BIOLOGY 173 Study Guide - Quiz Guide: Dna Replication, Reaction Rate, Catechol

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Enzyme: proteins that catalyze biological reactions
Never consumed in the reaction
Bind to substrate and stabilize reaction intermediate
Lower activation energy
Tertiary/Secondary
Ionic bonds tertiary
Polypeptide bonds secondary
Heat disrupts tertiary structutre
Measuring enzyme rate
disappearance /appearance of reactant or product
Change in concentration vs time
Polyphenoloxidase: potato enzyme
Catechol → orthoquinone (colored)
Orthoquinone: slows growth of fungi
Gets into insects intestines and causes problems in development
As rxn progresses, absorption increases (spectrophotometry)
Chemical defense of potatoes
It has starch, other things want starch
Turns brown upon injury
Lab 1 - Reaction Rate
1 both enzyme-substrate, 1 enzyme, 1 substrate
Find best enzyme volume
Effect of enzyme concentration of reaction rate
½, ¼, ⅛
higher reaction rate → plateaus (low substrate)
Effect of substrate concentration on reaction rate
Substrate dilution
Higher reaction rate → plateaus
(limited enzyme, all active sites
filled)
Reaction Rate
Double reactants → double reaction rate
Rate is determined by limiting reactant
Product vs time diff than substrate vs rate
Graph Stuff
Vmax = max rate of rxn
All active sites are filled
Enzymes are saturated
High Vmax means enzyme is
processing a lot of substrate into
product
Km = substrate concentration @ half
maximal rate
Varies with temp, pH, inhibitors
Measures affinity of enzyme for
substrate
Lower Km the more likely the enzyme is operating at its Vmax
Good affinity for substrate
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Will operate even at low substrate
Competitive Inhibition
Competes for active site
Similar to substrate
Vmax is the same plateaus later
Km will be higher
Takes more substrate to get the same amount of product bec some active sites are used
up by inhibitor
Noncompetitive inhibition
Changes shape of active site
Acts on enzyme, not active site
Lower Vmax
May or may not change Km
Depends on whether substrate binding/processing are affected
Can be reversible or irreversible
Inhibitors
Potassium Arsenite
disulfide groups
Non-competitive
Nothing much happens, tells the
nature of the protein
Para-hydrobenzoic acid
Resembles catechol
Competitive
Potassium cyanide (KCN) → chelate
Reacts with iron/copper
Non-competitive
PTU → chelate
Reacts with copper
Competitive
Stronger inhibitor
Focuses only on copper
EDTA / Citric Acid → chelate
Reacts with iron or copper if present
non - competitive
Sodium Chloride → chelate
Denature protein by interfering with ionic bonds
Non-competitive
Takes a lot of salt to inhibit
Determining competitive/non
Compare rate at low/high [substrate]
w/ and w/out inhibitor → % inhibition
% inhibition @ high [subs] < @ low → competitive
% inhibition @ high [subs] = @ low → non-competitive
Look at graph
If its competitive, the changing of substrate concentration will change the degree of
inhibition.
Low substrate concentration means higher inhibition.
Non competitive doesn’t matter, substrate concentration is irrelevant.
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Document Summary

Bind to substrate and stabilize reaction intermediate. 1 both enzyme-substrate, 1 enzyme, 1 substrate. Effect of enzyme concentration of reaction rate. Higher reaction rate plateaus (low substrate) Effect of substrate concentration on reaction rate. Gets into insects intestines and causes problems in development. Higher reaction rate plateaus (limited enzyme, all active sites filled) Product vs time diff than substrate vs rate. High vmax means enzyme is processing a lot of substrate into product. Km = substrate concentration @ half maximal rate. Lower km the more likely the enzyme is operating at its vmax. Takes more substrate to get the same amount of product bec some active sites are used up by inhibitor. Nothing much happens, tells the nature of the protein. Depends on whether substrate binding/processing are affected. Reacts with iron or copper if present. Denature protein by interfering with ionic bonds. Takes a lot of salt to inhibit. W/ and w/out inhibitor % inhibition.

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