PROTEINS structure, function and properties.pptx

Describes protein structure, function and their properties

1. sssSaphan Protein structure, function and properties By George Kazibwe

2. Proteins: Structure Large molecules that are polymers of amino acids Present in every cell in the body They are involved in most of the body’s functions and life processes- versatile molecules! The sequence of amino acids is determined by DNA

3. Proteins : structure Cont’d Amino acid chains can be classified basing on the number of amino acid residues in a chain: Peptides: fewer than 50 amino acids Dipeptides: 2 amino acid residues Tripeptides: 3 amino acid residues Oligopeptides: 4-10 amino acid residues Polypeptides: more than 10 amino acid residues Proteins: more than 50 amino acid residues Typically 100 to 10,000 amino acids are linked together Chains are synthesized based on specific bodily DNA

4. Functions of Proteins Structure – collagen in skin and bone Catalysis - enzymes in metabolism Movement -actin and myosin in muscle contraction Transport -hemoglobin in oxygen transport, albumin in fatty acids transport Hormones -cell growth, metabolism Protection -antibodies, spermine & spermidine Storage - ferritin for iron storage in the liver Regulation -rhodopsin in visual process Cellular identity-surface markers e.g TCRs Cell signaling/communication-e.g. insulin Organization of cell molecules- chaperones Energy sources- gluconeogenic and ketogenic amino acids Acid base balance- due to amphoteric properties Fluid balance- osmotic pressure

5. Amino Acid Structure Amino acids are relatively simple molecules containing both an amino group and acid group with exception of Proline- imino group. More than 10o natural amino acids exist but only 20 alpha amino acids are involved in protein synthesis

6. Amino acid structure cont’d R-group or side chain nomenclature The R-group defines the behavior of amino acids It also identifies an amino acid

7. Amino Acid structure cont’d Alpha Vs Beta amino acids What does L-stand for?

8. General properties of amino acids (aas) As it is the case with other organic compounds, aa properties are greatly determined by the functional groups They can join to form proteins Have acidic and basic functional groups Have a chiral nature with exception of glycine Alanine

9. The magic 20 amino acids Constituents of proteins Essential Vs Non-essential amino acids *-branched amino acids

10. Remember the 10 Essential aas Arginine is essential in children. Why?

11. 4 amino acid subdivisions Amino acids are divided into four subgroups depending on the nature of the side chain; Non polar (hydrophobic) & uncharged Polar (hydrophilic) & uncharged Acidic (polar and charged)-negatively charged Basic (polar and charged)-positively charged Three letter abbreviations make it easier to relate the name of the specific amino acid e.g. Ala- Alanine, Leu- Leucine etc

12. Amino acid subdivisions Cont’d

13. Zwitterionic amino acids An amino acid with both positive & negative regions whose net charge is zero is called a zwitterion . The pH at which an amino acid forms a zwitterion is called an isoelectric point.

14. Combining Amino acids Amino acids are joined together by a peptide bond Amino acids in a chain are called amino acid residues

15. Levels of Protein Structure There are four levels of protein structure: Primary Secondary Tertiary Quaternary Primary structure Defines the sequence of amino acids that comprise a protein It serves as a foundation upon which all higher levels of protein structure build.

16. Levels of Protein Structure cont’d Secondary structure -due to protein folding Alpha helices (cork screw structures) and Beta pleated sheets (zig-zag structures) are common secondary protein structures Forces: hydrogen bonds, disulfide bonds, hydrophobic and ionic interactions

17. Levels of Protein Structure Cont’d Tertiary structure It is a three-dimensional conformation forming distinct independently folded regions called domains. The domains are created from a single polypeptide chain.

18. Levels of protein structure cont’d Quaternary structure Only applies to proteins that are composed of more than one polypeptide chain. Each of the polypeptide is called a subunit.

19. END OF PART I Assignment. List down examples of secondary, tertiary and quaternary proteins highlighting their functions in biological systems. Explain why the primary protein does not play any functions in biological systems. Give a detailed account of why the metabolism of branched chain amino acids is of special concern in humans. With examples, explain the role of amino acids in neurotransmission. Explain why proteins are referred to as versatile molecules.