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2. Biochemistry > Week 3 (carbohydrate metabolism) > Flashcards

Week 3 (carbohydrate metabolism) Flashcards

1
Q

What is metabolism?

A

The chemical processes that occur in living organisms, resulting in growth, production of energy, and elimination of waster.

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2
Q

Define catabolism

A

The break down of complex molecules, releasing energy

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3
Q

Define synthesis (anabolism)

A

Formation of complex molecules from simple starting materials

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4
Q

What are metabolic pathways?

A

A series of reactions connected together.

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5
Q

What is direction and speed of a pathway determined by?

A

The relative concentrations of each substrate.
Enzymes

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6
Q

Explain the rate limiting step in metabolic pathways

A

The rate limiting step controls how quickly the initial substrate is converted into the end product. The slowest step determines the speed of all reactions in the pathway.

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7
Q

What is Gibbs free energy and state its equation

A

Is a measure of available chemical energy.
G = H - TS
H: enthalpy (heat content)
T: temperature (Kelvins)
S: entropy (heat loss)

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8
Q

What type of reaction will be:
1. spontaneous
2. not spontaneous

A
  1. exergonic
  2. endergonic
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9
Q

Describe enzymes

A

Protein
Catalyse reactions in metabolism
Very specific
Act as control points in metabolism

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10
Q

What is enzyme action affected by?

A

Substrate concentration
Enzyme activity and concentration
Inhibition
Co-enzymes and co-factors

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11
Q

What do enzymes have binding sites for?

A

Substrate
Co-enzymes
Co-factors
Inhibitors

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12
Q

Explain competitive inhibitors

A

Prevent the substrate from binding
Competes for active site

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13
Q

Explain non-competitive inhibitors

A

Does not prevent substrate binding
Alters shape of enzyme

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14
Q

Explain allosteric enzymes

A

Usually contain 2 or more subunits.
Binding of the substrate alters the shape of enzyme.
Substrate binding increases the affinity for further substrates.

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15
Q

What does the first part of an enzymes name represent?

A

Substrate

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16
Q

What does the second part of an enzymes name represent?

A

Reaction

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17
Q

List the actions of enzymes and explain what happens

A

Kinase: add/removes phosphate group.
Dehydrogenase: removed H (oxidisation)
Decarboxylase: add/remove carboxyl group
Isomerase/mutase: rearranges (forms isomers)
Transferase: transfers functional groups
Hydrolase/lipase: adds water (hydrolysis)

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18
Q

Explain the role of enzymes in reversible reactions

A

The reactions in both directions is catalysed by the same enzyme.

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19
Q

Explain the role of enzymes in irreversible reactions

A

The reaction in each direction will be catalysed by different enzymes.

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20
Q

What is energy needed for in the body?

A

Synthesis of complex molecule
Active transport of molecules and ions
Muscular contraction
Cellular movement

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21
Q

What is ATP?

A

The energy currency of the body

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22
Q

What happens to ATP in anabolism/synthesis?

A

It is used up

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23
Q

What happens to ATP in catabolism?

A

Produces ATP

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24
Q

What happens to carbohydrates. lipids and alcohol during metabolism?

A

Broken down or stored for energy
Synthesis of body molecules

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25
Q

What happens to proteins during metabolism?

A

Synthesis of body molecules
Can be used for energy

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26
Q

What happens to minerals in metabolism?

A

Act as co-factors
Important for nervous and muscle action

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27
Q

What happens to vitamins during metabolism?

A

Act as co-enzymes and antioxidants

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28
Q

Name the key carbohydrates that are supplied in the diet

A

Monosaccharides
Disaccharides
Polysaccharides

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29
Q

Name the 4 monosaccharides that naturally occur in food

A

Glucose
Fructose
Galactose
Ribose

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30
Q

Name the 3 disaccharides and state what monosaccharides they are made from

A

Sucrose = glucose +fructose
Maltose = glucose + glucose
Lactose = glucose + galactose

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31
Q

Name and explain the two polysaccharides that make up starch

A

Amylose (15-30%): long, largely unbranched chains of D-glucose.
Amylopectin (70-85%): branched chains of D-glucose.

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32
Q

What is glycogen?

A

Mammalian storage polysaccharide of glucose.

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33
Q

What is cellulose?

A

The main polysaccharide found in plant cell walls.
A non-starch polysaccharide.
Major component of dietary fibre.
Individual chains are bound to each other through hydrogen bonding to form cellulose microfibrils.
Provide strength to cell walls in all directions.

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34
Q

What are non-starch polysaccharides?

A

Isomers of glucose joined together

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35
Q

What state is a carbohydrate in when it is absorbed?

A

Monosaccharide

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36
Q

What is carbohydrate metabolism actually representing?

A

Glucose metabolism

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37
Q

What is glycolysis?

A

The breakdown of glucose to liberate energy in the form of ATP.
Takes places in the cytosol.
1 6 carbon glucose is split into 2 3 carbon pyruvate.

38
Q

Name the two stages of glycolysis

A

Investment stage (uses ATP)
Pay off stage (creates ATP)

39
Q

Explain step 1 of glycolysis: phosphorylation of glucose

A

Irreversibly ‘traps’ glucose in the cell.
Lowers (glucose) in the cell.
Highly thermodynamically favourable.
Uses ATP.
Under substrate level control.
Hexokinase

40
Q

Explain step 2 of glycolysis: isomerisation of G-6-P

A

Changing toa pentagonal ketose allows easier further phosphorylation. Allows for creation of potentially symmetrical molecule.
Reversible
Direction and rate = under substrate level control.
Isomerisation of G-6-P.

41
Q

Explain step 2 of glycolysis: phosphorylation of F-6-P

A

Irreversible
The committed step of glycolysis.
Uses ATP.
Requires magnesium as a cofactor.
Phosphofructokinase-1 (PFK-1) is a key enzyme of control.
ATP = powerful inhibitor.
Produces a ‘symmetrical’ molecule for splitting.

42
Q

Explain step 4 of glycolysis: splitting

A

Reversible
Two halves are not quite the same = DHAP + GAP.
Need to have both halves in the form of GAP.
Aldolase

43
Q

Explain step 5 of glycolysis: triose phosphate interconversion

A

Reversible
Allows for continual breakdown using one pathway.
End of the investment stage.
Triose phosphate isomerase.

44
Q

Explain step 6 of glycolysis: oxidation of GAP

A

Reversible
First energy yielding step of glycolysis.
NAD+ to reduced to NADH.
Generates a high energy phosphate compound (1,3BisPG)
Allows for ATP production in subsequent steps.
Glyceraldehyde 3-phosphate dehydrogenase.

45
Q

Explain step 7 of glycolysis: first ATP production

A

Reversible
Substrate level phosphorylation of ADP.
1,3 BisPG donates phosphate to form ATP.
Phosphoglycerate kinase.

46
Q

Explain step 8 of glycolysis: rearrangement

A

Phosphoglucomutase
Reversible

47
Q

Explain step 9 of glycolysis: dehydration

A

Enolase
Reversible
Releases water

48
Q

Explain step 10 of glycolysis: second ATP production

A

Irreversible
Substrate level phosphorylation of ADP.
Loss of phosphate from PEP leads to tautomerisation which helps drive the reaction.
Pyruvate kinase (PK) requires magnesium as a co-factor.
PK = highly regulated enzyme

49
Q

Describes hexokinase

A

Has allosteric enzyme kinetics.
Ensures glucose is only irreversibly entered into glycolysis at high glucose.
Ensures carbohydrate utilisation in muscle and adipose tissue influenced by glucose availability.

50
Q

Describes glucokinase

A

Ensures utilisation of glucose even at low glucose.
Key for glucose uptake from portal system.
Key to regulating glucose metabolism and supply.

51
Q

Give the chemical equation for glycolysis

A

Glucose + 2NAD+ + 2ADP + 2Pi –> 2 pyruvate + 2 NADH + 2ATP

52
Q

What is the net gain of ATP during glycolysis?

A

2 ATP

53
Q

What is anaerobic catabolism?

A

2 ATP can be generated per glucose, without oxygen but needs to recycle NAD+ used in the conversion of glyceraldehyde 3-phosphate to 1,3 Bisphosphoglycerate.
This is achieved by dehydration reaction forming lactate.

54
Q

What is the chemical equation for anaerobic catabolism?

A

Glucose + 2Pi + 2ADP <–> 2 lactate + 2ATP + 2H2O

55
Q

What is involved in the Cori cycle?

A

Lactate can be recycled back to glucose in the liver by gluconeogenesis.

56
Q

Name the 3 key enzymes that are involved in irreversible reactions

A

Hexokinase
Phosphofructokinase (PFK-1)
Pyruvate kinase

57
Q

What is enzyme activity controlled by?

A

Hormones
Other metabolites

58
Q

What is phosphofructokinase?

A

The key enzyme in control of glycolysis

59
Q

What is inhibition reversed by?

A

Insulin
AMP
Fructose 6-phosphate
Catecholamines (in muscle)

60
Q

What is inhibition enhanced by?

A

Glucagon
Citrate
Catecholamines (in liver)

61
Q

What is pyruvate kinase activated by?

A

Fructose 1,6 bisphosphate
Insulin (via counteracting glucagon)

62
Q

What is pyruvate kinase inhibited by?

A

ATP
Glucagon
Alanine (signalling an abundance of building blocks)

63
Q

What happens to pyruvate during:
1. anaerobic catabolism
2. aerobic catabolism
3. synthetic
4. gluconeogenic

A
  1. converted to lactate
  2. converted to acetyl CoA via the TCA cycle and oxidative phosphorylation.
  3. converted to alanine (amino acid)
  4. converted back to form glucose
64
Q

What is PFK1 inhibited by?

A

ATP (energy availability)

65
Q

What is the TCA cycle fed by?

A

The breakdown products of carbohydrates, lipids and proteins.

66
Q

How is energy generated in the TCA cycle?

A

Through NADH, FADH2 and GTP

67
Q

What is a by-product of the TCA cycle?

A

Carbon dioxide

68
Q

What is pyruvate converted into?

A

Acetyl CoA

69
Q

What is a MPC?

A

Mitochondrial pyruvate carrier

70
Q

What does an NCP do?

A

Carries the pyruvate molecule through both the outer and inner mitochondrial membranes into the matrix, via facilitative diffusion.

71
Q

Where does the TCA cycle occur?

A

Matrix of the mitochondria

72
Q

Is the conversion of pyruvate into acetyl CoA an irreversible or reversible reaction?

A

Irreversible
A committal step in energy metabolism.

73
Q

What 2 co-enzymes catalyse the conversion of pyruvate into acetyl CoA?

A

Pyruvate dehydrogenase
Riboflavin thiamin

74
Q

What is acetyl CoA?

A

A 2 carbon skeleton derived from carbohydrates, fatty acids and amino acids.
It ‘feeds’ the TCA cycle.

75
Q

Where does glycolysis and anaerobic catabolism of CHO happen?

A

In the cytosol

76
Q

Describe the role of electron carriers in the TCA cycle

A

Act as proton and electron acceptors in reduction reactions.
Carry electrons to the respiratory chain.
Feed electrons to the respiratory chain.
Feeding electrons through the respiratory chain produces ATP.,

77
Q

Name the steps of the TCA cycle

A
  1. Formation of citrate (entry of acetyl CoA)
  2. Formation of isocitrate
  3. Oxidation of isocitrate to a-ketoglutarate + carbon dioxide.
  4. Oxidation of alpha-ketoglutarate to succinyl CoA.
  5. Conversion of succinyl CoA to succinate.
  6. Oxidation of succinate to fumarate.
  7. Hydration of fumarate to malate.
  8. Oxidation of malate to oxaloacetate
78
Q

What is the TCA cycle otherwise known as?

A

Krebs cycle
Citric acid cycle

79
Q

What is oxidised during the TCA cycle?

A

Acetyl CoA to form carbon dioxide and water

80
Q

What is reduced during the TCA cycle?

A

NAD+ and FAD+ pick up electrons and are reduced to NADH and FADH

81
Q

How many molecules of acetyl CoA is produced in one revolution of the TCA cycle?

A

1

82
Q

How many molecules of NADH are produced in one revolution of the TCA cycle?

A

3

83
Q

How many molecules of FADH is produced in one revolution of the TCA cycle?

A

1

84
Q

How many molecules of GTP are produced in one revolution of the TCA cycle?

A

1

85
Q

How is the TCA cycle controlled?

A

The rate of the TCA cycle is adjusted to meet ATP demand, which is dependent on supply of acetyl CoA and the availability of NAD+ and FAD+.
It is specifically controlled by 3 irreversible reactions: citrate synthesis, isocitrate dehydrogenase and alpha-ketoglutarate dehydrogenase.

86
Q

What happens during anaplerotic reactions?

A

Constant levels of TCA intermediates are maintained

87
Q

What happens during cataplerotic reactions?

A

Utilisation of TCA intermediates for biosynthetic pathways.

88
Q

How can oxaloacetate be regenerated?

A

Can be formed directly from pyruvate, by the enzyme pyruvate carboxylase.

89
Q

Why is the regeneration of oxaloacetate important?

A

It keeps the TCA cycle operating when amino acids are synthesises.
It is an important step in gluconeogenesis.

90
Q

What is the control of the TCA cycle dependent on?

A

The supply of acetyl CoA, NAD+ and FAD+.

91
Q

Name the types of metabolism where the TCA cycle is a common pathway

A

CHO metabolism
Lipid metabolism
Alcohol metabolism
Amino acids metabolism
Ketone oxidation

92
Q
A

2. Biochemistry (7 decks)

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