2.4 - Enzymes Flashcards
What is an enzyme?
A biological catalyst. They speed up metabolic reactions in living organisms by lowering the required activation energy and are not used up during the reaction.
How is activation energy lowered?
- Enzyme holds two substrate molecules together so that they can bond more easily
- Fitting into active site puts strain on bonds of substrate so they can be broken more easily.
Outline the induced fit model.
- Substrate and enzyme molecules have their own Eₖ and are moving. They collide randomly.
- Substrate molecule binds to an enzyme’s active site, forming an enzyme-substrate complex.
- Enzymes reduce Eₐ by holding substrate in a way that causes the reaction to occur more easily.
- Enzyme-product complex is formed.
- The products no longer fit the shape of the active site and move out. Enzyme is free to catalyse the same reaction with other substrate molecules.
What is an intracellular enzyme?
An enzyme made and retained inside the cell. e.g. catalase.
What is an extracellular enzyme?
An enzyme made and retained outside of the cell. e.g. amylase.
List 3 factors affecting enzyme activity.
- Temperature
- pH
- Enzyme concentration
How does temperature affect enzyme activity?
- As temp. increases, so does Eₖ and no. of successful collisions therefore increasing RoR.
- Optimum temperature is reached when enzyme activity is at its greatest.
- When temperature is too high vibrations break bonds which hold the enzyme’s shape together. This causes irreversible change to the shape of the active site and the enzyme denatures. Enzyme activity decreases.`
What is the temperature coefficient?
Q₁₀ - shows how much the RoR changes when the temperature is raised by 10°C.
At temps. before the optimum, a Q₁₀ value of 2 means that the rate doubles every 10°C increase.
Most enzymes have a Q₁₀ value of 2.
How do you calculate Q₁₀?
Q₁₀ = Rate at higher temp. ÷ Rate at lower temp.
How does pH affect enzyme activity?
As pH is moved away from the optimum enzyme activity decreases and enzymes denature.
H⁺ and OH⁻ ions in strong acids/alkalis break ionic bonds which hold tertiary structure in place.
Examples of enzyme pH adaptation
Pepsin works best in acidic conditions (stomach/intestines) - pH 2
Salivary amylase tends to work best in neutral conditions (mouth) - pH 6
Alkaline phosphatase tends to work best in alkaline conditions - pH 9
How does enzyme concentration affect enzyme activity?
When the substrate conc. is less than enzyme conc. RoR is limited.
When substrate conc. is equal to enzyme conc. maximum RoR is reached.
When substrate conc. is greater than enzyme conc. there is no change to the RoR, it remains at max.
What is a cofactor?
- A non-protein substance which binds to an enzyme for the enzyme to work.
- They are often inorganic molecules or ions. e.g. Cl⁻
- They help the substrate and enzyme bind but do bot directly participate in the reaction.
- They are not used up or changed in any way.
What is a coenzyme?
- An organic cofactor.
- They participate in the reaction and are changed by it.
- Often act as carriers moving chemicals between enzymes.
- Continually recycled during the process.
What is a prosthetic group?
A cofactor which is tightly bound to an enzyme.
e.g. Zn⁺ ions are a prosthetic group for Carbonic Anhydrase. The Zn⁺ ions are a permanent part of the enzyme’s active site.
