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 (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