5.2.3 liver function

Question 1

ornithine cycle

Answer 1

series of biochemical reactions to convert ammonia to urea

Question 2

list some metabolic functions of the liver

Answer 2

• control of blood glucose/amino acid/lipid levels
• synthesis of bile, plasma proteins & cholesterol
• synthesis of RBC in fetus
• storage of vitamins (A, D, B12), iron & glycogen
• detoxification of alcohol & drugs
• breakdown of hormones
• destruction of RBC

Question 3

storage of glycogen in liver

Answer 3

• glycogen forms granules in cytoplasm of hepatocytes
• glycogen broken down to release glucose when required into blood

Question 4

examples of enzymes in liver cells which render toxic molecules less toxic

Answer 4

1. catalase
   - converts hydrogen peroxide to oxygen & water
   - high turnover number of 5 million
2. cytochrome P450
   - group of enzymes used to breakdown drugs

Question 5

how is alcohol broken down in hepatocytes (detoxification)

Answer 5

• enzymes ethanol dehydrogenase
• resulting compound = ethanal
• dehydrogenated further by enzyme ethanal dehydrogenase
• final compound = ethanoate (acetate)
• acetate combined with coenzyme A forming acetyl coenzyme A = enters process of aerobic respiration
• hydrogen atoms released from alcohol combined with another coenzyme NAD forming reduced NAD

Question 6

what is NAD also required for

Answer 6

to oxidise and breakdown fatty acids for use in respiration

Question 7

what can lead to condition ‘fatty liver’

Answer 7

• if liver has to detoxify alcohol, it uses up its stores of NAD
• has insufficient left to deal with fatty acids
• fatty acids then converted back to lipids/stored fat in hepatocytes
• liver becomes enlarged

Question 8

describe the process of deamination

Answer 8

• removes amino group & produces ammonia
• ammonia = soluble & toxic
• also produces organic compound = keto acid which can enter respiration directly

Question 9

write the deamination equation

Answer 9

pg 29 textbook

Question 10

describe the ornithine cycle

Answer 10

• ammonia is soluble/toxic so must be converted to less toxic form quickly

1. ammonia combined with carbon dioxide to produce urea
2. ammonia & carbon dioxide combine with amino acid ornithine to form citrulline
3. citrulline converted to arginine by addition of further ammonia
4. arginine then reconverted to ornithine by removal of urea

Question 11

why is ammonia converted into urea

Answer 11

• urea less soluble & less toxic
• urea can be passed back into blood & transported around body to kidneys
• in kidneys = urea filtered out of blood & concentrated in urine
• urine able to be safely stored in bladder until released from body

Question 12

summarise the ornithine cycle as an equation

Answer 12

pg29 of textbook