73 - Glucose Tolerance Curves

Question 1

How does glucose enter cells?

Answer 1

Facilitated by GLUT transporters, SGLT in intestines.

Hydrophilic, so can’t diffuse across cell membranes.

Question 2

Where is GLUT3 expressed?

Answer 2

In the brain

Question 3

Where is GLUT4 expressed?

Answer 3

Muscle, adipose tissue

Question 4

Km of GLUT3

Answer 4

Low (1.6mmol/L).

Therefore is saturated all the time (under physiological conditions)

Question 5

Km of GLUT4

Answer 5

Medium (5mmol/l, around that of the physiological concentration of glucose in the blood)

Question 6

Reason for high GLUT2 Km

Answer 6

GLUT2 is found in the liver.
Glucose concentration in the hepatic portal vein is significantly higher than that in general circulation, because of uptake of glucose from the gut.
High Km allows for GLUT2 to function at high glucose concentrations without saturation.

Question 7

Features of GLUT transporters
1
2
3

Answer 7

• Uniporter specific for hexoses
• Energy-independent facilitative transport of glucose
• Glucose diffusion depends on the glucose gradient: high extracellular glucose concentration favours entry of glucose into cells via GLUT.

Question 8

Fasting blood glucose physiologically

Answer 8

4.5-5 mmol/l

Question 9

Fasting blood glucose in DM

Answer 9

Over 7.8mmol/l

Question 10

Increase in blood glucose after a meal in a non-diabetic

Answer 10

4.5-6mmol/l

Question 11

GLUT-mediated glucose intolerance

Answer 11

Aspects of DM could be also mediated by improper GLUT4 transport

Question 12

Major sites of glycogen metabolism

Answer 12

Liver and kidney cortex

Question 13

Areas of glycogen metabolism under hypoxic conditions

Answer 13

Astrocytes and cancer cells

Question 14

Linkages between glucose monomers in glycogen

Answer 14

Alpha 1.4-glycosidic linkage to form strings.

Alpha-1,6-glycosidic linkage to form branches.

Question 15

Rate-limiting step of glycogen breakdown

Answer 15

Glycogen phosphorylase.

Cleaves a glucose-1-phosphate from glycogen

Question 16

Rate-limiting step in glycogen formation

Answer 16

Glycogen synthase.

Question 17

Regulation of glycogen phosphorylase

Answer 17

Glucagon form the liver.

Adrenaline for muscle glycogen.

Question 18

When is glucagon secreted into the blood?

Answer 18

When [glucose] drops below 4.5mmol/L

Question 19

Glucagon receptor

Answer 19

GPCR.

Adenylate cyclase generates cAMP from ATP, which activates PKA.

Question 20

Three precursors of gluconeogenesis

Answer 20

Lactate
Alanine
Glycerol

Question 21

Role of Cori cycle

Answer 21

Converts lactate from other tissues to glucose

Question 22

Roles of alanine cycle
1
2
3

Answer 22

Conversion of alanine from muscle to glucose.
Pyruvate can be converted to alanine.
Can transport alanine to liver for detoxification in the urea cycle.

Question 23

Energy supply to skeletal muscle during rigorous activity
1
2
3
4
5

Answer 23

• During rigorous muscular activity, TCA cycle and electron transport chain cannot supply enough ATP because of the limitation of O2 supply.
• Derive all the ATP from glycolysis
• Inefficient: only 2 ATP/Glucose in glycolysis
• Rapid degradation of glycogen to meet the energy need
• Pyruvate conversion to lactate generates NAD+ for earlier steps in glycolysis

Question 24

Function of hepatic glycolysis

Answer 24

Generate acetyl-CoA for fatty acid synthesis

Question 25

Function of hepatic gluconeogenesis

Answer 25

Generate glucose to maintain blood glucose

Question 26

Function of glycolysis in muscle

Answer 26

Generate ATP for muscle contraction

Question 27

Why is muscle glycogen not depleted when glucagon is released?

Answer 27

Muscle cells lack glucagon receptors.

Question 28

Effect of insulin on skeletal muscle

Answer 28

Upregulation of GLUT4

Question 29

Effects of glucagon

1-4

Answer 29

1) Increased glycogenolysis
2) Increased gluconeogenesis
3) Reduced glycogen synthesis
4) Reduced glycolysis
Leads to the production of glucose

Question 30

Effects of insulin

1-7

Answer 30

1) GLUT4 to membrane (in muscle and adipose tissue)
2) Glycolysis (in liver)
3) Amino acid uptake, protein synthesis (in muscle)
4) Fatty acid synthesis (in liver)
5) Glycogen synthesis (in liver and muscle)
6) Inhibits TAG breakdown (in adipose)
7) Inhibits glycogen breakdown (in liver)