Enzymes

Question 1

What are enzymes and what do they do

Answer 1

Biological catalysts (proteins) that increase rates of reactions without undergoing permanent change themselves (without being used up in the process)

Question 2

Name the classes of enzymes

Answer 2

oxidoreductases, transferases, hydrolases, lyases, isomerases, ligases

Question 3

What do oxidoreducatses do? give an example

Answer 3

transfer of electrons (H+). Eg: alcohol dehydrogenase

Question 4

What do transferases do? give example

Answer 4

transfer a functional group from one molecule to another. Eg: hexokinase

Question 5

what do hydrolases do? give example

Answer 5

Break down a molecule using water. Eg: alkaline phosphate

Question 6

what do lyases do? give example

Answer 6

add or remove groups without hydrolysis usually to double bonds. Eg: citrate lyase

Question 7

what do isomerases do? give example

Answer 7

transfer of groups within molecules. Eg: phosphoglycerate mutase

Question 8

what do ligases do? give example

Answer 8

join 2 substrates. Eg: pyruvate carboxylase

Question 9

what is the most abundant enzyme in living organisms? and what class is it part of?

Answer 9

RuBisCO (lyase class)

Question 10

What is an isoenzyme (isozyme)

Answer 10

different forms of the same enzyme within an organism, they catalyse the same reaction, have similar AA sequences and share a common evolutionary origin

Question 11

What type of proteins are enzymes?

Answer 11

globular proteins, have hydrophobic internal residues, hydrophilic external residues.

Question 12

what is the active site?

Answer 12

3D cleft where substrates are bound, usually extends to the internal hydrophobic pocket where the reaction occurs, contains catalytic groups that participate in the making and breaking of bonds

Question 13

What are coenzymes/cofactors

Answer 13

Cofactors can be organic molecules (coenzymes - derived from vitamins weakly bound to the enzyme, can act as co-substrates and are converted into products) or inorganic metal ions. cofators/coenzymes that are tightly bound are called prosthetic groups

Question 14

What is a vitamin

Answer 14

organic compounds essential for normal growth and nutrition that cannot be synthesized by the body. (many vitamins are precursors for coenzymes)

Question 15

GIven vitamin (niacin) name: coenxyme - reaction catalysed - deficiency

Answer 15

NAD+, NADP+ - Oxidation - Pellagra
NADH, NADPH - Reduction

Question 16

What is the international unit of enzyme activity

Answer 16

one I.U: amount of enzyme required to catalyse the conversion of 1umol of substrate (or product) per minute at 25C

Question 17

What is special about enzymes (what makes them work well)

Answer 17

They work under mild conditions of temp and pH, they are highly specific for substrates and for reaction catalysed, have immense catalytic power (can increase reaction rates up to 10^12 fold), they can be regulated

Question 18

What does the pH profile of an enzyme depend on?

Answer 18

charge state of enzyme and/pr substrate due to ionisation of amino acids or substrate, enzyme denaturation at extreme pH

Question 19

what are thermophilic organisms?

Answer 19

enzymes that are very resistant to denaturation at high temp.

Question 20

what temp range do psychrophiles like?

Answer 20

low temp <15C

Question 21

what temp do mesophiles like?

Answer 21

midrange temperature

Question 22

what is the lock and key hypothesis

Answer 22

large enzyme with active site (lock), small molecule substrate (key)

Question 23

what is the induced-fit hypothesis

Answer 23

substrate binding results in conformational change in enzyme

Question 24

what is transition state binding

Answer 24

enzyme active site binds subtrate but has greater affinity for the transition state intermediate in the reaction pathway - thus drives reaction

Question 25

define absolute specificity and give example

Answer 25

the enzyme will catalyse only one reaction. eg: maltase only acts on maltose

Question 26

define group specificity and give example

Answer 26

the enzyme will act only on molecules that have specific functional groups. eg: tyrosine kinase

Question 27

define linkage specificity and give exmaple

Answer 27

the enzyme will act on a particular type of chemical bond regardless of the rest of the molecular structure. eg: amylase clease alpha 1-4 glycosidic bonds in starch

Question 28

define sterochemical specificity and give example

Answer 28

the enzyme will act on a particualr steric or optical isomer. eg: D-amino acid oxidase acts only on D-amino acids

Question 29

enzyme catalysis

Answer 29

enzymes increase rate of reaction by lowering the activation energy barrier. no change in overall thermodynamics. no change in enzyme (true catalyst)

Question 30

what are the 6 ways enzymes achieve rate enhancement

Answer 30

1) proximity and orientation effects, 2) acid/base catalysis, 3) electrostatic interactions, 4) covalent catalysis, 5) transition state stabilisation, 6) metal ion catalysis

Question 31

What is proximity and orientation

Answer 31

enzyme acts as a template to bring reactants close together and ina favourable orientation for reaction to occur (not a chance encounter between molecules in solution)

Question 32

what is acid/base catalysis

Answer 32

side chain groups of some amino acids in active site can act as acids or bases by donating/accepting protons from substrates or intermediates OR one aa side chain acts as an acid and another as a base simultaneously to facilitate reaction (concerted acid-base catalysis)

Question 33

what is covalent catalysis

Answer 33

amino acid side chains can react with substrate to form a covalent intermediate (usually nucleophilic attack on substrate C)

Question 34

what is transition state binding

Answer 34

enzyme active site promotes formation of transition state intermediates. TS - highly unstable intermediates where bonds are made/broken

Question 35

what are electrostatic/environment effects

Answer 35

enzyme active site excludes H2O - allows electrostatic stabilization of transition states through favourable charge distributions

Question 36

what is metal ion catalysis

Answer 36

metal ion is held in place by specific residues (usually His). charge can stabilise intermediates and can polarize substrates to make them more reactive.

Question 37

What is carbonic anhydrase important for

Answer 37

enzyme important for maintaining the pH of blood and other tissues. Found in RBC’s. The bicarbonate ion product is the major form of transport for CO2 in the blood. one of the fastest known enzymes

Question 38

what is the mechanism of carbonic anhydrase

Answer 38

1) zinc polarises and deprotonates water generating a hydroxide ion, 2) CO2 substrate binds to the active site and it positioned for optimal interaction with -OH, 3) the hydroxide ion (nucleophile) attacks the carbonyl C of CO2, converting it to bicarbonate ion HCO3-, 4) enzyme is regenerated and the bicarbonate ion is released

Question 39

what is lysozyme important for?

Answer 39

cleaves the polysaccharide in bacterial cell wall, binds 6 sugar units in a long active site cleft, cleaves the glycosidic bond between residues 4 and 5

Question 40

what is enzyme kinetics

Answer 40

effect of substrate concentration on initial ratesof enzyme catalysed reactions