1. Amino Acids, Proteins & Enzymes Chapter 16
DE CHEMISTRY – King William HS
Amino Acids, Proteins & Enzymes Chapter 16

2. Amino Acids Building blocks of proteins
Central carbon atom bonded to two functional groups (ammonium & carboxylate) called the a carbon
The a carbon is also bonded to hydrogen and a side chain
Different side chains = different amino acids

3. Amino acid structure

4. Different amino acids

5. Classification of amino acids
Nonpolar  R = hydrogen, alkyl or aromatic group = hydrophobic
Polar  R = hydroxyl, thiol or amide group = hydrophilic
Acidic  R = carboxylate group
Basic  R = amino group which ionized to give ammonium

6. Amino acid stereoisomers
All a carbon are attached to four different atoms (EXCEPT glycine)…so they are chiral!
Amino acids can be labeled as D and L stereoisomers

7. Amino acids as acids and bases
Isoelectric point = pH where amino acid is neutral (usually between )

8. Proteins Linked amino acids through peptide bonds
Peptide bond – an amide bond that forms when the –COO- group of one amino acid reacts with the –NH3+ of another amino acid
Dipeptide = two amino acids
Tripeptide = three amino acids
Polypeptide = many amino acids
N-terminal amino acid (far left amino acid and has a free NH3+ group

9. Peptide bonds
C-terminal end amino acid (far right and has a free COO- group

10. Naming Peptides

11. Primary structure of the protein
Protein – polypeptide of 50 or more amino acids
Primary structure – sequence of amino acids held together

12. Secondary structure of proteins
Secondary – the geometry (shape) of the chain (helix or sheet)
Alpha helix looks like a spiral staircase
Beta pleated sheet look like sheets of paper (les common than alpha helix)
Triple helix has three peptide chains woven together (EX: Collagen – the most abundant protein in the body – about 1/3 of proteins in vertebrates)

13. Alpha (a) Helix

14. Beta (b) Pleated Sheets

15. Triple helix

16. Tertiary Structure
Attractions and repulsions between R groups of amino acids in the polypeptide chain
1. Hydrophobic interactions
2. Hydrophilic interactions
3. Salt bridge
4. Hydrogen bonding
5. Disulfide bonds

17. Tertiary Structures

18. Globular Proteins
Globular – spherical in shape because polypeptide chains fold over on top of each other because of R groups interactions (tertiary structure)
1. cell synthesis, transport & metabolism
EX: myoglobin (stores O2 in skeletal muscles)
1. high [ ] in sea mammals (can stay
under water longer

19. Fibrous Proteins
Long, thin fiber shaped proteins usually involved in cell/tissue structure
1. alpha keratins (hair, wool, skin & nails)  alpha helix
2. beta keratins (feathers of birds & scales or reptiles)  beta pleated sheets

20. Quaternary Structure
Contains two or more tertiary subunits (protein chains)
Held together by the same interactions as tertiary structures
EX: Hemoglobin

21. Hemoglobin
Has four subunits (a2b2) and they must all be combined to transport oxygen (4 molecules)

22. Denaturation of Proteins
Disruption/destruction of secondary and tertiary structures of a protein
1. increase in temperature
2. change in pH
No longer biologically active
Proteins unfold

23. Enzymes
Biological catalysts (increases the rate of reaction by lowering energy of activation)
Enzyme names end with “ase”
Most are globular proteins

24. Types of Enzymes

25. Factors affecting enzyme activity
Temperature (directly proportional)
1. optimal temperature (37oC)
2. > 50oC (protein shape destroyed…
therefore enzyme activity = zero) pH
1. optimal pH (7.4)
2. changes destroy structure and enzyme no longer binds to substrate

26. Enzyme inhibition Inhibitors cause enzymes to lose catalytic ability
Competitive inhibitors – structure and polarity similar to substrate
Noncompetitive inhibitors – structure does not resemble the substrate

27. Competitive inhibitors

28. Noncompetitive inhibitors

29. Irreversible inhibition
Enzyme permanently loses all catalytic capability