BSC-2010 Lecture Notes - Lecture 2: Enzyme Inhibitor, Allosteric Regulation, Competitive Inhibition

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15 Nov 2016
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
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
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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