Metabolism and regulation

Question 1

In the post-absorptive state what are the 3 main sources of glucose?

Answer 1

Glycogenolysis
Lipolysis
Protein breakdown

Question 2

Where does glycogenolysis occur?

Answer 2

In the liver (directly) and in skeletal muscle (indirectly)

Question 3

What is the mechanism involved in hepatic glycogenolysis?

Answer 3

Enzymatic conversion of glycogen to glucose

Question 4

How does skeletal muscle indirectly produce glucose?

Answer 4

Glucose-6-phophate  ATP, pyruvate and lactate. Lactate then processed by the liver which releases glucose into the blood (which can then be used)

Question 5

How does lipolysis produce glucose?

Answer 5

Hydrolysis of triglycerides produce glycerol and fatty acids. Glycerol is converted enzymatically to glucose the liver.

Question 6

How can protein break down produce glucose?

Answer 6

Amino acids converted by the alpha-keto acid to glucose in the liver

Question 7

Define gluconeogenesis

Answer 7

The process of generating new molecules of glucose from non-carbohydrate sources

Question 8

How is fat stored?

Answer 8

Within adipocytes which then form tissue called adipose tissue

Question 9

What % of all energy stored in the body do triglycerides account for?

Answer 9

78%

Question 10

Name 3 main functions of lipids

Answer 10

Energy reserves
Structural part of cell membranes
Hormone metabolism

Question 11

Where are high density lipoproteins formed?

Answer 11

Liver

Question 12

Where are low density lipoproteins formed?

Answer 12

Plasma

Question 13

What is the main function of high density lipoproteins?

Answer 13

To remove excess cholesterol from the blood and tissue

Question 14

What is the main function of low density lipoproteins?

Answer 14

To transport cholesterol to cells throughout the body.

Question 15

A positive net gain in amino acids is called …

Answer 15

Anabolic

Question 16

A negative net gain in amino acids is called …

Answer 16

Catabolic

Question 17

What is the most common cause of a positive nitrogen balance?

Answer 17

Pregnancy

Question 18

What is the most common cause of a negative nitrogen balance?

Answer 18

Malnutrition

Question 19

Where and by what process is alanine converted to pyruvate?

Answer 19

Transamination occurs in the liver

Question 20

What is produced when glutamate undergoes oxidative deamination?

Answer 20

Ammonium (NH4+) which quickly dissociates into ammonia (NH3)

Question 21

Where are the enzymes utilised in the urea cycle found?

Answer 21

Cytosol of hepatocytes or the mitochondria (in the liver)

Question 22

What is arginine cleaved by arginase to produce?

Answer 22

Urea and ornithine

Question 23

Outline the urea cycle (provide key enzymes and substrates)

Answer 23

Arginine (+ arginase)  >urea and ornithine.
Ornithine (+NH3 +CO2) > citrulline
Citrulline (+ammonia)  >arginine

Question 24

What happens if the urea cycle does not occur (/not at a sufficient rate)?

Answer 24

High levels of ammonia in the blood

Question 25

What is the problem of high levels of ammonia in the blood?

Answer 25

Ammonia is neurotoxic (prevents the Krebs cycle occurring)

Question 26

Describe the action of lipoprotein lipase:

Answer 26

Breakdown of triglycerides (found in lipoprotein) into 2 free fatty acid and a monoglyceride.

Question 27

Describe the action of hepatic lipase:

Answer 27

Conversion of IDL to LDL.

Question 28

Where is bile secreted?

Answer 28

Liver

Question 29

Describe the role of bile:

Answer 29

To emulsify fats

Question 30

Where is bile stored and concentrated?

Answer 30

The gall bladder