Chap 6- Enzyme Action

Question 1

Enzyme def

Answer 1

Enzymes accelerate the rate of reactions by factors of as much as a million or more.

Question 2

What is carbonic anhydrase and what does it so?

Answer 2

Enzyme that catalyses the reaction of adding water to carbon dioxide, which facilitates the transport of carbon dioxide from the tissues to the lungs where it is expelled. One of the fastest known enzymes.

Question 3

Substrates def

Answer 3

Reactants for an enzyme. Enzymes are highly specific both in their reactions and their substrates.

Question 4

Proteolytic enzymes def

Answer 4

Their biological function is to catalyze the hydrolysis of a peptide bond. They differ markedly in their degree of substrate specificity, for example, papain will cleave any peptide bond whereas trypsin is quite specific and cleaves on the peptide bonds only on the carboxyl side of lysine and arginine residues.

Question 5

What causes the specificity of an enzyme?

Answer 5

It is due to the precise interaction of the substrate with the enzyme. This precision is a result of intricate three dimensional structure of enzymes.

Question 6

What are the names of the six major classes of enzymes?

Answer 6

1. Oxidoreductases
2. Transferases
3. Hydrolyases
4. Lyases
5. Isomerases
6. Ligases

Question 7

Oxidoreductases def

Answer 7

These enzymes transfer electrons between molecules, meaning they catalyze oxidation-reduction reactions.

Question 8

Transferases def

Answer 8

These enzymes transfer functional groups between molecules. Aminotransferases are prominent in amino acid synthesis and degradation, where they shuffle amine groups between donor and acceptor molecules

Question 9

Hydrolyases def

Answer 9

A hydrolyase cleaves molecules by the addition of water. Trypsin, is a Hydrolyases example

Question 10

Lyases def

Answer 10

A Lyase adds atoms or functional groups to a double bond or removes them to form double bonds. The lyase fumerase is crucial to aerobic fuel metabolism

Question 11

Isomerases def

Answer 11

These enzymes move functional groups within a molecule. We will meet triose phosphate Isomerases in glycolysis.

Question 12

Ligases def

Answer 12

They join two molecules in a reaction powered by ATP hydrolysis. DNA Ligases is an example.

Question 13

Cofactors def

Answer 13

Small molecules that are needed for the catalytic activity of many enzymes

Question 14

Apoenzyme def

Answer 14

The name for an enzyme without its cofactor.

Question 15

Holoenzyme def

Answer 15

The term for a catalytically active enzyme.

Question 16

What are the two groups of cofactors

Answer 16

Coenzymes- Small organic molecules, derived from vitamins and metals.

Question 17

Prosthetic (helper) groups def

Answer 17

Tightly bound coenzymes

Question 18

Gibbs free energy def

Answer 18

A thermodynamic property that is a measure of useful energy or energy that is capable of doing work.

Question 19

What two thermodynamic properties of the reaction do we have to consider to understand how enzymes operate?

Answer 19

1. The free energy difference between the products and reactants. Determines whether the reaction will take place spontaneously.
2. The free energy required to initiate the conversion if reactants into products. Determines the rate of the reaction. Enzymes only affect this one.

Question 20

Conditions of free energy

Answer 20

1. If change in G is negative, the reaction is spontaneous.
2. If the change in G is positive, the reaction cannot take place spontaneously
3. If the change in G is 0, the system is at equilibrium
4. The change in G of a reaction is independent on the path of the transformation
5. The change in G doesn’t tell us anything about the rate of the reaction.

Question 21

Can an enzyme alter the equilibrium of a chemical reaction?

Answer 21

No, an enzyme cannot alter the laws of thermodynamics. The same amount of product will be formed with or without an enzyme present but without, it might take hours or centuries to form

Question 22

Why does the rate of product fοrmation level off with time?

Answer 22

The reaction has reached equilibrium. S is being converted to P but P is also being converted into S at such a rate that the amount of P remains constant. Enzymes decrease the time it takes to reach equilibrium but don’t change where it is.

Question 23

Transition state def

Answer 23

The transition state is a fleeting molecular structure that is no longer the substrate but is not yet the product. It is the least stable and least occurring species along the reaction because it is the one with the highest free energy.

Question 24

Activation energy def.

Answer 24

The difference in free energy between the transition state and the substrate. Enzymes function to lower the activation energy. Because the activation energy is lower, more molecules have the energy required to reach the transition state and more products will be formed faster.

Question 25

What is the first step in catalysis?

Answer 25

The formation of an enzyme-substrate complex. Occurs when substrates bind to a specific region of the enzyme called the active site. Most enzymes are highly selective of which substrates can bind to

Question 26

What are the catalytic groups and what do they do?

Answer 26

They are amino acid residues that directly participate in the making and breaking of bonds.

Question 27

What are some similarities between active sites of enzymes.

Answer 27

The active sites are three dimensional clefts or crevices that are formed by groups that come from different parts of the amino acid sequence. The active site takes up a small part of the total volume of an enzyme. Active sites are unique micro environments Substrates are bound to enzymes by multiple weak attractions. These weak reversible interactions are mediated by electrostatic interactions, hydrogen bonds, and van der waals forces, powered by the hydrophobic effect. The specificity of binding depends on the precisely defined arrangement of atoms in active site. Because the enzyme and the substrate interact by means of short range forces that require close contact, a substrate must have the matching shape to fit the site.

Question 28

Induced fit def

Answer 28

Enzymes are flexible and the shapes of the active sites can be markedly modified by the binding of a substrate, process is called induced fit. The mechanism of catalysis is dynamic, involving structural changes with multiple intermediates of both reactants and the enzyme.

Question 29

Binding energy def

Answer 29

The energy released on binding of a substrate to an enzyme. The maximal binding energy is released when the enzyme facilitates the formation of the transition state.

Question 30

Transition-state analogs def

Answer 30

Compounds that resemble the transition state of a reaction but are not capable of being acted on by the enzyme. Demonstrates the importance if the formation of the transition state to enzyme catalysis. The inhibitory power of transition state analogs underscores the essence of catalysis: selective binding of the transition state.

Question 31

What are the two properties of enzymes that make them useful for catalysts?

Answer 31

Rate enhancement and substrate specificity

Question 32

What are the general characteristics of enzyme active sites?

Answer 32

The active site is a three dimensional cleft or crevice. It makes up only a small part of the enzymes volume. Enzymes have unique micro environments. A substrate binds to the active sites can with multiple weak interactions. The specificity of the active sites depends on the active site’s precise three dimensional structure.

Question 33

What does an apoenzyme require to become a holoenzyme?

Answer 33

A cofactor

Question 34

Why are vitamins necessary for good health?

Answer 34

Vitamins are converted into coenzymes that are required for most biological reaction.

Question 35

What is the fundamental mechanism by which enzymes enhance the rate of chemical reactions?

Answer 35

Enzymes facilitate the formation of the transition state.

Question 36

What is the structural basis for enzyme specificity?

Answer 36

The intricate three dimensional structure of proteins allow the construction of active states that will recognize only specific substrates.

Question 37

What would be the result of an enzyme having a greater binding energy for the substrate than for the transition state?

Answer 37

There would be no catalytic activity. If the enzyme substrate complex is more stable than the enzyme-transition-state complex, the transition state would not form and catalysis would not take place.

Question 38

Proteins are thermodynamically unstable. The change in G of the hydrolysis of proteins is quite negative, yet proteins can be quite stable. Explain this apparent paradox. What does it tell you about protein synthesis?

Answer 38

Protein hydrolysis has a large activation energy. Protein synthesis requires energy to proceed.

Question 39

Suggest why the enzyme lysozyme, which degrades cell walls of some bacteria, is present in tears

Answer 39

Lysozyme helps protect the fluid that surrounds eyes from bacterial infection.