Glucose Metabolism in Physiological and Pathological Conditions Flashcards Preview

MD1 Metabolism > Glucose Metabolism in Physiological and Pathological Conditions > Flashcards

Flashcards in Glucose Metabolism in Physiological and Pathological Conditions Deck (69):
1

How does glucose cross the cell membrane?

Facilitated diffusion via glucose transporters

2

Which tissues express GLUT1?

Foetal tissue
Cancer cells

3

Which tissues express GLUT2?

Liver
Kidney
Intesting
Pancreatic beta-cell

4

Which tissues express GLUT3?

Brain

5

Which tissues express GLUT4?

Muscle
Adipose tissue

6

What do glucose transporters depend on for the transport of glucose?

Availability of glucose in extracellular compartment

7

What is the relationship between insulin and GLUT4?

Insulin receptor stimulation facilitates translocation of GLUT4 to cell membrane

8

What are most of the GLUT4 molecules in cell associated with?

GLUT4 storage vesicles (GSVs) in cytosol

9

Is GLUT3 activity under the control of insulin?

No, it's always active

10

What is the activity of GLUT3 at different plasma glucose concentrations?

High activity at all plasma glucose concentrations

11

What is the relationship between an enzyme's Km value and its affinity for a substrate?

Low Km = high affinity

12

Why does GLUT3 have such a low Km?

Because needs to operate at full capacity regardless of plasma concentration because brain needs to work all the time

13

Why does GLUT4 have a moderate Km?

Needs to work well at higher plasma concentrations because body needs to store extra glucose at those times

14

Why does GLUT2 have such a high Km?

Glucose in hepatic portal vein can reach very high concentration after meal
Liver only takes up glucose for storage when its in plentiful supply

15

What is glucose intolerance in part attributed to?

Impaired glucose uptake by GLUT4

16

What are the blood glucose and GLUT4 levels in non-diabetics?

Maintain blood glucose levels
GLUT4 fluctuates

17

How do blood glucose levels change in people with diabetes?

Always high
Fluctuate a lot

18

Which tissues express enzymes for glycogenolysis?

Liver
Muscle
Kidney cortex

19

What is the role of glycogenolysis in muscle?

Sustain muscular activity

20

What is the role of glycogenolysis in the liver and kidney cortex?

Maintain blood glucose concentration

21

Which enzyme does muscle lack that disallows it from contributing to blood glucose maintenance via glycogenolysis?

Glucose-6-phosphatase

22

Which cells express enzymes for glycogenolysis in hypoxic conditions?

Astrocytes
Tumour cells

23

What is a neurovascular unit?

Blood capillary
Astrocyte
Neuron

24

What is the role of astrocytes in glucose metabolism?

Astrocytes take up glucose from capillary > store as glycogen

25

Why do astrocytes store glycogen?

Critical to protection of neurons in ischaemic stroke > still have source of glucose

26

What are the bonds in glycogen between glucose monomers?

Alpha-1,4-glycosidic linkage
Alpha-1,6-glycosidic linkage

27

Breaking which bond in glycogen gets the most amount of glucose?

Alpha-1,4-glycosidic linkage

28

What is a rate limiting step?

Catalyses irreversible reaction
Can be regulated

29

What is the enzyme involved in the rate-limiting step of glycogen breakdown?

Phosphorylase

30

What is UDP-glucose?

Activated glucose

31

What does UDP-glucose phosphorylase do?

Catalyses reversible reaction
Activates glucose

32

What is the rate-limiting enzyme in glycogen synthesis?

Glycogen synthase

33

What is the relationship between phosphorylase and glycogen synthase?

Inhibiting one activates the other

34

What are the fates of glucose-1-phosphate from glycogen?

Converted to glucose-6-phosphate
Used in
- Hypoxic tumour cells > pentose phosphate pathway
- Liver and kidney > glucose
- Muscle and tumour cells > energy
- Astrocytes > lactate > pyruvate in neurons

35

What are the liver and kidney specialised to do in terms of glucose metabolism?

Glucose producers

36

What are muscle and other organs specialised to do in terms of glucose metabolism?

Glucose utilisers

37

What is the function of glycolysis in muscles?

Generate ATP for muscle contraction

38

What is the function of glycolysis in the liver?

Generate acetyl-CoA for fatty acid synthesis

39

What is the function of liver and kidney cortex gluconeogenesis?

Generate glucose to maintain blood glucose levels

40

What is the difference between glucokinase and hexokinase?

Same enzyme
Called glucokinase in liver and kidney
Called hexokinase in other tissues

41

What are the rate limiting enzymes in glycolysis and glycogen breakdown?

1) (Glycogen) phosphorylase
2) Glucokinase/hexokinase
3) Phosphofructose kinase-1 (PFK-1)
4) Pyruvate kinase

42

What limits glycolysis?

Shortage of NAD

43

Where is the majority of NAD located?

In mitochondria > not available for glycolysis in cytosol

44

How is glycolysis sustained in anaerobic conditions?

NAD generated by lactate dehydrogenase-catalysed reaction

45

What does lactate dehydrogenase do?

Reduce pyruvate to lactate to make NAD

46

What happens to the lactate generated by lactate dehydrogenase?

Exported to liver
Liver converts to glucose
Glucose goes back to muscle for use

47

Does lactate dehydrogenase catalyse a reversible or irreversible reaction?

Reversible

48

What are the rate limiting enzymes of gluconeogenesis?

1) Glucose-6-phosphatase (G-6-Pase)
2) Fructo-1,6-bisphosphatase (FBPase-1)
3) Phosphoenolpyruvate carboxykinase (PEPCK)

49

What are the precursors of gluconeogenesis, and what are their main sources?

Muscle > alanine
Muscle > lactate
Adipose tissue > glycerol

50

What does adrenaline control in glucose metabolism in muscles, and why?

Stimulates glycogenolysis
To sustain muscular activity

51

What does insulin control in glucose metabolism in muscles, and why?

Stimulates glycogen synthesis
Store glycogen for future use

52

What does glucagon control in glucose metabolism in the liver and kidney cortex?

Stimulates glycogenolysis and gluconeogenesis
NOT glycolysis
To maintain blood glucose concentration

53

What does insulin control in glucose metabolism in the liver and kidney cortex?

Stimulates glycogen synthesis and glycolysis
To store glucose as glycogen and fatty acid

54

Where is adrenaline released from?

Adrenal medulla

55

Where is insulin released from?

Pancreas

56

Where is glucagon released from?

Pancreas

57

What is the role of glucocorticoids in glucose metabolism?

Long-term
Anti-insulin activity

58

What is the relationship between glucagon and insulin?

Reciprocally regulated

59

What stimulates the release of insulin?

High blood glucose

60

What stimulates the release of glucagon?

Low blood glucose

61

Which metabolic pathways are involved in gluconeogenesis?

Cori cycle
Alanine cycle

62

What is the Cori cycle?

Conversion of lactate from other tissues to glucose

63

What is the alanine cycle?

Conversion of alanine from muscle to glucose

64

Why can't the citric acid cycle and electron transport chain supply enough ATP during rigorous muscular activity?

Limitation of O2 supply

65

How does muscle generate energy during rigorous muscular activity?

Derive all ATP from glycolysis
Rapid degradation of glycogen

66

Is glycolysis efficient?

No, only generates 2 ATP/glucose

67

How does the muscle provide alanine to the liver?

Protein breakdown
Pyruvate from glycolysis converted

68

How is alanine involved in the liver urea cycle?

Pyruvate + amino group > alanine (in muscle)
Carried to liver
Conversion to pyruvate liberates amino group > urogenesis > urea

69

When is most to all of the body's glycogen stores used up?

Prolonged fasting