Biology 172 Lecture 6

lower Vmax (fewer products in a given time) (fewer active sites)

increase [S] to a maximum rate (velocity, Vmax)

• Environmental Factors
• Irreversible Inhibition
• Reversible Inhibition
• Allosteric Enzymes

kinetic energy

• inhibitor binds to enzyme by covalent bonds, conformation is altered
• e.g nerve gas

• Competive inhibitor
• Noncompetive inhibitor

blocks the active site

• Compete with S for active site of enzyme Often resemble S
• Bind to enzyme with weaker bonds

have knowledge of active site / "S" structure

• Molecule binds away from active site and alters active site function
• NOT overcome by changes in substrate concentration (i.e Vmax will be LOWER)
• Reversible and non-reversible (covalent modification enzyme)

a regulatory molecule binds away from the active site.

other site

Percisely Regulated

the R-group of amino acids. For example, none of the R-groups can absorb visible light, or bind oxygen (O2) as a carrier.

non-protein factors that can work with protein to provide a broader range of chemistries at active sites, allowing enzymes to catalyze a wider range of reactions

• small non-protein molecules required for an enzyme to function normally.
• Usually inorganic (metal) ions

• Organic cofactors: NAD, CoA, vitamins
• Derived form vitamins - hence the dietary requirement
• Provide enzymes with a broader range of catalytic reactions

• Competitive inhibitors
• Most of the rest are non-competitive inhibitors

synthesizes cholesterol and many other metabolites

reductase is an enzyme that catalyzes the first step in the pathway

• HMG-CoA reductase uses HMG-CoA as a substrate
• Decreases blood cholesterol.
• Its mechanism of action is to inhibit cellular synthesis of cholesterol.
• When cellular synthesis of cholesterol is decreased with Lipitor, cells respond by taking up cholestrol from the blood

Lipitor, Zocor, Crestor, Pravachol are all competitive inhibitors of HMG-CoA reductase

• Reverse transcriptase is a key enzyme for HIV replication
• Multiple AIDS drug target this enzyme for inhibition

competitive inhibitor, binds at active site

non-competitive inhibitor, binds adjacent to active site

• Fatty Acids
• Triglycerides
• Phospholipids
• Other Lipids

• Not polymers
• Mostly composed of hydrocarbon
• Mostly hydrophobic
• Fuel storage, membranes, hormones
• Very diverse class of biological molecules. Waves, some pigments, vit A, vit D, cholesterol
• Store a LOT of energy - so release a lot of energy when broken down

• Hydrocarbon chains with terminal carboxyl group
• May be saturated (no double bonds) or unsaturated (with double bonds)
• Not water soluble

fluidity

• no double-bonds in hydrocarbon chain
• solid at room temperature

• double-bonds in hydrocarbon chain
• liquid or oil = more fluid

glycerol linked by ester linkages to 3 acids

condensation (dehydration) reaction

linkage between glycerol and a fatty acid

Triacylglycerol = fats

• like triacylglycerides, but phosphate-containing compound replaces one fatty acid
• Have polar part (hydrophilic hear) and a non-polar part (hydrophobic tail)
• major component of membranes / make membranes

both hydrophilic and hydrophobic regions

• Passive Transport
• Active Transport

• provide permeability barriers for the cell
• composed of lipid bilayer (mostly phospholipids)

• Length and degree of saturation of the phospholipid tails
• Cholesterol
• Temperature

• Phospholipids "drift" within one side of the bilayer
• Fluidity and permeability is enhanced by unsaturated fatty acid tails
• cholesterol (a steroid) stabilizes the membrane

• Amphipathic
• Stabilizes membranes by interacting with fatty acid tails of phospholipids

• From one species to another
• From one organelle type to another
• Phospholipids are different on each side of the bilayer
• Proteins are different on each side of the bilayer
• Different inside and outside faces
• Different lipids in the bilayer and different proteins on the cytoplasmic and extracellular sides of the membrane

cytoplasmic side when it fuses

outside (extracellular) face of plasma membrane