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BIOL Exam I - Ex. 4
Enzyme Activity and Environmental Effects
| Question | Answer |
|---|---|
| enzyme | - the name will usually end in -ase (ex. catalase, alpha-amylase, tyrosinase) - protein that typically catalyzes (facilitates) reactions - not altered or consumed by the reaction |
| Why do reactions need to be ‘facilitated’? | - most biological chemical reactions only occur at meaningful rates when in the presence of an enzyme because of the activation energy barrier - basically, a certain amount of E is required to start a chemical reaction; enzymes lower that |
| What changes in the presence of the enzyme? | the activation energy (E.A) |
| active site | the region of an enzyme where substrate molecules bind and undergo a chemical reaction |
| substrate | - the material upon which an enzyme acts - what gets converted into products |
| Enzymes bind and stress reactants to catalyze reactions through ___, ___, and ___. | - orientation - physical strain - chemical change |
| What affects rates of enzyme controlled reactions? | - the physical and chemical environment of the enzyme (pH, temperature, etc.) - availability of necessary co-factor - presence of molecules that act as inhibitors - relative concentration of substrate, enzyme, and product |
| Because pH also influences shape and therefore reaction rate, each enzyme has a(n) ___. | optimal pH |
| How does temperature affect enzyme reaction rate? | - as temp. increases, molecules move faster, so collisions between substrates and active sites occur more often - however, at some point, thermal agitation begins to disrupt the weak bonds holding the protein together and the protein eventually denatures |
| Some enzymes require ___ to function normally. These are either metal ions or small organic molecules called ___. | - cofactors - coenzymes |
| How does substrate concentration (SC) affect enzyme reaction rate? | - the rate of product formation increases linearly at low SC - the reaction rate reaches maximum speed at high SC (called V.max) - at V.max, all active sites on the enzymes are occupied, so no more product can be made |
| What is tyrosinase? What are some examples of its effect? | - an enzyme that catalyzes the biosynthesis of the pigment melanin from the amino acid tyrosine - skin coloration, browning of fruits |
| What is the cofactor of tyrosinase? | copper ions |
| Explain how dopachrome is produced. | - in the presence of O2, tyrosinase (E) catalyzes the hydroxylation of tyrosine into DOPA - E then catalyzes DOPA into dopaquinone - dopaquinone then spontaneously converts into dopachrome |
| You can monitor the activity of tyrosinase by looking at the color of the solution. Over time, what do you think will happen to the color of a DOPA solution after the addition of tyrosinase? | - the solution will begin clear and then turn brown - will get darker the longer the reaction proceeds |
| spectrophotometer | an instrument which measures the amount of light (of a specificed wavelength) which passes through a medium |
| How does a spectrophotometer work? | - a cuvette containing the solution is inserted - light passes thru the cuvette/solution and then strikes a detector - detector records what light is transmitted - using this info, the wavelengths that were absorbed can be determined |
| Once you find a product's peak absorbance (or maximum absorbance wavelength) what do you use it for? | to measure enzyme activity |
| What does tyrosinase convert more of: DOPA or tyrosine? | tyrosinase is much better at converting DOPA to dopaquinone than it is at converting tyrosine to DOPA |
| In exercise 4, where did you find the enzyme? The substrate? | - the enzyme tyrosinase was found in a potato - the substrate (DOPA) was in a stock solution |
| serial dilution | - prepared when the set of dilutions range over at least two orders of magnitude - geometric progression - ex: 20 mM -> 10 -> 5 -> 2.5 -> 1.25 mM |
| denaturation of an enzyme | - the loss of catalytic activity when placed in a hostile environment - enzyme remains physically intact (just modified) |
| What is a blank and what is it used for? | - contains all of the components of the solution except the test substance - to calibrate a spectrophotometer |
| In section 4.2, you used a blank containing a buffer solution and potato homogenate (but no DOPA) to calibrate the spectrophotometer. Why is this blank necessary? | - to be able to detect JUST the effect of E on ab. (not reactants or buffer), the spec. must be zeroed using a solution w/ everything but DOPA - when the cuvette w/ E is placed in the spec. any change in ab. that is detected is due solely to the product |
| Your hypothesis is: "Lowering the pH of solution containing tyrosinase will decrease the rate at which it catalyzes the production of dopachrome from DOPA." What is the null hypothesis? Negative/positive controls? Independent/dependent variables? | - NH: "Lowering the pH will not affect the enzymatic activity of tyrosinase." - NC: no enzyme run (buffer + DOPA) - PC: normal run (buffer + DOPA + tyrosinase) - IV: pH of solutions - DV: rate of reaction / dopachrome production |
| In lab you used the SpectroVis Plus Spectrophotometer to measure the light that was absorbed by dopachrome, a dark orange/brown molecule. Is a solution that appears dark orange in color absorbing orange wavelengths of light? | - no, it is REFLECTING orange wavelengths of light - (it is absorbing blue wavelengths of light; ~470 nm) |
Created by:
jessica.gvc
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