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Biomed > Biochem Lec 3 - Lipid Metabolism - Cholesterol and steroid metabolism > Flashcards

Biochem Lec 3 - Lipid Metabolism - Cholesterol and steroid metabolism Flashcards

1
Q

cholesterol is a what alcohol

A

steroid alcohol

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2
Q

function of cholesterol

A

-structrual component of membranes, modulating fluidity
-precursor of bile acids, steroid hormones and vitamin D

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3
Q

what organ plays a central role in cholesterol regluation

A

liver

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4
Q

choelsterol enters the liver from

A

-diet
-cholesterol synthesized de novo by the liver
-extrahepatic tissues

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5
Q

cholesterol is eliminated from the liver as

A

-unmodified cholesterol in the bile
-converted to bile salts that are secreted into intestinal lumen
-secreted as VLDL

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6
Q

structure of cholesterol

A

-4 fused hydrocarbon rings w a 8 acrbon, branched hydrocarbon chain attached to carbon 17 of the D ring

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7
Q

cholesteryl esters structure

A

esterified form (w a FA attached at carbon 3)

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8
Q

sterols structure

A

steroids w a 8-10 carbon, branched hydrocarbon chain attached to carbon 17 of the D ring and OH group at carbon 3 on ring A

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9
Q

cholesterol is synthesized by virtuall all tissues in humans, but what are the largest contributors

A

-liver
-intestine
-adrenal cortex
-reproductive tissues, including ovaries, testes, and placenta

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10
Q

synthesis of cholesterol phases

A

conversion of acetyl CoA to HMG-CoA
conversion of HMG-CoA to squalene
conversion of squalene to cholesterol

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11
Q

what is the rate limiting product in the second step of cholesterol synthesis

A

mevalonate - the rate limiting product

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12
Q

what is the enzyme for the second step of cholesterol synthesis (conversion of HMG-CoA to squalene)

A

HMG-CoA reductase is the key enzyme for cholesterol synthesis

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13
Q

what is statins

A

most common cholesterol lowering drugs (inhibits HMG-CoA reductase

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14
Q

what does cholesterol do

A

inhibits the reductase and catalyzes its breakdown

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15
Q

what cannot be metabolized to CO2 and H2O in humans

A

ring structure of cholesterol

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16
Q

how are intact sterol nucleus eliminated from the body

A

eliminated from the body by conversion to bile acids and bile salts in the liver

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17
Q

how are bile/salts synthesized

A

by cholesterol

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18
Q

where is bile produced and stored

A

bile produced in the liver, stored in the gallbladder
bile is water soluble so it can be excreted

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19
Q

bile can pass directly from the liver to where

A

to the intestine or stored in the gall bladder

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20
Q

what does bile help w

A

helps emulsify fats and fat soluble vitamins thereby aiding absorption

21
Q

what enzyme is the rate-limiting step in bile acid synthesis (cholesterol degradation)

A

cholesterol 7-alpha hydroxylase catalyzes the rate liminating step in bile acid synthesis (modifies structure)

22
Q

before bile acids leave the liver

A

they are conjugated to a molecule of either glycine or tuarine

23
Q

cholesterol and other steroids are derivatized to

A

improve solubility and are excreted in solution

24
Q

cholesterol is converted to bile acids and then what and where

A

and then bile salts in the liver

25
Q

bile contains

A

bile salts, cholesterol, phospholipids, and bile pigments (bilirubin [yellow] and biliverdin [green])

26
Q

the yellow-green bile is produced by what and stored where

A

produced by hepatocytes
stored in the gall bladder

27
Q

bile helps do what

A

emulsify fats and fat soluable vitamins, thereby aiding in absorption

28
Q

almost all (>95%) the bile salts secreted into the intestine are reabsorbed where and reused

A

small intestine
smaller percent is lost in feces

29
Q

what are lipoproteins

A

spherical macromolecular complexes of lipids and specific proteins (apolipoprotein or apoproteins)

30
Q

lipoprotein particules include

A

chylomicrons (CM)
very low density lipoproteins (VLDL)
low density lipoproteins (LDL)
high density lipoproteins (HDL)

31
Q

how do lipoproteins differ

A

differ in lipid and protein composition
density is a ratio of protein: lipid composition

32
Q

function of lipoproteins

A

function in lipid transport

33
Q

chylomicron function

A

transport lipids from intestine to peripheral tissues

34
Q

where are chylomicrons assembled

A

assmebled in the intestine

35
Q

VLDL (very low density lipoprotein) production site

A

produced in liver

36
Q

VLDL function

A

transports lipids from liver to peripheral tissues

37
Q

what happens when VLDL gets depleted?

A

they become LDLs

38
Q

LDL function

A

transport cholesterol to issues

39
Q

“bad cholesterol”

A

LDL

40
Q

“good cholestero”

A

HDL

41
Q

HDL function

A

transports cholesterol from peripheral tissues to the liver

42
Q

cholesterol plaques lead to

A

artherosclerosis

43
Q

why is LDL bad

A

consist of core cholesterol esterified to fatty acids and a protein/cholesterol coat
LDLs deposit cholesterol in the arteries

44
Q

why is HDL good

A

transports cholesterol to the liver for the conversion to bile acids and for disposal

45
Q

cholesterol is a precursor of all classes of what

A

steroid hormones (glucocorticords (cortisol), mineralocorticoids (aldosterone), and sex hormones (androgens, estrogens, progestins)

46
Q

synthesis and secretion of steroid hormones occur in

A

adrenal cortex (cortisol, aldosterone, and androgens)
ovaraies and placenta (estrogens and progestins)
testes (testosterone)

47
Q

how are steroid hormones transported

A

by blood from site of synthesis to target organs

48
Q

why must steroid hormones be complexed with a plasma protein

A

bc of their hydrophobicity

49
Q

steroid hormone sequence

A

cholesterol -> pregnenolone -> progesterone

Biomed (18 decks)

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