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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
Which substance acts in a negative feedback loop hexokinases 1-3?
Glucose 6 phosphate
26
Hexokinases 1-3 have a high affinity for glucose. T/F?
False - they have a low affinity for glucose
27
Which enzyme is responsible for the step of glycolysis which commits the glucose molecule to the glycolysis pathway?
Phosphofructokinase
28
What downstream products act as negative feedback inhibitors of phosphofructokinase?
ATP | Citrate
29
How is NAD+ replenished in anaerobic conditions?
By conversion of pyruvate to lactate
30
How can fructose be used in glycolysis?
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
31
How can galactose be used in glycolysis?
It is converted to glucose-1-phosphate then G6P by a number of enzyme-mediated steps
32
Which enzyme is responsible for the conversion of pyruvate to lactate?
Lactate dehydrogenase
33
Which enzyme is responsible for the conversion of pyruvate to acetyl coenzyme A?
Pyruvate dehydrogenase
34
How many molecules of ATP can be produced from one molecule of NADH in the TCA cycle?
3
35
How many molecules of ATP can be produced from one molecule of FADH2 in the TCA cycle?
1
36
How many molecules of ATP can be produced from one molecule of GTP?
1
37
What is the committed step for the pentose phosphate pathway?
dehydrogenation of G6P
38
What is the pentose phosphate pathway of glucose metabolism used for?
The synthesise of nucleotides for the formation of ribose-5-phosphate
39
What is the name of the process by which glucose is converted to glycogen?
Glycogenesis
40
G6P is converted to G1P in glycogenesis using which enzyme?
Phosphoglucomutase
41
Which enzyme is used to converted G1P to USP-glucose in glycogenesis?
Glucose 1 phosphate uridyltransferase
42
UDP-glucose is split into glycogen and UDP in the final step of glycogenesis by which enzyme?
Glycogen synthase
43
What is gluconeogenesis?
the synthesis of glucose from a non-carbohydrate source such as lactate, pyruvate, glycerol or certain amino acids
44
In what organs does gluconeogenesis occur?
Primarily the liver but also the kidneys
45
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?
Glucokinase Phosphofructokinase Pyruvate kinase
46
Which enzyme is used to bypass glucokinase in gluconeogenesis?
Glucose 6 phosphatase
47
Which hormones can stimulate the expression of glucose 6 phosphatase?
Adrenaline | Glucocorticooids
48
Which hormones suppresses the expression of glucose 6 phosphatase?
Insulin
49
In gluconeogenesis how is phosphofructokinase bypassed?
By 1,6 - bisphosphatase
50
How is pyruvate kinase bypassed in gluconeogenesis?
Pyruvate is converted to oxaloacetate by pyruvate carboxylase and then converted to phosphoenolpyruvate by phosphoenolpyruvate carboxykinase
51
How can lactate be used in gluconeogeneis?
By converting it to pyruvate
52
How can glycerol be used in gluconeogenesis?
By converting it to DHAP
53
How can amino acids be used in gluconeogenesis?
by conversion to pyruvate
54
Why can fatty acids not be used in gluconeogenesis?
Because carbon atoms are lost when fatty acids and oxidised to acetyl coA
55
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?
Level of Gene expression
56
Via which transporter is insulin transported into pancreatic beta cells?
GLUT2
57
How does the increase in ATP in pancreatic beta cells due to the influx of glucose cause the secretion of insulin?
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
What metabolic processes does insulin stimulate?
Glucose transport Glycogen synthesis Fatty acid synthesis
59
What metabolic processes does insulin suppress?
Lipolysis | Gluconeogenesis
60
Which enzyme does insulin work on to stimulate glycolysis?
Glucokinase
61
Which enzymes does insulin work on to suppress gluconeogenesis?
It inhibits G6Pase and PEPCK
62
Which enzyme does glucagon work on to suppress glycolysis?
inhibition of Glucokinase
63
Which enzymes does glucagon work on to stimulate gluconeogenesis?
G6Pase and PEPCK
64
Which enzyme is responsible for the conversion of glycogen to glucose-1-phosphate in order to release glucose from storage?
Glycogen phosphorylase
65
Which enzymes does insulin work on in order to increase glycogenesis and decrease the release of glucose from glycogen?
Stimulate glycogen synthase | inhibits glycogen phosphorylase
66
In addition to stimulate storage of glycogen as glucose, what additional affect does insulin have on muscle cells?
Increases insertion of GLUT4 transporters to increase glucose uptake by these cells
67
Which enzymes does glucagon work on in order to decrease glycogenesis and increase the release of glucose from glycogen?
Inhibits glycogen synthase | Stimulates glycogen phosphorylase
68
The stimulation of the release of glucose from glycogen in the liver can be elicited by glucagon and also by ...?
Noradrenaline
69
In muscles, glycogen is broken down into glucose under the action of which stimulus?
Noradrenaline
70
Why is it important that insulin also works to inhibit lipolysis?
This leads to a reduction in fatty acid concentration which results in a switch to the oxidation of glucose in muscle
71
Adrenaline works to stimulate which enzyme in the liver to convert triglycerides to glycerol to encourage oxidation of fatty acids rather than glucose?
Hormone sensitive lipase
72
Describe how an increase in plasma glucose concentration results in insulin release from beta cells.
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
How is proinsulin converted to insulin?
By cleaving the c-peptide from proinsulin
74
What is the term for GI hormones such as GIP and GLP which stimulate pancreatic insulin in a feedforward mechanism in response to food?
Incretins
75
Which branch of the nervous system is capable of increasing insulin release?
Parasympathetic nervous system
76
During fasting between meals, how is blood glucose concentration maintained?
Insulin levels decrease and glucagon levels rise to cause the promotion of glycogenolysis and gluconeogenesis and the inhibition of glycolysis and glycogenesis.
77
Ketone bodies are used rather than glucose in periods of starvation. Why is this important?
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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