enzymes Flashcards
biological molecules
how do enzymes act as biological catalysts?
- each enzyme lowers activation energy of reaction it catalyses
- to speed up reaction (enzymes are proteins)
what does enzymes catalyse for?
- a wide range of intracellular and extracellular reactions that determine structures and functions from cellular to whole-organism level
describe the induced-fit model of enzyme action
- before the reaction, enzyme active site is not complementary to substrate
- substrate binds to the active site
- causing the active site to change shape slightly so its complementary to its substrate
- so enzyme-substrate complex forms
- causing bonds in substrate to stress when its brought closer together, lowering activation energy
describe how models of enzyme action have changed over time
- initially lock and key model which is now outdated
- active site a fixed shape, complementary to one substrate
-now induced-fit model
explain the specificity of enzymes
- specific tertiary structure determines shape of active site - dependent on sequence of amino acids (primary structure)
-active site is complementary to a specific substrate
-only this substrate can bind to active site, inducing fit and forming an enzyme-substrate complex
what does catabolic (breaking down) reactions require
- maltose + water→ alpha glucose + alpha glucose (with the enzyme maltase)
- the maltose + water require enough kinetic energy (Ek) to collide hard enough to react (break and form new bonds)
- this is called the activation energy
how does an enzyme work?
an enzyme works by forming an “enzyme-substrate complex” which strains bonds, lowering the activation energy which is the energy needed to break and form new bonds. This can be shown on a graph.
after the reaction, the enzyme remains unchanged and can continue to act on substrate
what does anabolic (building up) reactions require?
- ADP (adenosine diphosphate) + phosphate →(ATP synthase) ATP ( adenosine triphosphate) + water
- same enzyme works by bringing substrates closer together
-this lowers activation energy needed for the reactions to take place - glucose + water → CO2 + water + energy (ATP)
what is the equation for hydrogen peroxide?
- hydrogen peroxide is a toxic cellular waste product. it must be broken down.
- hydrogen peroxide → water + oxygen
- the arrow represents catalase
what does the general progress of reaction graph look like, with labels?
- -initially lots of substrate and empty active sites
- many enzyme substrate complexes can form
-reaction starts off fast - -less substrate, more product
-more difficult for enzyme substrate complexes to form
-reaction slows - no more substrate
- no enzyme substrate complexes
- reaction stopped
successful collisions: when enzyme-substrate complexes form
- no more substrate
what’s the calculation to mean rate of reaction?
mean rate= amount of product formed ÷ time taken to form product
describe and explain the effect of enzyme concentration on rates of enzyme-controlled reactions
● As enzyme concentration increases, rate of reaction increases
○ Enzyme concentration = limiting factor (excess substrate)
○ More enzymes so more available active sites
○ So more enzyme-substrate complexes form
● At a certain point, rate of reaction stops increasing / levels off
○ Substrate concentration = limiting factor (all substrates in use)
Describe and explain the effect of substrate concentration on
the rate of enzyme-controlled reactions
● As substrate concentration increases, rate of reaction increases
○ Substrate concentration = limiting factor (too few substrate
molecules to occupy all active sites)
○ More enzyme-substrate complexes form
● At a certain point, rate of reaction stops increasing / levels off
○ Enzyme concentration = limiting factor
○ As all active sites saturated / occupied (at a given time)
Describe and explain the effect of temperature on
the rate of enzyme-controlled reactions
● As temperature increases to optimum, rate of reaction increases
○ More kinetic energy
○ So more enzyme-substrate complexes form
● As temperature exceeds optimum, rate of reaction decreases
○ Enzymes denature - tertiary structure and active site change
shape
○ As hydrogen / ionic bonds break
○ So active site no longer complementary
○ So fewer enzyme-substrate complexes form
Describe and explain the effect of pH on
the rate of enzyme-controlled reactions
● As pH increases / decreases above / below an optimum, rate of
reaction decreases
○ Enzymes denature - tertiary structure and active site
change shape
○ As hydrogen / ionic bonds break
○ So active site no longer complementary
○ So fewer enzyme-substrate complexes form
Describe and explain the effect of concentration of competitive inhibitors on
the rate of enzyme-controlled reactions
● As concentration of competitive inhibitor increases, rate of
reaction decreases
○ molecule with a similar shape to substrate
○ Competes for / binds to active site
○ So substrates can’t bind
○ So fewer enzyme-substrate complexes form
● Increasing substrate concentration reduces effect of inhibitors
(dependent on relative concentrations of substrate and inhibitor)
what does the rates of reaction and volume of products produced graph look like with a competitive inhibitor?
graph 1:
-reaction slows
-competitive inhibitor binds to active site
-prevents enzyme substrate complexes from forming
graph 2:
-you can increase the rate of product formation by adding more substrate
-the additional substrates will out compete the inhibitor
what does the rates of reaction and volume of products produced graph look like with a non competitive inhibitor?
graph 1:
-reaction slows and odes not complete
-non competitive inhibitor binds to allosteric binding site
-active site changes shape permanently
-no enzyme substrate complexes form
graph 2:
-you cant increase the rate of product formation by adding more substrate
-the enzymes are out of action
-the only way to overcome this is to add more enzymes (new ones without non competitive inhibitor as it would overcome enzyme straight away)
