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Year 1 Semester 2 > Metabolism > Flashcards

Metabolism Flashcards

1
Q

Define metabolism

A

Mechanisms which couple the demand for energy (which is constant), with the fuel supply (which is intermittent)

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2
Q

Define catabolism

A

Degradation of molecules to release energy

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3
Q

Define anabolism

A

Synthesis of new molecules to store energy

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4
Q

Describe the first stage of metabolism

A

Digestion in the GI tract - absorption and transport in the blood

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5
Q

Describe stage 2 of metabolism

A

In the cell cytoplasm:

  • Anabolic - nutrients built into storage molecules such as glycogen/protein/lipid
  • Catabolic - nutrients broken down to pyruvic acid and acetyl CoA
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6
Q

Describe stage 3 of metabolism

A

In mitochondria:

-Catabolism requiring oxygen to completely breakdown food and generate ATP

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7
Q

How much oxygen do humans consume?

A

Roughly 350 ml O2/min but can increase 5 times during exercise

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8
Q

Define oxidation

A

Gain of O2 from molecules or loss of hydrogen (or loss of electrons from molecules)

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9
Q

Define reduction

A

Loss of O2 from molecules or gain of hydrogen (or addition of electrons)

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10
Q

Name the two important coenzymes involved in metabolism

A
  • Nicotinamide adenine dinucleotide (NAD)

- Flavin adenine dinucleotide (FAD)

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11
Q

What is the role of the coenzymes in metabolism?

A

They transfer hydrogen/electrons, to oxidise molecules in reversible redox reactions during metabolism

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12
Q

How much energy is released when ATP is hydrolysed to ADP + Pi?

A

Approximately -30.5 kJ/mol

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13
Q

What is the first law of thermodynamics?

A

The total energy of a system (i.e. the universe) is constant - energy can neither be created nor destroyed… can be converted from one form to another

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14
Q

Define Gibbs free energy of activation

A

The energy needed to transform substrates into the transition state

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15
Q

Define Exergonic

A

Releases more energy than input (favourable)

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15
Q

Define Exergonic

A

Releases more energy than input (favourable)

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16
Q

Define endergonic

A

Requires more energy input than it yields (unfavourable)

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17
Q

How is glucose transported into a cell?

A

Glut receptors e.g Glut2 and Glut4 - enhanced by insulin

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18
Q

Is glycolysis catabolic or anabolic?

A

Catabolic

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19
Q

Where does glycolysis take place within the cell?

A

Cytosol

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20
Q

How many steps are there in glycolysis?

A

10

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21
Q

What are the 3 stages of glycolysis?

A
  • Investment
  • Cleavage
  • Energy Harvest
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22
Q

How many ATP are used in glycolysis?

A

2

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23
Q

How many ATP are generated in glycolysis?

A

4

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24
Q

What is the net gain of ATP in glycolysis?

A

2

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25
Q

What is step 1 of glycolysis?

A
  • Phosphorylation of glucose at carbon 6
  • Requires ATP (investment stage)
  • Locks glucose inside the cell (maintains glucose gradient)
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26
Q

What enzyme is used in step 1 of glycolysis?

A

Hexokinase

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27
Q

What is step 2 of glycolysis?

A
  • Conversion of glucose-6-phosphate (aldose) to fructose-6-phosphate (ketose)
  • Glucose-6-phosphate - ring structure opens to enable isomerisation and subsequent ring closure - fructose-6-phosphate
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28
Q

What enzyme is used in step 2 of glycolysis?

A

Phosphoglucose isomerase

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29
Q

What is step 3 of glycolysis?

A
  • Fructose-6-phosphate phosphorylated at carbon 1 - fructose 1,6-bisphosphate (FBP)
  • Requires ATP (investment stage)
  • Key regulatory point
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30
Q

What enzyme is used in step 3 of glycolysis?

A

Phosphofructokinase-1 (PFK)

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31
Q

What are steps 4 and 5 of glycolysis?

A
  • Aldolase cleaves the FBP (6 carbons) into 2 trioses
  • Glyceraldehyde-3-phosphate (GAP)
  • Dihydroxyacetone phosphate (DHAP)
  • These two are interchangeable and one can become the other through the use of the enzyme triose phosphate isomerase (step 5 technically)
  • Only glyceraldehyde-3-phosphate used in the rest of glycolysis
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32
Q

What is step 6 of glycolysis?

A
  • Oxidation & phosphorylation GAP by NAD+ and Pi
  • First high energy intermediate - aldehyde oxidation (exergonic reaction) drives synthesis of the 1,3-bisphosphoglycerate
  • Aerobic conditions - 2NADH + 2H+ enters citric acid cycle
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33
Q

What enzyme is used in step 6 of glycolysis?

A

Glyceraldehyde-3-phosphate dehydrogenase

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34
Q

What is step 7 of glycolysis?

A
  • First formation of ATP (energy harvest)

- The newly formed high-energy phosphate bond used to synthesise ATP and 3-phosphoglycerate (3PG)

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35
Q

What enzyme is used in step 7 of glycolysis?

A

Phosphoglycerate kinase

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36
Q

What is step 8 of glycolysis?

A

-3PG converted to 2PG - essential preparation for next energy harvest step

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37
Q

What enzyme is used in step 8 of glycolysis?

A

Phosphoglyceromutase

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38
Q

What is step 9 of glycolysis?

A

2PG dehydration to form phosphoenolpyruvate (PEP) - converts low energy ester bond of 2PG into high-energy intermediate phosphate bond

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39
Q

What enzyme is used in step 9 of glycolysis?

A

Enolase

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40
Q

What is step 10 of glycolysis?

A

Hydrolysis of PEP high-energy bond to generate ATP and pyruvate (physiological irreversible reaction)

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41
Q

What enzyme is used in step 10 of glycolysis?

A

Pyruvate kinase

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42
Q

What are the possible fates of pyruvate?

A
  • Anaerobic - converted to lactate
  • Aerobic - converted to Acetyl-CoA
  • High cellular energy levels - fatty acids or ketone bodies
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43
Q

What happens after glycolysis in anaerobic conditions?

A
  • Pyruvate + NADH + H+ <======>Lactate + NAD+
  • For glycolysis to be able to continue in anaerobic conditions, NAD+ must be replenished
  • When ATP demand is high and O2 depleted, homolactic fermentation regenerates NAD+
  • Reversible reaction which enables glycolysis to continue for short amounts of time
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44
Q

What enzyme is used to convert pyruvate to lactate?

A

Lactate dehydrogenase

45
Q

What mechanisms control rate of glycolysis?

A
  • Key enzymes
  • High [ATP] inhibit enzyme activity
  • Intermediate substrates (e.g fructose-6-P) stimulate PFK activity
  • High [citric acid] inhibits
  • Low pH inhibits
  • Hormones
46
Q

What are the 3 key regulation enzymes in glycolysis?

A
  • Hexokinase - allosterically inhibited by G-6-P
  • Phosphofructokinase - most important site of control - first step to unique glycolysis - high [ATP] inhibits PFK by binding allosterically - high [AMP] activates PFK
  • Pyruvate kinase - inhibited by high ATP and alanine and activated by FBP
46
Q

What are the 3 key regulation enzymes in glycolysis?

A
  • Hexokinase - allosterically inhibited by G-6-P
  • Phosphofructokinase - most important site of control - first step to unique glycolysis - high [ATP] inhibits PFK by binding allosterically - high [AMP] activates PFK
  • Pyruvate kinase - inhibited by high ATP and alanine and activated by FBP
47
Q

Define the citric acid cycle

A

Redox reactions to harness energy via electron carriers (NAD+ & FAD), producing CO2

48
Q

Define oxidative phosphorylation

A

Oxidation of coenzymes: electron transfer and reduction of O2 and ATP synthesis (ADP phosphorylation)

49
Q

Explain acetyl CoA synthesis

A

In the mitochondrial matrix:

  • pyruvate (& fatty acids/amino acids) are degraded into acetyl groups
  • Acetyl groups are added to Coenzyme A (CoA) forming acetyl CoA
49
Q

Explain acetyl CoA synthesis

A

In the mitochondrial matrix:

  • pyruvate (& fatty acids/amino acids) are degraded into acetyl groups
  • Acetyl groups are added to Coenzyme A (CoA) forming acetyl CoA
50
Q

What is formed from each cycle of the citric acid cycle?

A
  • 2 CO2
  • 1 GTP
  • 3 NADH + H+
  • 1 FADH2
51
Q

What is the 1st step of the citric acid cycle?

A

Condensation of the acetyl group (2-carbon) of acetyl CoA with the keto acid oxaloacetate (4-carbon) by citrate synthase

52
Q

Is the first step of the citric acid cycle endergonic or exergonic?

A

Highly exergonic due to the thioester bond having a large -deltaG

53
Q

How are NADH + H+ and CO2 formed in the citric acid cycle?

A
  • A number of dehydrogenation steps occur in the citric acid cycle resulting in NADH + H+ formation
  • The keto acids formed are quite reactive - they can be decarboxylated which results in CO2 released
54
Q

How is GTP generated in the citric acid cycle?

A
  • CoA bonds with one of the carbon chain molecules to form succinyl-CoA
  • The high energy thioester bond of succinyl-CoA generates GTP on conversion to succinate
54
Q

How is GTP generated in the citric acid cycle?

A
  • CoA bonds with one of the carbon chain molecules to form succinyl-CoA
  • The high energy thioester bond of succinyl-CoA generates GTP on conversion to succinate
55
Q

Where does FAD come from?

A

It is a coenzyme formed from the vitamin riboflavin (vitamin B2)

56
Q

FAD in the citric acid cycle

A
  • FAD bound to the enzyme succinate dehydrogenase (only citric acid cycle enzyme bound to the inner mitochondrial membrane)
  • FAD reduced to FADH2
  • Reoxidised via the electron transport chain
57
Q

How is the citric acid cycle regulated?

A

Inhibition of enzymes involved in the citric acid cycle by levels of:

  • ATP
  • Acetyl CoA
  • NADH
  • CO2
58
Q

How much ATP will one molecule of NADH + H+ generate?

A

Roughly 2.5 ATP

59
Q

How much ATP will one molecule of FADH2 generate?

A

Roughly 1.5 ATP

60
Q

What is the metabolic waste product of the citric acid cycle?

A

Carbon dioxide

61
Q

What is the first part of the electron transport chain?

A

Reduced coenzymes deliver electrons to complexes I & II (NADH + H+ delivers to I and FADH2 delivers to II)

62
Q

What happens to each complex as the electrons are transferred through the chain?

A

Each complex is reduced, then oxidised

63
Q

What does the energy released in the electron transport chain do?

A

Pumps H+ into intramembranous space

64
Q

What transfers the electrons between complexes in the electron transport chain?

A
  • Coenzyme Q (from I and II to III)

- Cytochrome c (from III to IV)

65
Q

What is the action of complex IV in the citric acid cycle?

A

Complex IV combines 2H+ and 1/2O2 to form H2O

66
Q

Why are the H+ ions pumped into the intra membranous space?

A

Because the energy generated from this proton gradient synthesises ATP

67
Q

Name and action of complex I

A

NADH-Q reductase - oxidises NADH + H+, reduces coenzyme Q

68
Q

Name and action of complex II

A

Succinate-Q-reductase - oxidises FADH2, reduces coenzyme Q

69
Q

Name and action of complex III

A

Q-cytochrome C oxidoreductase - oxidises coenzyme Q, reduces cytochrome c

70
Q

Name and action of complex IV

A

Cytochrome C oxidase - oxidises cytochrome c, reduces O2 to H2O

71
Q

What inhibits the electron transport chain?

A

Cyanide:

  • Found in smoke, apricot & other fruit pips, cassava
  • Symptoms: confusion, dizziness, vomiting seizure
  • Binds to iron in the enzyme, prevents the electron transport chain from working, halts ATP production

Carbon monoxide also binds to the same enzyme

72
Q

What enzyme to cyanide and carbon monoxide both bind to to inhibit the electron transport chain?

A

Cytochrome C oxidase

73
Q

How is ATP synthesised after the electron transport chain?

A

The proton gradient creates:

  • A pH gradient - H+ concentration in matrix lower than in intermembranous space
  • A voltage across the membrane

Both conditions strongly attract H+ back inside the matrix

Only free permeable region is via complex V - ATP synthases (molecular rotary motors)

74
Q

Energy yield of cellular respiration

A
  • Glycolysis - Net gain of 2 ATP per glucose molecule
  • Citric Acid Cycle - Total gain of 2 ATP from 2 pyruvate molecules
  • Electron transport chain/oxidative phosphorylation - 28 ATP generated
  • Total (accounting for shuttle costs) = about 30 ATP per glucose molecule
75
Q

What happens in the absorptive/fed state?

A

Nutrients are plentiful - fuels broken down and excess stored (anabolism)

76
Q

What can insulin promote?

A
  • Glucose uptake
  • Fatty acid synthesis
  • Protein synthesis
77
Q

What happens in the postabsorptive/fasting state?

A

Storage molecules broken down for energy (catabolism) - biosynthesis slows down

78
Q

What is the primary aim of the postabsorptive state?

A

To maintain blood glucose levels within homeostatic range of 70 - 110mg/dl or 4-7mmol/L

79
Q

Where does blood glucose come from in the postabsorptive state?

A

Glycogenolysis:

  • liver glycogen, roughly 100g (enough for about 3-5 hours of activity)
  • muscle glycogen (only utilised within muscle)

Gluconeogenesis (formation of glucose from noncarbohydrate molecules):

  • occurs mainly in the liver
  • lipolysis of fatty acids to generate glycerol which will then become glucose
  • catabolism of muscle protein - deamination of amino acids which is then used to make glucose
80
Q

Describe glycogen

A
  • A branched polysaccharide storage molecule for glucose
  • Liver and skeletal muscle are the main glycogen reservoirs
  • Glycogen stores change constantly, with changes in nutritional states
81
Q

How does the liver utilise glycogen?

A
  • Maintains blood glucose levels

- Enough glycogen for 3-5 hours of moderate exercise or 12 hours of overnight fast

82
Q

How do muscles utilise glycogen?

A

Store glycogen for muscle contraction - channelled into glycolysis (not released into bloodstream)

82
Q

How do muscles utilise glycogen?

A

Store glycogen for muscle contraction - channelled into glycolysis (not released into bloodstream)

83
Q

Define glycogenesis

A

Synthesis of glycogen from glucose

84
Q

When does glycogenesis occur?

A

When glucose supplies exceed demand for ATP

85
Q

Define glycogenolysis

A

Breaking down of glycogen to release glucose

86
Q

How is glycogenolysis stimulated?

A

Stimulated by low blood glucose

87
Q

Explain the process that forms glycogen from glucose?

A
  • Glucose
  • Glucose-6-phosphate
  • Glucose-1-phosphate
  • Glycogen
87
Q

Explain the process that forms glycogen from glucose?

A
  • Glucose
  • Glucose-6-phosphate
  • Glucose-1-phosphate
  • Glycogen
88
Q

What can promote glycogenolysis?

A
  • Glucagon
  • Adrenalin
  • Cortisol
  • Growth hormone
89
Q

What enzymes are required for glycogenolysis?

A
  • Glycogen phosphorylase

- Debranching enzyme

90
Q

Explain glycogenolysis in the liver

A
  • Glycogen
  • Glucose-1-phosphate
  • Glucose-6-phosphate
  • Glucose
  • Released into bloodstream (Glut2), for uptake by all cells, but especially brain and RBCs
91
Q

Explain glycogenolysis in muscle

A
  • Glycogen
  • Glucose-1-phosphate
  • Glucose-6-phsophate
  • No G-6-Pase enzyme, instead G-6-P enters glycolysis
92
Q

Define gluconeogenesis

A

Formation of glucose from non carbohydrate sources

93
Q

What are examples of non carbohydrate sources used in gluconeogenesis?

A
  • Glycerol from triglycerides
  • Glucogenic amino acids (alanine & glutamine)
  • Lactate
94
Q

How is most fat stored?

A
  • Triglycerides/ triacylglycerols

- Glycerol molecule undergoes condensation with 3 fatty acids

95
Q

Describe lipolysis and how glycerol can be used in respiration

A
  • Fat breakdown into glycerol and fatty acids is known as lipolysis - reverse of lipogenesis
  • Fatty acids and glycerol released from adipose tissue and metabolised mainly by the liver
  • Glycerol feeds into gluconeogenesis but can also be utilised by most cells - converted into glyceraldehyde-3-phosphate then goes through glycolysis (1/2 glucose = 15 ATP aerobically)
96
Q

Describe how fatty acid chains are used in respiration

A

-Undergo beta-oxidation
-Broken down into 2-carbon acetic acid and fused to Coenzyme A giving acetyl CoA
-FAD and NAD+ reduced feeding into electron transport chain
Acetyl-CoA goes into the citric acid cycle

97
Q

When will ketone bodies form?

A

Ketone bodies are formed when carbohydrate intake is inadequate and the beta-oxidation product - acetyl-CoA - is in excess (for citric acid cycle metabolism)

98
Q

What is the limiting factor of the citric acid cycle when glucose is low and why?

A

Oxaloacetate is the limiting factor when glucose is low because it is converted to pyruvate in gluconeogenesis

99
Q

What ketone bodies could acetyl-CoA be converted to?

A
  • Acetoacetate
  • 3-hydroxybutyrate
  • Acetone
100
Q

What happens to excess protein?

A
  • Excess protein cannot be stored

- Amino acids are oxidised for energy or converted to fat

101
Q

Define deamination

A

Removal of amine group (NH2) prior to oxidation or storage

101
Q

Define deamination

A

Removal of amine group (NH2) prior to oxidation or storage

102
Q

Define transamination. Why is it useful?

A
  • Process by which some amino acids can be converted to keto acids - e.g. amine group transferred to keto-glutamate = glutamic acid
  • Modified keto acids generate pyruvate or keto acid intermediates for citric acid cycle (or converted to glucose - gluconeogenesis)
102
Q

Define transamination. Why is it useful?

A
  • Process by which some amino acids can be converted to keto acids - e.g. amine group transferred to keto-glutamate = glutamic acid
  • Modified keto acids generate pyruvate or keto acid intermediates for citric acid cycle (or converted to glucose - gluconeogenesis)

Year 1 Semester 2 (26 decks)

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