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AminoAcids/Proteins

Biochemistry, Medicine, Phase 1

TermDefinition
Amino acids (aa) (1) small organic molecules with a carboxylic acid (COOH) group and an amino group (H2N) both linked to their alpha-carbon atom plus a side chain (R); have 3 and 1 letter code
Side chain distinguishes one amino acid from another
Amino acids (2) protein building blocks; 20 universal amino acids; water soluble and electrically charged at physiological pH
Peptide bond covalent bond between two adjacent amino acids; formed by enzyme reaction; very strong; hydrolysis only by enzyme (digestion or lysosome)
Polypeptide more than one amino acid a covalently bonded to another amino acids
Amino group N-terminal of amino acid
Carboxyl group C-terminal of amino acid
L-form amino acids the only form found in proteins
D-form amino acids occur as part of bacterial cell walls and in some antibiotics
Glycine only amino acid without an optimal isomer
Positively charged amino acids arginine, lysine, histidine
Negatively charge amino acids aspartic acid, glutamic acid
Essential amino acids (adults) cannot be synthesised de novo by humans; we lack the necessary enzymes; threonine, methionine, lysine, valine, leucine, histidine, phenylalanine, tryptophan
Hydrophilic amino acids aspartic acid, glutamic acid, arginine, lysine, histidine, asparagine, glutamine, serine, threonine, tyrosine
Hydrophobic amino acids alanine, glycine, valine, leucine, isoleucine, proline, phenylalanine, methionine, tryptophan, cysteine
Other roles of amino acids taste enhancers (MSG; glu); neurotransmitters; synthesis of neurotransmitters
Epinephrine synthesised from tyrosine (1)
Dopamine synthesised from tyrosine (2)
Histamine synthesised from histidine
Serotonin synthesised from tryptophan
pKa of side groups measure of the ease with which groups give up their protons; at physiological pH the carboxyl and amino groups are attached to the alpha carbon and fully ionised; the lower the pKa the stronger the acid; only the pKa of R-groups are relevant (polar)
2.3 pKa of carboxyl group
9.8 pKa of amino acid group
pKa influence on structure and function of proteins; charge on amino acid depends on local pH
Phenylketonuria (PKU) defective phenylalanine hydroxylase (phe > try); reduced tyr results in reduced dopamine and melanin production; protein rich food increases phenylalanine levels which can be toxic
Albinism Defective tryosinase (try > melanin)
Created by: emmaallde