BMS100_BCH1-08_F22_Proteins_Pre-learning_STUDENT.pptx

Lecture 5: Proteins + Enzymes 1 Pre-learning Dr. Rhea Hurnik BMS 100 Outline Proteins Classification Shape, composition Structure: Primary, secondary, tertiary, quaternary Denaturation Enzymes 1 General properties Mechanisms Acid Base, Covalent catalysis Cofactors and Coenzymes Effect of tem...

Lecture 5: Proteins + Enzymes 1 Pre-learning Dr. Rhea Hurnik BMS 100 Outline Proteins Classification Shape, composition Structure: Primary, secondary, tertiary, quaternary Denaturation Enzymes 1 General properties Mechanisms Acid Base, Covalent catalysis Cofactors and Coenzymes Effect of temperatures and pH Regulation Protein classification: Shape • Proteins can be classified based on their shape or their composition:  A) Shape: Fibrous Protein Globular Protein Long and rod-shaped Compact & spherical Generally has structural function • Provides strength Generally has dynamic function • Eg. Enzymes to catalyze reactions • Eg. Carrier proteins Often insoluble in water Often soluble in water Eg. Keratin, Collagen Eg. Enzymes, albumin, hemoglobin Protein classification: composition • Proteins can be classified based on their shape or their composition:  B) Composition: • Simple – composed of only amino acids • Conjugated – composed on protein portion & non-protein portion  Protein portion – contains only amino acids  Non-protein portion – called prosthetic group • A conjugated protein without its prosthetic group is called “apoprotein” Protein Structure • There are 4 important levels of protein structure:  Primary  Secondary: alpha helical or beta sheet  Tertiary: how it folds in 3D space  Quaternary Protein Structure Primary • Primary protein structure  Polypeptide chain  Linear sequence of amino acids • Synthesized via translation from mRNA transcript derived from a gene (DNA)  Amino acids are held together via peptide bond Protein Structure Secondary • Regularly repeating backbone conformations formed by H-bonds between carboxyl and amino groups  Two main types • Alpha helix • Beta pleated sheet Protein Structure Secondary • Secondary Protein structure  Alpha Helix: • Each carboxyl group Hbonds with an amino group 4 amino acids away • Forms rigid, rod-like structures • Often depicted schematically like piece of curled ribbon Protein Structure Secondary • Secondary protein structure  Beta-pleated sheet • Two or more polypeptide segments of a protein line up side-by side  Held together by Hbonds between distant carboxyl and amino groups • Often depicted schematically with tip pointing in C-terminal direction Protein Structure Secondary • Super-secondary structure within a protein are combination of alpha helices and/or beta-pleated sheets  Here are some examples: Protein Structure Tertiary • Three-dimensional folded structure created by side chain interactions, such as:  H-bonds  Salt bridges  Disulfide bridges  Hydrophobic interactions Protein Structure Tertiary Pause the video and try to name the interactions between amino acid side chains H2 N Protein Structure Tertiary H2 N Salt bridge Protein Structure Tertiary • Disulfide bonds are very important in extracellular proteins  Strong bonds: help protect the protein from denaturation during changes in blood pH or salt concentrations  What is an example of an extracellular protein that is held together by disulfide bonds? Protein Structure Quaternary • Many proteins have multiple polypeptide subunits  The association of all the subunits form the quaternary structure of a protein • Now it is a functional protein! • Consider hemoglobin: • 4 subunits: • 2 Beta subunits • 2 alpha subunits • The final 3-D shape of a protein dictates its function Protein Structure Quaternary • A couple definitions:  A protein composed of two subunits is called a dimer  A protein composed a several subunits is called an oligomer • Hemoglobin is an example of an oligomer (tetramer)  A protein composed of many subunits is called a multimer  A protomer is any repeating structural unit within a multimeric protein • Hemoglobin has a pair of αβ protomers Protein Folding • Following protein translation, proteins are folding into their secondary, tertiary, and quaternary shapes. • Chaperones are proteins that help other proteins: • Fold into their correct shape • Get to their correct cellular locations  Common chaperones are the hsp (heat shock proteins) which can: • Bind and stabilize portions of the protein not yet folded  Chaperones are eventually released via ATP hydrolysis • Refold proteins partially unfolded due to stress (could be heat)