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metabolism 3206 > cholesterol, TG & PL > Flashcards

cholesterol, TG & PL Flashcards

1
Q

,,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

A

cholesterol

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2
Q

what is the starting material to make cholesterol?

A

acetate

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3
Q

formation of cholesterol: three acetates come together to form ____________

A

mevalonate

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4
Q

formation of cholesterol: mevalonate converts to phosphorylated ____________

A

5-C isoprene

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5
Q

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

A

6

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6
Q

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

A

cholesterol

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7
Q

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

A

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

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8
Q

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

A

HMG-CoA

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9
Q

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

A

thiolase (aka acetyl-CoA acetyl transferase)

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10
Q

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

A

reversible

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11
Q

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

A

HMG-CoA synthase

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12
Q

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

A

irreversible

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13
Q

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

A

HMG-CoA reductase

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14
Q

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

A

irreversible

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15
Q

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

A

HMG-CoA reductase

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16
Q

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

A

true

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17
Q

three phosphates are transferred stepwise from ___ to mevalonate.

A

ATP

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18
Q

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

A

decarboxylation and hydrolysis

19
Q

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

A

isoprenes

20
Q

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

A

squalene

21
Q

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

A

squalene synthase

22
Q

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

A

lanosterol

23
Q

does insulin inhibit or stimulate cholesterol synthesis

A

stimulates

24
Q

does glucagon inhibit or stimulate cholesterol synthesis

A

inhibits

25
Q

does a DROP in ATP supply inhibit or stimulate cholesterol synthesis

A

inhibit

26
Q

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

A

AMP-dependant protein kinase (AMPK)

27
Q

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

A

stimulates

28
Q

statins _______ (stimulate/inhibit) HMG-CoA reductase

A

inhibit

29
Q

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

A

triacylglycerols (aka triglycerides or triacylglycerides)

30
Q

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

A

dehydration

31
Q

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

A

glycolysis and gluconeogenesis

32
Q

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

A

glycerol 3-phosphate dehydrogenase

33
Q

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

A

glycerol kinase

34
Q

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

A

phosphatidic acid

35
Q

what is an advantage of making phospatidic acid?

A

it can then be made into triacylglycerol OR phospholipid

36
Q

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

A

phosphatidic acid phosphatase (aka lipin)

37
Q

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

A

triacylglycerol

38
Q

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

A

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

39
Q

where does glyceroneogenesis occur in the body?

A

in the adipose tissue and the liver

40
Q

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

A

false!

41
Q

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

A
  • 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
42
Q

does insulin inhibit or stimulate triacylglycerol synthesis?

A

stimulates

43
Q

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

A

insulin

metabolism 3206 (7 decks)

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