The Special One
Gly
Glycine
Simplest Amino Acid
ClaimSmallest amino acid — seen everywhere in the body
UniqueNO chiral carbon — the only amino acid without one (R group = just H)
FunctionInhibitory neurotransmitter for the spinal cord
Board HitTetanus toxin (found in dirt) blocks glycine release from spinal cord → muscles can't relax → diaphragm locks up → can't breathe
Aromatic Amino Acids
Big, bulky ring structures
Phe
Phenylalanine
Aromatic • Essential
EnzymeRecognized by chymotrypsin (cuts to its right side)
EnergyBoth glucogenic AND ketogenic
DiseasePKU — can't convert Phe → Tyr → musty/mousy odor, intellectual disability
Trp
Tryptophan
Aromatic • Essential
MakesSerotonin (a monoamine neurotransmitter) and melatonin
AlsoWithout Trp → can't make niacin (B3) → Pellagra (3 D's: Dermatitis, Diarrhea, Dementia)
DepletedCarcinoid syndrome uses up all the Trp to make serotonin → Trp deficiency → pellagra
DiseaseHartnup's Disease — Trp spills into the urine (defective neutral AA transporter)
EnergyBoth glucogenic AND ketogenic
Tyr
Tyrosine
Aromatic • Hydroxyl
MakesCatecholamines: Dopamine, Epinephrine, Norepinephrine
AlsoMakes melanin (skin pigment) and thyroid hormones
BondsHas extra OH group → involved in O-linked bonds (phosphorylation target!)
Basic Amino Acids
Extra NH₃⁺ = positive charge
Lys
Lysine
Basic • Essential
ChargePositive — extra NH₃⁺ group
EnzymeRecognized by trypsin (cuts to its right side)
EnergyPurely KETOGENIC — one of only 2 (Lys + Leu)
Only KETOGENIC: Lys + Leu. "You can't LIE about KETOgenic — it's only Lysine and LEUcine."
MigratePositive → migrates toward cathode (−)
Arg
Arginine
Basic • Essential
ChargePositive — extra NH₃⁺ group (guanidinium)
EnzymeAlso recognized by trypsin
FunctionPrecursor to nitric oxide (NO) via nitric oxide synthase — vasodilation
MigratePositive → migrates toward cathode (−)
Acidic Amino Acids
Extra COO⁻ = negative charge
Asp
Aspartate
Acidic
ChargeNegative — extra COO⁻ group
FunctionReinforcement of behavior via the NMDA pathway (ex: gambling, addictions)
DrugMemantine (and Galantine) blocks glutamate inhibition of NMDA → increases pathway activity → treats Alzheimer's
MigrateNegative → migrates toward anode (+)
Glu
Glutamate
Acidic
ChargeNegative — extra COO⁻
FunctionMain excitatory neurotransmitter in the brain
LinkGlutamate → GABA (via glutamate decarboxylase). The GABA connection is huge — see below.
MigrateNegative → migrates toward anode (+)
Sulfur-Containing
Disulfide bonds
Cys
Cysteine
Sulfur • Disulfide King
ContainsSulfur — has the MOST sulfur of any amino acid
FunctionMakes disulfide bonds (S—S) — critical for protein folding and stability
Board Hit4 hormones with lots of disulfide bonds: "PIGI" — Prolactin, Insulin, Growth Hormone, Inhibin
PIGI — like a piggy bank: Prolactin, Insulin, Growth Hormone, Inhibin. All held together by disulfide bonds from cysteine.
Met
Methionine
Sulfur • Essential
ContainsSulfur
FunctionAlso makes disulfide bonds
SpecialStart codon (AUG) codes for Met — first amino acid in every protein
Amide Amino Acids
N-linked bonds • end in "-ine"
Asn
Asparagine
Amide
BondsInvolved in N-linked bonds (glycosylation)
RememberEnds in "-ine" → has an extra amine group (NH₂)
Gln
Glutamine
Amide
BondsInvolved in N-linked bonds
FunctionMajor fuel for enterocytes (intestinal cells) and immune cells
RememberEnds in "-ine" → extra amine group
Hydroxyl Amino Acids
O-linked bonds • extra -OH
Ser
Serine
Hydroxyl
BondsInvolved in O-linked bonds
SpecialFound in the active site of many enzymes (serine proteases: trypsin, chymotrypsin, elastase, thrombin)
ExtraHas extra -OH group → phosphorylation target for kinases
Thr
Threonine
Hydroxyl • Essential
BondsInvolved in O-linked bonds
ExtraHas extra -OH group
EnergyBoth glucogenic AND ketogenic
Branched-Chain Amino Acids (BCAAs)
Can't "LIV" without them
Leu
Leucine
BCAA • Essential
EnergyPurely KETOGENIC — one of only 2 (Lys + Leu)
TransportAll 3 BCAAs share the same transport protein in the collecting duct of the kidney
Iso
Isoleucine
BCAA • Essential
EnergyBoth glucogenic AND ketogenic
TransportShares transport protein with Leu and Val
Val
Valine
BCAA • Essential
DiseaseMaple syrup urine disease — can't break down BCAAs → sweet-smelling urine
EnzymeBranched-chain amino acid dehydrogenase needs 5 vitamins (same as pyruvate DH and α-ketoglutarate DH)
Ketogenic vs Glucogenic Summary
Purely Ketogenic (2 only)
Lysine and Leucine
Ketogenic = broken down into acetyl-CoA → used to make ketones
Can NOT be used to make glucose
Ketogenic = broken down into acetyl-CoA → used to make ketones
Can NOT be used to make glucose
Both Glucogenic & Ketogenic (4)
PHE, ISO, THR, TRP
Can go both ways — broken down into intermediates that feed into gluconeogenesis OR ketogenesis "PITT" — PHE, ISO, THR, TRP. Like Brad Pitt — he can play any role (glucogenic or ketogenic).
Can go both ways — broken down into intermediates that feed into gluconeogenesis OR ketogenesis "PITT" — PHE, ISO, THR, TRP. Like Brad Pitt — he can play any role (glucogenic or ketogenic).
🧠 The GABA Connection
NH₄⁺ + αKG → Glutamate → GABA
Ammonium (NH₄⁺) comes from urea and acid: NH₃ + H⁺ = NH₄⁺
The Le Chatelier principle: increase things on the right → shifts left. Increase things on the left → shifts right → more glutamate → more GABA.
GABA is inhibitory — more GABA = things slow down. This is the key link:
The Le Chatelier principle: increase things on the right → shifts left. Increase things on the left → shifts right → more glutamate → more GABA.
GABA is inhibitory — more GABA = things slow down. This is the key link:
►Liver failure → can't clear ammonia → ↑NH₄⁺ → ↑glutamate → ↑GABA → hepatic encephalopathy (patient slows down, becomes comatose)
►Kidney failure → can't clear urea → ↑urea → same pathway → uremic encephalopathy
►DKA → ketones are acidic → ↑acid → ↑NH₄⁺ → ↑GABA → diabetic coma
►Any disease with high acid, urea, or ammonia will increase GABA → patients go to sleep/coma but do not wake up
Enzyme Recognition Cheat Sheet
| Enzyme | Recognizes | Action |
|---|---|---|
| Chymotrypsin | PHE, TRP, TYR (aromatics) | Cuts to their right side |
| Trypsin | LYS, ARG (basic) | Cuts to their right side |
| Serine proteases | Have Ser in active site | Trypsin, chymotrypsin, elastase, thrombin |
🎯 Board Blitz
10 random questions from a pool of 18 — reload for a new set