Biochemistry of the Liver

Question 1

what are the 6 functions of the liver?

Answer 1

first destination of most nutrients/xenobiotics absorbed from GI tract
Bile production
Elimination of unwanted molecules (metabolism, excretion)
Secretion of plasma proteins (albumin)
Storage of important molecules (fuel, iron, Vitamins)
Regulate metabolism

Question 2

what might be sign of liver disease in the faeces?

Answer 2

pale stools
(not breaking down haemoglobin into bilirubin which colours faeces)

Question 3

which 2 processes of metabolism is the liver linked to?

Answer 3

carbohydrate and lipids = fuel storage

amino acid = urea cycle

Question 4

what is electrophoresis?

Answer 4

separation of proteins (in blood plasma) by size

Question 5

what are the functions of plasma proteins?

Answer 5

maintain oncotic or colloid osmotic pressure (hydration, BP regulation)
Transport hydrophobic substances (steroid hormones, free fatty acids, bilirubin, cholesterol)
pH buffering
Enzymatic - blood clotting
Immunity

Question 6

what does albumin do?

Answer 6

oncotic pressure, BP, transport substances etc

Question 7

what do alpha globulins do?

Answer 7

transport lipoproteins, lipids, hormones and bilirubin
retinol binding protein (transports Vit A)
Eg. ceruloplasmin

Question 8

Name 2 Beta globulins and their functions

Answer 8

transferrin
- transfers Fe3+
- indicator of iron deficiency
Fibrinogen
- inactive form of fibrin
- clotting of blood

Question 9

what is the most abundant plasma protein?

Answer 9

albumin (50%)

liver synthesises 14g pe3r day

Question 10

what controls synthesis of albumin?

Answer 10

hormones (eg. those released in response to a meal - insulin etc)

Question 11

what can cause low levels of albumin?

Answer 11

liver disease

starvation/low protein diet

Question 12

albumin is negatively charged and water soluble, true or false?

Answer 12

true

Question 13

albumin transports which lipophilic substances?

Answer 13

fatty acids
bilirubin
thyroid hormones

Question 14

what exogenous substances does albumin transport?

Answer 14

drugs like aspirin

Question 15

albumin has low affinity for hydrophobic molecules, how do they have a large transport capacity?

Answer 15

high concentration

multiple binding sites

Question 16

how is iron transported in the body?

Answer 16

as ferric ion Fe3+ (bound to transferrin)

Question 17

how is iron stored?

Answer 17

stored in Fe2+ form in cells bound to ferritin (can be oxidised to Fe3+ to be released and used again)

Question 18

what processes is iron involved in?

Answer 18

component of haemoglobin, myoglobin, cytochromes

Question 19

which redox reaction is redox of iron linked to?

Answer 19

copper

Question 20

how is copper transported in the body?

Answer 20

bound to ceruloplasmin

Question 21

what results from a copper deficiency?

Answer 21

Wilson’s disease

Question 22

name some hydrophobic hormones

Answer 22

steroid hormones (derived from cholesterol)
T3/T4 thyroid hormones

Question 23

how are hydrophobic hormones transported in the body?

Answer 23

bound to specific transport molecules

• thyroxine bound to thyroid binding globulin
• cortisol bound to cortisol binding globulin

Question 24

why are transport proteins important for hydrophobic proteins?

Answer 24

would be eliminated by liver/kidney without them

extend half life and increase plasma conc

Question 25

describe the structure of lipoproteins

Answer 25

core of hydrophobic lipids surrounded by shell

free cholesterol dispersed throughout

Question 26

what is the function of lipoproteins?

Answer 26

fat transport between organs and tissues

Question 27

what is the function of LDL?

Answer 27

cholesterol transport to peripheral tissues

Question 28

what is the function of HDL?

Answer 28

reverse cholesterol transport

removes excess cholesterol from cells, transported back to liver and excreted as bile salts via biliary system or faeces

Question 29

which organ is capable of metabolising and excreting cholesterol?

Answer 29

only the liver

Question 30

what substances does the liver store?

Answer 30

Vit A, D, B12

Iron

Question 31

where does iron come from?

Answer 31

breakdown of haemoglobin, stored associated with ferritin

Question 32

cholesterol is the precursor for which 3 compounds?

Answer 32

bile acids
steroid hormones
Vitamin D

Question 33

what is the function of cholesterol?

Answer 33

increase rigidity of mammalian cell membranes

Question 34

cholesterol metabolism is important in which 2 diseases?

Answer 34

cardiovascular disease

Development of gall stones

Question 35

how is cholesterol transported in the body?

Answer 35

most esterified to long chain fatty acids
30% in free form
Low solubility in water

Question 36

how is cholesterol stored?

Answer 36

incorporated into core of lipoproteins and solubilised, stored in lipid droplets

Question 37

describe the structure of cholesterol

Answer 37

sterol ring

Question 38

what is required for the synthesis of cholesterol in the liver?

Answer 38

18 mol acetyl CoA (C atoms)
16 mol NADPH (reducing power)
36 mol ATP (energy)

Question 39

what is the rate limiting enzyme in cholesterol synthesis?

Answer 39

HMG-CoA reductase

controls production of precursor mevalonic acid

Question 40

what increases/decreases activity of HMG-CoA reductase?

Answer 40

stimulated by fasting
inhibited by dietary/intrahepatocyte cholesterol
Target of statins

Question 41

what are the products from cholesterol?

Answer 41

Vit D
Steroid hormones (corticosteroids, androgens, estrogens)
Bile salts (main metabolic product)

Question 42

what is the process through which drugs lower plasma LDL?

Answer 42

bind bile salts and inhibit reabsorption in enterohepatic circulation
Increased bile salt excretion/synthesis
Cholesterol conc in liver decreases
Number of LDL receptors of hepatic cells increases
Uptake of LDL from plasma increases

Question 43

what is the role of cytochrome P450?

Answer 43

detoxifying in the liver