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Biochemistry > Week 4 - Metabolism 1 > Flashcards

Week 4 - Metabolism 1 Flashcards

1
Q

What is metabolism?

A

The complete set of catabolic and anabolic reactions that occur within living cells

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2
Q

What is catabolic breakdown?

A

Biochemical reactions that ‘break down’ molecules into smaller ones

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3
Q

What is an anabolic reaction?

A

Biochemical reactions that synthesis large molecules from smaller ones

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4
Q

What are the components of catabolic pathways?

A
  • protein breakdown
  • lipid oxidation
  • carbohydrate oxidation
  • nucleotide hydrolysis
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5
Q

What are the components of anabolic pathways?

A
  • protein synthesis
  • lipid synthesis
  • carbohydrate synthesis
  • nucleotide synthesis
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6
Q

Catabolic reactions are..

A

exergonic (energetically favourable)

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7
Q

Anabolic reactions are…

A

endergonic (energetically unfavourable)

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8
Q

What does a larger change in G mean?

A

Means that ATP is very ‘willing’ to transfer uts phosphates. This in turn relates to the structure of ATP and uts hydrolysis products

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9
Q

How do cells obtain energy?

A

Cells obtain energy through oxidation of organic molecules (food).
Energy is stored in covalent bonds of these organic molecules

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10
Q

What happens to a NADH and NADPH?

A

They ‘pick up’ energy in the form of 2 high energy electrons and a proton (a hybride ion)

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11
Q

What is the most important molecule for metabolism?

A

Acetyl CoA

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12
Q

How could we describe a reaction of -10 change in G?

A

exergonic reaction/ energetically favourable

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13
Q

Why must anabolic reactions normally be coupled to catabolic reactions?

A

Because anabolic reactions are endergonic and require energy

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14
Q

What is meant by a redox reaction?

A

a reaction where one molecule is reduced and another is oxidised

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15
Q

What is the function of activated carrier molecules?

A

to transfer energy from one reaction/pathway to another

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16
Q

Which metabolic intermediate is common in energy generation from fat, carbohydrate and protein?

A

Acetyl CoA

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17
Q

Does glycolysis occur in the absence of oxygen?

A

Yes but does involve oxidation

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18
Q

How many reactions does glycolysis consist of?

A

10

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19
Q

Why is ATP hydrolysed in reactions 1 to 3?

A
  • phosphorylate the sugar
  • couple the reaction to make it energetically favourable
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20
Q

What is reduced in glycolysis?

A

NAD

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21
Q

What is generated from glycolysis?

A

ATP

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22
Q

What occurs during Step 1 of glycolysis?

A
  • Glucose phosphorylated by Hexokinase (traps glucose)
  • Glucose has transporters which allow it to move in and out of the cell
  • Glucose - 6 - phosphate cannot access these transporters
  • The phosphate group comes from ATP = ADP + Pi
  • irreversible step
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23
Q

What are kinases?

A

Enzymes that add phosphate groups to molecules

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24
Q

What occurs during Steps 2 - 3 of glycolysis?

A
  • Glucose - 6 - phosphate undergoes isomerismation to Fructose - 6 - phosphate
  • Then Fructose - 6 phosphate is phosphorylated to form Fructose 1,6-biosphosphate
    (preparing glucose so that is can be used to generate more energy)
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25
What occurs during Step 4 of glycolysis?
- Aldolase splits F 1,6-BP into 2 x 3C molcules (two isomers) - G-3-P is on the glycolysis pathway - Dihydroxyactone phosphate is not
26
What occurs during Step 5 of glycolysis?
- Dihydroxyacetone phosphate is an isomer of G-3-P and can be easily converted - 2 x molecules of G-3-P are generated
27
What occurs during Steps 6-10 of glycolysis?
- forms a carboxylic acid with high phosphate transfer potential - Generates 2 x ATP and 2 x NADH - end product is pyruvate
28
Summarise Step 6
- enzyme 1 binds to G-3-P and catalyses its oxidation - NAD+ accepts the elctrons and is reduced - enzyme is displaced by Pi to create a high energy sugar-phosphate called 1-3-biphophoglycerate
29
Summarise Step 7
- This intermediate binds to enzyme 2 which catalyses the transfer of Pi to ADP, this creating ATP and generating a carboxylic acid called 3-phosphoglycerate
30
Where does lactate come from?
NAD+ must regenerate to enable glycolysis to continue. When no oxygen is available to act as an electron acceptor NADH passes the electrons to pyruvate to from lactate.
31
What is PFK?
It is the most important regulatory and rate limiting enzyme in glycolysis
32
What is PFK activated by?
AMP F 2,6, BP
33
What is PFK inhibited by?
ATP lower pH as lactate Citrate
34
What is gluoneogenesis?
The formation of glucose from non-carbohydrate precursers eg, lactate, glucogenic amino acids and glycerol
35
Where does gluoneogenesis occur?
in the liver as the liver is responsible for maintaining blood glucose
36
What occurs during glucneogenesis?
essentially it is the reverse of glycolysis (pyruvate - glucose)
37
What occurs during Step 1 of gluconeogenesis?
- pyruvate carboylast has a biotin prosthetic group - serves as a CO2 carrier - biotin is not carboxylated unless acetyl coA is present (allosteric regulation)
38
Where does the enzyme pyruvate carboxylase come from?
present in the mitochondria
39
What is biotin?
Biotin is an activated carrier of CO2
40
What occurs during Step 2 of glucose-genesis?
- PEP carboxylase is a cytosolic enzyme - Oxaloacetate needs to escape from the mitochondria but it needs converting to malate first as in the form oxaloacetate it cannot leave the mitochondria - Then the malate gets oxidised back to oxaloacetate
41
What occurs during the cori cycle?
Lactate - pyruvate + 6-P - glucose
42
What happens to lactate produced in the muscle during heavy exercise?
1- It can be taken up by some tissues eg the heart and converted back to pyruvate and used for energy (TCA cycle) 2 - Be transported to the liver and converted back to glucose via the cori cycle
43
What is the net ATP yield of glycolysis?
2 ATP
44
What is the biochemical reason for lactate formation from pyruvate?
To quickly regenerate NAH+ for use in glycolysis. It would be necessary when energy is needed very quickly, or oxygen is limiting
45
Which reactions of glycolysis do you think are most energetically favourable?
The ones that can be used to make ATP (must be lots of energy left over to do this) and or the ones that are coupled to ATP hydrolysis, because ATP hydrolysis releases lots of free energy. Reactions 1,3,10 are very energetically favourable
46
What is the main regulatory enzyme of glycolysis? and by what mechanism is it regulated?
Phosphofructokinase (step3), regulated allosterically
47
Thermodynamically explain why gluconeogenesis isnt the direct reversal of glycolysis
Because steps 1,3,10 of glycolysis are so energetically favourable , they are essentially irreversible
48
What is the role of biotin in gluneogensis?
Biotin is the prosthetic group of pyruvate carboxylase. Binds CO2 and transfers it to pyruvate to form oxaloacetate at the start of gluconeogenesis.
49
How does the TCA cycle start?
pyruvate moves into the mitochondria where it is decarboxylated to form acetyl coA
50
What occurs during pyruvate dehydrogenase complex reaction?
- huge enzyme (bigger then most ribosomes) - 3 enzymes in one - very complex 4 step reaction - NADH is generated to enable efficient recycling of the enzyme - irreversible reaction
51
What occurs during the rest of the TCA cycle?
- Acetyl CoA (2-C) condenses with 4-C oxaloacetate to form 6-C tricarboxylic acid, citric acid - 8 more reactions (4 oidation reactions) regenrate oxaloacetate - energy released from reactions is captured in - 3x NADH - 1 x FADH2 - 1 x GTP
52
What is citrate synthase?
- binds to oxaloacetate then acetyle coA - an intermediate Enol is formed from Acetyl COA which attacks oxaloacetate and forms citryl coA - citrate synthase can only hydrolyse citryl coA - thus preventing Acetate and CoA formation
53
What 2 enzymes are regulated allosterically during the TCA cycle?
1 - Isocitrate dehydrogenase 2 - alpha-ketoglutarate dehydrogenase
54
What is isocitrate dehydrogenase stimulated by?
ADP NAD+ Isocitrate
55
What is isocitrate dehydrogenase inhibited by?
ATP NADH
56
What is alpha-kenoglutarate dehydrogenase stimulated by?
ATP
57
What is alpha-ketoglutarate dehydrogenase inhibited by?
Succinyl CoA ATP NADH
58
When does Biotin get carboxylated?
only when Acetyl CoA is present (allosteric regulation)
59
What is anapleurosis?
Reactions that replenish TCA cycle
60
Why is PDH reaction considered irreversible? And what are the consequences of this
Irreversible as it is so energetically favourable. That means that acetyle CoA cannot be converted to pyruvate. Pathways that generate acetyl coA can therefore not enter the gluconeogenic pathway
61
What are the products of each turn of the TCA cycle?
3 x NADH 1 x FADH 1 x GTP
62
Why is it important that citrate synthase cannot hydrolase Acetyl CoA directly?
If it hydrolysed Acetyle CoA directly, it would result in acetate and CoA as products and this would not facilitate the generation of energy through the TCA cycle
63
What is meant by an analeurotic reaction?
A reaction that replenishes TCA cycle intermediates
64
Why do you think the TCA cycle is considered aerobic?
This relates to the use of oxygen downstream of the TCA cycle in the respiratory chain. In the respiratory chain, oxygen is required to accpet electrons from NADH and FADH and regerate NAD and FAD for the TCA cycle. If no oxygen was present, then NADH and FADH would accumulate and the TCA cycle would halt.

Biochemistry (10 decks)

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