1. Levels of Protein Structure 16.5

2. Videos
Chaperone assisted formation
proteine structure
more chaperones

3. 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

4. 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

5. 2o-Secondary Structure
Interaction between Amino- and Carboxyl groups residues from the peptide backbone forming
H-Bonds N-H…….O=C

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

7. 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)

8. 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

9. 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

10. 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!!!!

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

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

14. 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….

15. 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

16. 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…

17. 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

18. 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

20. 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