AP Biology Unit 3A

biological catalysts of enzymes

proteins; facilitation of chemical reactions; and highly specific

function of the bio catalyst “facilitation of chemical reactions”

• increases rate of reaction without being consumed or degraded

• reduces activation energy

• doesn’t change free energy released or required

• required for most bio reactions

function of the bio catalyst “highly specific”

enzyme and substrate binding is highly specific

substrate

• reactant that binds to enzyme(s)

• enzyme-substrate complex: temporary association

product

end result of reaction

active site

binding site for substrates

induced fit

substrate binding causes active site to change in conformation change (slightly)

• does not change primary/secondary/tertiary structure

properties of enzymes

• reaction specific

• not consumed in reaction

• affected by cellular condition

How do enzymes affect the rate of bio reactions

enzymes are biological catalysts that facilitate chemical reactions in cells by lowering the activation energy

how do enzymes lower the E_A barrier

• enzyme-substrate complex stabilizes the transition state

enzymes do not

affect the change in free energy

enzymes do

speed up reactions by lowering activation energy

how is hydrolysis relevant in enzymes

how is synthesis relevant in enzymes

catalysts are chemical agents that speed up reactions without being

consumed by the reaction

facts that affect enzyme function

• Salt concentration

• enzyme concentration

• pH levels

in a fixed substrate concentration

• increase in enzymes = increase in reaction rate

• more enzymes = more collisions with substrate

• reaction rate levels off (horizontal line on graph)

• [enzymes] = [substrates] 

• substrate becomes limiting factor

in a fixed enzyme concentration

• increase in substrates = increase in reaction rate

• more substrates = more collisions with enzyme

• reaction rate levels off

• enzymes become limiting factor

• all active sites are occupied

initial velocity

• higher frequency of substrate binding to enzyme’s active site

• the reaction decreases over time because product to substrate ratio increases

rate of reaction can be measured by

• product formation

• disappearance of substrate

overtime reaction decreases because

product to substrate (P/S) ratio increases; substrates slowly decrease as product increases

units for rate of reaction

M/sec

rate of reaction can be calculated using what formula

slope formula; using two points

substrates can be

consumed, denatured, broken, etc. 

• but NOT enzymes

the best temperature for an enzyme is where on the graph

the peak of the graph

if you keep increasing heat, the reaction will decline. why?

the proteins are fragile and will denature due to high temperature

the best pH for an enzyme is where on the graph

the peak of the graph; the enzyme will start to denature past the peak 

enzymes can be renatured in temp/pH levels by

putting it back in the most optimal temperature/pH level

once active site is denatured, the substrate

will no longer fit to the active site

positive control is

something that will give indicate a reaction

negative control is

something that will not indicate a reaction

denatured proteins can be used as 

negative controls

competitive inhibitor molecules

(irreversibly or reversibly) binds to the active site, but does not cause a reaction like a normal substrate would

• increase in substrate can reduce inhibition because it increases the chance the substrate will bind to the enzyme

• structurally identical to the enzyme/active site

noncompetitive inhibitor molecules

binds to the allosteric site, changing the activity of the enzyme, causing the substrate to no longer fit to the active site

• enzyme changes shape (conformation)

• increasing substrates does not reduce inhibition

• irreversible