Amino Acid Synthesis Part 1

Question 1

definition of conditionally essential AA?

Answer 1

synthesis can be limited under certain pathological conditions

Question 2

Selenocysteine
ex. of presence

Answer 2

21st AA
Special Serine-tRNA recognizes UGA (stop) codon, and serine is enzymatically converted into selenocysteine
ex. present in glutathione peroxidase

Question 3

Pyrrolysine

Answer 3

22nd AA found in bacteria
Has dedicated tRNA it is attached to unlike selenocysteine

Question 4

Essential amino acids

Answer 4

How Is Lying Like Making Pancakes That Taste Vile?
Histidine
Isoleucine
Lysine
Leucine
Methionine
Phenylalanine
Threonine
Tryptophan
Valine

Question 5

Non-essential AA

Answer 5

Go Send AAA:
Alanine
Asparagine
Aspartate
Glutamate
Serine

Question 6

In mammals phenylalanine is

Answer 6

a precursor of tyrosine

Question 7

AA synthetic precursors:

Answer 7

Alpha-ketoglutarate
3-phosphoglycerate
Oxaloacetate
Pyruvate
Phosphoenolpyruvate + Erythrose-4-phosphate
Ribose-5-phosphate

Question 8

Alpha-ketoglutarate family of AA synthesis

Answer 8

Parent: Glutamate
Children: Glutamine, Proline, Arginine

Question 9

3-phoshoglycerate family of AA synthesis

Answer 9

Parent: Serine
Children: Glycine, Cysteine

Question 10

Oxaloacetate family of AA synthesis

Answer 10

Parent: Aspartate
Children: Asparagine, Methionine, Threonine, Lysine

Question 11

Pyruvate family of AA synthesis

Answer 11

Parent: Alanine
Children: Valine, Leucine, Isoleucine

Question 12

Phosphoenolpyruvate + Erythrose-4-phosphate family of AA synthesis

Answer 12

Parent: none
Tryptophan, phenylalanine, tyrosine
*Tyrosine can be derived from phenylalanine in mammals

Question 13

Ribose-5-phosphate family of AA synthesis

Answer 13

only child: histidine
therefore pentose phosphate pathway is not important in AA synthesis in mammals since histidine is essential

Question 14

Porphyrin derivation
Porphyrin synthesis pathway

Answer 14

Heme in hemoglobin
Derived from glycine and succinyl-coA in higher mammals, and glutamate in plants/bacteria

1) Succinyl coA + glycine –> a-amino-b-ketoadipate
Enzyme: delta-aminolevulinate synthase
2) a-amino-b-ketoadipate –> delta-aminolevulinate + CO2
Enzyme delta-aminolevulinate synthase
3) 2 delta-aminolevulinate + H2O –> porphobilinogen
4) 4 porphobilinogen –> protoporphyrin
5) Protoporphrin + Fe –> porphyrin

Question 15

Porphyria disease

Answer 15

accumulation of porphyrin intermediates

Question 16

Degradation of heme into bile pigments

Answer 16

Biliverdin is bluish color seen in bruises (linearized), bilirubin is yellow and travels in blood bound to serum albumin

1) Heme –> biliverdin + Fe2+ + CO
Enzyme: heme oxygenase
2) Biliverdin –> bilirubin
Enzyme: biliverdin reductase
Cofactor: NADPH
3) Bilirubin –> bilirubin diglucuronide –> in liver, bilirubin excreted in bile
Enzyme: glucuronyl bilirubin transferase

4) Bilirubin diglucuronide (bile) –> urobilinogen (converted to stercobilin by intestinal bacteria and excreted in feces)

OR reabsorbed in intestines:
5) Urobilinogen transported to kidney –> urobilin (excreted in urine)

Question 17

Physiological vs pathological jaundice

Answer 17

Jaundice: yellowish pigmentation of skin and eyes due to bilirubin accumulation

Physiological jaundice: insufficient glucouronyl bilirubin transferase in infants, treatment is UV photochemical therapy to break down bilirubin

Pathological jaundice: impaired liver due to cancer or hepatitis, blocked bile secretion due to gallstones and pancreatic cancer

Question 18

Creatine/phosphocreatine overview

Answer 18

Requires glycine, arginine, and methionine
Phosphorylation of creatine to phosphocreatine
Phosphate group acts as buffer store to produce ATP especially in muscles

Question 19

Creatine and Phosphocreatine synthesis pathway

Answer 19

1) Glycine + Arginine –> guanidinoacetate (+ ornithine byproduct)
Enzyme: amidinotransferase
2) Guanidinoacetate + Methionine –> Creatinine
Enzyme: methyltransferase
3) Creatinine + ATP –> phosphocreatinine + ADP
Enzyme: creatinine kinase

Question 20

Glutathione biosynthesis pathway

Answer 20

Ingredients: glutamate, cysteine, glycine
1) glutamate + cysteine + ATP –> Glu-cys intermediate
Enzyme: gamma glutamyl cysteine synthetase

2) Glu-cys intermediate + Glycine + ATP –> Glutathione (GSH reduced)
Enzyme glutathione synthetase

Question 21

Glutathione reduced vs oxidized form

Answer 21

Enzyme: glutathione peroxidase and glutathione reductase
Reduced: monomer, active form of antioxidant can act as H donor
Oxidized: dimer form with disulfide bridge

Question 22

Derivation of dopamine, norepinephrine and epinephrine and associated diseases

Answer 22

Dopa → dopamine → norepinephrine → epinephrine are derived from tyrosine
Parkinson’s: dopamine under production, treated with L-dopa
Schizophrenia: linked with overproduction of dopamine

Question 23

Derivation of serotonin and function

Answer 23

Serotonin is derived from tryptophan
Function: regulation of intestinal movement and feel-good hormone

Question 24

Derivation of histamine and function

Answer 24

Histamine is derived from histidine
Function: released during allergic reaction, stimulates HCl secretion in stomach, vasodilator
*treatment of duodenal ulcers is a histamine antagonist

Question 25

Derivation of GABA and function

Answer 25

GABA is derived from glutamate
Function: inhibitory signals in the CNS, muscle tone
*underproduction can lead to epileptic seizures and is treated with GABA analogs