Lecture no. 2 basics of biochemistry -
- 2. Course grade distribution Final Exam 40% Mid Term Exam 20% Quizzes 20% Assignments 20% Total 100%
- 8. Proteins Proteins are polymers of amino acids Each has a unique 3D shape Amino acid sequences vary Proteins are major component of cell parts The provide: support and structural components Several types of proteins are identified: receptor, contractile, defense, enzymes, structural
- 9. Building Blocks: Amino Acids There are 20 different types of amino acids All have this general formula The R group is a variable group
- 11. Polar vs. Non-polar Amino Acids Some amino acids are polar while some are non-polar
- 12. Amino acids may be either polar or non-polar depending on the composition of their side chain Polar amino acids have hydrophilic R groups, while non-polar amino acids have hydrophobic R groups
- 13. The localization of polar and non-polar amino acids will be determined by the type of protein and its function: Water soluble proteins: •Non-polar amino acids tend to be found in the center of the molecule (stabilize the structure) •Polar amino acids tend to be located on the protein surface (capable of interacting with water molecules)
- 15. Membrane-bound proteins: •Non-polar amino acids tend to be located on the regions of the surface in contact with the membrane •Polar amino acids will generally line interior pores (to create hydrophilic channels)
- 16. Significance of polar & non-polar amino acids polar amino acids non-polar amino acids Hydrophilic can make hydrogen bonds found in hydrophilic channels & parts of proteins projecting from membranes found on surface of water- soluble proteins hydrophobic forms van der Waals (hydrophobic interactions) with other hydrophobic amino acids found in proteins in interior of membranes found in interior of water- soluble proteins
- 17. Peptide Bonds Proteins are formed by condensation A peptide bond is formed
- 18. Four levels of protein structure
- 19. Primary Structure Primary structure is a chain of amino acids number & unique sequence of amino acids determine the properties of primary structure each position is occupied by one of 20 different amino acids sequence of amino acids is determined by DNA sequence in genes linked by peptide bonds
- 20. Secondary structure formed by interaction between amino and carboxyl i.e. -NH and -C=O groups weak hydrogen bonds are formed between – H & = O there are two types: a-helix and b-sheet α- helix formed / polypeptide coils up e.g. sheep wool β- pleated sheet formed e.g. silk in spider web regular repeated folding of amino acid chain secondary structure is stabilized by hydrogen bonds
- 21. Tertiary structure These are globular proteins with irregular conformation tertiary structure is the folding up of the polypeptide chain, secondary structure or alpha helix it gives three dimensional globular shape i.e. shape of active site the structure is stabilized by disulphide bridges, hydrogen, ionic& hydrophobic bonds tertiary structure used as enzymes to catalyze biochemical reactions
- 22. Quaternary structure made of several polypeptide subunits joined together they maybe conjugated proteins i.e. proteins which combine with a prosthetic group (non- protein molecules) prosthetic groups includes: metals e.g. iron in haemoglobin, nucleic acids as in ribosomes , carbohydrates as in glycoprotein or lipids as in glycolipids
- 23. Denaturation of Proteins change in protein’s usual regular structure due to: High temp Change in pH Addition of organic solvent (alcohol, acetone) These factors break the bonds that stabilize the structure
- 24. Protein Functions Function Examples Structure Transport Enzymes Movement Hormones Antibodies storage – collagen/keratin/fibrin – myoglobin/hemoglobin, bind & transport oxygen – lysozyme, speeding up metabolic reactions – actin (and myosin tropomyosin (and troponin) – insulin, regulate blood glucose – immunoglobulin – albumin in egg, casein in milk