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mcat biochem > Ch 2 - Enzymes > Flashcards

Ch 2 - Enzymes Flashcards

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MCAT flashcards
1
Q

What are enzymes?

A

biological catalyst that are unchanged by the reactions they catalyze and are reusable

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2
Q

What do oxidoreductase do?

A

catalyze oxidation-reduction reactions that involve the transfer of electrons

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3
Q

What do transferases do?

A

move a functional group fro one molecule to another molecule

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4
Q

What do hydrolases do?

A

catalyze cleavage with the addition of water

- breaking of compound into 2 products with water

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5
Q

What do lyases do?

A

catalyze cleavage without the addition of water and without the transfer of electrons

  • the reverse reaction (synthesis) is often more important biologically
  • cleavage of small molecules into 2 produces or synthesis of small organic molecules
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6
Q

What do isomerases do?

A

catalyze the interconversion of isomers, including both constitutional isomers and stereoisomers
- rearrangement of bonds within a compound

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7
Q

What do ligases do?

A

responsible for joining two large biomolecules, often often of the same type

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8
Q

What is the difference between exergonic and endergonic reactions?

A
  • ex: release energy; delta G is negative

- end: requires energy; delta G > 0

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9
Q

How do enzymes affect activation energy?

A

they lower the activation energy necessary for biological reactions

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10
Q

How do enzymes affect free energy and enthalpy?

A
  • enzymes do not alter free energy (G) or enthalpy (H) change that accompanies the reaction nor the final equilibrium position
  • they change the rate (kinetics) at which equilibrium is reached
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11
Q

How do enzymes act?

A
  • by stabilizing the transition state
  • providing a favorable microenvironment
  • bonding with the substrate molecules
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12
Q

Where is the site of catalysis?

A

the active site on an enzyme

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13
Q

How is binding to the active site explained?

A
  • lock and key theory: the enzyme and substrate are exactly complementary
  • induced fit theory: the enzyme and substrate undergo conformational changes to interact fully
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14
Q

What do some enzymes require to be active?

A

metal cation factor or small organic coenzymes

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15
Q

What is saturation kinetics?

A

as substrate concentrations increases, the reaction rate does as well until a maximum value is reached

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16
Q

What do Michaelis-Menten and Lineweaver-Burk plots represent?

A

the relationship of saturation kinetics as a hyperbola and line

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17
Q

How can enzymes be compared?

A

on the basis of their Km and Vmax values

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18
Q

What do cooperative enzymes display?

A

a sigmoidal curve because of the change in activity with substrate binding

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19
Q

What can affect enzyme activity in vivo?

A
  • temperature and pH
  • changes in temp and pH can result in denaturing of the enzyme and loss of activity due to loss of secondary, tertiary, or, if present, quaternary structures
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20
Q

What can affect enzyme activity in vitro?

A

salinity

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21
Q

What is feedback inhibition?

A

regulatory mechanism whereby the catalytic activity of an enzyme is inhibited by the presence of high levels of a product later in the same pathway
- helps maintain homeostasis: as product levels rise, the pathway creating that product is appropriately downregulated

22
Q

What is reverse inhibition?

A

characterized by the ability to replace the inhibitor with a compound of greater affinity or to remove it using mild laboratory treatment

23
Q

What is competitive inhibition? How can it be overcome and what happens to Km and Vmax? Binding site?

A
  • type of reverse
  • results when the inhibitor is similar to the substrate and binds at the active site
  • can be overcome by adding more substrate
  • Vmax is unchanged and Km increases
  • binding: active site
24
Q

What is noncompetitive inhibition? What happens to Km and Vmax? Binding site?

A
  • type of reverse
  • results when the inhibitor binds with equal affinity to the enzyme and the enzyme-substrate complex
  • Vmax decreases, Km is unchanged
  • binding: allosteric site
25
Q

What is mixed inhibition and how is Km and Vmax affected? Binding site?

A
  • type of reverse
  • results when the inhibitor binds with equal affinity to the enzyme and the enzyme-substrate complex
  • Vmax is decreased
  • Km is increased or decreased depending on if the inhibitor has higher affinity for the enzyme of enzyme-substrate complex
  • binding: allosteric site
26
Q

What is uncompetitive inhibition an dhow is Km and Vmax affected? Binding site?

A
  • type of reverse
  • results when the inhibitor binds only with the enzyme-substrate complex
  • Km and Vmax both decrease
  • binding: allosteric site
27
Q

What is irreversible inhibition?

A
  • the prolonged or permanent inactivation of an enzyme, such that it cannot be easily renatured to gain function
28
Q

What can occupy allosteric sites causing what?

A

can be occupied by activators, which increases either affinity or enzymatic turn over

29
Q

How are zymogens secreted and activated?

A
  • secreted in an inactive form

- activated by cleavage

30
Q

What are the key features of enzymes?

A
  • lower activation energy
  • increase the rate of the reaction
  • do not alter the equilibrium constant
  • are not changed or consumed in the reaction (appear in both reactants and products)
  • are pH and temperature sensitive
  • do not affect the overall delta G
  • are specific for a particular reaction or class of reactions
31
Q

What are the major enzyme classifications?

A

LIL HOT

  • Ligase
  • Isomerase
  • Lyase
  • Hydrolase
  • Oxidoreductase
  • Transferase
32
Q

How do catalysts exert their effect?

A
  • by lowering the activation energy

- they make it easier for the substrate to reach the transition state

33
Q

What are cofactors and coenzymes and how do they differ?

A
  • they are activators that induce conformational changes in the enzyme to promote activity
  • cofactors are inorganic (minerals)
  • coenzymes are organic (vitamins)
34
Q

What are prosthetic groups?

A

tightly bound cofactors and coenzymes that are necessary for enzyme function

35
Q

What is Km?

A
  • michaelis constant used to measure enzyme affinity for substrates
  • concentration of S where enzyme is functioning at half of Vmax
  • high Km has a low enzyme affinity for substrate
36
Q

What is Michaelis-Menten equation?

A

v = Vmax[S]/Km + [S]

37
Q

What are the effects of increasing [S] on enzyme kinetics?

A
  • if [S] is low, increasing it will drastically increase the enzyme activity
  • if [S] is already high, increasing will not have any effect
38
Q

What are the effects of increasing [E] on enzyme kinetics?

A

increase Vmax

39
Q

What is the difference between Michaelis-Menten and Lineweaver-Burk plot”

A
  • michaelis: v v. [S] –> hyperbolic curve

- lineweaver: 1/v v. 1/[S] (-1/Km v. 1/Vmax) –> linear curve

40
Q

What is enzyme cooperativity?

A
  • cooperativity refers to the interactions between subunits in a multsubunit enzyme or protein
  • the binding of substrate to one subunit induces a change in the other subunits from the T (tense) state to the R (relaxed) state, which encourages binding of substrate to the other subunits and vice versa
41
Q

What are the effects of temperature on the function of enzymes and what is the ideal temperature?

A
  • increased temperature generally increases enzyme activity
  • once body temperature reached, activity drops fat as enzyme is denatured
  • ideal temp: 37 C, 98.6 F, 310 K
42
Q

What are the effects of pH on the function of enzymes and what is the ideal pH in most enzymes, gastric enzymes, and pancreatic enzymes?

A
  • enzymes are maximally active within small pH range
  • outside of this range, activity drops quickly with changes in pH as the ionization of the active site changes and the protein is denatured
  • most: 7.4
  • gastric: 2
  • pancreatic: 8.5
43
Q

What are the effects of salinity on the function of enzymes?

A
  • changes in salinity can disrupt the bonds of enzyme, causing disruption of tertiary and Quaternary structure, which leads to loss of enzyme function
44
Q

Of the 4 types of reversible inhibitors, which could potentially increase Km?

A
  • competitive increases Km because the substrate concentration has to be higher to reach the half maximum velocity in the presence of the inhibitor
  • a mixed inhibitor will increase Km only if the inhibitor preferentially binds to the enzyme over the ES complex
45
Q

What are examples of transient modifications?

A

allosteric activation or inhibition

46
Q

What are examples of covalent modifications?

A

phosphorylation and glycosylation

47
Q

Why are some enzymes released as zymogens?

A
  • they are precursors of active enzymes

- critical that certain enzymes remain inactive until arriving at their target site

48
Q

What determines an enzymes specificity?

A

the 3D shape of its activation site

49
Q

Are enzymes altered during catalysis?

A

No. A molecules that breaks intramolecular bonds to provide activation energy would not be able to be reused.

50
Q

How does the ideal temperature for a reaction change with or without an enzyme catalyst?

A

ideal temperature is generally lower with a catalyst than without

mcat biochem (12 decks)

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