Enzymes Flashcards
(29 cards)
What are enzymes?
Globular proteins with complex and unique tertiary structures
they’re biological catalysts because they increase rate of a chemical reaction without being used up in the reaction itself
What is activation energy?
Energy required to start a reaction
How do enzymes speed up rate of reaction?
Lower activation energy for a chemical reaction meaning reactions are able to take place at lower temperatures
What are intracellular enzymes and give an example?
Enzymes acting within cells that produce them
catalase = catalyses breakdown of hydrogen peroxide into oxygen and water
What are extracellular enzymes and give an example?
Enzymes acting outside the cells that produce and secrete them
Amylase = secreted by salivary glands, pancreas, and small intestine to break down starch into maltose
How does an enzyme bind to a substrate?
1) enzymes unique tertiary structures determines shape of their active site which is complementary to substrate
2) substrate binds to active forming enzyme-substrate complex
3) temporary bonding between R groups within the active site and substrate lowering activation energy to help break down substrate into products
4) products released from the active site leaving enzyme free to be used again
What are the two models of enzyme action?
- induced fit
- lock and key model
What is the lock and key model?
Model suggests substrate fits perfectly into the enzyme’s active site in the same way that a key fits into a lock
What is the induced fit model?
Model suggests substrate does not fit perfectly into the enzyme’s active site
as substrate enters enzyme the active site changes shape slightly putting strain on the substrate’s bonds lowering activation energy
What causes enzymes to denature?
- extreme temperature
- extreme PH
How can extreme temperatures or PH’s cause enzyme denaturing?
Changes enzyme’s tertiary structure causing the active site to change shape so that the substrate no longer fits
means that enzyme-substrate complexes cannot be formed and the enzyme is denatured
What factors affect the rate of enzyme controlled reactions?
- temperature
- pH
- substrate concentration
- enzyme concentration
Describe and explain how temperature affects the rate of reactions?
1) as temp increases rate of reaction increases = molecules have more ke causing more collisions and enzyme-substrate complexes
2) maximum rate reached at the optimum temp = optimum temp is the temperature enzyme works fastest at
3) temp increases past optimum rate decreases then stops = too much ke causes active site to change shape and enzyme denatures
What is the temperature coefficient?
Q10 is a value showing how much rate of reaction changes when temperature is increased by 10°C
What is the calculation for temperature coefficient?
Q10 = R2 ÷ R1
R2 = rate of reaction at higher temp
R1 = rate of reaction at lower temperature
Describe and explain how PH affects the rate of reactions?
1) below optimum pH rate of reaction is low = acidic conditions (H+) ions break ionic/hydrogen bonds and denature enzymes
2) maximum rate of reactions reached at optimum PH = pH enzyme works fastest at
3) above optimum pH rate of reaction is low or zero = alkaline conditions (OH) ions break ionic/hydrogen bonds and denature enzymes
Describe and explain how substrate concentration affects rate of reaction?
1) as substrate conc increases reaction rate increases = more substrate molecules form more enzyme-substrate complexes
2) as substrate conc increases further rate plateus = saturation point reached when all active sites occupied by a substrate (enzyme conc becomes limiting factor)
Describe and explain how enzyme concentration affects rate of reaction?
1) as enzyme conc increases reaction are increases = more enzyme molecules form more enzyme-substrate complexes
2) as enzyme conc increases further rate plateus = all substrate molecules available are being acted upon (substrate conc becomes limiting factor)
What are enzyme inhibitors?
Molecules that bind to enzymes to reduce their activity
What are the 2 effects of enzyme inhibitors?
Reversible = form weak bonds (e.g hydrogen) with enzyme
Irreversible = form strong bonds (e.g covalent) with enzyme
What are the 2 types of enzyme inhibitors?
Competitive = bind to active site
Non-competitive = bind away from active site
Describe and explain how competitive inhibitors work?
Bind to active site of enzyme due to their similar shape to substrate preventing enzyme-substrate complexes
bind to active site of the enzyme preventing substrate from binding, reducing formation of enzyme-substrate complexes
decreases rate of enzyme catalysed reaction
What affect do most competitive inhibitors have?
Reversible as only temporarily bind to enzyme
How can competitive inhibitors be overcome?
By increasing substrate concentration competitive inhibitor effect is reduced
more likely that substrates will bind to active sites rather than inhibitor molecules
