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AminoAcids/Proteins
Biochemistry, Medicine, Phase 1
| Term | Definition |
|---|---|
| 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
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