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Biochemistry - 730A > lipid metabolism > Flashcards

lipid metabolism Flashcards

1
Q

what are lipids?

A

heterogenous
water INsoluble
hydrophobic
MAJOR source of energy

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2
Q

what are the common classes of lipids?

A

fatty acids
triacylglycerol
glycerophospholipid
steroid
sphingoglycolipid

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3
Q

where does lipid digestion begin?

A

stomach

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4
Q

lipase - what about it

A

catalyzes the digestion of lipids

it is an acid stable enzyme (therefore it can withstand stomach acid)

lipase mainly targets triacylglycerols

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5
Q

where does emulsification of lipids occur

A

the duodenum
lipase attaches to fat
the mixing in the gut and action of bile salts allow the breakdown of fat into fatty droplets

smaller fat droplets allow lipase to work more efficiently

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6
Q

what molecules do pancreatic enzymes degrade?

A

TAG - pancreatic lipase
Cholesterol esters - cholesterol esterase
phospholipids - phospholipase A2, lysophospholipase

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7
Q

Degradation of TAGs

A

TAG —pancreatic lipase—-> 2-monoacylglycerol

degradation of TAGs releases 2 Fatty Acids (C1 and C3)

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8
Q

Degradation of cholesterol esters

A

cholesteryl ester –cholesterol esterase–> cholesterol

releases Fatty acids

cholesteryl esterase activity INCREASES with INCREASED presence of bile salts

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9
Q

degradation of phospholipids

A

phospholipase A2 removes 1 FA (fatty acid) from C2, leaving a lysophospholipid

lysophospholiase removes the FA at C1 leaving a glycerophosphoryl base

phospholipid –phospholipase–> glycerophosphoylcholine

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10
Q

pancreatic enzymes in digestion of lipids

A

pancreatic enzymes breakdown dietary lipids and also release FAs in the process through hydrolysis reaction

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11
Q

what do bile salts do?

A

bile salts emulsify large fat droplets into small fat droplets

because there is more “surface area” (because there is more fat droplets spread out) lipase action increases = increased lipid absorption

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12
Q

Hormonal control of lipid digestion in sm. intestine

A

cholecystokinin (in blood to stomach

secretin (in blood to sm. intestine)

gut endocrine cells secrete both hormones by the stimulation of the presence of dietary lipids

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13
Q

what type of cell absorbs lipids?

A

intestinal mucosal cells (enterocytes)

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14
Q

what components make up a mixed micelle?

A

lipids, bile salts, fat soluble vitamins (A,D,E,K)

lipids = 2-monoacylglycerol, long chain FA, cholesterol

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15
Q

what even is a mixed micelle?

A

a mixed micelle is a disk shaped cluster of amphipathic (both hydrophilic and phobic) lipids.

hydrophobic groups are on the inside of the micelle

hydrophilic groups are on the outside of the micelle

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16
Q

where is the primary site of lipid absorption

A

brush border membrane of enterocytes

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17
Q

resynthesis of TAGs and cholesteryl esters

A

the mixture of lipids (mixed micelles) absorbed by the enterocytes are REsynthesized into complex lipids in the ER of the cell

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18
Q

what lipids are resynthesized?

A

triacylglycerol

cholesteryl ester

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19
Q

in the enterocyte cell, what resynthesized components come together in the chylomicron?

A

phospholipids, TAGs, Cholesteryl ester

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20
Q

where does the chylomicron go after collecting all these lipids?

A

to the lymphatic system

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21
Q

what is lipid malabsorption?

A

fats that are not absorbed in the small intestine pass to our colon - resulting in STEATORRHEA - fatty stools

  • blockage of bile salts and blockage of pancreatic juice to sm. intestine
  • defective cells
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22
Q

what are chylomicrons

A

chylomicrons are lipid droplets surrounded by phospholipids, unesterified cholesterol, and apolipoprotein
- these things increase the stability of the droplet

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23
Q

how are chylomicrons secreted?

A

chylomicrons are released by exocytosis from the enterocytes

they enter the lacteals of the lymphatic vessels of the small intestine villi

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24
Q

what pathway do chylomicrons take?

A

lymphatic pathway –> blood

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25
Q

in the blood, chylomicrons…

A

chylomicrons carry around lipid components

the TAG components are drawn off the chylomicron by muscle and fat cells

TAG components are hydrolyzed by lipoprotein lipase and release fatty acids into the tissues

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26
Q

how are dietary lipids used by the tissues

A

TAGs - lipoprotein breaks it down
- muscle and adipose tissues use it

FAs - taken up by muscle cells and adipocytes
- travel in blood
- produce energy
- stored as TAGs

Glycerol - used by liver to produce glycerol-3-phosphate

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27
Q

what are the two forms of fatty acids in the body

A

free FAs
Fatty acyl esters in TAGs

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28
Q

What is cool about Free FAs

A

Free FAs can be oxidized to produce energy in the liver and muscle

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29
Q

structure of FAs

A

hydrophobic hydrocarbon chain and terminal
hydrophilic carboxyl group

amphipathic molecule

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30
Q

fatty acid esters

A

more than 90% of FAs in the plasma are FA esters

these FAs esters are contained in circulating lipoprotein particles

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31
Q

How do unesterified (FREE) FAs transported?

A

in circulation with albumin

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32
Q

Saturation of FAs

A

single bonds - saturated FAs

double bonds - unsaturated FAs
- cis bonds cause a kink in the FA chain
-this causes FAs to not pack as tightly together
- this leads to lower melting point
- double bonds spaced at 3 carbon intervals (C9, C12, C15)

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33
Q

longer hydrocarbon chain

A

higher melting point

34
Q

arachidonic acid

A

20:4 (5,8,11,14)

20 carbons long
4 C=C bonds between C5-6, C8-9, C11-12, C14-15

35
Q

what are the 2 essential FAs

A

linoleic acid - omega 6 FAs
alpha-linolenic acid - omega 3 FAs

36
Q

what can carbs and proteins be converted into

A

carbs and proteins can be converted to fatty acids and stored as triacylglycerols

37
Q

where does FA synthesis usually occur

A

liver (mainly)
lactating mammary glands
adipose tissue (less)

in cytosol

38
Q

OVerview of FA synthesis

A

incorporates carbons from acetyl CoA into the growing FA chain

uses ATP and NADPH

FAs are synthesized by the repetitive addition of 2C units to the growing end of the hydrocarbon chain

39
Q

acetyl coA has to move from mitochondria to the cytosol

A

acetyl coA + oxaloacetate -> citrate

citrate crosses membrane to cytosol where its reconverted to oxaloacetate and acetyl CoA

this is the production of cystolic acetyl CoA

40
Q

where does desaturation of FA occur?

A

in the smooth ER

41
Q

what are solid lipids called?

A

fats

42
Q

what are liquid lipids called?

A

oils

43
Q

what makes up a triacylglycerol

A

3 molecules of fatty acid esterified to a molecule of glycerol

these 3 molecules of FA will usually be different from each other (one unsaturated, one saturated, one either)

44
Q

Why can’t TAGs form stable micelles?

A

they are only slightly soluble in water

their outside is not completely hydrophilic

45
Q

where are TAGs stored?

A

they are stored as oily droplets in the cytosol of adipocytes in adipose tissue

these droplets act as a major energy reserve for the body

46
Q

during TAG synthesis, what is the INITIAL acceptor of FAs

A

glycerol 3 phosphate

where does this occur?

in the liver

BUUUTTTTT - steps of TAG synthesis also occur in adipose tissue

47
Q

what form must FAs be in when being converted into TAGs?

A

FA-CoA form

48
Q

TAG synthesis

A

glucose-3-phosphate —FA-CoA—>TAG

49
Q

whats up with TAGs and the liver?

A

well, the initial step of TAGsynthesis occurs in the liver

TAGs however, are not mainly stored in the liver as they are stored in the adipose tissue

50
Q

FA stored in adipose are WHAT

A

they are the major fuel storage reserve of the body

51
Q

how much energy does FA oxidation produce?

A

9 kcal/gram

way more than carbs (4) or proteins (4)

52
Q

release of FAs from TAGs

A

initiated by hormone sensitive lipase

this enzyme removes a FA from carbon 1/3 of the TAG

53
Q

BETA OXIDATION YASSSS

A

major catabolic pathway for FAs

2 carbon fragments are removed from the carboxyl end of the FA-CoA producing Acetyl CoA, NADH, and FADH2

occurs in the mitochondria

54
Q

what is the first step to beta oxidation?

A

LCFA (long chain fatty acid) transported into mitochondria via carnitine shuttle

SCFA (12 carbons or less) can enter mitochondria without carnitine shuttle

55
Q

2 carbon fragments are removed from carboxyl ends of FA CoA - and what does this produce?

A

(2 carbon) AcetylCoA, NADH, and FADH2

56
Q

odd carbon chain beta oxidation

A

2 carbon Acetyl CoA, NADH, FADH2, AND a 3 carbon Propionyl CoA

propionyl CoA is metabolized into succinyl CoA

Succinyl coA can then ENTER THE KREBs CYCle!!

57
Q

what is the difference between BO in saturated and unsaturated FAs?

A

unsaturated FAs provide less energy than saturated FAs

unsaturated FAs require more enzymes to do BO

58
Q

beta oxidation of VLCFAs (very long chain)

A

go through preliminary b oxidation in peroxisomes

then they go in the carnitine shuttle and go through normal process

59
Q

what happens with excess acetyl CoA from beta oxidation in the liver?

A

acetyl-CoA is converted into ketone bodies!!

this happens if you are intaking A LOT of lipids and LOW carbs

also happens if you are starving - your body will consume fats

diabetes is a part of using ketone bodies for fuel bc of carb catabolism issues

60
Q

what happens when rate of ketone body formation is greater than their use?

A

ketone body levels rise in blood (ketonemia) and rise in the urine (ketouria)

seen in type 1 diabetes

FRUITYYYYY odor (acetone)

61
Q

phospholipidssss YASSS (what are they made of)

A

they are polar, ionic

composed of alcohol attached to a diacylglycerol or sphingosine

62
Q

what are the 2 types of phospholipids?

A

glycerophospholipids (glycerol backbone)

sphingolipids (contain sphingosine)

63
Q

how are glycerophospholipids formed?

A

from phosphatidic acid and an alcohol

64
Q

SIGNIFICANT Sphingophospholipid

A

sphingomyelin - it is part of the myelin of nerve fibers

65
Q

where are phospholipids synthesized?

A

in the Smooth ER girl

66
Q

what are the two most abundant phospholipids in eukaryotes?

A

phosphatidylethanolamine and phosphatidylcholine

67
Q

phosphoglyceride degradation

A

phospholipases cleave phospholipids at a specific site

68
Q

degradation of sphingomyelin

A

use of sphingomyelinase breaks down sphingomyelin and leaves a ceramide

69
Q

glycolipids - where are they found?

A

in nerve tissue

70
Q

what do glycolipids have to do with blood groups

A

glycolipids are actually a source of blood group antigens and tumor antigens

their carb portion is antigenic

71
Q

what differentiates sphingomyelin from glycosphingolipids?

A

sphingomyelin has a phosphate, GSLs don’t

72
Q

what determines the type of glycosphingolipids?

A

the amount and type of carbohydrates present

73
Q

neutral glycosphingolipids

A

aka cerebrosides

ceramide monosaccharides

has galactose or glucose as the sugar

74
Q

acidic glycosphingolipids

A

negatively charged

75
Q

what are ceramides

A

sphingosine + fatty acid (FA)

76
Q

what enzyme is involved in the synthesis of glycosphingolipids?

A

glycosyl transferase

77
Q

where does the synthesis of glycosphingolipids occur?

A

the GOLGI

78
Q

what enzymes are involved in the degradation of glycosphingolipids

A

beta-galactosidase
neuraminidase

79
Q

prostaglandins + eiconasoids origin

A

polyunsaturated fatty acids with 20 carbons

80
Q

what do prostaglandins and eiconasoids do?

A

they are EXtremely potent and exhibit physiologic (inflammatory) and pathologic (hypersensitivity)

81
Q
A

Biochemistry - 730A (4 decks)

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