BGM1002/L06 Enzymes II Flashcards
Name the 5 mechanisms of enzyme catalysis.
Proximity
Orientation
Strain/distortion
Acid-base catalysis
Covalent catalysis
Describe proximity in enzyme catalysis.
How closely packed substrate molecules are
Describe orientation in enzyme catalysis.
Ensuring substrates have the correct relative orientation
Describe strain/distortion in enzyme catalysis
Binding puts a strain on the bond making it easier for the reaction to occur
Describe acid-base catalysis in enzyme catalysis.
Protons are donated/accepted or hydroxyls generated
Overcomes very low concentrations of reactive molecules in environment
Describe covalent catalysis in enzyme catalysis.
Temporary covalent bond formation between enzymes and substrates
What does the interaction between enzyme and substrate depend on in terms of enzyme structure?
Specific 3D shape of active site
Hydrogen bonds
Name the 2 models for ligand interaction.
Lock and key
Induced fit
Describe the lock and key hypothesis.
Binding site of enzyme is complementary to substrate shape
Describe the induced fit hypothesis.
Contact between part of binding site and substrate induces a change in shape of active site and bind to substrate
What type of bond does the enzyme urease catalyse?
Esterase bond
What type of enzymes are in EC1?
Oxidoreductases
Oxidation/reduction reactions
What type of enzymes are in EC2?
Transferases
Transfer of one functional group from one substrate to another
What type of enzymes are in EC3?
Hydrolases
Formation of two products from one substrate by hydrolysis
What type of enzymes are in EC4?
Lyases
Non-hydrolytic addition/removal of groups/ cleavage of bonds
What type of enzymes are in EC5?
Isomerases
Intramolecular rearrangement
What types of enzymes are in EC6?
Ligases
Joining of two molecules requiring energy
What type of enzymes are in EC7?
Translocases
Movement of ions or molecules across membranes
What is Kcat?
Enzyme turnover number
Number of substrate molecules converted to product by 1 enzyme in 1 second
How can enzyme activity be measured?
Measure disappearance of substrate
Measure appearance of product
When is enzyme rate fastest?
In the first moments of a reaction
At low [S], what determines rate of reaction?
Number of substrate molecules
What occurs as [S] increases?
Higher chance of enzyme colliding with a substrate and catalysis occurring
Higher proportion of substrate molecules will have bound to an active site at any one time
What is the relationship between rate of reaction and substrate concentration for a 1st order reaction?
Directly proportional
What is the Michaelis and Menten equation?
v = (Vmax[S])/(Km+[S])
What is Vmax?
The maximal rate of reaction when all enzymes are saturated with substrate
How is the Michaelis-Menten equation derived?
ES=K1[E][S]
ES=(k1+k2)[ES]
k1[E][S]=(k1+k2)[ES]
([E][S])/[ES]=(k1+k2)/k1
What does Km measure?
Stability of the ES complex
What is the relationship between ES stability and Km?
Inversely proportional
What is the relationship between Km and Vmax?
Km causes V = 0.5Vmax
When does Vmax occur?
At infinite [S]
How is Vmax found?
Fit data to non-linear least squares fitting programme
Use a Lineweaver-Burk plot or MM curve fitting
