2.4 enzymes Flashcards
explain the lock and key model of enzyme action
a specific indented area on the enzyme called the active site is where the substrate molecules fit.
They fit because the tertiary structure gives it a shape which is complimentary to the substrate
name 5 factors that affect the rate of enzyme controlled reactions
substrate concentration
enzyme concentration
pH
temperature
enzyme inhibitors
how does substrate concentration affect the rate of enzyme reaction
as substrate concentration increases so does the rate of reaction. This is because more enzyme-substrate complexes can occur and as as a result more product is formed.
As the substrate concentration increases further the reaction will reach a maximum (the saturation point). This is due to all the enzymes active sites being occupied with the substrate molecules and if any more substrate is added they can’t successfully collide and fit into the active site.
How does enzyme concentration affect the rate of enzyme reaction
As enzyme concentration increases more active sites become available which can increase the rate of successful collisions and ESCs. If the enzyme concentration continues to increase and the substrate concentration is fixed all the substrate molecules would have occupied an enzyme active site so by increasing the amount of enzymes there would be no impact on the rate of reaction.
how does temperature affect the rate of reaction
As temperature increases more kinetic energy will be gained and both molecules will move faster and the number of successful collisions will increase.
However, paste the optimum the large amount of kinetic energy may break the weak hydrogen bonds within the enzyme and alter its’ tertiary structure, changing the active site (denature) so no more ESC can occur as the substrate no longer fits
What is the temperature coefficient
refers to the increase in the rate of a process when the temperature increase by 10C
Q = rate +10C / rate at TC
How does pH affect the rate of reaction
A H+ ion is attracted to negatively charged ions.
Excess H+ ions can interfere with the hydrogen bonds within the enzymes tertiary structure and bond externally, changing its active site so the substrate no longer fits and no more ESC can occur.
How do competitive inhibitors work
Competitive inhibitors are substances whose molecules have a similar shape to the substrate and it occupies the active site so that less ESC can occur
How do non-competitive inhibitors work
they attach to the enzymes allosteric site and disrupt the enzymes tertiary structure and change its’ active site shape so the substrate molecules no longer fit and no more ESC can occur
What is end-product inhibition
cells do not need to accumulate too much of an end product, so the product of the last enzyme can act as an inhibitor to the first enzyme of the metabolic pathway, attaching to its allosteric site and changing the active site stopping the metabolic pathway.
When the concentration of the product falls it de-attaches from the enzyme and the metabolic pathway resumes
what are enzymes
enzymes are proteins which catalyse reaction in an organism and act as a biological catalyst
Define biological catalyst
Enzymes reduce activation energy required in a reaction so that there is no need to for extreme temperature and pH. They speed up metabolic reactions and aren’t used up in the reaction
explain the induced fit model of enzyme action
when the substrate molecules fit into the active site, the active site slightly changes shape to mould itself around the substrate
Give some examples of metabolic poisons and how they work
CYANIDE - inhibits aerobic respiration. CN- ions bind irreversibly to an enzyme found in mitochondria and inhibits the final stage of aerobic respiration, causing total cell failure
SNAKE VENOM - inhibits the enzyme AChE which is important at neurotransmitter synapses and breaks down ACh. If AChE is inhibited the ACh stays attached to the receptors and keeps muscles contracted
How do some medicinal drugs act as inhibitors
ASPIRIN-salicylic acid binds to enzymes that catalyse the formation of prostaglandins (cell signalling molecule) produced when tissues are infected or damaged
PROTEASE INHIBITORS (HIV) - Normally protease is used to cut viral RNA. If it is inhibited the RNA is not cut into smaller pieces so it can’t be implanted into the host cells DNA to replicate
