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 velocity
Km = 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!