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POM Flashcards (Y1) > Cell metabolism > Flashcards

Cell metabolism Flashcards

1
Q

Describe an oxidation-reduction reaction

A

Electron transfer

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2
Q

Describe a ‘ligation requiring ATP cleavage’ reaction

A

Formation of covalent bonds (i.e., carbon-carbon bonds)

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3
Q

Describe an ‘isomerization’ reaction

A

Rearrangement of atoms to form isomers

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4
Q

Describe a ‘group transfer’ reaction

A

Transfer of a functional group from one molecule to another

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5
Q

Describe a ‘hydrolytic’ reaction

A

Cleavage of bonds by the addition of water

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6
Q

Describe the ‘addition/removal (functional groups)’ reaction

A

Addition of functional groups to double bonds or their removal to form double bonds

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7
Q

Outline the phosphorylation of Glucose

A

Glucose —–> glucose-6-phosphate by hexokinase
ATP—> ADP
Group transfer

Reaction is essentially irreversible and commits the cell to the subsequent reactions
Also traps glucose inside the cell by means of the negative charge

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8
Q

Outline the conversion to fructose-6-phosphate

A

Glucose-6-phosphate —-> fructose-6-phosphate by phosphoglucose isomerase
Isomerisation
Reason: fructose can be split into equal halves when subsequently cleaved.

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9
Q

Outline the phosphorylation to fructose-1,6-bisphosphate

A

Fructose-6-phosphate —-> fructose-1,6-bisphosphate by phosphofructokinase
ATP—->ADP
Group transfer
Regulation of phosphofructokinase is a key control step for the entry of sugars into the glycolysis pathway.

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10
Q

Outline the 2 step conversion to Glyceraldehyde-3-phosphate

A

Fructose-1,6-biphosphate —-> glyceraldehyde-3-phosphate + dihydroxyacetone phosphate by aldolase
Hydrolytic
Two high energy compounds have been generated

Dihydroxyacetone phosphate —-> glyceraldehyde 3-phosphate by triose phosphate isomerase (TPI)
Isomerisation

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11
Q

Which enzyme causes the only enzymopathy that is fatal?

A

TPI deficiency

Sufferers die within the first 6 years of their lives

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12
Q

Outline the conversion of Glyceraldehyde-3-phosphate

A

Glyceraldehyde 3-phosphate —-> 1,3-bisphosphoglycerate by glyceraldehyde 3-phosphate dehydrogenase
NAD+ (+Pi) —-> NADH
Redox and group transfer
NADH generated used to generate more ATP via oxidative phosphorylation in mitochondria

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13
Q

Outline the conversion into 1,3-bisphosphoglycerate

A

1,3-bisphosphoglycerate —-> 3-phosphoglycerate by phosphoglycerate kinase
ADP —-> ATP
Group transfer

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14
Q

What do kinases do?

A

Kinases transfer phosphate groups to molecules.

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15
Q

Outline the 2 step conversion of 3-phosphoglycerate

A

3-phosphoglycerate —-> 2-phosphoglycerate by phosphoglycerate mutase
Isomerisation
Phosphate group moves from the 3 to the 2 position

2-phosphoglycerate ----> phosphoenolpyruvate + H2O by enolase 
Group removal (and hydration)
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16
Q

Outline the last step, where pyruvate is formed

A

Phosphoenolpyruvate —-> pyruvate by pyruvate kinase
ADP —-> ATP
Group transfer

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17
Q

What is the net result of glycolysis?

A

2 ATP

2 NADH which can be used to generate ATP

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18
Q

Outline Alcoholic Fermentation of Pyruvate

A

pyruvate —-> acetaldehyde by pyruvate decarboxylase
H+ (in) —-> CO2 (out)

acetaldehyde —-> ethanol by alcohol dehydrogenase
NADH + H+ —-> NAD+

Characteristic of yeasts
Can occur under anaerobic conditions

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19
Q

Outline how Lactate is formed from Pyruvate

A

Pyruvate —-> lactate by lactate dehydrogenase
NADH + H+ —-> NAD+
Anaerobic - characteristic of mammalian muscle when oxygen is a limiting factor, e.g. during intense activity

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20
Q

How is Pyruvate involved in generation of Acetyl Coenzyme A?

A

Pyruvate + HS-CoA —-> acetyl CoA + CO2 by pyruvate dehydrogenase complex
Occurs in the mitochondria
Acetyl CoA is then committed to entry into TCA cycle

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21
Q

Why is it essential that NAD+ is regenerated?

A

Allows glycolysis to occur anaerobically
Conditions where rate of formation of NADH is greater than rate of NADH oxidation
Needed for dehydrogenation of glyceraldehyde-3-phosphate to produce ATP

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22
Q

How much free energy is required to break down creatine phosphate?

A

-43 Kj/mol

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23
Q

How is creatine phosphate used as a buffer for ATP?

A

Creatine phosphate —-> creatine + ATP
ADP + H+ —-> ATP
In muscle, the amount of ATP needed during exercise is only enough to sustain contraction for around one second
Reservoir of creatine phosphate is on hand to buffer demands for phosphate

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24
Q

Why do athletes take creatine kinase supplements?

A

It acts as a buffer for ATP

25
Q

What is thiamine pyrophosphate a cofactor of?

A 
The PDH (Pyruvate Dehydrogenase) complex
Readily loses a proton and resulting carbanion attacks pyruvate
26
Q

What condition does a deficiency in thiamine result in and what are the symptoms of this condition?

A

Beri-Beri

Damage to peripheral nervous system, weakness of musculature and decreased cardiac output

27
Q

How much free energy is required to hydrolyse ATP

A

-31 Kjmol^-1

28
Q

How much free energy is required for Glucose Combustion

A

-2872 Kjmol^-1

29
Q

How much free energy is required for Glucose Metabolism

A

-1178 Kjmol^-1

30
Q

How much of each product is formed from 1 turn of Kreb’s Cycle?

A

3 NADH
2 CO2
1 FADH2
1 GTP

31
Q

Why does the Krebs cycle only occur under aerobic conditions?

A

Bulk of ATP generated when the reduced coenzymes are re-oxidised with the help of oxygen (oxidative phosphorylation).
This re-oxidation means that the TCA cycle only operates under aerobic conditions.

32
Q

What are the 7 molecules that could arise from degradation of all 20 amino acids?

A 
Pyruvate
Acetyl CoA
Acetoacetyl CoA
Alpha-ketoglutarate
Succinyl CoA
Fumarate
Oxaloacetate
33
Q

Explain Transamination with an example

A

Allows production of non-essential amino acids
An amine group is transferred from one amino acid to a keto acid forming a new pair of amino and keto acids

Alanine + alpha-ketoglutarate → pyruvate + glutamate by alanine aminotransferase
Group Transfer

Pyruvate then decarboxylated to form acetyl CoA that enters Kreb’s cycle
Glutamate is reconverted into alpha-ketoglutarate by glutamate dehydrogenase

34
Q

What is the purpose of the Glycerol Phosphate Shuttle?

A

To carry electrons from NADH from the cytosol into the mitochondrial matrix

35
Q

Where in the body is the Glycerol-Phosphate Shuttle used?

A

Skeletal Muscle

Brain

36
Q

Explain how the Glycerol-Phosphate Shuttle works

A

Cytosolic glycerol-3-phosphate dehydrogenase transfers electrons from NADH to DHAP to generate Glycerol-3-Phosphate

Membrane bound form of same enzyme transfers electrons to FAD to get passed to Co-enzyme Q (part of electron transport chain), also reforming DHAP

37
Q

Where in the body is the Malate-Aspartate Shuttle used?

A

Liver
Kidney
Heart

38
Q

Outline the processes in the Malate-Aspartate Shuttle

A

Aspartate (+ alpha-ketoglutarate) —-> oxaloacetate (+ glutamate) by aspartate transaminase
This occurs in the cytosol; reverse occurs in the matrix.
Redox and transamination

39
Q

Explain how 38 ATP molecules are formed

A 
Glycolysis → 2 ATP + 2 NADH → 8 ATP
Pyruvate Conversion → 2 NADH → 6 ATP
TCA cycle: 
6 NADH → 18 ATP
2 FADH2 → 4 ATP
2 GTP → 2 ATP

Three ATP molecules formed by the re-oxidation of each NADH molecule
Two ATP molecules formed by the re-oxidation of each FADH2 molecule

40
Q

What is the Warburg Effect?

A

Mutations in genes of Fumerase, Succinate Dehydrogenase, Isocitrate Dehydrogenase, decreases Kreb’s Cycle activity which enhances anaerobic glycolysis

Preferential generation of lactate from glucose even in increased O2 availability

41
Q

What are the 5 main classes of lipids?

A 
Free FAs
Triacylglycerols
Phospholipids
Glycolipids
Steroids
42
Q

What is the difference between an unsaturated and a saturated fatty acid?

A

Unsaturated FA has a C=C

43
Q

What does a triacylglycerol molecule consist of?

A

3 FAs attached to a glycerol molecule

44
Q

What type of bond in triacylgylcerols helps to neutralise carboxylic acid groups and hence keep pH in cell within a normal range?

A

Ester linkages

45
Q

How is over half of the body’s energy needs including the liver but not the brain generated?

A

Fatty Acid (FA) oxidation

46
Q

What is the purpose of Beta-Oxidation and where does it occur?

A

To produce Acetyl CoA

Mitochondria

47
Q

Outline the reaction converting Fatty Acids into Acyl CoA

A

Occurs outside of mitochondrial membrane

Fatty Acid + ATP + HS-CoA → Acyl CoA + AMP + PPi

Catalysed by Acyl CoA Synthase

48
Q

Why is AMP produced?

A

It is a high energy consuming reaction, so 2 high energy bonds are broken to synthesise the Acyl CoA

49
Q

What is the purpose of the Carnitine Shuttle?

A

To transport the Acyl CoA species into the matrix

50
Q

Outline the reactions in the Carnitine Shuttle

A

Acyl from Acyl CoA added to the Carnitine to form Acyl Carnitine and CoA, catalysed by Carnitine acyltransferase I

Acyl Carnitine transported into matrix via Translocase and Carnitine exported into cytoplasm via Translocase

Acyl Carnitine in matrix loses its Acyl group to CoA to form Acyl CoA in matrix and Carnitine

51
Q

What are the symptoms of Primary Carnitine Deficiency?

A

Autosomal recessive disorder

Encephalopathies, cardiomyopathies, muscle weakness and hypoglycaemia

52
Q

When do the symptoms of Primary Carnitine Deficiency usually occur?

A

During infancy or early childhood

53
Q

What does a mutation in the gene SLC22A5 do?

A

Encodes a carnitine transporter resulting in reduced ability of cells to take up carnitine

54
Q

How many FADH2 and NADH are produced from one complete Beta-Oxidation?

A

1 FADH2 and 1 NADH

55
Q

How many Acetyl CoA, FADH2 and NADH are produced from the complete Beta Oxidation of 16C-Palmitoyl CoA?

A

8 Acetyl CoA
7 FADH2
7 NADH

56
Q

Outline the steps of the beta oxidation cycle

A

Acyl CoA undergoes a sequence of oxidation, hydration, oxidation and thiolysis reactions

Results in the production of one molecule of acetyl CoA and an acyl CoA species which is 2 carbons shorter than the original

57
Q

What is needed for the entry of acetyl CoA into the TCA cycle?

A

Oxaloacetate

Acetyl CoA generated by β-oxidation enters TCA cycle only if β-oxidation and carbohydrate metabolism are balanced

58
Q

What occurs when fat breakdown predominates over Beta-Oxidation?

A

Ketone bodies are formed

e.g - during fasting, acetyl CoA forms acetoacetate, D-3-hydroxybutyrate and acetone known collectively as ketone bodies

59
Q

How many net molecules of ATP are generated from metabolism of Palmitate?

A

Palmitoyl CoA + 7 FAD + 7 NAD + 7 CoA + 7 H2O → 8 Acetyl CoA +7 FADH2 + 7 NADH

7 FADH2 = 7 x 2 =14

7 NADH = 7 x 3 = 21

8 Acetyl CoA = 12 x 8 = 96 (Because it enters the Kreb’s Cycle and undergoes oxidative phosphorylation)

2 Phosphate bonds are hydrolysed at start of beta oxidation to produce Acyl CoA = 2

14 + 21 + 96 - 2 = 129

POM Flashcards (Y1) (28 decks)

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