SAC 2 revision Flashcards
What is the lock and key model?
It is a model that suggests that the substrate has a very specific shape complementary to the enzyme is binds to. Only that specific enzyme with this shape can bind to the enzyme. It fits like a key into a lock.
What is the induced fit model?
It is a model that suggests that the enzyme can change shape slightly to better fit with substrate. It is more accurate than the lock and key model.
What is the role of enzymes?
They increase the rate of reaction by decreasing the activation energy.
What is the role of coenzymes?
Coenzymes do not bind at the main active site of the enzyme but at an allosteric site (another active site, not the main one). They are energy carriers and without them reactions could not occur.
What are the coenzymes involved in photosynthesis?
NADP+/NADPH and ADP+Pi/ATP
What are the coenzymes involved in respiration?
NAD+/NADH and ADP+Pi/ATP
What are the factors that affect enzyme function?
Temperature, pH, substrate concentration, enzyme concentration, competitive/non-competitive inhibitors
How does temperature affect enzyme function?
An enzyme has an optimum temperature.
If the temperature goes above the optimum, the enzyme’s active site denatures meaning the enzyme changes shape and the substrate cannot bind to the enzyme so the reaction cannot occur.
If the temperature goes below the optimum, there is less kinetic energy, meaning less collisions so the reaction will occur at a slower rate. The reaction can still occur but just at a slower rate.
How does pH affect enzyme function?
An enzyme has an optimum pH
An enzyme can denature above or below this optimum range. The enzyme’s active site denatures meaning the enzyme changes shape and the substrate cannot bind so the reaction cannot occur.
How does enzyme concentration affect enzyme function?
If enzyme concentration increases, it will increase the rate of reaction to a point until there is not enough substrate and then substrate concentration becomes a limiting factor. If there are more enzymes, more reactions can occur between the substrate and the enzyme. But if there are not enough substrate to the amount of enzymes, the reaction rate cannot increase and has reached the maximum point.
How does substrate concentration affect enzyme function?
If substrate concentration increases, it will increase the rate of reaction to a point until there is not enough enzymes and then enzyme concentration becomes a limiting factor. If there are more substrates, more reactions can occur between the substrate and the enzyme. But if there are not enough enzyme to the amount of substrate, the reaction rate cannot increase and has reached the maximum point.
How do competitive inhibitors affect enzyme function?
Competitive inhibitors bind to the main active site of an enzyme, blocking the substrate from binding. This means the reaction cannot occur. If there is an increase of substrate concentration, there is a chance of the inhibition to be overcome and the reaction to be able to occur.
How do non-competitive inhibitors affect enzyme function?
Non-competitive inhibitors bind to an allosteric site (another active site) of the enzyme. This causes the enzyme to change shape meaning the main active site is not complementary to the substrate and it cannot bind to the enzyme. This means no reaction can occur. The overall rate is slower.
What are the stages of photosynthesis?
Light dependent stage and the light independent stage (Calvin Cycle)
What is the word equation for photosynthesis?
carbon dioxide + water ———> glucose + oxygen + water
chlorophyll and light energy on the arrow
What is the chemical equation for photosynthesis?
6CO2 + 12H2O ———> C6H12O6 + 6O2 + 6H2O
chlorophyll and light energy on the arrow
What are the inputs of the light dependent stage?
water, NADP+, ADP+Pi
What are the outputs of the light dependent stage?
oxygen gas, NADPH (H+ ions), ATP
What happens in the light dependent stage?
The light energy is captured by the chlorophyll and used to split the water molecules into hydrogen ions and oxygen.
The oxygen gets released from the cell.
NADP+ collects H+ ions and ADP become ATP
What are the inputs of the light independent stage?
carbon dioxide, NADPH, ATP
What are the outputs of the light independent stage?
glucose, water, NADP+, ADP+Pi
What happens in the light independent stage (Calvin Cycle)
The NADPH carries H+ ions to the Calvin Cycle.
Rubisco binds to carbon dioxide to facilitate carbon fixation.
Glucose is produced.
As well as NADP+ and ADP
Where does the light dependent stage occur?
thylakoids, grana
Where does the light independent stage occur?
stroma
What is Rubisco and its role?
Rubisco is the main enzyme that facilitates the Calvin Cycle. It binds to carbon dioxide and controls the first step of the cycle, carbon fixation.
What are the issues with Rubisco? What is this process called?
Rubisco has the affinity to bind to oxygen instead of carbon dioxide. A process called photorespiration occurs. This decreases the rate of photosynthesis and this process is wasteful for the plant.
What makes Rubisco bind with oxygen?
Temperature - high temperatures can cause the active site of Rubisco to change shape and denature meaning it can bind with oxygen.
Substrate concentration - if there is a high amount of oxygen within the cells, Rubisco can bind to oxygen to decrease it. However this decreases the rate of photosynthesis as well.
