, via what enzyme?

Answer 33

glycerol kinase

Question 34

this is the precursor to TGs and phospholipids. fatty acids are attached by the enzyme acyl transferases. releases CoA.

Answer 34

phosphatidic acid

Question 35

what is an advantage of making phospatidic acid?

Answer 35

it can then be made into triacylglycerol OR phospholipid

Question 36

this removes the 3-phosphate from the phospatidic acid and yields 1,2-diacylglycerol

Answer 36

phosphatidic acid phosphatase (aka lipin)

Question 37

once 1,2-diacylglycerol is produced from phosphatidic acid, the third carbon is then acylated with a third fatty acid which yields _________

Answer 37

triacylglycerol

Question 38

where does glycerol 3-phosphate (backbone of TG) come from under starvation/low carbohydrate/uncontrolled DM conditions?

Answer 38

during lipolysis (TG's are broken down for energy), glycolysis is inhibited, so DHAP is not readily available to make glycerol 3-phosphate. therefore cells make DHAP via glyceroneogenesis

Question 39

where does glyceroneogenesis occur in the body?

Answer 39

in the adipose tissue and the liver

Question 40

true/false: adipose cells have glycerol kinase that can make glycerol 3-phosphate on site during starvation conditions

Answer 40

false!

Question 41

know the steps of glyceroneogenesis that makes pyruvate into glycerol 3-phosphate than can be then used for triacylglycerol synthesis

Answer 41

- pyruvate goes to oxaloacetate by pyruvate carboxylase -oxaloacetate goes to phosphoenolpyruvate by PEP carboxykinase -phosphoenolpyruvate goes to DHAP -DHAP goes to glycerol 3-phosphate by glycerol 3-phosphate dehydrogenase -glycerol 3-phosphate can then be used for triacylglycerol synthesis

Question 42

does insulin inhibit or stimulate triacylglycerol synthesis?

Answer 42

stimulates

Question 43

lack of _____ results in: increased lipolysis, increased fatty acid oxidation (ketone body formation), and failure to synthesize fatty acids. (e.g. diabetes)

Answer 43

insulin