Chapter03FALL05 - Chapter 3 - Amino Acids and Primary...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
Chapter 3 - Amino Acids and Primary Structure of Proteins Functions of proteins: 1- catalysts - enzymes for metabolic pathways 2- storage and transport - e.g. myoglobin and hemoglobin 3- structural - e.g. actin, myosin 4- mechanical work - movement of flagella and cilia, microtubule movement during mitosis, muscle contraction 5- decoding information - translation and gene expression 6- hormones and hormone receptors 7- specialized functions - e.g. antibodies Structure of amino acids There are 20 common amino acids called α -amino acids because they all have an amino (NH 3 + ) group and a carboxyl group (COOH) attached to C-2 carbon ( α carbon). At pH of 7, amino group is protonated (-NH 3 + ) and carboxyl group is ionized (COO - ). The amino acid is called a zwitterion . pKa of a carboxyl group = 1.8 - 2.5 pKa of a amino group = 8.7 - 10.7 The α carbon is chiral or asymmetric ( 4 different groups are attached to the carbon; exception is glycine.) Amino acids exist as stereoisomers (same molecular formula, but differ in arrangement of groups). Designated D (right) or L (left). Amino acids used in nature are of L configuration. carboxylate group at top --> points away side chain at bottom α amino group orientation determines NH 3 + on left = L NH 3 + on right = D
Background image of page 1

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

View Full DocumentRight Arrow Icon
6 Can also use RS system of nomenclature. Structures of 20 common amino acids: Amino acids are grouped based upon the properties and structures of side chains. 1) aliphatic (R groups consist of carbons and hydrogens) glycine - R=H smallest a.a. with no chiral center alanine - R=CH 3 methyl group valine R = branched; hydrophobic; important in protein folding leucine R= 4 carbon branched side chain isoleucine R = 2 chiral centers proline R = ring; puts bends or kinks in proteins; contains a secondary amino group 2) aromatic (R groups have phenyl ring) phenylalanine - very hydrophobic tyrosine - hydrophobic, but not as much because of polar groups tryptophan - “ Absorb UV light at 280 nm --> used to estimate [protein] 3) sulfur-containing R groups methionine - sulfur is internal (hydrophobic)
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 7

Chapter03FALL05 - Chapter 3 - Amino Acids and Primary...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online