GI/Liver 3: Liver

Question 1

What is transferrin?

Answer 1

A protein that transports 2x iron ions in the blood.

Question 2

What large spherical protein consisting of 24 subunits can contain up to 5000 atoms of iron?

Answer 2

Ferritin.

Question 3

Where is most ferritin in the body?

Answer 3

In cell cytoplasm, especially in the liver/spleen/bone marrow, and in reticuloendothelial cells.

Question 4

Why might ferritin levels be raised in a patient who does not have high iron levels?

Answer 4

In liver disease; damage to hepatocytes releases ferritin.

Question 5

What is the only known cause of low ferritin levels?

Answer 5

Iron deficiency.

Question 6

Name 3 key functions vitamins provide in the body.

Answer 6

1. Gene activators
2. Free-radical scavengers
3. Coenzymes/cofactors in metabolic reactions

Question 7

Vitamin A can be ingested as retinol in meat/eggs/dairy. How can vegans ensure they also have enough Vitamin A?

Answer 7

Eating vegetables e.g. carrots/spinach, which contain carotenoids - this can be converted into retinol (Vitamin A) in the intestines.

Question 8

What can Vitamin A deficiency cause?

Answer 8

Visual problems - can ultimately lead to blindness.

Question 9

Why does Vitamin D deficiency cause rickets in children, or osteomalacia in adults?

Answer 9

Vitamin D deficiency effectively leads to deficiency of calcium because Vitamin D increases intestinal absorption of calcium, reabsorption and formation of bone, and reduced renal excretion of calcium.

Question 10

Why might a patient with kidney disease have calcium deficiency?

Answer 10

Vitamin D is converted into its active form by the kidneys, and then is vital in maintaining calcium levels. This active form is not stored and needs to be constantly produced by the kidneys.

Question 11

What fat-soluble vitamin is responsible for the synthesis and activation of some clotting factors.

Answer 11

Vitamin K

Question 12

Deficiency of what water-soluble vitamin causes scurvy?

Answer 12

Vitamin C

Question 13

Name 3 functions of Vitamin C.

Answer 13

Collagen synthesis.
Antioxidant.
Iron absorption.

Question 14

Why can diseases that increase cell turnover (e.g. leukaemia) cause folate deficiency?

Answer 14

Folate is required for DNA synthesis. A patient with a disease with high cell turnover will require more folate.

Question 15

Which organ produces many of the clotting factors involved in the coagulation cascade?

Answer 15

The liver.

Question 16

What are the three key components of an amino acid?

Answer 16

Amino group
Side chain (R group)
Carboxylic acid group

Question 17

Which part of an amino acid contains nitrogen?

Answer 17

Amino group

Question 18

The structure of which part of an amino acid varies between different amino acids to give different properties?

Answer 18

The side chain.

Question 19

What is the body’s main source of nitrogen?

Answer 19

From dietary protein.

Question 20

Give an example of a non-protein molecule created using an amino group cleaved from amino acid.

Answer 20

Nitrogenous base e.g. guanine.

Question 21

Name three different ways nitrogen is lost from the body.

Answer 21

Renal excretion as urine.
Faecal loss.
Skin/hair/sweat loss.

Question 22

Where are amino acids used to make glucose or triglycerides?

Answer 22

The liver.

Question 23

Where is albumin made?

Answer 23

The liver.

Question 24

How do amino acids travel across the enterocyte cell membrane?

Answer 24

Via a co-transporter.

Question 25

The carbon backbone of amino acids can be used either to produce glucose/TCA cycle substrates, or to produce acetyl CoA/acetoacetyl CoA.

What are the two terms used for these two different types of amino acids?

Answer 25

Glucogenic and ketogenic.

Question 26

Most amino acids are glucogenic or both glucogenic and ketogenic. What two amino acids are solely ketogenic?

Answer 26

Leucine and lysine.

Question 27

What is transamination?

Answer 27

An enzyme-mediated process that transfers an amino group from one amino acid to a keto-acid e.g. pyruvate to form a different amino acid (and the keto-acid of the original amino acid).

Question 28

What does ammonia combine with to form carbamoyl phosphate, which then allows ammonia to enter the urea cycle?

Answer 28

Bicarbonate.

Question 29

What is a byproduct of the urea cycle? (Not urea!)

Answer 29

Fumarate

Question 30

Name three substances that are required for the urea cycle, other than the required enzymes.

Answer 30

Carbamoly phosphate, aspartate, H2O.

Question 31

Where does the urea cycle occur?

Answer 31

Hepatocytes (in the liver). Initially occurs in mitochondria and then in cell cytoplasm.

Question 32

What is ubiquitin?

Answer 32

A small protein which acts as a marker for proteasome to destroy old proteins.

Question 33

Why can corticosteroid treatment cause hyperglycaemia?

Answer 33

Corticosteroids have the same effect as cortisol, stimulate gluconeogenesis.

Question 34

In the glucose-alanine cycle, where is alanine transported from and where is it transported to?

Answer 34

From muscle cells, to the liver.

Question 35

What is the purpose of the glucose-alanine cycle?

Answer 35

To remove ammonia from the muscle cells and transport it to the liver to enter the urea cycle for safe removal from the body.
The carbon-backbone of alanine is recycled into glucose so it can be sent back to the muscle cells for glycolysis.

Question 36

Roughly how much albumin does the liver make per day?

Answer 36

10-15g

Question 37

What percentage of ammonia is converted into urea in the liver?

Answer 37

100%

Question 38

How are non-essential amino acids synthesised?

Answer 38

By transamination.

Question 39

What main liver enzyme often catalyses transamination?

Answer 39

ALT (alanine transaminase)

Question 40

Name two main functions of albumin.

Answer 40

1. Oncotic pressure maintenance.
2. Transport (e.g. of bilirubin, hormones etc.).

Question 41

What can ammonia toxicity cause?

Answer 41

Confusion, brain damage, coma, and death.

Question 42

Name two sources of ammonia.

Answer 42

Protein catabolism.
Intestinal bacterial metabolism.

Question 43

Can triglycerides diffuse through cell membrane?

Answer 43

No.

Question 44

Why can insulin resistance lead to fatty liver?

Answer 44

Insulin increases fat storage in adipocytes.
In insulin resistance, there is increased lipolysis in adipocytes, leading to increased level of triglycerides in circulation. These end up at the liver which stores them, as there is higher blood glucose levels and therefore less demand for lipids to be used as an energy source.

Question 45

What are the four main types of lipoproteins?

Answer 45

Very low-density lipoprotein (VLDL)
Low-density lipoprotein (LDL)
High-density lipoprotein (HDL)
Chylomicrons

Question 46

How dense are chylomicrons relative to the other main types of lipoproteins? How does this relate to their main function?

Answer 46

Chylomicrons are the least dense, because they have a high lipid to protein ratio (more lipid than protein, and lipids are less dense than protein). This is because their key function is to transport dietary fats from the small intestine to muscles and adipose tissue.

Question 47

What happens to remnant chylomicrons, after they have delivered triglycerides to the muscles and adipose tissue?

Answer 47

They go to the liver, where they are recycled to form VLDLs and LDLs.

Question 48

What are VLDLs and what is their main function?

Answer 48

VLDLs are lipoproteins synthesised in the liver. Their key function is to deliver triglycerides and cholesterol to peripheral tissues.

Question 49

What is the main role of LDLs?

Answer 49

To deliver cholesterol to the peripheral tissues.

Question 50

What is the main role of HDLs?

Answer 50

To remove excess cholesterol from the tissues and return it to the liver to be made into bile

Question 51

Why can it be difficult to lower cholesterol through diet alone?

Answer 51

Only 10% of cholesterol comes from diet. Mostly it is synthesised by the body.

Question 52

What is the difference in purpose of the mitochondrial beta oxidation pathway and the peroxisomal beta oxidation for fatty acids?

Answer 52

Mitochondrial: primarily to oxidise fatty acids so they can be condensed into ketone bodies for energy.
Peroxisomal: main role is detoxification e.g. of very long chain fatty acids which are toxic.

Question 53

How do fatty acids regulate gene expression?

Answer 53

By controlling activity of key transcription factors.

Question 54

What is lipotoxicity?

Answer 54

Accumulation of lipids in non-adipose tissue, which can impact metabolism e.g. by causing insulin resistance, defective mitochondria. Lipotoxicity causes cell dysfunction and death.

Question 55

What does lipotoxicity lead to in the liver?

Answer 55

Fatty liver/steatosis -> (steatohepatitis) -> fibrosis -> cirrhosis.

Question 56

Fatty acid oxidation is a source of reactive oxygen species (ROS). What does this result in?

Answer 56

Oxidative stress, which induces Kupffer cells to release cytokines (causing hepatitis). ROS also activate stellate cells (which causes fibrosis).
(A build up of ROS can damage DNA/RNA/proteins and can cause cell death as a result).

Question 57

What are reactive oxygen species (ROS)?

Answer 57

A type of free radical, they are unstable molecules containing oxygen, they easily react with other molecules in the cell. Function relates to cell signalling and regulation. A build up of ROS can damage DNA/RNA/proteins and can cause cell death as a result.