Metabolic pathways and ATP production II

Question 1

What are the products of one turn of the TCA cycle?

Answer 1

3 x NADH 1 x FADH2 1 x GTP 2 x CO2

Question 2

Where are the Krebs’ Cycle enzymes found?

Answer 2

Mitochondrial Matrix

Question 3

Which Krebs’ Cycle enzyme is not found in this location?

Answer 3

Succinate Dehydrogenase

Question 4

What happens in Transamination?

Answer 4

An amine group is transferred between an amino acid and a keto acid to generate a new amino acid and keto acid (the basis of the malate-aspartate shuttle) EXAMPLE: alanine + alpha-ketoglutarate  pyruvate + glutamate (enzyme = alanine aminotransferase)

Question 5

What are the two ways of electrons from NADH entering the mitochondrial matrix? Where are these two transport mechanisms found?

Answer 5

Glycerol Phosphate Shuttle – skeletal muscle, brain Malata-Aspartate Shuttle – liver, kidney, heart

Question 6

Describe the glycerol phosphate shuttle.

Answer 6

Cytoplasmic glycerol-3-phosphate dehydrogenase transfers electrons from NADH to dihydroxyacetone phosphate converting it to glycerol-3-phosphate Glycerol-3-phosphate is converted by mitochondrial glycerol-3-phosphate back into Dihydroxyacetone phosphate and the electrons are passed via FAD to coenzyme Q

Question 7

What different types of reactions are NADPH and NADH involved in?

Answer 7

NADPH = Anabolic NADH = Catabolic

anabolic is building up

catabolic is breaking down

Question 8

What are the components involved in the malate-aspartate shuttle?

Answer 8

Malate (in) Alpha-ketoglutarate (out) Oxaloacetate (converted from malate) Glutamate (in) Aspartate (out)

Question 9

what are the 6 types of metabolic reaction? explain ones i dont know

Answer 9

• reduction and oxidation - ligation requiring ATP cleavage (Formation of covalent bonds) - Isomerisation (Rearrangement of atoms to form isomers) - Group Transfer (transfer of the functional group from one molecule to another) - Hydrolytic (cleavage of bonds by the addition of water) - Addition or removal of functional groups (this is the formation or removal of double bonds)

Question 10

how is acetyl CoA made from pyruvate?

Answer 10

pyruvate + Hs - CoA ——> acetyl CoA + CO2 this happens in the mitochondria and then moves into the krebs cycle

Question 11

what is a description of the TCA cycle?

Answer 11

A continuous cycle of eight reactions, starting with 2 carbon atoms from acetyl CoA being condensed with the 4 carbon unit of oxaloacetate to give a 6 carbon unit, citrate

Question 12

what is reaction 1?

Answer 12

1. : Oxaloacetate (4C) + ——> Citrate (6C) the enzyme is citrate synthase 2C acetyl group from acetyl CoA is transferred to the 4C oxaloacetate to form 6C citrate

Question 13

what is reaction 2?

Answer 13

Citrate (6C)———–> Isocitrate (6C) - Citrate is isomerised to give isocitrate Enzyme = Aconitase

Question 14

what is reaction 3?

Answer 14

Isocitrate (6C) —————> a- ketoglutarate (4C) Isocitrate is OXIDISED to form a-ketoglutarate changing from 6C to 5C - the enzyme is isocitrate dehydrogenase

Question 15

what is reaction 4?

Answer 15

a-ketoglutarate ———–> succinyl-CoA - Similar to reaction catalysed by Pyruvate Dehydrogenase Complex - changes from 5C - 4C - Enzyme = a-ketoglutarate dehydrogenase complex

Question 16

what is reaction 5?

Answer 16

succinyl-CoA ————-> Succinate both 4 C - CoA is displaced by phosphate molecule which is transferred to GTP - Enzyme = succinyl CoA synthetase - GDP + Pi —> GTP

Question 17

how does GTP / GDP work?

Answer 17

GTP + ADP —> GDP + ATP

using enzyme nucleoside diphosphokinase

Question 18

what is reaction 6?

Answer 18

Succinate (4C) ———-> Fumarate (4C) - Succinate is OXIDISED and some FADH2 is generated from FAD - Enzyme = succinate dehydrogenase

Question 19

what is reaction 7?

Answer 19

Fumarate————-> Malate - Addition of water molecule breaks a double bond - enzyme = fumarate

Question 20

what is reaction 8?

Answer 20

Malate ———> Oxaloacetate Dehydrogenation of malate to give oxaloacetate -Enzyme = malate dehydrogenase

Question 21

what does one turn of the krebs cycle give?

Answer 21

• 3 x NADH • 1 x GTP • 1 x FADH2 • 2 x CO2 - 2 x ATP

Question 22

where are most of the krebs cycle enzymes? what is the exception?

Answer 22

soluble proteins located in mitochondrial matrix space. SUCCINATE DEHYDROGENASE - this is an integral membrane protein which is attached to the inner surface of inner mitochondrial membrane

Question 23

what conditions does the krebs cycle work under?

Answer 23

operates under AEROBIC CONDITIONS because of NAD+ and FAD being regenerated

Question 24

how much ATP does the reoxidation of co factors via oxidative phosphorylation make?

Answer 24

• 1 NADH –> 3ATP - 1FADH2 –> 2ATP - 1GTP –> 1 ATP therefore one acetyl CoA (3x NADH) + (1x FADH) + ( 1x GTP)

Question 25

what is the theoretical maximum yield of ATP?

Answer 25

Question 26

what is the general strategy of degradation of amino acids?

Answer 26

• Amino Acid group is removed (eventually excreted as urea)
• Carbon skeleton is either funnelled into production of glucose or fed into krebs’ cycle.

Question 28

what does the degradation of all 20 amino acids give rise to?

Answer 28

• pyruvate
• acetyl CoA
• Acetoacetyl CoA
• a-ketoglutarate
• Succinyl CoA
• fumarate
• oxaloacetate

Question 29

what is a transamination reaction?

Answer 29

• a reaction in which an amine group is transferred from one amino acid to a keto acid thereby forming a new pair of amino and keto acids.

Question 30

where does transamination come into role in cell metabolism?

Answer 30

• Alanine undergoes transamination by the action of enzyme Alanine Aminotransferase
• Pyruvate can enter the TCA cycle
• Glutamate is converted back to a-ketoglutarate by Glutamate Dehydrogenase, this also makes NH4+ which is converted back to urea

Question 31

what do high levels of alanine aminotransferase suggest?

Answer 31

hepatic disorders … eg Hep C

Question 32

why does the NADH need to be moved from glycolysis to be used in oxidative phosphorylation?

Answer 32

• to regenerate NAD+
• There is only a finite amount of NAD+ so unless it’s regenerated, glycolysis will stop

Question 33

how does the NADH cross the cytosol?

Answer 33

• The NADH cross the cytosol into the matrix of the mitochondrion by:
  
  • Glycerol Phosphate Shuttle - skeletal muscle, brain
  • Malate-Aspartate Shuttle - liver, kidney, heart

Question 34

how does the glycerol phosphate shuttle work?

Answer 34

Electrons from NADH, rather than NADH itself are carried across the mitochondrial membrane via a shuttle.

Cytosolic glycerol-3-phosphate dehydrogenase transfers electrons to Dihdroxyacetone phosphate to form glycerol 3-phosphate

A membrane bound form of the same enzyme transfers the electrons to FAD. The electrons then get transferred to co-enzyme Q, part of the electron transport chain

Question 35

how does the malate-aspartate shuttle work?

Answer 35

Uses 2 membrane carriers + 4 enzymes.

1. Hydride Ion (H-) is transferred from cytoplasmic NADH to oxaloacetate to give malate (catalysed by cytosolic malate dehydrogenase (MDH)).
2. Malate is transported into mitochondria where it is rapidly re-oxidised by NAD+ to give oxaloacetate and NADH (catalysed by mitochondrial MDH).

Question 36

are NADPH and NADH anabolic or catabolic?

Answer 36

NADPH = anabolic

NADH - catabolic

Question 37

why is NADPH important in cholesterol synthesis?

Answer 37

• NADPH helps catalyse the final reaction of many, that leads to cholesterol synthesis
• The C=C double bond is reduced by the transfer of a hydride ion

Question 38

what is NADP+ ?

Answer 38

NADP⁺ is similar to NAD⁺, the only differing by a phosphate group attached to one of the ribose rings.

Like NAD⁺, NADP⁺ can pick up two high-energy electrons and a proton collectively known as a hydride ion (H-).

NADP is an electron carrier

the phosphate group does not participate but it has a different structure so it can bind to different enzymes than NAD+