Flashcards in Lecture 36: Amino Acids as Precursors Deck (43)
What are the 4 functions of glycine as a precursor?
1. Inhibitory transmitter
2. Glycocholic acid (bile salt)
3. Purine synthesis
4. Heme synthesis
Describe glycine's function as an inhibitory transmitter.
It inhibits impulses traveling down the spinal cord to stimulate skeletal muscle
How does glycine contribute to purine synthesis?
It's directly incorporated into de novo purine synthesis
What are the 2 purines?
How does glycine contribute to heme synthesis?
Glycine condenses with succinyl-CoA in the first step of heme synthesis and is a building block for porphyrin 9 which coordinates with iron
What are the 2 predominant circulating AAs?
What is the main function of serine?
Important source of single carbon fragments (from the R group) => transferred to a folate derivative which can use the C in a variety of ways depending on its oxidative/reductive state (tetrahydrofolates)
What are the 3 functions of glutamine?
1. Amino group and NH4+ transporter
2. Amino group donor for purine biosynthesis
3. Amino group donor for amino sugar biosynthesis
Describe the synthesis of amino sugars.
Glutamine donates an amino group to F6P which produces glucosamine-6-phosphate => all amino sugars are derived from glucosamine-6-P
What are the 4 functions of glutamate?
1. Excitatory NT
2. Precursor to GABA
3. Amino group donor for AA synthesis
4. Ammonia fixation reactant
Describe the synthesis of GABA.
Decarboxylation of alpha carboxyl using PLP as a cofactor = GABA
What does GABA stand for?
What drugs is the GABA receptor a target for?
Benzodiazepines and barbiturates
What are the 2 functions of methionine?
1. Methyl group source
2. Polyamine synthesis
How does methionine donate a methyl group?
Methionine + ATP => S-adenosyl methionine (SAM)
What is another name for S-adenosyl methionine (SAM)?
How does methionine contribute to polyamine synthesis?
SAM is decarboxylated using PLP leaving behind propylamine residue attached to sulfur which serves as a precursor for polyamines
What are 2 examples of polyamines? What is their role?
+ charged and allow for compact packing of DNA/RNA
What are the 2 functions of arginine?
1. Urea precursor
2. NO source
What is the function of NO?
Short-lived second messenger that acts near its synthesis site
What 2 cofactors does NO synthesis from arginine require?
What 3 AAs contribute to the synthesis of creatine?
What is the main function of histidine? Describe the mechanism
Histamine precursor via histidine decarboxylation
What are the 2 main functions of histamines
1. Stimulates systemic reactions to allergens
2. Stimulates acid release in the stomach
What cofactor does the synthesis of histamines from histidine require?
What is the main function of phenylalanine?
Precursor for tyrosine
What are the 10 essential AAs (meaning we cannot make them)?
I Want To Kill VHRs. FML
Describe the mechanism of tyrosine synthesis using phenylalanine (overall and 2 steps)
Coupling of 2 enzymes through the cofactor tetrahydrobiopterin:
1. Dihydrobiopterin reductase: NADH + 7,8-dihydrobiopterin => NAD+ + 5,6,7,8-tetrahydrobiopterin
2. Phenylalanine hydroxylase: 5,6,7,8-tetrahydrobiopterin + phenylalanine + O2 => tyrosine + H2O + 7,8-dihydrobiopterin
What is phenylketonuria (PKU)? When is this screened for? Treatment?
Phenylalanine hydroxylase deficiency: excess phenylalanine impairs neural development
Screened for at birth
Treatment: inhibit intake of phenylalanine and take tyrosine supplements