Proteins

2008-2009

Proteins Structure:

Elements: C, H, O, N monomer = amino acids

20 different polymer = polypeptide

one or more polypeptide chains folded & bonded together

large & complexcomplex 3-D shape

Rubisco

hemoglobin

growthhormones

H2O

Amino acids Structure

central carbon amino group carboxyl group (acid) R group (side chain)

variable different for each aaResults in unique chemical

propertieslike 20 different letters of

an alphabetcan make many words

(proteins)

—N—H

HC—OH||O

R

|—C— |

H

Effect of different R groups:Nonpolar amino acids

nonpolar & hydrophobic

Effect of different R groups:Polar amino acids

polar or charged & hydrophilic

Ionizing in cellular watersH+ donors

Sulfur containing amino acids Form disulfide bridges

covalent cross links betweens sulfhydryls stabilizes 3-D structure

You wonderedwhy permssmell like rotten eggs?

H-S – S-H

Building proteins Peptide bonds

covalent bond between NH2 (amine) of one aa & COOH (carboxyl) of another

C–N bond

peptidebond

dehydration synthesis

H2O

4 Classes of Protein Structure

1. Primary Structure – aa sequence determined by gene (DNA)

Phenylalanine

**slight change in sequence can affect protein’s structure & its function just one aa change can make all the difference!**

2. Secondary Structure – folding due to interactions between adjacent (local) aa’s

a. Alpha (α) Helix b. Pleated Sheet

Secondary Structure of a Protein

3. Tertiary Structure

• Overall primary and secondary structure

• Hydrophobic interactions• H-bonds

• Disulfide bridges• Ionic bonds between opposite

charges

4. Quarternary Structure – more than one polypeptide bonded together

**Increased complexity = increased stability!**

Protein structure (review)

amino acid sequencepeptide bonds

1°

determinedby DNA

R groupsH bonds

R groupshydrophobic interactionsdisulfide bridges(H & ionic bonds)3°

multiple polypeptideshydrophobic interactions

4°

2°

Form determines function!!!

Conjugated Proteins Protein backbone with nonprotein group attached1. Chromoprotein – pigment molecule attached

Ex: Hemoglobin

2. “Glyco” & “Lipo”Proteins – in cell membrane; carb or lipid attached – used in cell identity

3. Nucleoproteins – proteins wrapped in DNAEx: histones (in chromosomes)

The Many Functions of Proteins Enzymatic Structural Transport Receptor Signalling Defense Movement (contractile) Storage