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BIOL Exam I - Ex. 4

Enzyme Activity and Environmental Effects

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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