5.2.3- Liver function

Question 1

What is the ornithine cycle

Answer 1

a series of biochemical reactions that convert ammonia to urea

Question 2

What metabolic functions is the liver responsible for?

Answer 2

1) Control of blood glucose levels, amino acid levels. lipid levels
2) Synthesis of bile, plasma proteins, cholesterol
3) Synthesis of red blood cells in the fetus
4) Storage of vitamins A, D, and b12, iron, glycogen
5) Detoxification of alcohol, drugs
6) Breakdown of hormones
7) Destruction of red blood cells

Question 3

How does liver stores sugar?

Answer 3

In the form of glycogen

100-200g of glycogen, which makes up 8% of the fresh weight of the liver

Question 4

What does the glycogen form in the cytoplasm of hepatocytes

Answer 4

Granules

Question 5

What is detoxification?

Answer 5

• The liver detoxifies substances that may cause harm such as hydrogen peroxide. others include alcohol or recreational drugs
• Toxins can be rendered harmless by oxidation, reduction, methylation or by combination with another molecules.
• Liver cells may contains that render toxic molecules less toxic such as catalase and cytochrome p450

Question 6

What is Catalase? (2 Points)

Answer 6

1) Converts hydrogen peroxide to oxygen and water

2) High turnover number of 5 million

Question 7

What is Cytochrome P450

Answer 7

1) Group of enzymes used to breakdown drugs including cocaine and various medical drugs
2) Also used in other metabolic reactions such as electron transport during respiration.
3) Their role in metabolising and cause the unwanted side effects of some medicinal drugs
4) A lot of variation between individuals

Question 8

What does alcohol or ethanol do the nerve activity

Answer 8

Depresses nerve activity

Question 9

Where and how is Alcohol broken down?

Answer 9

Broken down in the hepatocytes

1) Enzyme ethanol dehydrogenase –> Resulting compound is ethanol
2) Further dehydrogenated with ethanAL dehydrogenase which produces acetate
3) Acetate is combined with co enzyme A forming acetyl co enzyme A which enters the process of aerobic respiration.

Question 10

What happens to the hydrogen atoms from the detoxification of alcohol?

Answer 10

1) Combined with another enzyme called NAD to form reduced NAD

Question 11

What is NAD required for?

Answer 11

NAD is required to oxidise and breakdown fatty acids for use in respiration.

Question 12

What happens if the liver has to detoxify too much alcohol?

Answer 12

1) It uses up its stores of NAD and has insufficient left to deal with fatty acids
2) The fatty acids are then converted back to lipids and stored as fat in the hepatocytes cuasing the lvier to become enlarged. –> This condition is known as ‘Fatty liver’, which can lead to alcohol related hepatitis or to cirrhosis

Question 13

How is urea formed?

Answer 13

1) Excess amino acids cannot be stored
2) Amino gorup makes them toxic
3) Undergo treatment in the liver to remove and excrete the amino component consisting of two processes known as Deamination and ornithine cycle

Question 14

What is the process of Deamination?

Answer 14

Amino acid –> O2 –> Keto Acid + Ammonia

Question 15

What is the process of ornithine cycle?

Answer 15

Ammonia + CO2 –> Urea + Water

1) Ammonia combined with carbondioxide occurs in the ornithine cycle
2) Amonia and carbon dioxide combine with the amino acid ornithine to produce citrulline
3) Converted to arginine by further ammonia
4) The arginine is then re-converted to ornithine by the removal of urea

Question 16

Why is Ammonia converted to urea?

Answer 16

1) Less soluble and less toxic than ammonia
2) Filtered out of the blood into the kidneys.
3) Can be safely stored in the bladder until it is released from the body