Enzymes Flashcards
What does catalysis acctually mean
Catalyse making and breaking covalent bonds between substrates at faster reaction rates
Reactions occur at a lower conditions eg ph or temp
How do you calculate keq equilibrium constant
K+1 (conc of 2 substrates)
/
K-1 (conc of products in reversible reaction)
Eg 100x100 units
/
2 x 2 units - the units left in reversible reaction
What is Keq correlated to
With energy released by the reaction
GIBBS FREE ENERGY - change from substrate to products
What does the Gibbs free energy value need to be for substrates to become products
-ve
Substrate must be at a higher energy level than end products
What is transition state
A form of substrate which is at high energy
If the transition state isn’t lowered eg by enzymes the reaction won’t reach equilibrium
Why don’t reactions happen spontaneously without enzymes
They need enzymes to lower activation energy to lower the transition state of the substrate
What does the ES complex reduce in order for reaction to reach equilibrium
Reduces transition state
This increases speed equilibrium is reached
Do active sites change after reaction?
No they are unaltered catalysts
There are 5 ways enzymes catalyse reactions - name them
1- proximity- substrates closer together
2- orientation- align correct bonds in substrates
3- strain - in induced fit the AS puts strain on bonds in substrate
4- acid base catalysis
5- covalent catalysis
How do enzymes use acid base catalysis to catalyse a reaction
Protons (H+) or hydroxyls (OH-) get donated
They are added into active site (introduced to charged side chains)
This overcomes the low concentration of reactive molecules
What is covalent cataclysms
When enzyme active sites temporarily bond covalently to substrates
There are 4 ways enzymes can be specific in their reactions - explain them
1- absolute - only work with 1 substrate
2- bond- the substrates need a specific bond eg oxygen bonds in esterase
3- group- only work on Eg hexose sugars
4- stereo - DISTINGUISH OPTIMAL ISOMERS eg L or D amino acids
There are 6 types of enzyme reaction, briefly explain them
1- oxidase/reductase - OIL RIG
2- transferase - transfer other groups to the substrates eg phosphates
3- lyases- rearrange bonds in substrates
4- hydrolases- insert H20 for hydrolysis eg of peptide bonds
5- isomerases - change the position of atoms
6- ligases/syntheses - synthesis of new molecules
What is the turnover number (Kcat)
Number of substrates converted by 1 enzyme in 1 second
Name an enzyme with very high Kcat
A and B amylase
Why do you always measure initial rate of reaction
Because the substrate conc is known
What increases rate of reaction
Increased substrate concentration- more ES complexes
What does V proportional to S mean
Velocity /rate of reaction depends on substrate concentration
What is it called when eventually all Es complexes are formed
Saturation of enzymes
What is the Michaelis menton equation for velocity
V = Vmax x (s) / km + (s)
What is v max
Maximum velocity shown when enzymes have reached saturation - infinite substrate concentration
V max could never be found so who do scientists find it
Plot the graph and the concentrations they did get to and then use computer to predict v max
Inhibitors can be irreversible and reversible, explain how some are irreversible
They bind to active site via covalent bonds
This prevents substrate binding
They bind to side chains such as cysteine or serine (reactive)
What side chains do irreversible inhibitors bind to in active site via covalent bond
Reactive chains like serine or cysteine
