Section2_amino_acids_09

Section2_amino_acids_09 - Amino Acids Amino Acids Proteins...

Info iconThis preview shows pages 1–11. Sign up to view the full content.

View Full Document Right Arrow Icon
8/31/09 1 Amino Acids Amino Acids Proteins are polymers of amino acids. So to understand protein properties, we must first understand the properties of amino acids. Amino acids can also function as neurotransmitters (glutamate, γ -aminobutyric acid), hormones (thyroxine), as bacterial cell wall components ( D -alanine) and as intermediates in many metabolic pathways.
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
8/31/09 2 Amino Acids We limit ourselves to the common α -amino acid in which the carboxylic acid and amino groups are attached to the same carbon - the α -carbon: H N H R C O C H O + H - α -Carbon Side Chain Only 20 α -amino acids are encoded in genetic material, and it is the R group (side chain) that varies among them. (pH 7.0) We now look at: 1) R groups 2) Chirality 3) Ionization Amino Acids: R-groups • Glycine (Gly, G) -H • Alanine (Ala, A) -CH 3 • Valine (Val, V) CH CH CH 3 A) Non-polar (aliphatic, hydrophobic) R C C O - O H + H 3 N
Background image of page 2
8/31/09 3 Amino Acids: R-groups • Leucine (Leu, L) CH 3 CH CH CH 2 • Isoleucine (Ile, I) CH 3 CH 2 CH CH 3 Amino Acids: R-groups • Proline (Pro, P) N H 2 C CH 2 CH 2 CH C O O - H 2 + A cyclic α -imino acid. • Methionine (Met, M) CH 3 S CH 2 CH 2
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
8/31/09 4 Amino Acids: R-groups • Phenylalanine (Phe, F) CH 2 • Tyrosine (Tyr, Y) CH 2 OH Phenolic hydroxyl pK a = 10.1 B) Aromatic Amino Acids: R-groups • Tryptophan (Trp, W) Indole ring N CH 2 H C) Polar, uncharged, hydrophilic • Serine (Ser, S) -CH 2 OH Alcohol pK a = 13.6 (not physiologically relevant)
Background image of page 4
8/31/09 5 Amino Acids: R-groups • Threonine (Thr, T) • Cysteine (Cys, C) CH 3 C OH H Alcohol pK a = 13.6 (not physiologically relevant) SH CH 2 Thiol pK a ~ 8.3 Two nearby Cys can form a disulfide bond in an oxidizing environment. S S CH 2 CH 2 Amino Acids: R-groups S S CH 2 CH 2 Disulfide bonds help stabilize protein structure
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
8/31/09 6 Amino Acids: R-groups • Asparagine (Asn, N) • Glutamine (Gln, Q) NH 2 C O CH 2 2 C O CH 2 CH 2 (amide side-chain) (amide side-chain) Amino Acids: R-groups • Aspartic Acid (Asp, D) (or aspartate) • Glutamic Acid (Glu, E) (or glutamate) D) Negative at pH 7 (Acidic) O - C O CH 2 Carboxyl pK a = 3.9 O - C O CH 2 CH 2 Carboxyl pK a = 4.2
Background image of page 6
8/31/09 7 Amino Acids: R-groups • Lysine (Lys, K) • Arginine (Arg, R) E) Positive at pH 7 (Basic) NH 3 + CH 2 CH 2 CH 2 CH 2 ε -Amino pK a = 10.5 2 C 2 + CH 2 CH 2 CH 2 Guanidino pK a = 12.5 Amino Acids: R-groups • Histidine (His, H) Imidazole pK a = 6.0 N N CH 2 H
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
8/31/09 8 Amino Acids: R-groups Amino Acids: R-groups (Polar)
Background image of page 8
8/31/09 9 Amino Acids: R-groups Amino Acids: R-groups Non- Polar Polar (Uncharged) Polar (+ve) Polar (-ve) Gly, G Ser, S Arg, R Glu, E Ala, A Thr, T Lys, K Asp, D Val, V Asn, N Leu, L Gln, Q Ile, I Tyr, Y Met, M Cys, C Pro, P His, H Phe, F Trp, W You are responsible for all 20 structures
Background image of page 9

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon