Pharos university Faculty of Allied Medical SCIENCE Biochemistry 1 (MLBC-201)

1. Pharos universityFaculty of Allied Medical SCIENCEBiochemistry 1(MLBC-201) Dr. Tarek El Sewedy Department of Medical Laboratory Technology Faculty of Allied Medical Sciences

2. Lecture 6 Structure And Function of proteins

3. Intended Learning Outcomes By the end of this lecture, students will learn: Protein structure , function , reactions.

4. Lecture Content • Levels of Protein structure: Primary, Secondary, Tertiary and Quaternary. • Protein structure • Classification of proteins. • Hydrolysis of proteins. • Denaturation of proteins.

5. Proteins • Proteins are Macromolecules consisting of long sequences of amino acids in peptidelinkage. • Protein accounts for almost 20% of total body weight. • The human body is made up of approximately 100 trillion cells - each one has a specific function. • Each cell has thousands of different proteins, which together make the cell do its job - the proteins are tiny machines within the cell. • One gram of protein or carbohydrate contains 4 calories, while one gram of fat has 9 calories.

6. Levels of protein structure • There are 4 levels of protein structure: • Primary • Secondary • Tertiary • Quaternary

7. 1. Primary structure of proteins • Describes the order of the amino acids joined together to make the protein (exact sequence of amino acids before folding). • The end of the peptide chain with the -NH2 group is known as the N-terminal, and the end with the -COOH group is the C-terminal

8. 2. Secondary Structure • It is the simple folding of a protein to create simple structures. • The secondary structure of a protein or polypeptide is due to hydrogen bonds forming between amide and carboxyl groups. • There are two possible types of secondary structure: • Alpha helix, the hydrogen bonding causes the polypeptide to twist into a helix. • Beta sheet the hydrogen bonding enables the polypeptide to fold back and forth upon itself like a pleated sheet.

9. Tertiary structure • Refers to the three-dimensional structure of the entire polypeptide chain. • result from four different bonds: • Ionic interactions • Hydrogen bonds • van der Waals forces • Disulphidebond

10. Quaternary Structure • It is the interaction between several chains of polypeptide subunits. • Not all proteins have quaternary structure, since they might be functional as monomers. • The quaternary structure is stabilized by the same range of interactions as the tertiary structure. • Hemoglobin is an example of a heterotetramer

11. Proteins could be classified by 3. structure • Simple • Conjugated • Glycoprotein: Immunogloulin. • Metalloprotein: Hemoglobin • Nucleoprotein: RNA bound protein • Phosphoprotein:casein • Lipoprotein: Low density lipoprotein (LDL), HDL. 1.Shape 2.Function • Globular • Fibrous • Catalyticas enzyme • Structural as collagen, keratin • storage as ferritin (store iron). • Protective as immunoglobulins • Regulatory : hormones as insulin • Communication as neurotransmitters • Motionas actin/myosin; in muscle • Transporter proteins as hemoglobin. • Carrier as albumin.

12. Fibrous proteins • Waterinsoluble and found as structural materials, e.g. collagen, keratin. Globular proteins • Compact, roughly spherical, water soluble and comprise all other types of protein as albumins and globulins.

13. Hydrolysis of proteins • Hydrolysis of proteins results in breaking down the peptide bonds to give amino acids thus it disrupts the primary structure of protein . • Hydrolysis can be achieved by Enzymes as Proteases. • Biological role of hydrolysis: • Convert inactiveprohormonesinto active hormones. ex; Proinsulin (inactive) → Insulin (active). • Digestion of protein by enzyme as trypsin and pepsin.

14. Inactive form Hydrolysis Active form

15. Protein denaturation It is a process in which proteins can lose their structures and function, without breaking the peptide bonds bydenaturing agents such as: • Heat, U.V radiation. • Heavy metal as mercury. • Soaps. • Organic acids as acetic acid. • Strong acids and bases as sulfuric acid and sodium hydroxide. Note:Denaturation disrupts 2ry,3ry,4ry structure of protein not 1ry structure.

16. All proteins have unique shapes that define their roles and interaction with other proteins. • Environmental factors and genetic mutations can affect a protein's structure, or three-dimensional shape, causing it to misfold. • Misfoldedproteins can no longer perform their functions leading to various diseases. • Misfolded proteins often clump together, forming aggregates. • The aggregates are toxic to some cells such as neurons and lead to diseases such as Alzheimer's Disease.

17. Students selected for assignment

18. ASSIGNMENTS • Selected students are requested to prepare slides about one of the following topics (To be delivered before next lecture): • Digestion of proteins • Essential amino acids. • Non essential amino acids • Physical properties of amino acids. • Chemical properties of amino acids. • Disease resulting from disturbance in amino acid metabolism. • Ketone bodies and amino acids • Translation of RNA

19. Suggested readings: Principles of Biochemistry, Donald J. Voet, Judith G. Voet, Charlotte W. pratt; Willey, 3rd ed.