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MCAT Biochem > Chapter 2 > Flashcards

Chapter 2 Flashcards

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MCAT flashcards
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

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2
Q

Enzyme Specificity

A
  • Given enzyme will only catalyze a certain reaction or type of reaction
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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
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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
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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)
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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)
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7
Q

Isomerases

A
  • Catalyze rearrangement of bonds within molecule
  • Catalyze reactions between stereoisomers and constitutional isomers
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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
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9
Q

Endergonic Reaction

A

Requires energy input
∆G > 0
endo in

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10
Q

Exergonic Reaction

A

Energy given off
∆G < 0
exo out

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11
Q

Kinetics

A
  • Largely effected by enzyme
  • By lowering activation energy, equilibrium is achieved faster BUT equilibrium position doesn’t change
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12
Q

Substrate

A

The molecule that an enzyme acts on

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13
Q

Enzyme-Substrate Complex

A

Physical interaction between enzyme and substrate

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14
Q

Active site

A

Location within enzyme where substrate is held during chemical reaction

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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

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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

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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)
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18
Q

Apoenzymes

A

Enzymes without their cofactors

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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
Q

Michaelis-Menten Equation

A

How rate of reactin depends of concentration of enzyme and susbtrate which forms product

P is product
26
Q

Velocity of Enzyme to Substrate Concentration

A
  • Enzyme concentration constant
27
Q

Reaction rate is half of vmax

A

Km is Michaelis constanst

28
Q

Lineweaver-Burk Plot

A
  • Double reciprocal graph of Michaelis-Menten equation
  • X intercept: -1/Km
  • Y intercept: 1/Vmax
29
Q

Enzyme Cooperativity

A
  • 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
Q

Michaelis-Menten vs Lineweaver-Burk Plots

A

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
Q

Km (Michaelis Constant)

A
  • 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
Q

Temperature Effect on Enzymes

A
  • 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
Q

pH Effect on Enzymes

A
  • 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
Q

Salinity Effect on Enzymes

A
  • 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
Q

Feedback Inhibition/Negative Feedback

A

Product of an enzymatic pathway when produced in excess turns off enzyme that start the pathway
* Helps maintain homeostasis

36
Q

Reversible Inhibition

A
  1. Competitive
  2. Noncompetitive
  3. Mixed
  4. Uncompetitive
37
Q

Competitive Inhibition

A
  • 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
Q

Noncompetitive Inhibition

A
  • 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
Q

Mixed Inhibition

A
  • 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
Q

Uncompetitive Inhibition

A
  • 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
Q

Irreversible Inhibition

A

Prolonged/permanent inactivation of an enzyme so that it can’t be easily renatured to regain function
* Ex: aspirin
* Common in drugs

42
Q

Allosteric/Transient Enzymes

A

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
Q

Covalently Modified Enzymes

A
  • Phosphorylation/dephosphorylation (can’t tell if will activate without experiments)
  • Glycosylation (covalent attachment of sugar moieties)
44
Q

Zymogens

A
  • Precursors of active enzyme
  • Critical that some enzymes (ex: digestive) remain inactive until arriving to desired location
45
Q

Metabolic Reactions

A
  • Cofactors/coenzymes usually small (metal/organic)
  • Can usually carry a charge
  • Include oxidation-reduction reactions and movement of functional groups

MCAT Biochem (7 decks)

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