Metabolism 4: Metabolic Pathways and ATP Production II

Question 1

Describe the TCA Cycle

Answer 1

https://i.imgur.com/VziHoBM.jpg

One turn produces: 
3 x NADH 
1 x GTP 
1 x FADH2 
2 x CO2

Question 2

Location of Krebs Cycle Enzymes

Answer 2

Krebs cycle enzymes are soluble proteins located in mitochondrial matrix space.

EXCEPT SUCCINATE DEHYDROGENASE - which is an integral membrane protein

Question 3

What is a transamination reaction

Answer 3

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

Question 4

Describe the transamination of alanine

Answer 4

Alanine undergoes transamination by the action of enzyme Alanine Aminotransferase.

Alanine+a ketoglutarate-> pyruvate + glutamate

Pyruvate can enter the TCA cycle.

Glutamate is converted back to a-ketoglutarate by Glutamate Dehydrogenase. This generates NH4+ which is ultimately converted to urea.

CLINICAL NOTE: Persistently elevated levels of alanine aminotransferase are a diagnostic for hepatic disorders such as Hepatitis C.

Question 5

how is NADH transported

Answer 5

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 6

Describe the glycerol phosphate shuttle

Answer 6

1. Cytosolic glycerol-3-phosphate dehydrogenase transfers electrons to Dihdroxyacetone phosphate to form glycerol 3-phosphate.
2. 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 7

Describe the Malate Aspartate Shuttle and how it transfers electrons

Answer 7

2 membrane carriers:
malate in, a-ketoglutamate out
and
glutamate in, aspartate out

Hydride Ion (H-) is transferred from cytoplasmic NADH to oxaloacetate to give malate (catalysed by cytosolic malate dehydrogenase (MDH)).

Malate is transported into mitochondria where it is rapidly re-oxidised by NAD+ to give oxaloacetate and NADH (catalysed by mitochondrial MDH).

A transamination reaction occurs so Glutamate and Oxalocetate is converted into Aspartate and a-ketoglutamate

Question 8

What is NADP+

Answer 8

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

NADP+ is also an ELECTRON CARRIER

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

Question 9

Describe how NADPH is useful in the biosynthesis of cholesterol

Answer 9

The C=C double bond is reduced by the transfer of a hydride ion.

Question 10

What two anabolic reactions is NADPH involved in?

Answer 10

biosynthesis of RNA and cholesterol