Flashcards in Enzymes Deck (59)
What is the activation energy?
The minimum amount of energy required for a reaction to occur
Why are enzymes better for increasing the rate of a reaction rather than temperature and concentration
You want to maintain the temperature and concentration at a set point
What are enzymes?
Biological catalysts that increase the rate of reaction by lowering the activation energy
Why don't enzymes affect the reaction equilibrium
It catalysed the reaction equally forwards and backwards
What is the active site?
The place where substrates bind and the chemical reaction occurs
What is the lock and key hypothesis
Where active sites are complementary in shape to the substrate
What is the INDUCED fit hypothesis
Binding of substrates cause conformational changes in the enzyme
What type of bonds are formed between the active site and substrate?
Week hydrogen binds which hold the substrate in the correct orientation but also allows it to be released
What does the Michaelis-Menton model propose?
That a specific complex between the enzyme and the substrate is a necessary intermediate. Represents that the rate is related to concentration of substrate
What is Vmax
The maximal rate when all enzymes active sites are saturated with substrate
What is Km?
The substrate concentration that gives half maximal velocity
What does a low Km value tell you?
The enzyme has a high affinity for the substrate
What is the lineweaver-Burk plot
Reciprocal graph that gives -1/Km at the X intercept and 1/Vmax at the y intercept
What is an enzyme inhibitor?
Molecules that slow down or prevent an enzyme reaction
What are the 2 types of inhibitors?
1. Irreversible - bind very tightly forming covalent bonds
2. Reversible - can freely dissociate as they don't form covalent bonds
What are the 2 types of reversible inhibitors
1- competitive (binds to active site. Affects Km not Vmax)
2- Non-competitive (bind to another site in the enzyme. Affects Vmax not Km)
Why do competitive inhibitors not affect Vmax?
Adding enough substrate will overcome the affect of the inhibitor so the maximum rate can still be reached
Why do competitive inhibitors affect Km?
The inhibitor competes with the substrate for the active site so the affinity decreases
Why do competitive inhibitors lower Vmax?
They decrease the turnover rate of the enzyme
Why does the active site of an enzyme only occur a small area?
A large proportion of the enzyme is needed to hold the shape of the active site
What is the units of enzyme activity
Micromoles per minute per litre
What affect does doubling the enzyme concentration have on the rate
It doubles the rate of reaction
Why does enzyme activity stay the same despite changes the enzyme concentration
The enzymes always work to the same activity. The rate at which they work doesn't not change.
What are the 2 long term regulation methods for enzymes
1. Change in protein synthesis
2. Change in protein degradation
What are the 2 short term regulation methods for enzymes
1. Changes in substate/product concentration
2. Change in enzyme conformation
State 3 ways in which enzyme conformation can be changed
1. Allosteric regulation
2. Covalent modification
3. Proteolytic cleavage
What graph shape do allosteric enzymes show
Why do allosteric enzymes show a sigmoidal graph for rate vs substrate concentration.
As the enzyme can exist in 2 forms (T and R state)
What do allosteric activators do
Increase the proportion of enzyme in the R state