Protein Structure & Function

Presented By:

Shyla Neher

February 4, 2004

Hierarchical Structure of Proteins• A proteins structure determines it’s function• Primary

– Linear sequence of amino acid residues• Peptide• Polypeptide

• Secondary– Results in the folding of localized parts of a

polypeptide chain– Stabilized by H bonding

• α-helix• β-sheet• turns

• Tertiary– Three dimensional arrangement of all amino acid

residues

– Results from hydrophobic interactions and hydrogen bonding

– Structure undergoes fluctuation

• Quaternary– Proteins that consist of 2 or more polypeptides

– The number and position of the polypeptide

Protein Folding & Modification

• Most proteins form into their Native confirmation• Folding is promoted by chaperones

– Molecular Chaperones

– Chaperonins

• Nearly all proteins undergo chemical modification after synthesis on a ribosome– Acetylation

– Phosphorylation

– Methylation

Enzymes

• Enzymes function to catalyze reactions– Lowers activation energy

– Increases rate by 106 - 1012

– Does not change equilibrium of reaction

– Catalysis occurs at the active site

• Enzymes show high specificity

Catalytic Action of an Enzyme

V max = Maximal enzyme velocityKm = Enzyme affinity for its substrate

Regulation of Protein Function

• Allosteric Mechanisms• Phosphorylation and Dephosphorylation• Proteolytic Activation• Compartmentation• pH and Temperature• Prosthetic Groups• Cofactors

Protein Purification

• In order to study protein it must be purified• Methods of Purification

– Centrifugation

– Electrophoresis

– Liquid Chromatography

– Enzyme & Antibody Assays

– Mass Spectrometry

– X-ray Crystallography

THANK YOU!