Enzymology

Question 1

What are simple enzymes?

Answer 1

A single, folded, polypeptide chain that catalyses reactions

Question 2

What is an enzyme complex?

Answer 2

A number of distinct enzymes that comprise several subunits, that exist together to perform a single function

Question 3

What are the two types of cofactors?

Answer 3

Metal ions and coenzymes

Question 4

What are cofactors?

Answer 4

Non-protein structures that some enzymes require for activity

Question 5

What is a holoenzyme?

Answer 5

An intact enzyme-cofactor complex

Question 6

When the cofactor is removed from a holoenzyme, what is the remaining protein called?

Answer 6

An apoenzyme

Question 7

What are enzymatic prosthetic groups?

Answer 7

Coenzymes that are tightly bound to the enzyme molecule

Question 8

All water-soluble vitamins are components or precursors of coenzymes. What is the exception?

Answer 8

Vitamin C

Question 9

Are coenzymes modified during the chemical reactions?

Answer 9

Coenzymes are modified during the reaction, and are then converted back into their original forms by other enzymes

Question 10

Are large or small amounts of coenzymes needed for reactions?

Answer 10

Small amounts

Question 11

What are the four characteristics of biological catalysts?

Answer 11

1. Effective in small quantities
2. Unchanged by the reaction
3. They do not affect the equilibrium of a reaction
4. They are very specific

Question 12

How do biological catalysts differ from conventional catalysts?

Answer 12

Biological catalysts show a high degree of specificity

Question 13

How is the enzyme Thrombin more specific than the enzyme Trypsin?

Answer 13

The enzyme Trypsin cleaves a polypeptide chain on the carboxyl side of lysine/arginine residues.
The enzyme Thrombin only cleaves arginine-glycine bonds in particular sequences of polypeptides

Question 14

What enzyme hydrolyses a peptide bond?

Answer 14

A proteolytic enzyme

Question 15

What was the first proposition of the mechanism of enzyme activity and how does it work?

Answer 15

The lock-and-key model suggests that the enzyme accommodates the specific substrate as a lock does a specific key

Question 16

What is the most accurate theorised mechanism of enzyme activity and how does it work?

Answer 16

The induced fit model suggests that the enzyme and the substrate become distorted upon binding

Question 17

What is an acid?

Answer 17

A substance that releases protons - it is a proton donor

Question 18

What is a strong acid?

Answer 18

A strong acid releases all of its protons and completely dissociates

Question 19

Is hydrochloric acid a strong or weak acid?

Answer 19

A strong acid

Question 20

What is a weak acid?

Answer 20

A weak acid only releases some of its protons and incompletely dissociates

Question 21

Is ethanoic acid a weak or a strong acid?

Answer 21

Weak acid

Question 22

Do stronger acids have a higher or lower pKa?

Answer 22

A lower pKa

Question 23

Do weaker acids have a higher or lower pKa?

Answer 23

A higher pKa

Question 24

At pH values above the isoeletric point, is the protein negatively or positively charged?

Answer 24

Negatively charged

Question 25

At pH values below the isoelectric point, is the protein negatively or positively charged?

Answer 25

Positively charged

Question 26

When the number of positive and negative charges of a protein are equal, pH = what?

Answer 26

pH = pI

Question 27

At the isoelectric point, what overall charge does a protein have?

Answer 27

A neutral charge

Question 28

What are enzymatic inhibitors?

Answer 28

Inhibitors bind to an enzyme and prevent/slow reactions from occurring

Question 29

What are competitive inhibitors?

Answer 29

They bind to the active site and compete against the substrate

Question 30

What are non-competitive inhibitors?

Answer 30

They bind to an alternative (allosteric) site and alter the shape of the active site to prevent the substrate from binding to the active site

Question 31

What is allostery?

Answer 31

The condition of a protein in which the structure and activity of the enzyme are modified by the binding of a metabolic molecule at an allosteric site

Question 32

What is an allosteric site?

Answer 32

A site on the enzyme alternative to the chemically active one