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MCAT Biochem > Lipid and AA Metabolism > Flashcards

Lipid and AA Metabolism Flashcards

1
Q

lipid digestion begins…

A

minimally in mouth

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2
Q

once lipids make it to the duodenum…

A

bile aids lipids in emulsification to inc lipid SA

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3
Q

role of pancreas in lipid digestion

A

release lipase, colipase, and cholesterol esterase to hydrolyzes lipid on 2-monoacylglycerol, free FA, and cholesterol

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4
Q

at the end of the ileum

A

micelles experience reabsorbtion as the ileum reabsorbs bile salts and any remaining fat is passed onto the colon

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5
Q

micelles are absorbed by…

A
  • brush border of intestinal mucosal cells
  • made into triacylglycerols and cholesteryl esters in mucosa to form chylomicrons
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6
Q

how do chylomicrons leave the intestines?

A

lacteals, re enter bloodstream via the thoracic duct, and empty into subclavian vein

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7
Q

A fall in insulin levels can activate which lipid management enzymes?

A

HSL, hydrolyzes triacylglycerols to form FA and glycerol

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8
Q

which hormones activate HSL?

A

epi, and cortisol

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9
Q

HSL role

A

released glycerol transported to liver

triacylglycerol hydrolization

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10
Q

LPL role

A
  • necessary for the metabolism of chylomicrons and very low density lipoproteins
  • releases free fatty acids from triacylglycerols
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11
Q

VLDL role

A

transporta triacylglycerols and FA from liver to tissues

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12
Q

IDL role

A

picks up cholesteryl esters from HDL to become LDL
picked up by liver

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13
Q

LDL

A

deliver cholesterol to cells

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14
Q

HDL

A

helps in lipoprotein formation
picks up cholesterol in blood vessels
and delivers it to liver and steroidogenic tissue

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15
Q

cholesterol derivation

A

LDL
HDL
de novo synthesis

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16
Q

describe de novo synthesis of cholesterol

A
  • occurs in liver
  • driven by acety CoA and ATP
  • citrate shuttle carries acetyl CoA from mitochondria to cytoplasm
  • NADPH (pentose phosphate pathway) helps in reduction
  • mevalonic acid synthesis by HMG CoA reductase in SER
17
Q

cholesterol synthesis regulation

A
  • insulin promotes
  • cholesterol net feedback
  • HMG-CoA reductase gene expression regulation
18
Q

LCAT

A
  • cholesterol transport
  • bloodstream
  • activated by HDL
  • adds a FA to cholesterol
  • CETP facilitates transfer of cholesteryl esters to other lipoproteins like IDL to form IDL
19
Q

where does FA synthesis occur

A
  • liver
  • adipose
20
Q

how does acetyl CoA make it to the cytosol? first step of FA synthesis

A
  • produced by PDH and couples with OAA to form citrate TCA
  • citrate can then diffuse across mitochondrial membrane and in cytosol lyase splits them
  • OAA returns to mitochondria to continue shuttling
21
Q

rate limiting step of FA synthesis

A
  • acetyl-CoA carboxylase using biotin and ATP to add CO2 to acetyl coa to form malonyl CoA
  • activated by insulin and citrate
22
Q

fatty acid synthase

A
  • B5 and NADPH required
  • malonyl CoA + acyl carrier protein ~> malonyl-ACP
  • palmitate formed
23
Q

where does triacylglycerol formation occur

A

liver, sent to adipose as VLDL

24
Q

describe the steps of FA catabolism

A

1) activation: FA attached to CoA by FA-CoA synthase
2) entry into mitochondria: large FA chains cannot diffuse and require carnitine shuttle via carnitine acyltransferase I to enter mitochondria
3) β-oxidation

25
Q

describe β-ox

A
  • releases one acetyl CoA (fasting state in liver and ketone synthesis), reduced NAD+ and FAD to NADH and FADH2

1) ox of FA to form double bond
2) hydration of double bond to form a hydroxyl group
3) oxidation of hydroxyl group to form carbonyl
4) splitting of B-ketoacid into shorter acyl or acetyl-CoA
5) even numbered FA forms 2 acetyl CoA, odd forms 1 acetyl Coa and 1 propionyl CoA, and by propionyl-CoA carboxylase makes methylmalonyl-CoA using B7 which then turns into succinyl CoA USING MUTASE AND B12 for TCA
6) in unsat additional isomerase and reductase required

26
Q

in a fasting state, liver converts acetyl coa from B-ox into…

A

ketone bodies
acetoacetate or B-hydroxybutyrate

27
Q

ketogenesis

A
  • mitochondria of liver cells
  • HMG CoA synthase, and then lyase follows and the acetoacetate formed can be reduced to 3-hydroxybutyrate
  • acetone product
28
Q

ketolysis generally

A

transferase activates acetoacetate from blood
oxidized to acetoacetyl-CoA (cannot occur in liver)

29
Q

ketolysis in brain

A

indirectly metabolize FA as ketone bodies after a long time of fasting

ketones metabolized to acetyl CoA and PDH inhibited

glycolysis and glucose uptake inhibited

30
Q

protein catabolism

A
  • proteins digested in small intestine down into aa, peptides
  • passive transport of aa into bloodstream
  • catabolized primarily in muscle and liver
  • transamination
  • glucogenic aa converted to glucose
  • ketogenic form ketones and acetyl coa
  • amino groups feed into urea cycle

MCAT Biochem (12 decks)

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