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Endocrine System > Carbohydrate Metabolism and Insulin > Flashcards

Carbohydrate Metabolism and Insulin Flashcards

1
Q

L glucose is found naturally whereas D glucose is not. T/F?

A

False - the opposite is true

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2
Q

Alpha-D-glucose is present in foodstuffs, What does the ‘alpha’ refer to?

A

Whether or not the hydroxyl group bins below (alpha) or above (beta) the first carbon atom

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3
Q

What type of bond holds two monosaccharides together to form a disaccharide?

A

Glycosidic bond

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4
Q

Why might some starches be slowly digested?

A

They are trapped in intact starch granules e.g. raw cereals and vegetables
They are resistant to amylase due to tightly packed 3D structure e.g. processed foods, raw potato
Associated with dietary fibre (beans/legumes)
Contain high levels of fat which delay gastric emptying

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5
Q

Why can humans not digest cellulose?

A

Because we do not have the enzymes required to cleave the beta glycosidic bonds in cellulose

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6
Q

Why is the brain dependent on a constant supply of glucose?

A

Fatty acids cannot cross the blood-brain barrier whereas glucose can

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7
Q

Why are erythrocytes dependent on a constant supply of glucose?

A

These cells have no mitochondria and therefore cannot oxidise fuels so can only gain energy from glycolysis

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8
Q

Between what concentration is glucose maintained in the fasted state?

A

4-5mM/l

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9
Q

Between what concentration is glucose maintained in the fed state?

A

8-12mM/l

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10
Q

What transporters can transport glucose down its concentration gradient by facilitated diffusion?

A

GLUT 1 - GLUT 5

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11
Q

What transporters can transport glucose against its concentration gradient by active transport?

A

SGLT 1 and 2

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12
Q

SGLT 1/2 transport glucose actively with which electrolyte?

A

Sodium

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13
Q

Which monosaccharides can GLUT1 transport?

A

glucose and galactose but not fructose

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14
Q

GLUT2 is capable of transporting glucose, galactose and fructose. It is present mainly on which tissues?

A

Liver
Pancreas beta cells
Small intestine
Kidney

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15
Q

Which transporter is the primary glucose transporter for neutrons?

A

GLUT 3

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16
Q

Which transporter is the insulin-responsive glucose transporter?

A

GLUT-4

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17
Q

Which tissues is GLUT-4 particularly expressed in?

A

Skeletal and cardiac muscle

adipocytes

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18
Q

Which transporter transports fructose but not glucose or galactose?

A

GLUT 5

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19
Q

Where is GLUT 5 transporter particularly present?

A

Small intestine

Sperm

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20
Q

During exercise, GLUT4 is translocated into adipose and muscle cells to produce more ATP independent of insulin. T/F?

A

True

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21
Q

What are the possible functions of glucose in a cell?

A

Production of ATP via glycolysis, TCA cycle and oxidative phosphorylation
Storage as glycogen
Storage of lipid from acetyl coA following glycolysis
Synthesis of sugars for RNA/DNA
Synthesis of glycolipids and glycoproteins

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22
Q

All pathways for any use of glucose in a cell require phosphorylation of glucose to…?

A

Glucose 6 phosphate

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23
Q

Phosphorylation of glucose traps glucose within the cell. T/F?

A

True

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24
Q

What is the other name from hexokinase 6?

A

Glucokinase

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25
Q

Which substance acts in a negative feedback loop hexokinases 1-3?

A

Glucose 6 phosphate

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26
Q

Hexokinases 1-3 have a high affinity for glucose. T/F?

A

False - they have a low affinity for glucose

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27
Q

Which enzyme is responsible for the step of glycolysis which commits the glucose molecule to the glycolysis pathway?

A

Phosphofructokinase

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28
Q

What downstream products act as negative feedback inhibitors of phosphofructokinase?

A

ATP

Citrate

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29
Q

How is NAD+ replenished in anaerobic conditions?

A

By conversion of pyruvate to lactate

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30
Q

How can fructose be used in glycolysis?

A

It is converted to fructose-1-phosphate by fructokinase and this is then converted to DHAP and glyceraldehyde-3-phosphate which are intermediates in glycolysis

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31
Q

How can galactose be used in glycolysis?

A

It is converted to glucose-1-phosphate then G6P by a number of enzyme-mediated steps

32
Q

Which enzyme is responsible for the conversion of pyruvate to lactate?

A

Lactate dehydrogenase

33
Q

Which enzyme is responsible for the conversion of pyruvate to acetyl coenzyme A?

A

Pyruvate dehydrogenase

34
Q

How many molecules of ATP can be produced from one molecule of NADH in the TCA cycle?

A

3

35
Q

How many molecules of ATP can be produced from one molecule of FADH2 in the TCA cycle?

A

1

36
Q

How many molecules of ATP can be produced from one molecule of GTP?

A

1

37
Q

What is the committed step for the pentose phosphate pathway?

A

dehydrogenation of G6P

38
Q

What is the pentose phosphate pathway of glucose metabolism used for?

A

The synthesise of nucleotides for the formation of ribose-5-phosphate

39
Q

What is the name of the process by which glucose is converted to glycogen?

A

Glycogenesis

40
Q

G6P is converted to G1P in glycogenesis using which enzyme?

A

Phosphoglucomutase

41
Q

Which enzyme is used to converted G1P to USP-glucose in glycogenesis?

A

Glucose 1 phosphate uridyltransferase

42
Q

UDP-glucose is split into glycogen and UDP in the final step of glycogenesis by which enzyme?

A

Glycogen synthase

43
Q

What is gluconeogenesis?

A

the synthesis of glucose from a non-carbohydrate source such as lactate, pyruvate, glycerol or certain amino acids

44
Q

In what organs does gluconeogenesis occur?

A

Primarily the liver but also the kidneys

45
Q

Gluconeogenesis is a reversal of glycolysis and all steps require ATP. Which enzyme mediated steps of glycolysis are irreversible and therefor need to be bypassed in this process?

A

Glucokinase
Phosphofructokinase
Pyruvate kinase

46
Q

Which enzyme is used to bypass glucokinase in gluconeogenesis?

A

Glucose 6 phosphatase

47
Q

Which hormones can stimulate the expression of glucose 6 phosphatase?

A

Adrenaline

Glucocorticooids

48
Q

Which hormones suppresses the expression of glucose 6 phosphatase?

A

Insulin

49
Q

In gluconeogenesis how is phosphofructokinase bypassed?

A

By 1,6 - bisphosphatase

50
Q

How is pyruvate kinase bypassed in gluconeogenesis?

A

Pyruvate is converted to oxaloacetate by pyruvate carboxylase and then converted to phosphoenolpyruvate by phosphoenolpyruvate carboxykinase

51
Q

How can lactate be used in gluconeogeneis?

A

By converting it to pyruvate

52
Q

How can glycerol be used in gluconeogenesis?

A

By converting it to DHAP

53
Q

How can amino acids be used in gluconeogenesis?

A

by conversion to pyruvate

54
Q

Why can fatty acids not be used in gluconeogenesis?

A

Because carbon atoms are lost when fatty acids and oxidised to acetyl coA

55
Q

Glucagon and adrenaline increase the activity of G6Pase and PEPCK to increase gluconeogenesis and decrease glucokinase activity to decrease glycolysis. At what level is this effect exerted?

A

Level of Gene expression

56
Q

Via which transporter is insulin transported into pancreatic beta cells?

A

GLUT2

57
Q

How does the increase in ATP in pancreatic beta cells due to the influx of glucose cause the secretion of insulin?

A

The increase in ATP blocks the action of a K-ATPase which pumps potassium out of the cell which increases the movement of calcium into the cell via L-type calcium channels and this then promotes insulin production and secretion

58
Q

What metabolic processes does insulin stimulate?

A

Glucose transport
Glycogen synthesis
Fatty acid synthesis

59
Q

What metabolic processes does insulin suppress?

A

Lipolysis

Gluconeogenesis

60
Q

Which enzyme does insulin work on to stimulate glycolysis?

A

Glucokinase

61
Q

Which enzymes does insulin work on to suppress gluconeogenesis?

A

It inhibits G6Pase and PEPCK

62
Q

Which enzyme does glucagon work on to suppress glycolysis?

A

inhibition of Glucokinase

63
Q

Which enzymes does glucagon work on to stimulate gluconeogenesis?

A

G6Pase and PEPCK

64
Q

Which enzyme is responsible for the conversion of glycogen to glucose-1-phosphate in order to release glucose from storage?

A

Glycogen phosphorylase

65
Q

Which enzymes does insulin work on in order to increase glycogenesis and decrease the release of glucose from glycogen?

A

Stimulate glycogen synthase

inhibits glycogen phosphorylase

66
Q

In addition to stimulate storage of glycogen as glucose, what additional affect does insulin have on muscle cells?

A

Increases insertion of GLUT4 transporters to increase glucose uptake by these cells

67
Q

Which enzymes does glucagon work on in order to decrease glycogenesis and increase the release of glucose from glycogen?

A

Inhibits glycogen synthase

Stimulates glycogen phosphorylase

68
Q

The stimulation of the release of glucose from glycogen in the liver can be elicited by glucagon and also by …?

A

Noradrenaline

69
Q

In muscles, glycogen is broken down into glucose under the action of which stimulus?

A

Noradrenaline

70
Q

Why is it important that insulin also works to inhibit lipolysis?

A

This leads to a reduction in fatty acid concentration which results in a switch to the oxidation of glucose in muscle

71
Q

Adrenaline works to stimulate which enzyme in the liver to convert triglycerides to glycerol to encourage oxidation of fatty acids rather than glucose?

A

Hormone sensitive lipase

72
Q

Describe how an increase in plasma glucose concentration results in insulin release from beta cells.

A

Glucose enters the cell via GLUT2 transporters and is metabolised to produced ATP. This ATP inhibits the action of a potassium channel which pumps potassium out of the cell and this causes depolarisation of the beta cell which opens voltage gated calcium ion channels. The resultant influx of calcium into the beta cell promotes the release of insulin from storage vesicles into the bloodstream

73
Q

How is proinsulin converted to insulin?

A

By cleaving the c-peptide from proinsulin

74
Q

What is the term for GI hormones such as GIP and GLP which stimulate pancreatic insulin in a feedforward mechanism in response to food?

A

Incretins

75
Q

Which branch of the nervous system is capable of increasing insulin release?

A

Parasympathetic nervous system

76
Q

During fasting between meals, how is blood glucose concentration maintained?

A

Insulin levels decrease and glucagon levels rise to cause the promotion of glycogenolysis and gluconeogenesis and the inhibition of glycolysis and glycogenesis.

77
Q

Ketone bodies are used rather than glucose in periods of starvation. Why is this important?

A

Less glucose use decreases gluconeogenesis meaning that precious fats and more importantly, proteins, are not used up in the process and so this allows increased survival during starvation

Endocrine System (12 decks)

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