Amino Acids Flashcards
Important biological functions of protein
- Enzymes, the biochemical catalysts
- Storage and transport of biochemical molecules
- Physical cell support and shape (tubulin, actin, collagen)
- Mechanical movement (flagella, mitosis, muscles)
- Decoding cell information (translation, regulation of gene expression)
- Hormones or hormone receptors (regulation of cellular processes)
- Other specialized functions (antibodies, toxins etc)
Under normal cellular conditions amino acids are dissociated ——-
zwitterions
Amino group = NH3+
Carboxyl group = COO-
Fischer projections
horizontal bonds from a chiral center extend toward the viewer, vertical bonds extend away from the viewer
Non-Polar Amino Acids
Ala-Gly-Val-Phe-Trp-Pro-Leu-Ileu-Met
Polar Charged Amino Acids
Basic (His-Arg-Lys)
Acidic (Asp-Glu)
Polar Un-charged Amino Acids
Ser-Cys-Tyr-Thr-Asn-Gln
Amino acids exhibit ————— (mirror image)
Stereoisomers
———– compounds that have the same molecular formula but differ in the arrangement of atoms in space
Stereoisomers
———— non-superimposable mirror images
Enantiomers
——— have four different groups attached
Chiral carbons
Clockwise path: absolute configuration —-
R
Counterclockwise path: absolute configuration
S
chemical synthesis of chiral molecules leads to a ———
racemic mixture (equal amount of L and D isomers)
All amino acids present in proteins are of —configuration
L-configuration
The (?) enantiomer is effective against morning sickness but the (?) is teratogenic and causes birth defects.
R
S
Importance of Cystine in proteins
Particularly important in protein folding and structural stability.
Over —- different amino acids are found in nature
200
Most are precursors to common amino acids or chemically modified derivatives
Some amino acids are chemically modified after incorporation into a polypeptide
Free standard amino acids undergo a number of reactions leading to modified free amino acids designated as ——————————————–
biologically active free non standard amino acids
The 21st amino acid ———————- is incorporated into a few proteins
Selenocysteine
Ionizable groups in amino acids:
(1) a-carboxyl
(2) a-amino
(3) some side chains
Each ionizable group has a specific pKa
AH <—-> B + H+
For a solution pH below the pKa, the ———- form predominates (AH)
For a solution pH above the pKa, the ———– form predominates (B)
protonated
un-protonated
Hydropathy
the relative hydrophobicity of each amino acid
The larger the hydropathy, the ——– the tendency of an amino acid to prefer a hydrophobic environment
greater
Hydropathy affects protein folding:
hydrophobic side chains tend to be in the interiorhydrophilic residues tend to be on the surface
——— linkage between amino acids is a secondary amide bond
Peptide bond
Peptide bond are formed by ————- of the a-carboxyl of one amino acid with the a-amino of another amino acid
condensation
Aspartame
- is a dipeptide methyl ester (aspartylphenylalanine methyl ester)
- About 200 times sweeter than table sugar
- Used in diet drinks