What are enzymes
a molecular catalyst in a biological system. Most but not all are proteins
Properties of enzymes:
- Have immense catalytic power
- Highly specific
- Usually catalyze only single chemical reaction or a set of closely related chemical reactions.
Components of a protein enzyme:
- 1 or more polypeptide chains.
- Cofactor: an additional non peptide component of an enzyme
- Coenzyme: a complex organic or metalloorganic cofactor
- Prosthetic group: covalently bound cofactor
- Holoenzyme: a complete, catalytically active enzyme
- Apoenzyme: protein portion of holoenzyme.
Many vitamins are precursors of
coenzymes
What is the transition state
the configuration (of atoms, bonds, electrons) along the reaction coordinate corresponding to the highest energy
At the transition state, there is an ____probability of forming reactants or products
equal
Change in free energy from reactants to transition state is called the
activation energy
Rate constant of a reaction (k) is ____ and ___ proportional to the activation energy
inversely and exponentially
Activation energy determines the rate of a reaction at a given:
temperature
The higher the AE =
slower rate
The lower the AE=
faster rate
Enzymes ____activation energy
lower
What is the active site of an enzyme
the location on enzyme where substrate(s) bind. Provides specific environment for reactions
Active site features:
- 10 or fewer aa
- water usually excluded from site
- Non polar envmt, so aa side chains become highly active
How is activation energy reduced
Loaned energy from weak, non covalent interactions between the substrate and active site. Each interaction releases a small amount of energy that can be offset against activation energy. The sum of these energies released by substrate active site interaction is called the binding energy
Activation energy -binding energy =
catalyzed activation energy
What is the lock and key hypothesis
Proposed that shape of substrate and active site must match in order for substrate to fit side
T/F There is a problem if weak interactions between enzymes and substrates are optimized in the enzyme substrate complex
T
What is the induced fit hypothesis
Once substrate bound, structure of enzyme shifts so active site assumes closer fit
Weak interactions between enzyme and substrate are optimized in the
transition state
poorer fit –> lower binding energy–> higher activation energy–> ____reaction rate
slower
Thrombin is a proteolytic enzyme and only cleaves between ____ and ____
argenine and glycine
What is catalysis
The active site can provide functional groups that interact transiently with the substrates
3 common types of catalysis involving functional groups are
- acid base
- covalent
- metal ion
Positively charged intermediates:
remove proton (base)
Negatively charged intermediates:
add proton (acid)
Specific acid/base catalysis:
acid or base from water
General acid/base catalysis:
proton donor/acceptor
What is covalent catalysis
A transient covalent link is formed between the enzyme and substrate or intermediate
What is metal ion catalysis
Metal ions can be tightly bound to enzyme or taken up with substrate. Ionic interactions between metal ion and substrate help orient substrate and/or stabilize charged transition state.
