BSC-2010 Lecture Notes - Lecture 2: Enzyme Inhibitor, Allosteric Regulation, Competitive Inhibition
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•competitive inhibition: binds at the active site; blocks substrate binding
•some pharmaceuticals, poisons, etc
•noncompetitive inhibition: binds at other location of protein; changes shape so that the
substrate no longer binds to active site
•allosteric regulation: a regulatory molecule binds to a protein at one site (not active site) and
affects the protein’s function at another site; may inhibit or stimulate an enzyme’s activity
•most allosterically regulated enzymes contain multiple subunits (multiple polypeptides;
quaternary structure)
•each subunit has its own active site
•activator: stabilizes active enzyme
•inhibitor: stabilizes inactive enzyme
•enzymes are proteins encoded by genes (DNA)
•changes (mutations) in genes lead to changes in amino acid composition of an enzyme
•altered amino acids in enzymes may result in novel enzyme activity or altered substrate
specificity (particularly near active site)
•under new environmental conditions a novel form of an enzyme may be favored
•ex: 6 amino acid changes improved substrate binding & breakdown of E. coli
•regulation of enzyme activity helps control metabolism
•genes that produce particular enzymes can be turned on/off (on = more, off = less)
•regulating activity of enzymes already in cell w/o producing more/less
• cooperativity: structural change such that entire complex is stabilized; increases the
likelihood of substrate binding to other sites; something happening at one subunit influences
activity at other subunits
•Diffusion: random (net) movement of molecules from a region of high concentration to low
concentrate
•molecules tend to spread out in available space
•driven by kinetic energy (thermal motion/heat)
•the warmer the glass of water the faster the diffusional process will happen
•rate of diffusion depends on concentration gradient and molecular size
•diffusion across a membrane - molecules cross barrier randomly through pores until
concentrations are equal on both sides
•at dynamic equilibrium: as many molecules pass one way as cross in the other direction
• a substance diffuses down its concentration gradient
•in the absence of other forces, substance diffuses from regions of high to low concentration
•creates randomized mixture
•spontaneous
•decreases free energy (∆ G < 0) and increases entropy
• in general, each substance independently diffuses down its own concentration gradient
•passive diffusion of small molecules across phospholipid bilayers: (excluding proteins)
•gases & small hydrophobic molecules - easily pass through hydrophobic core
•small uncharged polar molecules - move through bilayer less rapidly
•large uncharged polar molecules - too big to pass through on their own
•ions - charged, cannot pass through hydrophobic core
•charged polar molecules - cannot pass through hydrophobic core
• phospholipid bilayer introduces selective permeability to a biological molecule
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