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Biochemistry > Unit 4 - Enzymes > Flashcards

Unit 4 - Enzymes Flashcards

1
Q

4 properties of enzymes

A
  1. Catalysts - increase the speed of a chemical reaction
  2. Not consumed during the reaction
  3. highly specific
  4. normally found only inside the cells (diseased/damaged cells let enzymes spill out, we in the lab can measure the enzyme activity in the blood)
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2
Q

Free energy change

A
  • delta G
  • the energy released or used in a chemical reaction represents the difference between the energy contents of the products and the reactants.
    delta G = free energy of product - free energy of reactants
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3
Q

Exergonic vs. endergonic reactions

A

Exergonic reaction = energy is released; There is less energy in product. Delta G is negative.

Endergonic reaction = energy is used; There is more energy in product. Delta G is positive.

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4
Q

Collision frequency

A
  • velocity of a chemical reaction depends on the frequency of collision between reaction molecules
  • collision frequency is influenced by the concentration of reactant molecules and how fast they move (their kinetic energy)
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5
Q

Transition state

A
  • an unstable, halfway transient phase in which bond and orientation are distorted as reactants are turned into products.
  • it possess a certain minimum energy.
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6
Q

On an energy diagram, be familiar with:

A
  • reactants come together
  • activation energy
  • transition state
  • product
  • delta G
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7
Q

Two ways to increase the rate of a reaction

A
  1. Raise the temperature

2. Lower the energy of activation

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8
Q

Velocity vs. Substrate concentration Plot

A

First order = area of linearity

Zero order = plateau

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9
Q

Linearity due to:

A
  • increasing concentrations of substrate when at low levels of concentration which increases velocity
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10
Q

Plateau due to:

A
  • high concentration of substrate reaches maximum velocity
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11
Q

Lock and Key Analogy

A
  • enzyme specificity
  • enzymes are specific (lock) for a certain substrate (key)
  • only the correct substrate that fits into the enzymes active site will react
  • creates enzyme-substrate complex (ES)
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12
Q

Active site

A
  • part of the enzyme responsible for its catalytic activity
  • a tiny segment, usually a crevice as a result of secondary and tertiary structures, on the enzyme that substrate binds to
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13
Q

Apoenzyme

A
  • the protein component of a conjugated enzyme

- doesn’t exhibit biological activity alone

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14
Q

Cofactor

A
  • the nonprotein component of a conjugated enzyme
  • doesn’t exhibit biological activity alone
  • many are inorganic ions
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15
Q

Conjugated enzymes

A
  • a subdivision of enzymes

- have both a protein and nonprotein component

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16
Q

Simple enzymes

A
  • a subdivision of enzymes

- consist only of protein

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17
Q

Coenzyme

A
  • a small organic molecule that is a cofactor
  • many vitamins function as coenzymes
    (ex. TTP = coenzyme from Vit B)
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18
Q

Substrate

A
  • the substance that is acted upon by the enzyme
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19
Q

Activation Energy

A
  • the minimum amount of energy needed before collision between molecules results in a reaction
  • after the reaction begins, enough energy is release to keep reaction going
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20
Q

V

A

= velocity

the rate of the enzyme-catalyzed reaction

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21
Q

Vmax

A
  • the maximum velocity at a finite amount of enzyme and saturated with substrate
22
Q

Km

A
  • Michaelis constant

- based on the affinity of substrate to enzyme complex.

23
Q

Michaelis-Menten equation

A
  • the relationship btwn the rate and the substrate concentration expressed mathematically

V = Vmax * ( [S] / ([S] + Km) )

24
Q

Lineweaver-Burke plot

A
  • rearrange Michaelis-Menten equation to simplify evaluation of Km and Vmax
  • uses inverses to obtain a straight line.

1/v = Km/Vmax * 1/[S] + 1/Vmax
Note: y = mx + b

25
Q

Five reasons for determining Km

A
  1. establishes approximate value for intracellular levels of substrate
  2. a means of comparing enzymes from different organisms or tissues from the same organism
  3. regulate activity of an enzyme by analyzing ligand-induced change via value of Km
  4. determine V max to measure total enzyme concentration by setting [S] > Km
  5. the substrate with the lowest Km has the highest affinity for the enzyme
26
Q

6 categories of Enzymes

A

HOT LIL

  • Hydrolase
  • Oxidoreductase
  • Transferase
  • Lyase
  • Isomerase
  • Ligase / Synthase
27
Q

Hydrolase

A
  • catalyze hydrolysis reactions ( a reaction where a water molecule breaks apart into 2 different products)
28
Q

Oxidoreductase

A
  • catalyze oxidation -reduction reactions

- includes: catalase, dehydrogenase, hydroxylase, oxidase, oxygenase, peroxidase, and reductases.

29
Q

Transferase

A
  • catalyze the transfer of a functional group between 2 substrates
  • includes: kinase (transfer of phosphate group) and aminotransferase (transfer of amino group)
30
Q

Lyase

A
  • catalyze the removal of certain groups without hydrolysis (usually by double bond formation)
  • ex: decarboxylase
31
Q

Isomerase

A
  • catalyze the conversion of a compound into another which is isomeric (same molecular formula different structural formula)
32
Q

Ligase / Synthase

A
  • catalyze the formation of new bonds from carbon to a nitrogen, oxygen, sulfur, or another carbon atom
33
Q

Temperature on the rate of an enzymatic reaction

A
  • the higher the temperature, the faster the reaction
  • BUT if the temperature is raised too high the enzyme will denature
  • optimum temperature = 37 degrees Celsius
34
Q

pH on the rate of an enzymatic reaction

A
  • each enzyme has its own optimum pH (because enzymes have acidic and basic groups)
  • Maximum activity = narrow range of pH
  • lower/higher pH values can cause denaturation
35
Q

Competitive inhibition

A
  • inhibitor binds to active site on enzyme
  • reversible
  • competes against substrate for binding site
    Ex: Methanol - oxidized to formaldehyde by ADH enzyme = toxic. Intravenous infusions of ethanol keeps ADH enzyme occupied by oxidizing ethanol instead
36
Q

Noncompetitive inhibition

A
  • inhibitor binds to an allosteric site on the enzyme which changes the enzymes structure = alters active site
  • reversible
    Ex: Heavy metal poisoning - Silver, mercury, and lead have a high affinity for sulfhydryl groups, when bound the protein’s structure changes and the enzyme can’t function.
37
Q

Irreversible inhibiton

A
  • formation of a covalent bond between inhibitor and enzyme at the active site.
  • blocks active site = enzyme is deactivated
    Ex: Sarin - a nerve gas that forms covalent bonds with serine residue on acetylcholinesterase enzyme which is important in transmission of nerve impulses => paralysis of respiratory system => death
38
Q

Cytochrome p450

A
  • absorb UV light at 450 nm
  • detoxification of xenobiotics via biotransformation
  • important in the metabolism of endogenous and exogenous substrates - make lipophilic / non-polar substances more soluble
  • found in highest concentrations in liver and GI tract
39
Q

Phase I Biotransformation

A
  • the addition of oxygen (typically in form of -OH) to make the compound more water soluble
40
Q

Phase II Biotransformation

A
  • if phase I was not enough for elimination, other water soluble groups are attached
  • ex: sulfates, glucuronic acid, and glutathione
41
Q

Consequences of Phase I and Phase II reactions on exogenous compounds

A
  1. Inactivation of compound
  2. Activation of compound
  3. Formation of toxic metabolite
42
Q

Acetaminophen

A
  • an example where the consequence of phase I/II reaction leads to the formation of toxic metabolite
  • 2/3 major routes of its metabolism includes phase II reactions
  • metabolism by CYP450 = NAPQI which can cause liver damage if too much is made at one time
  • antidote = N-acetylcysteine which blocks acetaminophen uptake by liver
43
Q

Clinical Importance of alkaline phosphatase

A
  • Liver diseases: Obstructive liver disease***

- Bone disease

44
Q

Clinical Importance of Creatine Kinase

A
  • assesses cardiac damage

- but is not very specific (many different tissue sources)

45
Q

Clinical Importance of Lactate dehydrogenase

A

`- AMI

  • megaloblastic anemia
  • liver disase
  • malignant disease
46
Q

Clinical Importance of Gamma Glutamyltransferase (GGT)

A
  • sensitive indicator of chronic alcoholism
  • most sensitive of the liver enzymes for gallbladder inflammation
  • elevated in most hepatobilliary disorders
47
Q

Clinical Importance of Amylase

A
  • elevated in pancreatic dysfunction
  • acute pancreatitis = amylase elevates within 12 hours of onset and returns to normal in 48-72 hours
  • chronic pancreatitis = amylase remains elevated
48
Q

Clinical Importance of Lipase

A
  • used in differential diagnosis of pancreatitis, specifically for acute pancreatitis
49
Q

Enzyme activity

A
  • IU = one international unit of any enzyme it that amount which will catalyze the transformation of one micromole of substrate per minute under specific conditions
50
Q

Isoenzyme

A
  • multiple molecular forms of an enzyme
51
Q

Isoform

A
  • multiple molecular forms of isoenzymes that result from enzyme modification of the parent form after its release from tissue

Biochemistry (14 decks)

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