Metabolic Functions Of The Liver

Question 1

Where is glucose stored and what is it stored as?

Answer 1

Liver

Glycogen

Question 2

What is the conversion of glucose to glycogen stimulated by?

Answer 2

Insulin

Question 3

Why would glycogen need to be degraded to glucose?

Answer 3

Exercise (skeletal muscle stores)

Fasting (liver stores)

Question 4

Summarise glycogenolysis

Answer 4

Glycogen -> glucose

Question 5

Describe the process of glycogenolysis

Answer 5

1. One residue of glycogen is removed and converted → glucose-1-P by glycogen phosphorylase
2. Glucose-1-P → Glucose-6-p by phosphoglucomutase
3. Glucose-6-P → Glucose by glucose-6-phosphatase
4. This glucose enters the bloodstream

Question 6

Summarise glyconeogenesis

Answer 6

Amino acids / lactate / pyruvate / glycerol → glucose

Question 7

What is gluconeogensis stimulated and inhibited by?

Answer 7

Stimulated - cortisol & glucagon

Inhibited - insulin

Question 8

Summarise lipogenesis

Answer 8

Acetyl-CoA → Fatty acids

Question 9

Where does lipogenesis take place?

Answer 9

cytoplasm of hepatocytes

Question 10

What does lipogenesis require?

Answer 10

ATP

NADPH

Question 11

What is lipogensis stimulated and inhibited by?

Answer 11

Stimulated - glucagon

Inhibited - adrenaline

Question 12

Describe the process of lipogenesis

Answer 12

1. Acetyl-CoA → Malonyl-CoA by acetyl carboxylase*
2. Fatty acid synthase adds malonyl-CoA to a growing fatty acid
3. Fatty acid linked to carrier protein

Question 13

Describe the regulation of lipogenesis

Answer 13

Activated by citrate

Inhibited by AMP

Question 14

Summarise lipolysis

Answer 14

Fatty acid → Acetyl-CoA

Question 15

When does lipolysis occur?

Answer 15

Fasting / stress

Question 16

By what process does lipolysis occur?

Answer 16

β-oxidation

Question 17

What happens to the Acetyl-CoA after lipolysis?

Answer 17

Enters TCA cycle
or
Used to produce ketone bodies

Question 18

What is lipolysis stimulated and inhibited by?

Answer 18

Stimulated - glucagon & adrenaline

Inhibited - insulin

Question 19

Describe the process of lipolysis

Answer 19

1. Long chains of fatty acids broken down → series of 2-carbon acetate units
2. Acetate units combined with co-enzyme A → Acetyl-CoA
3. Acetyl-CoA can be combined with oxaloacetate → citrate for the beginning of TCA cycle

Question 20

Summarise protein synthesis

Answer 20

Amino acids → Protein

Question 21

What is protein synthesis stimulated by?

Answer 21

Insulin and GH

Question 22

Which proteins are synthesised in the liver?

Answer 22

Albumin
Blood clotting factors
Angiotensinogen

Question 23

Which blood clotting factors produced in the liver are Vitamin K dependent?

Answer 23

2, 7, 9, 10

Question 24

Summarise transamination

Answer 24

Amino group of amino acids transferred to ketoacids

Question 25

Describe the process of transamination

Answer 25

Either: - Amino group added to alpha-ketoglutarate → glutamate by aminotransferase or - Amino group added to oxaloacetate → aspartate by aspartate aminotransferase

Question 26

Summarise deamination

Answer 26

Amino group removed → ketoacid + ammonia

Question 27

Describe the process of deamination

Answer 27

1. Amino group removed from amino acid → ketoacid + ammonia by glutaminase 2. Ammonia → ammonium ion 1. Must be removed due to toxicity by: - glutamine or - urea cycle

Question 28

Why is ammonia toxic to cells:

Answer 28

- Reduces TCA cycle activity - Affects neurotransmitter synthesis - Creates an alkaline pH

Question 29

Describe the process of detoxification of ammonia

Answer 29

1. Ammonia is used to synthesise glutamine when combined with glutamate 2. Glutamine is used to synthesise nitrogen compounds 3. Ammonia transported to kidney: - Directly excreted or - Transported to liver to make urea

Question 30

what is the enzyme involved in lipolysis?

Answer 30

triglyceride lipase

Question 31

what happens to the products of lipolysis?

Answer 31

- fatty acids -> mitochondria for beta-oxidation | - glycerol -> hepatocytes -> glycerol-3-phosphate -> glycolysis

Question 32

describe the process of ketogenesis

Answer 32

2-Acetyl-CoA Acetoacetyl CoA (+ Acetyl-CoA) - thiolase HMG-CoA - HMG-CoA synthase Acetoacetate (+ Acetyl-CoA) - HMG-CoA lyase beta-hydroxybutyrate + Acetone

Question 33

how does Acyl-CoA enter the mitochondria for beta-oxidation?

Answer 33

<12 carbons: diffusion | >12 carbons: carnitine shuffle

Question 34

what is the purpose of ketogenesis?

Answer 34

uses excess acetyl-CoA | exceeding capacity of Krebs' cycle

Question 35

what is ketogenesis activated by?

Answer 35

- low G-3-P - low ATP demands - high glucagon

Question 36

what is ketogenesis inhibited by?

Answer 36

high insulin

Question 37

why do heart and skeletal muscle preferentially utilise ketone bodies for energy?

Answer 37

preserve glucose for the brain

Question 38

what is ketosis?

Answer 38

build-up of ketone bodies in the blood

Question 39

what can cause ketosis?

Answer 39

- diabetic ketoacidosis - alcoholic ketoacidosis - starvation

Question 40

describe the pathophysiology of diabetic ketoacidosis

Answer 40

1. lack of insulin -> glucose not taken up by cells -> cannot be used for glucogenesis/glycolysis 2. beta-oxidation stimulated for energy 3. high acetyl-coA -> ketones -> ketosis -> acidosis

Question 41

what are symptoms of ketoacidosis?

Answer 41

- hyperventilation | - vomiting

Question 42

how does ketoacidosis affect the blood?

Answer 42

- excessive ketones lower pH of blood | - impairs ability of haemoglobin to bind oxygen