Exam 2: Enzymes Flashcards
What is catalysis
the lowering of activation energy of a reaction causing it to speed up.
What are the characteristics of an enzyme (6)
- Increases the rate of a reaction
- Can catalyze both a forward and backward reaction.
- They can be present in low concentrations
- Transition state of reacting substrates bound in enzyme active site
- they obey the laws of thermodynamics
- They can be regulated.
Do not effect equilibrium
highly specific to substrates
What is a transition state
structural form of substrate with highest energy state along the complete rxn pathway
What is the activation energy
the difference between the transition state and reactants
What is an active site
unique binding site on the enzyme for a substrate to bind, a cleft or crevice in enzyme.
How does the active site help with catalysis
the R groups of the AAs in the active site interact with the transition state helping speed up rxn. The shape of the active site can force a substrate to adapt its conformation to be similar to the transition state
What is the difference between catalysis in vitro and in vivo
the crowding effects in a cell make the activation energy levels lower, rxn is faster
Explain enzyme specificity
before thought of as lock and key. Now induced fit: substrate bonds noncovalently to active site, changing conformation of the enzyme to make it perfectly fit to substrate.
What` are the 2 classes of enzyme cofactors
metal ions: Mg, Zn, Co
coenzymes: small organic molecules usually not covalently attached.
What are the 6 types of enzymes, how are they classified
classified by type of rxn.
oxidoreductase: oxidation reduction rxns
transferase: transfers a group from a mol to another
hydrolase: cleaves a bond using H2O
lyase: removes or add groups to a double bond
ligase: forms a new bond
isomerase: rearrangement
What groups does transferase often move?
amino, carbonyl, carboxyl, methyl, phosphate, acetyl
Name an example of an oxidoreductase enzyme
alcohol dehydrogenase
Name an example of a transferase enzyme
hexokinase
Name an example of a hydrolase enzyme
chymotrypsin
Name an example of a lyase enzyme
pyruvate decarboxylase
Name an example of an isomerase enzyme
alanine racemase
Name an example of a ligase enzyme
pyruvate carboxylase
What is km
michaelis menten constant. measures enzyme affinity for substrate. [substrate at 1/2 Vmax]
What does a large and small km mean
large: enzyme has low affinity
small: enzyme has high affinity
What is kcat
the # of substrate mols converted to product per unit of time by an enzyme mol under saturating conditions (steady state). vmax/[E total]
What does a large and small kcat mean
large: more product per unit of time
small: less product per unit of time
what kind of kcat and km values does the ideal enzyme have
small km and large kcat
What is the formula for the specificity constant? what does it represent
the overall efficiency of the enzyme
kcat/km
What are the values for the y and x axis on the michaelis menten plot
x: [S]
Y: Vo
What are the values for the y and x axis on the Lineweaver Burke Plot
X: 1/Vo
Y: 1/[S]
What is the formula for the slope of a lineweaver burke plot
slope=km/Vmax
What is the x and y intercept on the lineweaver burke plot
y intercept: 1/Vmax
x intercept: -1/km
What are the 2 kinds of multisubstrate rxns
- sequential: can be ordered ( enzyme binds to substrate A then B must go next, 1 specific order) or random ( 2 substrates but can be added in any order, rate can change depending on order)
- Double displacement: ping pong, enzymes can have altered conformations, rxns happen one at a time but they rely on each other
What are the 2 types of enzyme inhibitors
irreversible: less common naturally, covalent bonding enzyme permanently inhibited
reversible: inhibitor binds reversibly to enzyme usually noncovalent bonds