S2- Enzymes Flashcards
a) What is activation energy?
b) What is the transition state?
c) What are enzymes? + what are their affects on chemical rxns
a) Minimum energy substrate must have for reaction to occur
b) high energy intermediate between substrate and product
c) biological catalysts that increase ROR by lowering activation energy (facilitate formation of transition state)
What are the key features of enzymes?
- highly specific
- unchanged after a reaction
- do not affect the rxn eqm
- increase ROR
- proteins
- may require cofactors
Clinically why are we interested in enzymes?
- inheritable genetic disorders
- overactive enzymes can cause disease
- measurement of enzyme activity for diagnosis
- inhibition of enzymes by drugs
a) What is the active site of an enzyme?
b) features of AS (5)
a) The place where the substrates bind and the chemical rxn occurs
b)
1. AS occupies small part of enzyme
2. formed by AAs from different parts of the primary sequence
3. AS are clefts or crevices
4. Two hypothesis: lock and key (AS is complementary to that of the substrate) or induced fit (substrate binds and causes change in shape forming AS)
5. substrates are normally bound to AS via non-covalent bonds
What is the Equation used to demonstrate how an enzyme works?
Enzyme + substrate Enzyme-substrate complex Enzyme + Product
a) How do reaction rates vary with enzyme concentration?
b) How do reaction rates vary with substrate concentration?
a) Linear pattern, as enzyme conc increaes rate of reaction directly increases as more enzyme-subsrate complexes will form as there is more Active sites
b) Rectangular hyperbola, velocity initially increases as more successful collisions but becomes constant as all the enzyme active sites are occupied and it reaches maximum velocity (VMAX)
What does the michaelis-menten model tell us about enzyme catalysis?
- Proposes that a specific enzyme-substrate complex is necessary intermediate for catalysis
- predicts a rectangular hyperbola for V vs [S]
V= Vmax[S]/ Km + [S] where Km= michaelis cosntant (M) and Vmax= maxmimal velocity (mol/min)
What is:
a) Vmax
b) Km
a) maximal rate when all enzyme active sites are saturated with substrate
b) substrate concentration that gives half maximal velocity (1/2 vmax)
a) What is the significance of Km?
b) What does a high Km mean?
c) What does a low Km mean?
a) km value gives a measure of affinity of an enzyme for its substrate
b) low affinity for substrate
c) high affinity for substrate
What is the lineweaver-burk plot?
- rearranges the michaelis menten equation into linear plot
- x intercept: -1/km
- y intercept: 1/vmax
a) What are enzyme inhibitors?
b) What are the types?
a) molecules that slow down or prevent an enzyme reactions including many drugs
b)
1. irreversible: bind very tightly, generally form covalent bonds (destroy function of enzymes)
- Reversible: non-covalent; can freely dissociate:
i) Competitive: binds at active site –> affects Km not Vmax
ii) Non-competitive: binds at another site on enzyme –> affects Vmax not Km
Outline the process of competitive inhibition
- The competitive inhibitor resembles the substrate
- it competes with the substrate for the AS
- Binds to AS hence reducing the proportion of enzyme molecules bound to substrate
- adding more substrate can overcome the effect of the inhibitor hence no affect on Vmax
- km increases
Outline the process of non-competitive inhibition
- the inhibitor binds at an alternative site and decreases the turnover number of the enzyme (no of substrate molecules converted into product when enzyme is fully saturated with substrate in a unit of time) thus lowering the vmax
- does not affect the km (affinity) of an enzyme for substrate as the substrate can still bind to the Active site
Summarise how i) Km and ii) vmax are affected during:
a) Competitive inhibition
b) Non-competitive inhibition
a) i) Km lowered, ii) vmax unaffected
b) i) km unaffected, ii) vmax lowered
