Enzymes

Question 1

What are enzymes?

Answer 1

Proteins that catalyze an increase in rate of a chem reaction
-Selectively convert starting molecules - substrates - into diff molecules - products.

Question 2

What do enzymes do to the energy of activation?

Answer 2

Lower it

Question 3

What important roles do enzymes play?

Answer 3

-All biochem reactions are enzyme catalyzed in living organism
-Digestion, metabolism, diagnosi, therapeutics
-Level of enzyme in blood are of diagnostic importance - good indicator in myocardial infarction
-Can be used therapeutically such as digestive enzymes
-Activity can be therapeutically targeted - inhibited or activated

Question 4

What are the 6 functional classes of enzymes?

Answer 4

1. Oxidoreductases - oxidation-reduction
2. Transferases - transfer groups of atoms
3. Hydrolases - hydrolysis
4. Lysases - add/remove atoms to/from a double bond
5. Isomerases - rearrange atoms
6. Ligases - Use ATP to combine molecules

Question 5

What do Oxidoreductases do? Examples?

Answer 5

-Catalyse oxidation/reduction rxns
-Act on many chemical groups to add or remove hydrogen atoms
-E.g Lactate dehydrogenase, catalase, peroxidase, phenylalanine hydroxylase

Question 6

What do Transferases do? Examples?

Answer 6

-Transfer a functional group (e.g amino acid or phosphate) between donor and acceptor molecules
-E.g Transaminases- transfer amino group NH2, Phosphotransferases (kinases), Transmethylases, transpeptidases, transacylases

Question 7

What do hydrolases do? Examples?

Answer 7

-Catalyse the cleavage of bonds by addition of water across a bond
E.g
-Protein hydrolysing enzymes - peptidases and proteases
-Carbohydrases - amylase, maltase, lactase
-Lipid hydrolyzing enzymes - lipase
-Deaminases, phosphatases

Question 8

What do Lyases do? Examples?

Answer 8

-Cleave various bonds (C-C, C-S, and certain C-N bonds) by means other than hydrolysis and oxidation
-E.g aldose, fumerase, carbonic anhydrase

Question 9

What do isomerases do? Examples?

Answer 9

-Catalyse inter-conversion of optical, geometric or positional isomers within a single molecule
-E.g isomerase, mutase

Question 10

What do Ligases (synthases/synthetases) do? Examples?

Answer 10

-Join 2 molecules w covalent bonds
-Catalyse reactions in which 2 chemical groups are joined w the use of energy from ATP
-E.g Acetyl-CoA Carboxylase, pyruvate carboxylase, glutamine synthetase

Question 11

Structure of enzymes?

Answer 11

-Proteins
-Globular shape
-Complex 3D structure

Question 12

Cofactor vs Coenzyme

Answer 12

Cofactor - small inorganic molecule or atom (Zn2+ or Fe2+). - tightly bound to apoenzyme

Coenzyme - small organic molecules (NAD+ or FAD)

Question 13

What is the apoenzyme part of the complex or holoenzymes?

Answer 13

Protein part

Enzyme without its non-protein moiety - inactive

Question 14

What is the Holoenzyme ?

Answer 14

Enzyme with its non-protein component - active

Question 15

Examples of inorganic ions that serve as cofactors for enzymes?

Answer 15

-Cu2+ - Cytochrome oxidase
-Fe2+ por Fe3+ - Cytochrome oxidase, catalase, peroxidase
-K+ - pyruvate kinase
-Mg2+ - hexokinase, glucose -6- phosphatase, pyruvate kinase
-Mn2+ - Arginase, ribonucleotide reductase
-Mo - Dinitrogenase
-Ni2+ - Urease
-Zn2+ - Carbonic anhydrase

Question 16

What does magnesium regulate?

Answer 16

Glycolysis

Question 17

Whta is the specificity of an enzyme determined by?

Answer 17

The active site

Question 18

What does the active site of an enzyme have?

Answer 18

-Contains amino acid side chains that participate in substrate binding and catalysis
-The shape and chemical environment inside the active site permits a chemical reaction to proceed more easily

Question 19

What are types of enzyme specificity and give examples?

Answer 19

1. Absolute - catalyze one type of rxn for a single substrate e.g urease catalyzes only the hdrolysis of urea
2. Group - catalyze one type of reaction for similar substrates e.g hexokinase adds a phosphate group to hexoses
3. Linkage - catalyze one type of rxn for a specific type of bond e.g chymotrypsin catalyses the hydrolysis of peptide bonds

Question 20

What is the free activation of energy?

Answer 20

The energy barrier separating reactant and products
-crossing the barrier requires activation energy

Question 21

When are molecules in the reaction said to be in transition state?

Answer 21

-When they are crossing the free energy of activation barrier

Question 22

Velocity

Answer 22

v = change in conc / time

-over time conc of substrate decreases and conc of product increases

Question 23

What did Michaelis and Menton postulate?

Answer 23

1. The enzyme first combines reversibly w its substrate to form ES complex in a relatively fast reversible step
2. The ES complex then breaks down in a slower second step (rate-limiting step) to yield the free enzyme and the product

Question 24

What is the Michaelis-Menten equation?

Answer 24

-The rate equation for an enzyme-catalyzed reaction
-Describes how reaction velocity varies w substrate conc

V (initial) = Vmax (substrate conc) / Km-constant + substrate conc

Km - the subtrate conc at which the reaction velocity is half of max velocity
-Use graph - vmax/2 - hit graph and go down to find substrate which is Km

Question 25

Does Km vary w conc of enzyme?

Answer 25

No

-Km is inversibly proportional w the enzyme affinity to the substrate

Question 26

What does a high or low Km reveal?

Answer 26

-Small Km reflects a high affinity for substrate

-Large Km reflects a low enzyme affinity for substrate

Question 27

What are advantages of Linewaver-Burk Plot?

Answer 27

-Requires few points to define Km
-Easily used to calculate Km and Vmax
-Used to determine the mechanism of action of enzyme inhibitors