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Biochemistry I > Chapter 3: Enzymes and Coenzymes > Flashcards

Chapter 3: Enzymes and Coenzymes Flashcards

1
Q

Digestive enzymes

A
  • Trypsin and pepsin

- Made from inactive precursors by proteolytic cleavage that reveals the active site

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2
Q

Clotting cascade enzymes

A
  • Thrombin

- Similar to digestive enzymes, made from inactive precursors by proteolytic cleavage that reveals the active site

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3
Q

Zymogens

A
  • The inactive precursors of digestive enzymes and enzymes in the clotting cascades
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4
Q

Zymogen examples

A
  • Trypsinogen
  • Pepsinogen
  • Prothrombin
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5
Q

Induced fit theory

A
  • Active site is flexible and three dimensional
  • Non-polar regions of substrate interact with non-polar regions of enzyme
  • Numerous non-covalent bonds of varying strength stabilize the enzyme-substrate complex
  • Geometry and charge are complementary between enzyme and substrate-binding site
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6
Q

Specificity of enzymes

A
  • Characteristic of formation of the enzyme-substrate complex (essential intermediate in enzyme-catalyzed reactions)
  • The ability of an enzyme to preferentially react with particular substrate molecules
  • Determined substrate-binding site that is distinct from, and often adjacent, to the active site
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7
Q

Catalase and urease

A
  • Enzymes that catalyze only a single reaction
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8
Q

Isoenzymes (isozymes)

A
  • Enzymes that catalyze the same reaction, but differ in structure
  • Some are tissue specific (presence of these is central to disease diagnosis)
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9
Q

Gibbs free energy change

A
  • Measure of the spontaneity of a given reaction
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10
Q

Endergonic reaction

A
  • Delta G > 0 (positive)
  • Energy is provided
  • Not energetically favored
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11
Q

Exergonic reaction

A
  • Delta G < 0 (negative)
  • Release energy as the high energy bond is broken
  • Energetically favored
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12
Q

Equilibrium

A
  • Delta G is equal to zero
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13
Q

Sum of free energy change less than zero (negative)

A
  • Coupled reaction can occur spontaneously as long as this is the case
  • Nonspontaneous reaction can be coupled with a spontaneous reaction
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14
Q

Simple proteins

A
  • Enzymes that are composed only of amino acids

- Can be conjugated proteins that contain non-proteinaceous material

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15
Q

Cofactors

A
  • Small molecules that are required by some enzymes for complete catalytic activity
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16
Q

Apoenzyme

A
  • An inactive protein lacking its cofactors
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17
Q

Holoenzyme

A
  • The active enzyme plus its cofactor
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18
Q

Metal ions

A
  • Inorganic molecules that can be cofactors
19
Q

Metalloenzymes

A
  • 2/3 of all enzymes

- Require tightly bound metal ions for maximal catalytic potential

20
Q

Transition metals

A
  • Zinc, iron, manganese, copper, cobalt

- Most commonly employed metal ion cofactors

21
Q

Lysine oxidase

A
  • Enzyme that is important in collagen biosynthesis

- Requires loosely bound copper for optimal activity

22
Q

Prosthetic groups

A
  • Organic coenzymes acting as cofactors

- Covalently attached to the enzyme molecule permanently

23
Q

Cosubstrates (ie. cytochrome c oxidase)

A
  • Small organic compounds that may be derived from the water-soluble B vitamins or nucleotide derivatives (such as ATP or GTP)
  • More loosely bound to the enzyme molecule
  • Sometimes called second substrates
24
Q

Second substrates

A
  • Another term that can refer to cosubstrates because they are often changed in a reaction and must be regenerated for the reaction to continue
25
Q

Nicotinamide adenine dinucleotide (NAD+)

A
  • A cosubstrate involved in the oxidation-reduction reactions of metabolism
26
Q

Nicotinamide adenine dinucleotide phosphate (NADP+)

A
  • Involved in reductive biosynthesis of lipids and nucleic acids
27
Q

NADPH

A
  • Produced in the pentose phosphate pathway and is partly responsible for the neutralization of harmful free radicals
28
Q

NADH oxidation

A
  • Generates energy inside the mitochondria during the process of oxidative phosphorylation, associated with cellular respiration
29
Q

Redox coenzymes

A
  • NADH
  • Flavin adenine dinucleotide (FAD)
  • Flavin adenine mononucleotide (FMN)
  • Both FAD and FMN are derivatives of riboflavin (vitamin B2)
30
Q

FADH2

A
  • FAD accepts 2 electrons and 2 protons to become reduced to this
  • Important carrier of high-energy electrons in the electron transport chain
31
Q

Enzyme nomenclature

A
  • Oxidoreductases
  • Transferases
  • Hydrolases
  • Lyases
  • Isomerases
  • Ligases
32
Q

Oxidoreductases

A
  • Catalyze energy-generating oxidation-reduction reactions involving the transfer of a hydride ion
  • Electron donor is oxidized (loses electrons)
  • Electron accepter is reduced (gains electrons)
  • Catalyze reactions involving electron flow
  • Use coenzymes from B vitamins
33
Q

Transferases

A
  • Catalyze the transfer of functional groups between molecules
  • Transaminases transfer and amino group
  • Kinases transfer the gamma-phosphoryl group of ATP in phosphorylation reactions
34
Q

Hydrolases

A
  • Special group of transferases that catalyze hydrolutic reactions
  • Water molecule is added to break a bond
35
Q

Lyases

A
  • Enzymes that form double bonds by breaking C-C, C-O, or C-N linkages
  • Decarboxylases eliminate the elements of CO2 from keto acids or amino acids
36
Q

Isomerases

A
  • Heterogeneous group of enzymes that catalyze the transfer of groups within the same molecule
37
Q

Ligases

A
  • Enzymes that facilitate bond formation between two substrates coupled to ATP hydrolysis
38
Q
  • Oxidoreductases
  • Transferases
  • Hydrolases
  • Lyases
  • Isomerases
  • Ligases
A
  • Oxidation-reduction reactions
  • Transfer of functional groups
  • Hydrolysis reactions
  • Group elimination to form double bonds
  • Isomerization
  • Bond formation coupled with ATP hydrolysis
39
Q

Activation energy review

A
  • Lowered by enzymes without affecting equilibria
40
Q

Rate of reactions review

A
  • Enzymes increase the rate of forward and reverse reactions equally stabilizing the transition state
41
Q

Cofactors review

A
  • Some enzymes require metal ions

- Some enzymes require organic prosthetic groups or coenzymes

42
Q

Coenzymes review

A
  • Most are derivatives of the water-soluble B vitamins
43
Q

Active site review

A
  • The location at which catalysis occurs in the enzyme molecule
44
Q

Enzyme Commission (EC) review

A
  • Designation followed by four digits
  • First digit indicates the major class of enzyme
  • Next digits allocate enzyme into three different subcategories

Biochemistry I (34 decks)

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