hepatic metabolism of lipids

Question 1

what are the 3 types of lipids in the body

Answer 1

triglycerides
phospholipids
cholesterol

Question 2

which lipids are composed of fatty acids

Answer 2

only triglycerides and phospholipids

cholesterol is NOT

Question 3

what are triglycerides mainly used for

Answer 3

as an energy store for times of increased energy demand

Question 4

what are phospholipids and cholesterol used for

Answer 4

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

Question 5

where is most of the bodies fat stored

Answer 5

in adipocytes which form tissues called adipose tissues

some fat is stored in hepatocytes

Question 6

structure of triglycerides

Answer 6

3 fatty acids bound to a glycerol molecule

Question 7

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

Answer 7

78%

Question 8

how much of dietary lipids are triglycerides

Answer 8

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

Question 9

what are lipids (chemically)

Answer 9

esters of fatty acids and certain alcohol compounds

Question 10

functions of lipids (3)

Answer 10

• Energy reserves
• Structural part of cell membrane
• Hormone metabolism

Question 11

what are lipoproteins

Answer 11

molecules made of lipids and protein

they are used to transport cholesterol in the blood to cells

Question 12

where is HDL formed

Answer 12

in the liver

Question 13

where is LDL formed

Answer 13

in the plasma

Question 14

what do HDL do

Answer 14

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

Question 15

what do LDL do

Answer 15

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

Question 16

why is LDL “bad:

Answer 16

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

Question 17

why is LDL essential

Answer 17

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

Question 18

why is HDL ‘good’

Answer 18

since it removes cholesterol from plasma

Question 19

where is VLDL synthesised

Answer 19

in hepatocytes

Question 20

what do VLDL do

Answer 20

carries triglycerides from glucose in liver to adipocytes

Question 21

what is fatty acid catabolism/lipolysis

Answer 21

the mechanism by which the body accesses energy stored as triglycerides

Question 22

how much energy comes from fatty acid catabolism

Answer 22

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

Question 23

where is adipose tissue found

Answer 23

in deposits underlying the skin or surrounding internal organs

Question 24

function of adipocytes

Answer 24

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

Question 25

where does fatty acid catabolism occur

Answer 25

mitochondria

Question 26

process of fatty acid catabolism/beta oxidation

Answer 26

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

Question 27

how are triglycerides broken down

Answer 27

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

Question 28

what stimulates triglyceride lipase

Answer 28

adrenaline and glucagon

Question 29

what happens to the fatty acids produced from lipolysis

Answer 29

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.

Question 30

what happens to glycerol when it enters hepatocytes

Answer 30

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

Question 31

what is beta oxidation

Answer 31

the process by which fatty acids are oxidised and degraded

Question 32

what by products are produced in beta oxidation

Answer 32

NADH and FADH2

Question 33

what happens in beta oxidation

Answer 33

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.

Question 34

what happens to excess acetyl coA

Answer 34

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

Question 35

what is ketogenesis

Answer 35

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

Question 36

what happens to acetoacetic acid

Answer 36

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

Question 37

what is acetoacetic acid

Answer 37

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

Question 38

uses of ketone bodies (2)

Answer 38

can travel in the blood to other tissues where they are then used for energy. c also play a significant role in disease states

Question 39

what is lipoprotein lipase

Answer 39

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

Question 40

what is hepatic lipase

Answer 40

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

Question 41

where is hepatic lipase expressed

Answer 41

in the liver and adrenal glands

Question 42

what is lipogenesis

Answer 42

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

Question 43

how much glycogen can the body store

Answer 43

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

Question 44

compare energy levels of fat with glycogen

Answer 44

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

Question 45

where are fatty acids synthesized

Answer 45

cytoplasm of hepatocytes

Question 46

what happens to glucose not converted to glycogen

Answer 46

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

Question 47

what is the citrate shuttle

Answer 47

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

Question 48

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

Answer 48

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

Question 49

what does fatty acid synthase do

Answer 49

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

Question 50

what stimulates lipogenesis

Answer 50

insulin

Question 51

what inhibits lipogenesis

Answer 51

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

Question 52

what are the 2 types of adipose tissue

Answer 52

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

Question 53

how does WAT store excess energy

Answer 53

as triglycerides

Question 54

how does BAT store excess energy

Answer 54

dissipates stored energy as heat

Question 55

what is WAT made of

Answer 55

mainly triglycerides which are stored in a large singular droplet surrounding the white triglyceride droplet is a thin ring comprising the cytoplasm and nucleus.

Question 56

what is BAT made of

Answer 56

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

Question 57

where is WAT found

Answer 57

under the skin surrounding inner organs