1
Q
Enzymes
A
Biological catalysts (don’t impact thermodynamis but help reaction proceed at faster rate by lowering activation energy)
* Lower activation energy (make it easier for substrate to reach transition state)
* Increase rate of reaction
* Don’t alter equilibrium constant
* Appear in reactants and products (not used up in reactions)
* Are pH and temperature sensitive (optimal activity in certain ranges)
* Ideal temperature is lower with catalyst than without (need higher temperature without catalyst to lead to better chance of completing)
* Don’t affect overall ∆G of reaction
2
Q
Enzyme Specificity
A
- Given enzyme will only catalyze a certain reaction or type of reaction
3
Q
Oxidoreductases
A
- Catalyze oxidation-reduction reactions (transfer of electrons between biological molecules)
- Have cofactor that acts as electron carrier (ex: NADP+)
- Reductant: electron donor
- Oxidant: electron acceptor
- Usually have dehydrogenase or reductase in name
4
Q
Transferases
A
- Catalyze movement of functional group from one molecule to another
- Straightforwardly named
- Kinases are also transferases
- Kinases: catalyze transfer of phosphate group (usually from ATP) to another molecule
5
Q
Hydrolases
A
- Catalyze breaking of compound into two molecules by adding water
- Common uses, named only for substrate
- Ex: phosphatase (cleaves phosphate group), peptidases (break down proteins), nucleases (break down nucleic acids), lipases (break down lipids)
6
Q
Lyases
A
- Catalyze clevage of single molecule into two products
- Don’t require water and don’t act as oxidoreductases
- Catalyze synthesis of two small organic molecules into single molecule (synthases)
7
Q
Isomerases
A
- Catalyze rearrangement of bonds within molecule
- Catalyze reactions between stereoisomers and constitutional isomers
8
Q
Ligases
A
- Catalyze addition/synthesis reactions (usually large similar molecules and require ATP)
- Synthesis reactions with smaller molecules
- Likely with nucleic acid synthesis
9
Q
Endergonic Reaction
A
Requires energy input
∆G > 0
endo in
10
Q
Exergonic Reaction
A
Energy given off
∆G < 0
exo out
11
Q
Kinetics
A
- Largely effected by enzyme
- By lowering activation energy, equilibrium is achieved faster BUT equilibrium position doesn’t change
12
Q
Substrate
A
The molecule that an enzyme acts on
13
Q
Enzyme-Substrate Complex
A
Physical interaction between enzyme and substrate
14
Q
Active site
A
Location within enzyme where substrate is held during chemical reaction
15
Q
Lock and Key Theory
A
Enzyme’s active site (lock) is already in appropriate shape for substrate (key) to bind
* No changes needed
* Less accurate
16
Q
Induced Fit Model
A
Active site of enzyme molds itself around substrate when it is present
* Tertiary/quaternary structure modified for enzyme to function
* More accurate
* Endergonic (requires energy)
Releasing substrate is exergonic reaction (releases energy)
Return to original shape once substrate releases
17
Q
Cofactors/Coenzymes
A
- Activators of enzymes (conformational change in enzyme promoting its activity)
- Small so can bind to active site
- Participate in catalysis of reaction by carrying charge through ionization, protonation, deprotonation
- Usually in low concentrations
- Attach in many ways (weak noncovalent to strong covalent)
18
Q
Apoenzymes
A
Enzymes without their cofactors
19
Q
Holoenzymes
A
Enzymes containing their cofactors
20
Q
Prosthetic Groups
A
- Tightly bound cofactors/coenzymes needed for enzyme function
21
Q
Cofactor
A
- Inorganic molecules
- Metal ions
- Ingested in dietary minerals
22
Q
Coenzyme
A
- Small organic groups
- Mainly vitamins/derivatives of vitamins
- Water-soluble vitamins (B vitamins and ascorbic acid)
23
Q
Increasing [S] Substrate
A
- Substrate concentration low: proportional increase in enzyme activity
- Substrate concentration high: when enzyme is saturated increasing substrate has no affect because vmax already attained
24
Q
Increasing [E] Enzyme
A
- Will always increase vmax regardless of starting concentration of enzyme
25
Michaelis-Menten Equation
How rate of reactin depends of concentration of enzyme and susbtrate which forms product
26
Velocity of Enzyme to Substrate Concentration
* Enzyme concentration constant
27
Reaction rate is half of vmax
Km is Michaelis constanst
28
Lineweaver-Burk Plot
* Double reciprocal graph of Michaelis-Menten equation
* X intercept: -1/Km
* Y intercept: 1/Vmax
29
Enzyme Cooperativity
* Interactions between subunits in a multisubunit enzyme/protein
* Binding of substrate to one subunit causes change in other subunit from T (tense) state to R (relaxed) state that encourage binding of substrate to other subunits
* In reverse direction, unbinding of substrate from one subunit cause change from R to T in remaining subunits promoting unbinding of substrate from remaining subunits
30
Michaelis-Menten vs Lineweaver-Burk Plots
Similarities:
* Account for values of Km and Vmax under various conditions
* Simple graphical interpretations and derived from Michaelis-Menten equation
Differences:
* Axes and visual representation
* Michaelis-Menten is v vs [S] (hyperbolic curve for monomeric enzymes)
* Lineweaver-Burk Plot is 1/v vs 1/[S] (Straight line)
31
Km (Michaelis Constant)
* Measure of an enzyme's affinity for its substrate
* Substrate concentration where an enzyme is function at 1/2 its maximal velocity
* Enzyme with higher Km has lower affinity for its substrate (requires higher substrate concentration to be half saturated)
32
Temperature Effect on Enzymes
* Double in velocity for every 10˚C increase in temperature until optimum temperature is reached
* At body temperature, activity falls off and enzyme denatures at higher temperature
* Some enzymes regain function if cooled
* Ideal: 37˚ C = 98.6˚ F = 310 K
33
pH Effect on Enzymes
* pH affects ionization of active site
* pH can lead to denaturation of enzyme
* Ideal blood ph is 7.4
* **acidemia:** blood pH < 7.35 (more acidic than physiologically neutral)
* Exceptions are digestive tract (ex: pepsin)
* Ideal (MOST): 7.4
* Ideal (gastric): 2
* Ideal (pancreatic): 8.5
34
Salinity Effect on Enzymes
* Altering concentration of salt can change enzyme activity in vitro (disrupting bonds)
* Causes disruption of tertiary/quaternary structure leading to loss of enzyme function
35
Feedback Inhibition/Negative Feedback
Product of an enzymatic pathway when produced in excess turns off enzyme that start the pathway
* Helps maintain homeostasis
36
Reversible Inhibition
1. Competitive
2. Noncompetitive
3. Mixed
4. Uncompetitive
37
Competitive Inhibition
* Binding site: Active site
* Substrates can't access enzyme binding sites if inhibitors in the way
* Impact on Km (bonding affinity): Increase
* Impact on vmax (amount of enzyme available to react): Unchanged
* Overcome by adding more substrate to make ratio higher
38
Noncompetitive Inhibition
* Binding site: Allosteric site
* Bind to allosteric site and change shape so normal molecules can't bind
* Can't be overcome by adding more substrate
* Impact on Km: Unchnaged
* Impact on vmax: Decreases
39
Mixed Inhibition
* Binding site: Allosteric site
* Inhibitor can bind to enzyme or enzyme-substrate complex with different affinity for each
* Impact on Km: if inhibitor binds to enzyme-substrate complext **lowers Km**, if inhibitor binds to enzyme **increases Km**
* Impact on vmax: Decreases
40
Uncompetitive Inhibition
* Binding site: Allosteric site
* Bind only to enzyme-substrate complex and lock substrate in enzyme preventing release
* Impact on Km: Decreases
* Impact on vmax: Decreases
41
Irreversible Inhibition
Prolonged/permanent inactivation of an enzyme so that it can't be easily renatured to regain function
* Ex: aspirin
* Common in drugs
42
Allosteric/Transient Enzymes
Enzymes with multiple bonding sites (active site and at least one other)
* Examples: Allosteric activation (makes active site more available for binding to substrate), allosteric inhibition (makes active site less available)
43
Covalently Modified Enzymes
* Phosphorylation/dephosphorylation (can't tell if will activate without experiments)
* Glycosylation (covalent attachment of sugar moieties)
44
Zymogens
* Precursors of active enzyme
* Critical that some enzymes (ex: digestive) remain inactive until arriving to desired location
45
Metabolic Reactions
* Cofactors/coenzymes usually small (metal/organic)
* Can usually carry a charge
* Include oxidation-reduction reactions and movement of functional groups
MCAT Biochem
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