BMP: Enzymes 4 Flashcards
Enzyme naming
- Most commonly used enzyme names have the suffix “-ase” attached to the name of the substrate of the reaction. Eg: urease (urea), sucrase (sucrose), lactase (lactose).
- Or to a description of the action performed. Eg: lactate dehydrogenase, adenylate cyclase.
- Some enzymes retain trivial historic names which give no clues as to the associated enzyme reaction. Eg: Papain, pepsin, trypsin.
What are the 6 major classifications of enzymes? Examples of each
- Oxidoreductases: catalyse oxidation - reduction reactions e.g. LDH
- Transferases: Catalyse the transfer of C-, N-, P- containing groups e.g. Kinases, methyltransferases
- Hydrolases: catalyse bond cleave by the addition of water e.g. phosphatases
- Lyases: Catalyse bond cleavage of C-C, C-O, C-S and some C-N bonds e.g. pyruvate decarboxylases
- Isomerases: Catalyse the racemisation of optical or geometric isomers e.g. racemases, isomerases
- Ligases: Catalyse the formation of bonds between C and O, S or N bonds coupled with the hydrolyses of high energy phosphates e.g. carboxylases
What are enzymes?
Protein catalysts that increase th velocity of a reaction without being used up themselves
What is the Active site? what happens here?
A 3D complex which is complementray ti the substrate molecule.
The substrate binds to the AS to form a Ezyme-substrate complex (ES). This forms Enzyme-product (EP) which dissociates into E and P
E + S –> ES –> EP –> E + P
What is turn over?
The number of substrate molecules converted to product by one enzyme molecule per second
Discuss specicity in terms of enzymes
Enzymes are very specific and only interact with a small number of similarly shaped substrates and can only catalyse one type of reaction
Absolute specificity - Only interacts with one substrate molecule
Group specificity - catalyses a family of related compounds
stereospecificity - most enzymes can distinguish between enatimers
What are cofactors?
Non-protein cofactors which associate with enzymes and are essential for enzymatic activity
What are examples of cofactors?
- metal ions
- non-protein organic molecules called coenzymes e.g. vitamins or vitamin dervivatives
What does:
- Holoenyme
- Apoenzyme
- Prosthetic group mean?
- Refers to the enyzme and its cofactor
- refers to the enzyme portion of the holoenzyme
- A tightly bound coenzyme which does not dissocate from the enzyme
What are the 2 ways of viewing enzyme mechanism of action?
- Treats catalysis in terms of energy changes that occur during the reaction; enzymes provide an alternate, energetically favourable reaction pathway different from the non-catalysed reaction.
- Describes how the active site chemically facilitates catalysis.
What is activation energy?
Activation energy is the barrier between substrates and products. It is the difference between reactants (A) and a high energy transition state intermediate (T*) when forming product (B).
A <-> T* <-> B
The minimum energy required by the reacting species in order for a reaction to occur
What is reaction velocity?
The number of substrate molecules converted to product per unit time
What factors effect reaction velocity?
- Substrate concentration:
- Increasing [S] increases ROR as more enzyme active sites are bound. This begins to level off as enzyme becomes saturated and further increase has no effec t
- Temperature:
- Increasing temperature increases ROR, this is because more molecules have sufficent energy to overcome the energy barrier to form products. Too much heat can denature
- pH
- Different enzymes have optimum pHs. Extremeties of pH can lead to denaturing of enzymes. For enzyme-substrate interaction to occur there require specific groups to be ionised/ unionized
*
What i the reaction model?
Enzyme and substrate bind reversibilty to form ES complex whihc subsequently breaks down to form product and enzyme
E + S –(k1)–> E + P
km = k-1 + k2 / k1
What is the michealis-menten equation?
Vo = Vmax / Km + [S]
What assumptions is there?
- [S] is small is much greater than [E], so that the amount of substrate bound by the enzyme at any one time is small.
- [ES] does not change with time as it is in ‘steady state’.
- Only initial velocities are used in analysis of enzyme reactions as it is only at this time when the reaction is linear with time.
What does a low anf high km mean?
•The Michaelis constant (Km) is characteristic for of an enzyme and its substrate, and reflects the affinity of the enzyme for that substrate. Km is numerically equal to [S] at which the reaction velocity is at ½Vmax. Km does not vary with the concentration of enzyme.
–Small Km: A numerically small (low) Km reflects a high affinity of the enzyme for substrate because a low concentration of substrate is needed to half-saturate the enzyme i.e. to reach ½Vmax
–High Km: A numerically large (high) Km reflects a low affinity for the substrate because a high concentration is required to half-saturate the enzyme.
What is ROR related too?
Directly proportional to enzyme conc at all [S]
What is the order of reaction during michealis-menten plot?
- When [S] much lower than km the reaction velocity is roughly proportional to [S]. First order
- When [S] is much greater than km the reaction is equal to Vm and velocity constant. Zero order
What is the lineweaver burk equation?
What is an inhibitor?
Any substance that can dimish the velocity of an enxyme catalysed reaction
How do reversible inhibitors bind to enzymes?
How is this reversd?
- Non-covaently
- •Dilution of the enzyme-inhibitor complex results in dissociation of the reversibly-bound inhibitor and recovery of enzyme activity.
What are irreversbile inhibitors? How do they bind?
- Irreversible inhibition occurs when aninhibited enzyme does not regain activity upon dilution of the enzyme-inhibitor complex.
- Some irreversible inhibitors act by forming covalent bonds with specific groups of enzymes
What happens during competitive inhibition?
What happens to km and vmax?
- •Occurs when the inhibitor binds reversibly to the same site that the substrate would normally occupy and, therefore competes with the substrate for that site.
