Levels of Protein Structure 16.5

Videos Chaperone assisted formation proteine structure more chaperones

Peptide/Protein Formation Peptide: small, up to 50 AA Proteins: large, several 100 AA and/or multiple peptide chains grouped together Ribosomes translates m-RNA into AA sequence: 3 nucleotide = 1 AA Also called the triplet code

1o Primary Structure Number and order of AA Reflected by peptide name Example: Alanylglycylserine 1o structure is the basis for all other levels of peptide/protein structure

2o-Secondary Structure Interaction between Amino- and Carboxyl groups residues from the peptide backbone forming H-Bonds N-H…….O=C

Typical 2nd structural patterns Alpha Helix b) Beta pleated sheet collagen, wool silk

3o - Tertiary Structure governed by R-side chain interactions There are 4 typical R-side chain interactions Hydrophobic interactions: at the center of a protein- non-polar side chains are attracted to each other (Ex: Ala and Leu) VdW 2. Hydrophilic interaction: at the periphery of a protein facing water based environment– polar side chains, forming H-bonds (Ser with Thr)

3o structure 3. Salt bridges/ionic bonds attraction between acidic and basic side chains (Ex: Lys with Glu) 4. Disulfide Bridges: covalent bonds -S-S- covalent bond formation two Cysteine react: -SH + HS- → -S-S- + H2 stabilizes the 3-D confirmation of large proteins, strongest of all interaction

Final Protein Structure Is the most energetic stable form a protein can from based on it’s AA sequence Remember: at 37oC the kinetic energy is high and the wear and tear from function substantial

4o – Quaternary Structure Multiple peptide chains aggregate together to form a large functional unit Governed by R-side chain interactions (see 3o structure…) Not all proteins have it!!!!

Globular Proteins Have a compact, spherical 3-D shape Very stable, function as enzymes and transport molecules Hemoglobin Enzyme

Fibrous Proteins Long, thin, fiber like shapes Used as structural components: wool, skin, scales, feathers, hair keratin collagen

What influences protein structure? pH (all interactions are based on environmental pH: blood/tissue pH 7.4, stomach pH 1-2…) mutations Silent M: base exchange leads to same AA (wobble) Point M: base exchange leads to new AA, different folding, non-functional Protein: sickle cell anemia, cystic fibrosis….

Denaturation Change in 3-D structure that renders a protein non-functional Exposure to non-physiological environment Disrupts 2nd, 3rd, 4th level of protein structure Generally: all proteins are sensitive especially to acid: The stomach has pH 1 and is foremost designed to digest The protein portion of food

The two sides of denaturation 1. Pepsin: digestive enzyme in the stomach is fully functional only at pH 1 – it denatures at pH 7.4 Overuse of anti-acids renders pepsin non-functional!!! 2. Salivary Amylase: digestive enzyme in the mouth is fully functional at pH 7.4 is denatured when it enters the stomach…

Generally Normal proteins are sensitive to heat, solvents, salt concentrations, acids, bases They are not sensitive to cold (not beyond freezing point though!) Proteins are always kept on ice in the laboratory

Thermal Denaturation Cooking (heating) is a first step in denaturing native proteins in our food –helps with digestion Raw foods have enzymes from lysosomes in cells that when broken up help with digestion Raw food movement: eating raw food adds more native enzymes to digestive tract

Perming or Straightening Hair Hair structure (smooth or curly) is determined by dissulfide bridges in certain places of the keratin Can be changed by forcing the hair in a certain position then breaking (reducing agents) and reforming (oxidizing agents) disulfide bridges