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MEH > Session 1 (B) > Flashcards

Session 1 (B) Flashcards

1
Q

Stage 1 of dietary carbohydrate metabolism involves the breakdown of carbohydrates into…

A

Monosaccharides

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2
Q

In which parts of the body does stage 1 breakdown of dietary carbohydrates take place and using which enzymes?

A

Saliva - Amylase

Pancreas - Amylase

Small intestine contains disaccharidases attached to the brush border membrane of epithelial cells - lactase, sucrose, pancreatic amylase, isomaltase

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3
Q

What does amylase in saliva break down?

A

Starch/glycogen into dextrins

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4
Q

What does amylase in the pancreas break down?

A

Sugars into monosaccharides

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5
Q

What do pancreatic amylase and isomaltase respectively break down?

A

Alpha 1-4 bonds

Alpha 1-6 bonds

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6
Q

What are three reasons for lactose intolerance?

A

Primary lactase deficiency

Secondary lactase deficiency

Congenital lactase deficiency

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7
Q

What monosaccharides is lactose composed of?

A

Galactose + Glucose

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8
Q

What are common symptoms of lactose intolerance?

A 
Bloating/cramps 
Flatulence
Diarrhoea 
Vomiting 
Rumbling stomach
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9
Q

What is the cause of primary lactase deficiency?

A

Absence of lactase persistence allele

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10
Q

In which group of people does primary lactase deficiency occur? Where in the world does it have the highest prevalence?

A

Adults

Northwest Europe

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11
Q

What causes secondary lactase deficiency?

A

Injury to the small intestine e.g. Gastroenteritis, Crohn’s, UC

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12
Q

What ages does secondary lactase deficiency affect? Is it generally reversible or irreversible?

A

Both infants and adults

Reversible

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13
Q

Congenital lactase deficiencies are extremely rare, what causes them and what effect will it have on a newborn child?

A

An autosomal recessive defect in lactase gene

Won’t be able to digest breast milk

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14
Q

How are monosaccharides absorbed from the gut lumen?

A

By active transport by the SDGT1 into intestinal epithelial cells

Then via GLUT2 into the blood supply

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15
Q

How does glucose get from the bloodstream into cells?

A

Via facilitated diffusion using transport proteins (GLUT1 - GLUT5)

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16
Q

Where is GLUT2 found?

A

On the membranes of kidney, liver, pancreatic beta cells and the small intestine

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17
Q

GLUT4 transporters are ______ regulated

A

Insulin

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18
Q

Where are GLUT4 transporters found?

A

Adipose tissue

Striated muscle

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19
Q

All tissues can metabolise glucose but which cells have an absolute requirement for glucose as their source of energy?

For what reasons?

A

Red blood cells
Neutrophils
Innermost cells of kidney medulla
Lens of the eye

Either have a poor oxygen supply or no mitochondria so can’t rely on the later stages of respiration and largely use glycolysis

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20
Q

CNS (brain) prefers glucose as a fuel but can use __________ _______ in times of ___________

A

Ketone bodies

Starvation

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21
Q

Stage 2 of carbohydrate metabolism involves the break down of glucose into metabolic intermediates. These metabolic intermediates release… (2)

A

Reducing power and energy

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22
Q

Where does glycolysis take place?

A

In the cytoplasm of cels

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23
Q

Glycolysis consist of which two main phases? What does each phase consist of?

A

Investment (involves investment of ATP)

Payback (release of more ATP than was invested)

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24
Q

What are the starting and ending molecules of glycolysis?

A

Glucose

2 x Pyruvate

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25
Q

What are the functions of glycolysis? (3)

A

Oxidation of glucose
NADH production (2 per glucose)
Synthesis of ATP from ADP (net gain of 2 per ATP)

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26
Q

Glycolysis can operate anaerobically with the addition of which enzyme?

A

Pyruvate dehydrogenase

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27
Q

What are some key enzymes in glycolysis? (3)

A

Hexokinase (glucokinase in liver)
Phosphofructokinase
Pyruvate kinase

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28
Q

What role does hexokinase (glucokinase in the liver) play in glycolysis?

A

It’s the first step

Converting glucose to glucose-6-phosphate

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29
Q

What role does phosphofructokinase play in glycolysis?

A

A key control enzyme in glycolysis

Converts fructose-6-phosphate to fructose-1,6-bisphosphate

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30
Q

What role does pyruvate kinase play in glycolysis?

A

The last step of glycolysis

Phosphoenolpyruvate —> Pyruvate

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31
Q

What is the difference between glucokinase and hexokinase?

A

Glucokinase has a lower affinity for glucose and is not inhibited by its product

32
Q

What happens to glucose in phase 1 of glycolysis? (3 steps)

A

Phosphorylation of glucose to G-6-P then conversion to fructose-6-phosphate and phosphorylation to fructose-1,6-bisphosphate

33
Q

What is the reason for phosphorylation of glucose? (2)

A

Makes glucose negatively charge preventing passage back across the plasma membrane

Increases reactivity of glucose for further steps of glycolysis

34
Q

How many moles of ATP are used in phase 1 of glycolysis per glucose?

A

2 moles of ATP

35
Q

Which reactions in phase 1 of glycolysis are irreversible and why?

A

(1) Glucose —> G-6-P
(2) F-6-P —> Fructose-1,6-bisphosphate

These reactions have a large -ve deltaG value (too much energy would be required to carry out the reverse reaction)

36
Q

What reaction of glycolysis commits glucose to metabolism via glycolysis?

A

Step 3 in Phase 1

F-6-P —> Fructose-1,6-bisphosphate

37
Q

The rate of glycolysis in cancer cells is…

A

Up to 200x greater than normal

38
Q

What happens at the start of phase 2 of glycolysis?

A

There is cleavage of 6C in to two 3C units

39
Q

Reducing power is produced in which form in phase 2 of glycolysis? How many molecules are produced per glucose?

A

NADH

2 per glucose

40
Q

ATP is synthesised by which process in glycolysis?

A

Substrate level phosphorylation - production of ATP from ADP + Pi

41
Q

Which reaction in phase 2 of glycolysis is irreversible and why?

A

Last step - Phosphoenolpyruvate —> Pyruvate

Large -ve delta G value

42
Q

What is the main regulator for glycolysis and in which 2 main ways is it regulated?

A

Phosphofructokinase

Hormonally
Allosterically

43
Q

How is PFK allosterically regulated in muscle?

A

Inhibited by high ATP

Stimulated by high AMP

44
Q

How is PFK hormonally regulated in the liver?

A

Stimulated by insulin

Inhibited by glucagon

45
Q

What is glycerol phosphate? What is it formed from? What is it used for? Where is it produced?

A

Important intermediate of glycolysis

Formed from DHAP

Important to TAG/phospholipid biosynthesis

Produced by glycolysis in the liver (can also be made directly) and in adipose tissue (essential here)

46
Q

Which enzyme catalyses the production of glycerol phosphate?

A

Glycerol 3-phosphate dehydrogenase

47
Q

What is 2,3-bisphosphoglycerate? Where is it produced? What is its function?

A

Important intermediate of glycolysis

RBCs

Regulates haemoglobin oxygen affinity

48
Q

Which enzyme catalyses the production of 2,3-BPG?

A

Bisphosphoglycerate mutase

49
Q

How many moles of NADH are produced per mole of glucose in glycolysis?

A

2

50
Q

Total [NAD+] and [NADH] in a cell are __________. So if NAD+ is all reduced glycolysis will _______.

How is this prevented?

A

Constant

Stop

51
Q

How is NAD+ typically regenerated in most cells? In which cells is this not possible and why?

A

NAD+ is regenerated from NADH in the last stage of carbohydrate metabolism

RBCs (or other cells with a reduced oxygen supply)
There are no stages 3 and 4 of carbohydrate metabolism in RBCs as they have no mitochondria

52
Q

How is NAD+ regenerated in RBCs and cells with an insufficient oxygen supply?

A

Through the action of lactate dehydrogenase

53
Q

What reaction does lactate dehydrogenase catalyse?

A

NADH + H+ + pyruvate NAD+ + Lactate

Converts pyruvate to lactate instead of passing it on to the link reaction

54
Q

What does the presence of lactate dehydrogenase allow a cell to do?

A

Regenerate NAD+ so glycolysis can continue

55
Q

Name some tissues more reliant on glycolysis and two reasons why this may be the case.

A

RBCs, skeletal muscle, skin, brain and GI

Low oxygen, no mitochondria

56
Q

What happens to the lactate produced in tissues in the heart?

A

Enters the blood and can be converted back to pyruvate and used directly as a source of energy

57
Q

What happens to any lactate produced in the tissues, in the liver and kidneys?

A

Converted back to pyruvate and used for gluconeogenesis

58
Q

What is the normal plasma lactate concentration?

A

Less than 1.6 mM

59
Q

What plasma lactate concentration is defined as hyperlactaemia? Is there a change in blood pH at this point and why?

A

2-5 mM

No, still below renal threshold

60
Q

What plasma lactate concentration is defined as lactic acidosis? How does this affect blood pH?

A

Above 5mM

Lowers blood pH, above renal threshold

61
Q

Galactose produced by the breakdown of dietary lactose can be used in which 2 ways?

A

To start glycolysis

To produce glycogen

62
Q

Which enzyme catalyses the phosphorylation of galactose to galactose-1-phosphate?

A

Galactokinase

63
Q

Deficiencies in which 3 enzymes can cause galactosaemia?

A

Galactokinase
Uridyl transferase
UDP-galactose epimerase

64
Q

What reaction does uridyl transferase catalyse?

A

Conversion of galactose-1P to glucose-1P (on its way to be used in glycolysis)

65
Q

What reaction does UDP-galactose epimerase catalyse?

A

Conversion of galactose-1P to UDP-galactose (on its way to forming glycogen)

66
Q

Where in the body is fructose metabolised? What can fructose be used for in the body?

A

In the liver

Can be modified for use in glycolysis

67
Q

What is the cause, features and clinical signs of essential fructosuria?

A

Fructokinase missing

Fructose in urine

No clinical signs

68
Q

What is the cause, result and treatment for fructose intolerance?

A

Adolase missing

Fructose-1-phosphate accumulates in the liver causing liver damage

Remove fructose from the diet

69
Q

The pentose phosphate pathway starts from…

A

Glucose-6-phosphate

70
Q

The pentose phosphate pathway is an important source of _________ and ________

A

NADPH

C5-sugar ribose

71
Q

The NADPH produced in the pentose phosphate pathway is required for… (3)

A

Reducing power for biosynthesis
Maintenance of GSH levels
Detoxification reactions

72
Q

The C5-sugar ribose produced in the pentose phosphate pathway is required for the synthesis of… (3)

A

Nucleotides
DNA
RNA

73
Q

Is ATP synthesised in the pentose phosphate pathway?

A

No

74
Q

Is carbon dioxide produced in the pentose phosphate pathway?

A

Yes

75
Q

What is the rate limiting enzyme of the pentose phosphate pathway?

A

Glucose-6-phosphate dehydrogenase

MEH (9 decks)

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