Enzymes
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60 Terms
What does an enzyme do?
Catalyze biochemical reactions by lowering activation energy
Which three bonds can form between polypeptides in a tertiary protein structure, creating its shape?
Hydrogen bonds, ionic bonds, disulfide bridge
What is metabolism?
The sum of all chemical reactions occurring in a cell or organism
Why are enzymes essential for metabolism?
They allow metabolic reactions to occur fast enough at normal body temperatures
How do enzymes affect structure and function?
Their specific tertiary structure determines their function
Why would metabolism be impossible without enzymes?
Most reactions would be too slow due to high activation energy
What is an intracellular enzyme?
An enzyme that catalyses reactions inside cells
Give an example of an intracellular enzyme
Catalase
What reaction does catalase catalyse?
The breakdown of hydrogen peroxide into water and oxygen
What is an extracellular enzyme?
An enzyme that catalyses reactions outside cells
Give an example of an extracellular enzyme
Amylase
What reaction does amylase catalyse?
The breakdown of starch into maltose
Why are digestive enzymes extracellular?
Digestion occurs outside cells in the gut lumen
What is an active site?
The region of an enzyme where the substrate binds
induced fit model of enzyme action,
Why are enzymes specific?
The active site is complementary to the substrate
What is an enzyme–substrate complex?
A temporary complex formed when a substrate binds to an enzyme
What is an enzyme–product complex?
A complex formed just before products are released
What happens to the enzyme after product release?
It is unchanged and can be reused
What does the lock-and-key hypothesis state?
The substrate fits exactly into the active site
What is a limitation of the lock-and-key model?
It does not explain flexibility of the active site
What does the induced-fit hypothesis state?
The active site changes shape when the substrate binds
Why is induced-fit considered more accurate?
It explains enzyme flexibility and specificity
What is activation energy?
The minimum energy needed for a reaction to occur
How do enzymes lower activation energy?
By stabilising the transition state and forming enzyme
Do enzymes change the overall energy of a reaction?
No, they only lower activation energy
How does temperature affect enzyme activity at low temperatures?
Molecules have less kinetic energy and fewer collisions occur
Why does enzyme activity increase with temperature initially?
Increased kinetic energy leads to more enzyme–substrate collisions
Why does enzyme activity decrease above the optimum temperature?
The enzyme denatures
What does denaturation mean?
The tertiary structure changes and the active site loses shape
What is the temperature coefficient (Q10)?
The factor by which reaction rate increases for a 10°C rise
What is the Q10 formula?
Q10
What is the typical Q10 value for enzyme-controlled reactions?
About 2
Why does pH affect enzyme activity?
It alters ionic and hydrogen bonds in the enzyme
What happens if pH is too high or too low?
The enzyme may denature
Why do different enzymes have different optimum pH values?
They function in different environments
Why does enzyme activity increase as substrate concentration increases?
More frequent enzyme–substrate collisions
Why does enzyme activity eventually plateau?
All active sites are occupied
What is the maximum rate of reaction called?
Vmax
What happens if enzyme concentration is increased (substrate in excess)?
Rate of reaction increases
Why does increasing enzyme concentration increase rate?
More active sites are available
Why are serial dilutions used in enzyme experiments?
To create a range of concentrations accurately
Why must variables be controlled in enzyme experiments?
To ensure valid and reliable results
Why is a water bath used in temperature investigations?
To maintain a constant temperature
What is a cofactor?
A non-protein substance required for enzyme activity
Give an example of an inorganic cofactor
Chloride ions
Which enzyme requires chloride ions as a cofactor?
Amylase
What is a coenzyme?
An organic molecule that assists enzyme action
What are vitamins often used for in enzymes?
As sources of coenzymes
What is an enzyme inhibitor?
A substance that reduces enzyme activity
What is a competitive inhibitor?
A molecule that binds to the active site
Why does a competitive inhibitor reduce enzyme activity?
It competes with the substrate
How can competitive inhibition be reduced?
By increasing substrate concentration
What is a non-competitive inhibitor?
A molecule that binds away from the active site
Why does a non-competitive inhibitor reduce enzyme activity?
It changes the shape of the active site
Can non-competitive inhibition be reversed by adding substrate?
No
What is reversible inhibition?
Inhibitor can detach from the enzyme
What is irreversible inhibition?
Inhibitor permanently binds to the enzyme
What is end-product inhibition?
When the final product inhibits an earlier enzyme in a pathway
Why is end-product inhibition important?
Prevents overproduction and saves energy
