Biochemical Aspects of Liver Metabolism

Question 1

Where is the first destination of most nutrients and xenobiotics absorbed from the GI tract?

Answer 1

Liver

Question 2

What does the liver produce?

Answer 2

Bile

Question 3

Name a plasma protein excreted from the liver?

Answer 3

Albumin

Question 4

What two roles does the liver have in regulation of metabolism?

Answer 4

1. Carbohydrate and lipid metabolism - fuel storage

2. Amino acid metabolism - urea cycle

Question 5

What allows seperation of proteins by size?

Answer 5

Electrophoresis

Question 6

What 4 plasma proteins can be seperated by electrophoresis?

Answer 6

1. Albumin
2. Alpha globulins
3. Beta-globulins
4. Gamma globulins

Question 7

What substances maintan oncotic or colloid osmotic pressure?

Answer 7

Plasma proteins

Question 8

What transports hydrophobic substances like steroid hormones, free fatty acids, bilirubin and cholesterol?

Answer 8

Plasma proteins

Question 9

How can plasma proteins be involved with pH buffering?

Answer 9

Amino-acid side chains can carry net charges

Question 10

What plasma proteins transport lipoproteins, lipids, hormones and bilirubin?

Answer 10

Alpha-globulins such as ceruloplasmin

Question 11

What alpha-globulin, other than ceruloplasmin, transports vitamin A?

Answer 11

Retinol binding protein

Question 12

What does deficiency of vitamin A cause?

Answer 12

Visual impairment

Question 13

What is vitamin A converted to?

Answer 13

Retinaldehyde, part of rhodopsin, a visual pigment

Question 14

Name two beta-globulins?

Answer 14

Transferrin and fibrinogen

Question 15

What two things does transferrin do?

Answer 15

Transports Fe3+

Indicator of iron deficiency

Question 16

What is an inactive form of fibrin and is involved in clotting of blood?

Answer 16

Fibrinogen

Question 17

What is the most abundant plasma protein?

Answer 17

Albumin

Question 18

How would you describe albumin?

Answer 18

Small, negatively charged, water-soluble

Question 19

What is the main determinant of plasma oncotic pressure?

Answer 19

Albumin

Question 20

What stimulates production of albumin in the liver?

Answer 20

Insulin

Question 21

What are levels of albumin like in liver disease?

Answer 21

Low

Question 22

What two factors can lead to low levels of albumin?

Answer 22

Starvation and low protein diets

Question 23

What does albumin have multiple binding sites for?

Answer 23

Hydrophobic molecules

Question 24

What is the affinity and capacity like for albumin?

Answer 24

Low affinity, but high capacity because of high concentration

Question 25

Name three endogenous lipophilic substances that albumin transports?

Answer 25

Fatty acids Bilirubin Thyroid hormones

Question 26

What important exogenous substances does albumin carry?

Answer 26

Aspirin

Question 27

What special structural feature of albumin allows it to carry hydrophobic molecules?

Answer 27

Hydrophilic clefts in globular domains

Question 28

What do haemoglobin, myoglobin and cytochromes all haev which is a key component?

Answer 28

Iron

Question 29

How is iron transported?

Answer 29

As ferric ion Fe3+ bound ti transferrin

Question 30

How is iron stored?

Answer 30

In cells bound to ferritin

Question 31

What is an essential trace element?

Answer 31

Copper

Question 32

How is copper transported?

Answer 32

In blood bound to ceruloplasmin

Question 33

What disease is related to a copper/ceruloplasmin deficiency?

Answer 33

Wilsons disease

Question 34

What are two hydrophobic hormones?

Answer 34

``` Steroid hormones (derived from cholesterol) T3/T4 thyroid hormones ```

Question 35

How is thyroxine transported?

Answer 35

Bound to thyroid-binding globulin

Question 36

How is cortisol transported?

Answer 36

Bound to cortisol-binding globulin

Question 37

What do transport proteins do to steroid hormones and T3/T4 thyroid hormones?

Answer 37

Extend biological half-life and increased plasma concentration

Question 38

What two substances are in teh core of lipoproteins (core of hydrophobic lipids)?

Answer 38

Cholesterol esters and triglycerides

Question 39

What two substances are in the shell of a lipoprotein?

Answer 39

Polar lipids and apoproteins

Question 40

What substances are involved in fat transport between organs and tissues?

Answer 40

Lipoproteins

Question 41

What is the density order for lipoproteins, starting with the least dense?

Answer 41

Chylomicrons, VLDL, IDL, LDL, HDL

Question 42

Where do chylomicrons originate and what is there function?

Answer 42

Intestine - transport of exogenous fat to liver

Question 43

Where does VLDL originate and what is its function?

Answer 43

Liver - transports endogenous fat to peripheral cells

Question 44

Where does IDL originate and what is its function?

Answer 44

VLDL - LDL precursor

Question 45

Where does LDL originate and what is its function?

Answer 45

VLDL/IDL/liver - cholesterol transport to peripheral tissues

Question 46

Where does HDL originate and what is its function?

Answer 46

Intestine/liver - reverse cholesterol transport

Question 47

What removes excess choleeterol from cells?

Answer 47

HDL

Question 48

How is cholesterol removed from cells?

Answer 48

Esterified with fatty acids, transported back to liver, excreted as bile salts via biliary system or faeces

Question 49

What is the only organ capable of metabolising and excreting cholesterol?

Answer 49

Liver

Question 50

What vitamin does the liver store for 10 months as retinol palmitate?

Answer 50

Vitamin A

Question 51

What vitamin does the liver store for 3 weeks?

Answer 51

Vitamin Dq

Question 52

What vitamin is stored in hte liver for a few years worth?

Answer 52

Vitamin B12

Question 53

What is cholesterol a precursor for (3 substances)?

Answer 53

1. Bile acids 2. Steroid hormones 3. Vitamin D

Question 54

What is a major component of gall stones?

Answer 54

Cholesterol

Question 55

Where in cells is cholesterol synthesised?

Answer 55

In cytoplasm or enzymes bound to ER membranes

Question 56

What other three organs, than the liver, are involved in cholesterol synthesis?

Answer 56

Intestine, adrenal cortex and gonads

Question 57

What three things does synthesis of 1 mol of cholesterol require?

Answer 57

1. Source of C atoms 2. Source of reducing power 3. Significant energy

Question 58

How many moles of acetyl-CoA is needed for 1 mol of cholesterol?

Answer 58

18 mol

Question 59

How many mol of NADPH is needed for 1 mol cholesterol?

Answer 59

16 mol

Question 60

How much energy is needed to make 1 mol of cholesterol?

Answer 60

36 mol of ATP

Question 61

What converts HMG CoA to mevalonic acid in cholesterol synthesis?

Answer 61

HMG-CoA reductase

Question 62

What does HMG-CoA reductase catalyse?

Answer 62

The reversible formation of mevalonic acid, so is rate limiting

Question 63

What is the synthesis and activity of HMG-CoA reductase stimulated by?

Answer 63

Fasting

Question 64

What does dietary cholesterol and high intrahepatocyte cholesterol do to HMG-CoA reductase?

Answer 64

Reduces activity

Question 65

What drugs target HMG-CoA reductase?

Answer 65

Statins

Question 66

What product from cholesterol has a role in the regulation of calcium and phosphorus metabolism?

Answer 66

Vitamin D

Question 67

What is the most abundant form of vitamin D in the circulatory system?

Answer 67

Vitamin D3

Question 68

Where are corticosteroids (21 carbon atoms) synthesised?

Answer 68

Adrenal cortex

Question 69

Where are androgens (19 carbon atoms) synthesised?

Answer 69

In testis

Question 70

Where are oestrogens (18 carbon atoms) synthesised?

Answer 70

In ovaries

Question 71

What is the main metabolic product of cholesterol?

Answer 71

Bile salts

Question 72

Where are bile salts synthesised and stored?

Answer 72

In liver | Stored as compoennet of bile in gall baldder

Question 73

What, once released into the duodenum, act as detergents for emulsifying ingested lipids?

Answer 73

Bile salts

Question 74

What agents bind bile salts and inhibit reabsorption in the enterohepatic circulation?

Answer 74

Anion exchange resins - cholestyramine

Question 75

What do anion exchange resins do to bile salt excretion and synthesis?

Answer 75

Increased bile salt excretion with increased synthesis of bile salts

Question 76

When there is increased synthesis of bile salts in teh liver, what does the concentration of cholesterol do?

Answer 76

Decrease and number of LDL receptors of hepatic cells increases

Question 77

When the number of LDL receptors of hepatic cells increases, what happens to the uptake of LDL cholesterol from plasma?

Answer 77

Increases leading to lower plasma LDL