Lecture notes
Lecture Notes
- Module
- Metabolic Pathways
- Institution
- Queen Mary, University Of London (QMUL)
Lecture notes of 5 pages for the course Metabolic Pathways at QMUL
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Amino acid biosynthesisLearning objectives:
1. Humans do not biosynthesise all AA (essential and non-essential AA)
2. Common intermediates used to biosynthesised AA
3. The biosynthesis of proline & ornithine via 2 different pathways
4. The biosynthesis of aromatic AA from common precurssors chorismata
LO1. HUMANS DO NOT BIOSYNTHESIS ALL AA (ESSESNTIAL AND NON ESSENTIAL AA)
Essential AA
Many AA not made by humans
- but made by plants and micro-organisms
- known as essential AA
must be in human diet
Non-essential AA (NEAA)
Made by humans
Tyrosine is misclassified as formed from phenylalanine and, therefore is an essential AA
- Previous lecture mention phenylalanine/tyrosine catabolism
LO2. COMMON INTERMIDIATES USED TO BIOSYNTHEIS AA
NEAA come from 4 common intermediates precursors
1. Pyruvate
2. Oxaloacetate Associated with the citric acid cycle
3. Α-ketoglutarate
4. 3-phosphoglycerate
Associated with glycolysis
Examples
Use of transamination
- Pyruvate => alanine
- oxaloacetate => aspartate => asparagine
- α-ketoglutarate => glutamate => glutamine Secondary transamination process on a side chain
transamination Process (reminder)
remove amide group from 1 AA
form α-ketoacid
place amide group on another α-ketoacid
form another AA
occur on the main chain as well as on the side chains (Asn, Gln)
LO3. THE BIOSYNTHESIS OF PROLINE & ORNITHINE VIA 2 DIFFERENT PATHWAYS
The glutamate family
glutamine
proline
arginine
(ornithine)
Glutamate to proline
4 steps
, Glutamate => glutamate-5-phosphate => glutamate-5-semialdehyde => Δ’- Pyrroline-5-carboxylate => proline
From glutamate to glutamate-5-semiphosphate
Phosphorylation to get activation
Followed by reduction reaction
Key points:
Glutamate-5-phosphate is
- Unstable as extremely reactive
- Therefore, not seen only implied to be there
A multi-enzyme system carried out this process
- The multi-enzymes keeps the highly reactive intermediate away from the environment and within the
enzyme structure.
Glutamate to ornithine
3 steps
Get to glutamate-5-semialdehyde and from their branch to ornithine
Or in glutamate to arginine
Glutamate to arginine
5 steps then urea cycle
Glutamate => N-Acetylglutamate => N-Acetylglutamate-5-phosphate => N-Acetylglutamate-5-semialdehyde => N-
acetylornithine => ornithine => (urea cycle) => arginine
- Ornithine has come from outside the urea cycle thus the process increases the concentration of ornithine
Take home message:
- metabolic pathways in the body are able to produce the same molecules via different means
- Simple processes have created ornithine by different routes
Urea cycle
Glutamate to ornithine
3-phosphoglycerate
Members of 3-phosphoglycerate family
- Serine
- Cysteine
- Glycine
To serine, 3 steps
1. oxidation step
2. Transamination step
3. Hydrolysis step
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