Lecture 30: The fate of Pyruvate REVISIT!!

Question 1

Does glycolysis require oxygen?

Answer 1

NOOO

Question 2

How is pyruvate oxidised?

Answer 2

It has a carbon dioxide removed and is hence converted into acetyl-CoA

Question 3

Did Harden and Young find out that inorganic phosphate is a limiting factor for photosynthesis?

Answer 3

Yes

Question 4

Do we have to worry about running out of ATP?

Answer 4

No, because there is a constant interconversion between ATP and ADP

Question 5

What happens if cofactors, like NAD+, run out?

Answer 5

Then glycolysis stops

Question 6

What is done to pyruvate to restore the supply of NAD+?

Question 7

What can pyruvate be converted to?

Answer 7

Ehanol in yeast cells, lactate in the muscles, acetyl coA(which can be further oxidised) under aerobic conditions in citric acid cycle

Question 8

How is NAD+ regenerated aerobically?

Answer 8

• Pyruvate us oxidised to acetyl coA in the citric acid cycle.
• In the electron transport chain, NADH transfers electrons to Oxygen , forming water and regenerating NAD+.

-

Question 9

Is it true that the regenration of NAD+ requires reduction of another compound?

Answer 9

Yes

Question 10

What do anaerobic conditions lead to ?

Answer 10

fermentation

Question 11

Define fermentation

Answer 11

“An ATP producing process in which organic compounds act both as electron donors and as electron acceptors”

(Glucose oxidised to pyruvate (glucose donates e-)
)

( Pyruvate reduced to ?? (pyruvate accepts e-)
)

Question 12

when is lactate the fermentation product?

Answer 12

In animal muscle, red blood cells, some cancer cells, lactobacillus:

Question 13

when is ethanol the fermentation product?

Answer 13

In plants and yeast

Question 14

In which organisms can the fermentation product be: Acetate and other carboxylic acids, hydrogen etc?

Answer 14

In Various other microorganisms

Question 15

How often are animal and plant cells usually anaerobic?

Answer 15

Animal and plant cells usually temporarily anaerobic

Question 16

When are animal cells usually anerobic?

Answer 16

During strenuous exercise

Question 17

Are cancer cells usually anaerobic?

Answer 17

Yes

Question 18

Why are red blood cells anaerobic?Because they don;t have a mitochondria

Question 19

Give some examples of environments that are permannetly anaerobic

Answer 19

Bacteria in marine and lake sediments, marshes, animal gut

Question 20

What was the early atmosphere like?

Answer 20

Anaerobic, so glycolysis could be run

Question 21

Why do we need to further oxidise pyruvate in the citric acid cycle?

Answer 21

Because this is the only way to release all of glucose’s energy, as the majority of pyruvate’s energy will still be stored in pyruvate at the end of glycolysis.

Question 22

So which produces more ATP anaerobic respiration or aerobic respiration?

Answer 22

Aerobic respiration

Question 23

Where does the citric acid cycle take place?

Answer 23

In the mitochondrial matrix

Question 24

How does pyruvate reach the mitochondrial matrix?

Answer 24

It is cotransported there with H+ ions

Question 25

What happens after pyruvate is cotransported into the mitochondria matrix?

Answer 25

It is decarboxylated, then converted into acetyl coA. This uses up a NAD+ and regenerates an NADH

Question 26

Why were original studies of the movement of pyruvate from the cytosol to the mitochondrial matrix conducted on liver and on pigeons?

Answer 26

Because they're both incredibly rich in mitochondria

Question 27

After pyruvate is converted into acetly coA, what can happen?

Answer 27

The acetyl can then enter the citric acid cycle and couple with 4C oxaloacetate to form 6C Citrate

Question 28

What happens after ocaloacetate is converted into citrate?

Answer 28

2 Carbon dioxide's are lost, and oxaloacetate is constantly reformed, and the cycle repeats over and over again

Question 29

What happens when fatty acids are broken down into acetyl coA?

Answer 29

They're oxidised in exacrtly the same way that acetly coA from glucose is (integration point between the 2 main sources of energy, fatty acids and sugars)

Question 30

Is it true that 2 carbon dioxide's are released for each acetyl group?

Answer 30

Yes

Question 31

What is the reactive group of coenzyme A?

Answer 31

The SH group

Question 32

Draw out the structure of coenzyme A

Question 33

What part of coenzyme A links to the acetate group?

Answer 33

The SH group

Question 34

Draw out the structure of acetyl coA

Question 35

Draw out the reaction for the conversion of pyruvate to acetyl CoA

Question 36

How do we know that the reaction for the conversion of pyruvate to acetyl CoA is irreversible?

Answer 36

Because the ΔG<<0 (no going back to glucose)

Question 37

What catalyses the conversion of pyruvate to acetyl CoA?

Answer 37

pyruvate dehydrogenase multienzyme complex

Question 38

Is it true that Pyruvatedehydrogenase complex is very big?

Answer 38

Yes, it is 4-10 x106 kDa i.e. larger than ribosomes

Question 39

How many different enzymes does the pyruvate dehydrogenase complex consist of?

Answer 39

3

Question 40

What are the 3 enzymes that the pyruvate dehydrogenase complex consists of?

Answer 40

pyruvate dehydrogenase component (E1) dihydrolipoyl transactetylase (E2) dihydrolipoyl dehydrogenase (E3)

Question 41

What is the function of E1?

Answer 41

decarboxylation of pyruvate

Question 42

What is the function of E2?

Answer 42

Transfer of the acetyl group to CoA

Question 43

What is the function of E3?

Answer 43

Reoxidation + the regeneration of the oxidised form of lipoamide

Question 44

Describe E1: Pyruvate dehydrogenase component

Answer 44

- Derived from vitamin B1 - Found in the outer seed coats of cereals incl. rice. - Deficiency in man results in “beri-beri” - Not simple process, requires TPP cofactor, which particpates in the decarboxylation of pyruvate - Hydrogen is lost, resulting in a negative C

Question 45

Describe E2: Dihydrolipyol transacetylase

Answer 45

Acetyl group is picked off TPP and transferred to CoA ADD MORE DETAIL As disulfide has been reduced, it has to be re-oxidised

Question 46

Describe E3: Dihydrolipyol dehydrogenase

Answer 46

Reoxidation of disulphide in lipoamide Reoxidation of FADH2 generates 1 NADH

Question 47

Which reactions are catalysed by the pyruvate dehydrogenase multi-enzyme complex

Answer 47

1)

Question 48

What is the equation that represents the conversion of pyruvate to acetyl-CoA?

Answer 48

Pyruvate + CoA-SH + NAD+ -----> Acetyl-CoA + CO2 + NADH

Question 49

What is a multienzyme complex?

Answer 49

A group of 2 or more non-covalently associated enzymes that catalyse two or more sequential steps in a metabolic pathway

Question 50

What are the advantages of multienzyme complexes?

Answer 50

- Product of the first reaction in the sequence remains attached - Serves directly as a substrate for the second reaction - Therefore rate of second reaction not limited by diffusion - Can channel intermediates between successive enzymes, thereby minimising side reactions - The reactions may be coordinately regulated

Question 51

How is pyruvate dehydrogemase controlled?

Answer 51

By phosphorylation. Kinase phosphorylates the enzyme. Kinase is stimulated by high energy status (AcetylCoA, ATP and NADH ) and inhibited by low energy status (ADP and NAD+ )

Question 52

The Sparker Effect

Question 53

Who discovered the citric acid cycle?

Answer 53

Szent-Györgyi and Krebs (both got Nobel prizes)

Question 54

Describe the sparker effect

Answer 54

- Mince liver to release its enzymes, add pyruvate, and measure oxygen consumption- should find that not much happens - Then add the trace of an organic acid with the pyruvate and mince liver, Should find that oxygen consumption is higher. - Realised that something must be being oxidised. The organic acids weren't used up so it could not be them . - The interpretations from this were that; organic acids work catalytically and one molecule of the organic acid can spark oxidation of an infinite amount of pyruvate - They repeated the experiment and realised that succinate accumulated and the same thing happened if a trace amount of fumurate was added. This proved that the pathwya was cyclic

Question 55

What can organic acids include?

Answer 55

Organic acids: citrate, fumarate, malate or succinate

Question 56

What is malonate a potent inhibitir for?

Answer 56

Malonate was found to be a potent inhibitor of respiration in all animal tissues

Question 57

What are the other names of the citric acic cycle?

Answer 57

Krebs cycle Tricarboxylic Acid Cycle TCA cycle

Question 58

What are the principle negative regulators of the citric acid cycle?

Answer 58

ATP and NADH are the principal negative regulators . The need for energy and for carbon skeletons is the main positive regulator

Question 59

If oxaloacetate is depleted from the citric acid cycle, what will happen?

Answer 59

The cycle will stop

Question 60

How is the withdrawal of citric acid cycle intermediates rectified?

Answer 60

Achieved by anaplerotic (ana pleros: to fill up, replenish) reactions. In humans, the main anaplerotic reaction introduces more oxaloacetate into the cycle, via carboxylation of pyruvate: Pyruvate+ CO2+ATP+H2O 🡪 oxaloacetate+ADP+Pi+2H+ (Catalysed by pyruvate carboxylase )

Question 61

is is true that 'Glucogenic amino acids can be used in anaplerotic reactions if needed Ketogenic amino acids can not'?

Answer 61

Yes

Question 62

is it true that Citric acid cycle is a shared pathway for breakdown of carbohydrates, fats and amino acids?

Answer 62

Yes

Question 63

is it true that the citric acid cycle mainly generates reduced coenzymes ?

Answer 63

Yes

Question 64

why are intermediates sometimes taken out of the citric acid cycle?

Answer 64

For biosynthesis i.e amino acid synthesis

Question 65

Do fats make sugar?

Answer 65

No

Question 66

What does each cycle of the citric acid/krebs cycle produce?

Answer 66

3 NADH FADH2 ATP Per glucose molecule, which produces 2 pyruvates 6 NADH 2 FADH2 2ATP