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liver & friends lectures > hepatic metabolism of lipids > Flashcards

hepatic metabolism of lipids Flashcards

1
Q

what are the 3 types of lipids in the body

A

triglycerides
phospholipids
cholesterol

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2
Q

which lipids are composed of fatty acids

A

only triglycerides and phospholipids

cholesterol is NOT

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3
Q

what are triglycerides mainly used for

A

as an energy store for times of increased energy demand

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4
Q

what are phospholipids and cholesterol used for

A

functions such as the synthesis of the cell membrane and the synthesis of steroid hormones.

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5
Q

where is most of the bodies fat stored

A

in adipocytes which form tissues called adipose tissues

some fat is stored in hepatocytes

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6
Q

structure of triglycerides

A

3 fatty acids bound to a glycerol molecule

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7
Q

how much of energy stored in the body is accounted for by triglycerides

A

78%

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8
Q

how much of dietary lipids are triglycerides

A

95%
the rest consist of phospholipids, free fatty acids (FFAs), cholesterol and fat
soluble vitamins

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9
Q

what are lipids (chemically)

A

esters of fatty acids and certain alcohol compounds

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10
Q

functions of lipids (3)

A
  • Energy reserves
  • Structural part of cell membrane
  • Hormone metabolism
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11
Q

what are lipoproteins

A

molecules made of lipids and protein

they are used to transport cholesterol in the blood to cells

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12
Q

where is HDL formed

A

in the liver

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13
Q

where is LDL formed

A

in the plasma

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14
Q

what do HDL do

A

remove excess cholesterol from blood and tissue

then deliver this cholesterol to the liver which secretes it into the bile
or converts it into bile salts

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15
Q

what do LDL do

A

the main cholesterol carriers and they deliver cholesterol to cells throughout the body

bind to plasma membrane receptors specific for a protein component
of the LDLs and are then taken up by the cells via endocytosis

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16
Q

why is LDL “bad:

A

because high plasma
concentrations can be associated with increased deposition of cholesterol in arterial walls and a higher incidence of heart attacks

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17
Q

why is LDL essential

A

is essential in supplying cells with the cholesterol they require to synthesise cell membranes and for steroid hormone production in the gonads and adrenal glands + aldosterone + cortisol

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18
Q

why is HDL ‘good’

A

since it removes cholesterol from plasma

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19
Q

where is VLDL synthesised

A

in hepatocytes

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20
Q

what do VLDL do

A

carries triglycerides from glucose in liver to adipocytes

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21
Q

what is fatty acid catabolism/lipolysis

A

the mechanism by which the body accesses energy stored as triglycerides

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22
Q

how much energy comes from fatty acid catabolism

A

under resting conditions approximately half the energy used by muscle, liver and the kidneys comes from the catabolism of fatty acids

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23
Q

where is adipose tissue found

A

in deposits underlying the skin or surrounding internal organs

24
Q

function of adipocytes

A

to synthesise and store triglycerides during periods of food uptake and when food is not being absorbed from the small intestine, to release fatty acids and glycerol into the blood for uptake & use by other cells in
order to provide the energy required for ATP formation

25
Q

where does fatty acid catabolism occur

A

mitochondria

26
Q

process of fatty acid catabolism/beta oxidation

A
  1. Molecule of coenzyme A link to the carboxyl at the end of a fatty acid
  2. breakdown of ATP —> AMP + 2Pi
  3. The coenzyme A derivative of fatty acid then proceeds through beta-
    oxidation reactions
  4. A molecule of acetyl coenzyme A is split off from the fatty acid and two pairs of hydrogen atoms are transferred to coenzymes (one pair to FAD and the
    other pair to NAD+)
  5. The hydrogen atoms from the coenzymes then enter the oxidative
    phosphorylation pathway to form ATP
  6. Another coenzyme A attaches to the fatty acid and the cycle is repeated
  7. Each passage through this sequence shortens the fatty acid chain by two
    carbons atoms until all the carbon atoms have transferred to coenzyme A
    molecules
  8. These molecules then lead to the production of CO2 & ATP via the Kreb’s
    cycle & oxidative phosphorylation
27
Q

how are triglycerides broken down

A

hydrolysed into fatty acids and glycerol by triglyceride lipase, which is stimulated by adrenaline and glucagon.

28
Q

what stimulates triglyceride lipase

A

adrenaline and glucagon

29
Q

what happens to the fatty acids produced from lipolysis

A

they enter the circulation where they bind immediately to albumin.

when bound to albumin they are soluble in blood and so can be transported to tissues including the liver.

30
Q

what happens to glycerol when it enters hepatocytes

A

it is is immediately converted into glycerol-3-phosphate, which then enters the glycolysis pathway.

31
Q

what is beta oxidation

A

the process by which fatty acids are oxidised and degraded

32
Q

what by products are produced in beta oxidation

A

NADH and FADH2

33
Q

what happens in beta oxidation

A

2carbon segments are progressively released from the fatty acid chain until acetyl co-A is generated.

Acetyl-co-A then binds immediately with oxaloacetate to form citrate and then enters the TCA cycle to release energy in the form of ATP.

34
Q

what happens to excess acetyl coA

A

it is converted into acetoacetic acid using HMG-coA as an intermediate, and then transported to other tissues.

35
Q

what is ketogenesis

A

process through which organisms produce ketone bodies by breaking down fatty acids and ketogenic amino acids.

36
Q

what happens to acetoacetic acid

A

some is converted to beta-hydroxybutyric acid, and small amounts to acetone

37
Q

what is acetoacetic acid

A

a keto acid, and together with beta-hydroxybutyric acid and acetone the three compounds are known as ketone bodies.

38
Q

uses of ketone bodies (2)

A

can travel in the blood to other tissues where they are then used for energy. c

also play a significant role in disease states

39
Q

what is lipoprotein lipase

A

an enzyme that hydrolyses triglycerides in lipoproteins (chylomicrons & VLDLs)
into 2 free fatty acids & 1 glycerol molecule

40
Q

what is hepatic lipase

A

Converts IDL (intermediate density lipoprotein) into LDL thereby packaging it with more triglycerides to be released in the body

41
Q

where is hepatic lipase expressed

A

in the liver and adrenal glands

42
Q

what is lipogenesis

A

an essential mechanism that provides an energy store which can be used at times when the body’s energy requirement cannot be met by glucose alone

43
Q

how much glycogen can the body store

A

~15g/kg
this can soon become depleted during times of starvation or high activity

44
Q

compare energy levels of fat with glycogen

A

much more fat can be stored within adipose tissue, and fat contains 2.5x the energy as the same quantity of glycogen

45
Q

where are fatty acids synthesized

A

cytoplasm of hepatocytes

46
Q

what happens to glucose not converted to glycogen

A

converted to pyruvate via the glycolysis pathway, and transported into the mitochondria where it is converted to acetyl Co-A

47
Q

what is the citrate shuttle

A

if not entering the TCA cycle, acetyl-CoA needs to leave the mitochondria and enter the cytosol.

but the inner mitochondrial membrane is impermeable to acetyl-coA, and therefore it must traverse the membrane in an altered form; as citrate.

  1. Acetyl-CoA joins with oxaloacetate to form citrate
  2. Citrate is able to cross the mitochondria membrane
  3. Citrate is then converted back into acetyl-CoA and oxaloacetate within the cytosol
48
Q

what happens to acetyl-CoA once it is in the cytosol

A

it can be converted to malonyl-CoA by acetyl-CoA carboxylase - important in the regulation of lipogenesis as it is allosterically activated by citrate and inhibited by AMP

49
Q

what does fatty acid synthase do

A

creates an elongated fatty acid chain from the malonyl-CoA molecules, adding two carbon atoms for each molecule of malonyl-coA. As the malonyl-CoA molecules are added they lose a carbon atom creating CO2

50
Q

what stimulates lipogenesis

A

insulin

51
Q

what inhibits lipogenesis

A

glucagon and adrenaline
and
negative feedback from the presence of lipoproteins in the blood.

52
Q

what are the 2 types of adipose tissue

A

white adipose tissue (WAT)
brown adipose tissue (BAT)

53
Q

how does WAT store excess energy

A

as triglycerides

54
Q

how does BAT store excess energy

A

dissipates stored energy as heat

55
Q

what is WAT made of

A

mainly triglycerides which are stored in a large singular droplet

surrounding the white triglyceride droplet is a thin ring comprising the cytoplasm and nucleus.

56
Q

what is BAT made of

A

smaller than white adipocytes and contain multitudes of small (multilocular) lipid droplets.

57
Q

where is WAT found

A

under the skin
surrounding inner organs

liver & friends lectures (7 decks)

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