14 Enzyme, Cofactors, and Catalysis

Question 1

Why do we need enzymes?

Answer 1

many reactions are highly exergonic = spontaneous, but it will take a long time i.e. sucrose +O2 -> Co2 and H2O, is thermodynamically favourable but takes so long

but in our body, sucrose conversion and release of chemical energy happens in seconds (catalysis by enzyme)

catalysis needed to sustain life. catalysts of biological systems = enzymes

Question 2

What are the 4 general properties of an enzyme?

Answer 2

1. higher reaction rates: compared to uncatalysed reactions and several orders greater than chemically catalysed reactions
2. milder reaction conditions: occurs under relatively mild conditions -<100C, atmospheric pressure, near neutral pH. Chemical catalysis requires harsher conditions
3. Greater reaction specificity: greater specificity of the identities of both reactants and products. chemical catalysis may produce either side products
4. capacity for regulation: enzymatic activity vary in response to other [substances] other than subtrates e.g. allosteric control, covalent modification, variation in [enzyme] synthesised

Question 3

Are most or all enzymes proteins?

Answer 3

most, catalytic RNA are enzymes but not proteins

Question 4

What are cofactors and 2 categories of cofactors?

Answer 4

cofactors are sometime needs by enzymes to catalyse reactions

metal ions: inorganic ions such as fe2+. Mg2+, Mn2+, Zn2+
coenzyme: organic or metalloorganic molecule (most are derived from vitamins in diet)

Question 5

What are prosthetic group?

Answer 5

conenzyme or metal ion that is ver tightly or even covalently bound to the enzyme

Question 6

What are the 6 classification of enzymes?

Answer 6

• oxidoreductases
• transferases
• hydrolases
• lysases
• isomerases
• ligases

Question 7

What is the type of reaction catalysed by oxidoreductases?

Answer 7

transfer of hydrogen and oxygen atoms or electrons from one substrate to another

AH+B -> A+BH

Question 8

What is the type of reaction catalysed by transferases?

Answer 8

transfer of a specific group (e.g. phosphate, methyl) from one substrate to another

A+BX -> AX+B

Question 9

What is the type of reaction catalysed by hydrolases?

Answer 9

transfer of functional groups to water (hydrolysis reactions)

A+H2O -> B+C

Question 10

What is the type of reaction catalysed by lyases?

Answer 10

non-hydrolytic removal or addition of a group to a substrate

A -> B+C

Question 11

What is the type of reaction catalysed by isomerases?

Answer 11

transfer of groups within molecules to yield isomeric forms

AB -> BA

Question 12

What is the type of reaction catalysed by ligases?

Answer 12

joining two molecules with the formation of new bonds and the simultaneous breakdown of ATP

A+B +ATP -> AB + ADP + Pi

Question 13

How is enzyme a biosolution to enzymatic deinking?

Answer 13

• lots of trees worth of paper are thrown away each year
• to recycle them, hazardous chemicals are thrown into our water supply to deink the papers
• using enzymes = less chemical pollutants (milder reaction conditions) and better paper strength (better reaction specificity)

Question 14

What is an enzyme-catalysed reaction?

Answer 14

Question 15

What is the reaction coordinate diagram?

Answer 15

Question 16

What is the transition state of the reaction coordinate diagram?

Answer 16

a fleeting molecular moment in which events such as bond breakage, bond formation, and charge development at which decay to either substrate (reactant) or product is equally likely

Question 17

What is the activation energy of the reaction coordinate diagram?

Answer 17

= difference between the energy levels of ground state and transition state

• energy barriers are crucial, without it complex macromolecules would spontaneously revert to simpler molecular forms, and the complex and highly ordered structures and metabolic processes of cells could not exist
• enzymes selectively lower activation energy for reactions needed for survival

Question 18

Illustration of catalysis

Answer 18

Question 19

Illustration of enzyme complementary to substrate vs enzyme complementary to transition state

Answer 19

Question 20

what is specificity of enzymes?

Answer 20

• extraordinary ability of enzyme to act on a particular substrate
• catalyse only one particular reaction
• producing into a specific product

Question 21

Which is more suitable to describe enzyme-substrate interaction: lock and key or induced fit?

Answer 21

induced fit
* more accurate description of specificity
* substrate binding alters the conformation of the enzymes so that they “fit” each other
* induced fit favours formation of transition state intermediate

Question 22

How are enzymes used against nerve poisons?

Answer 22

• neurotoxins such as DIPF and sarin were used militarily as nerve gas by inhibiting breakdown of acetylcholine (ACh)
• ACh needs to be broken down as it causes activation of motor neurons (muscles will keep getting activated)
• these poisons can be inactivatedby enzyme paraoxonase
• this enzyme occurs as 2 isoforms with different activities. individuals express widely differing levels of the enzyme
• large observed differences in individuals sensitivity to nerve poisons (ppl react differently)

symptoms: spasm, contractions

Question 23

How are enzymes used against blood coagulation cascade?

Answer 23

• when a blood vessel is damaged, a clot forms as a result of platelet aggregation and formation of insoluble fibrin network (traps additional blood cells)
• various components of the cascade include enzymes and non-enzymtic protein cofactors
• such control of clotting is of extreme importance since formation of even one inappropriate blood clot may have fata consequences e.g. thrombin (enzyme) triggers a shutdown of clot formation to limit clotting process