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
2
Q
Clotting cascade enzymes
A
- Thrombin
- Similar to digestive enzymes, made from inactive precursors by proteolytic cleavage that reveals the active site
3
Q
Zymogens
A
- The inactive precursors of digestive enzymes and enzymes in the clotting cascades
4
Q
Zymogen examples
A
- Trypsinogen
- Pepsinogen
- Prothrombin
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
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
7
Q
Catalase and urease
A
- Enzymes that catalyze only a single reaction
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)
9
Q
Gibbs free energy change
A
- Measure of the spontaneity of a given reaction
10
Q
Endergonic reaction
A
- Delta G > 0 (positive)
- Energy is provided
- Not energetically favored
11
Q
Exergonic reaction
A
- Delta G < 0 (negative)
- Release energy as the high energy bond is broken
- Energetically favored
12
Q
Equilibrium
A
- Delta G is equal to zero
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
14
Q
Simple proteins
A
- Enzymes that are composed only of amino acids
- Can be conjugated proteins that contain non-proteinaceous material
15
Q
Cofactors
A
- Small molecules that are required by some enzymes for complete catalytic activity
16
Q
Apoenzyme
A
- An inactive protein lacking its cofactors
17
Q
Holoenzyme
A
- The active enzyme plus its cofactor
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
Nicotinamide adenine dinucleotide (NAD+)
- A cosubstrate involved in the oxidation-reduction reactions of metabolism
26
Nicotinamide adenine dinucleotide phosphate (NADP+)
- Involved in reductive biosynthesis of lipids and nucleic acids
27
NADPH
- Produced in the pentose phosphate pathway and is partly responsible for the neutralization of harmful free radicals
28
NADH oxidation
- Generates energy inside the mitochondria during the process of oxidative phosphorylation, associated with cellular respiration
29
Redox coenzymes
- NADH
- Flavin adenine dinucleotide (FAD)
- Flavin adenine mononucleotide (FMN)
- Both FAD and FMN are derivatives of riboflavin (vitamin B2)
30
FADH2
- FAD accepts 2 electrons and 2 protons to become reduced to this
- Important carrier of high-energy electrons in the electron transport chain
31
Enzyme nomenclature
- Oxidoreductases
- Transferases
- Hydrolases
- Lyases
- Isomerases
- Ligases
32
Oxidoreductases
- 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
Transferases
- 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
Hydrolases
- Special group of transferases that catalyze hydrolutic reactions
- Water molecule is added to break a bond
35
Lyases
- 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
Isomerases
- Heterogeneous group of enzymes that catalyze the transfer of groups within the same molecule
37
Ligases
- Enzymes that facilitate bond formation between two substrates coupled to ATP hydrolysis
38
- Oxidoreductases
- Transferases
- Hydrolases
- Lyases
- Isomerases
- Ligases
- Oxidation-reduction reactions
- Transfer of functional groups
- Hydrolysis reactions
- Group elimination to form double bonds
- Isomerization
- Bond formation coupled with ATP hydrolysis
39
Activation energy review
- Lowered by enzymes without affecting equilibria
40
Rate of reactions review
- Enzymes increase the rate of forward and reverse reactions equally stabilizing the transition state
41
Cofactors review
- Some enzymes require metal ions
| - Some enzymes require organic prosthetic groups or coenzymes
42
Coenzymes review
- Most are derivatives of the water-soluble B vitamins
43
Active site review
- The location at which catalysis occurs in the enzyme molecule
44
Enzyme Commission (EC) review
- Designation followed by four digits
- First digit indicates the major class of enzyme
- Next digits allocate enzyme into three different subcategories
