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Common and repeated strategies unique to catabolic and anabolic amino acid pathways:
-Anabolic repeated reactions:
A. Phosphorylation followed by reduction
-Energy input early in the pathway
B. Transamination using pyridoxial phosphate late in pathway- to protect N
Amino acids are derived from metabolic intermediates from…:
- Citric Acid Cycle
- Pentose Phosphate Pathway
Chemical rearrangements that are characteristic of Amino Acid synthesis:
1) transaminations (2) single carbon transfers (3) nitrogen group transfers from glutamine (amide nitrogen) – catalyzed by glutamine amidotransferases (for amide)
Important, recurring themes in amino acids synthesis:
1. Very costly in energy
2. Phosphorylation precedes reduction
This happens early in many pathways. Why?
Phosphorylation precedes reduction because it is the energy invested that will push the pathway forward.
3. Overlapping, complementary pathways
4. Nitrogen is most often added late in the pathway. Why?
Nitrogen is added late in the pathway because amine groups are very reactive.
Transformation of sulfur into a biologically useful form:
this happens by incorporating sulfur into specific amino acids, Cys and Met.
How sulfur is incorporated into specific amino acids:
specialized mechanisms incorporate sulfur-
- (1) Production of sulfide
- a. Comes from environmental sulfates
- b. Sulfate (SO4(2-)) is “activate” by ATP
- c. Reduced using 8 electrons producing sulfide (S2-) (like N fixation)
- (2) Utilization of sulfide
- a. Step 1: serine is “activated” b Acetyl-CoA
- b. Step 2: acetate is replaced by sulfide
Amino acids that incorporate sulfur:
Cys and Met.
Nucleotide synthetic pathways:
De novo pathway and salvage pathway.
De novo pathway (expensive):
begins with metabolic precursors- amino acids, CO2, ribose 5-phosphate, and NH3-. It does not begin with free bases,
-Purine ring => from small precursors and attached to ribose
-Pyrimidine ring => from orotate, then attached to ribose phosphate
Salvage pathways (tend to use this one):
recycling of free bases and nucleotides from catabolic pathways.
Important precursors for purine:
small procurers attached to ribose
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