Biochemistry Part 3

Question 1

Define enzyme

Answer 1

Catalyse chemical reactions which together make up metabolism

Question 2

Describe the specificity of enzymes?

Answer 2

Limited range of substrates

Some can identify stereoisomers

Question 3

Why are enzymes so potent?

Answer 3

They can convert many substrate molecules into product per second

Question 4

What is the transition state?

Answer 4

Reaction intermediate species which has the greatest free energy

Question 5

How do enzymes reduce activation energy?

Answer 5

Providing alternative reaction pathways

Question 6

What is the cause of glycogen storage disease?

Answer 6

Defective glycogen synthesis/breakdown in muscle, liver and kidney

Question 7

What does catalytic activity of many enzyme depend upon?

Answer 7

Presence of small molecules, called cofactors or coenzymes

Question 8

Describe cofactors

Answer 8

Metal ions, inorganic (form a neat co-ordination centre in the enzyme)

Question 9

How do coenzymes mostly associate with the enzyme?

Answer 9

Transiently

Question 10

What happens to coenzymes during the course of reaction?

Answer 10

Change charge or structure during the course, but are regenerated

Question 11

What are tightly bound coenzymes called?

Answer 11

Prosthetic groups

Question 12

What is an enzyme without a cofactor called?

Answer 12

Apoenzyme

Question 13

What is an enzyme with a cofactor called?

Answer 13

Holoenzyme

Question 14

Give some examples of metal ions and their functions?

Answer 14

Zinc, Iron, Copper

Involved in redox reactions
Stabilise transition states

Question 15

Describe the origin of coenzymes?

Answer 15

Many are derived from vitamins

Question 16

What are coenzymes involved in (give examples)?

Answer 16

Involved in redox reactions
- NAD+, FAD

Involved in transfer processes

• CoA transfers acetyl groups
• ATP transfers phosphate groups

Question 17

What does a substrate bind to?

Answer 17

Active site on an enzyme

-cleft or crevice

Question 18

What does an active site contain?

Answer 18

• amino acids essential for catalytic activity

- amino acids for highly specific interactions

Question 19

What is the induced fit model?

Answer 19

Binding of substrate induces a conformational change in enzyme, results in complementary fit

Question 20

Describe chymotrypsin?

Answer 20

pancreatic serine proteases

Contain reactive serine residue

hydrophobic pocket binds aromatic amino acids

Question 21

Describe trypsin?

Answer 21

pancreatic serine proteases

Contain reactive serine residue

negatively charged Asp interacts with positively charged Lys or Arg

Question 22

Describe elastase?

Answer 22

pancreatic serine proteases

Contain reactive serine residue

active site partially blocked, only amino acids with small or no side chains can bind

Question 23

What affects enzyme activity?

Answer 23

Temperature and pH

Question 24

What is an isozyme?

Answer 24

isoforms of enzymes, they catalyse the same reaction but have different properties and structure (and sequence)

Question 25

When can isozymes be synthesised?

Answer 25

Different stages of foetal and embryonic development

Question 26

Where are isozymes present?

Answer 26

Different tissues and different cellular locations

Question 27

Describe the roll of lactate dehydrogenase?

Answer 27

(Heart) – promotes aerobic metabolism

(Muscle) promotes anaerobic metabolism

Question 28

What is the clinical use of isozymes?

Answer 28

Diagnostic purposes

• stroke
• heart disease
• cancer

Question 29

Give an example of a clinical use of an isozyme?

Answer 29

Creatine kinase (CK) is a dimeric protein which binds to the muscle sarcomere
>M form is produced in skeletal muscle (MM)
>B form is produced in brain (BB)
>Heart produces both types, forms a heterodimer (MB)
>appearance of brain type in blood suggests stroke or tumour
>appearance of heart type suggests heart attack

Question 30

How can enzyme activity be regulated?

Answer 30

Covalent modification
-side groups of serine, threonine, tyrosine

Can convert enzyme to active or inactive form

• glycogen phosphorylase
• phosphorylation converts inactive a form to active b form

Question 31

What carried out phosphorylation?

Answer 31

Protein kinase

Question 32

Define zymogens

Answer 32

Inactive precursor of enzyme- irreversibly transformed into active enzymes by cleavage of a covalent bond

Question 33

Give examples of zymogens in the pancreas

Answer 33

Trypsinogen and chymotrypsin, inactive precursors

Question 34

Give examples of zymogens in the small intestine

Answer 34

enteropeptidase cleaves trypsinogen to form active trypsin which cleaves chymotrypsinogen to form active chymotrypsin

Question 35

Which enzymes are regulated by proteolysis?

Answer 35

Digestive enzymes
Blood coagulation enzymes
Dissolving blood clot enzymes
Programmed development enzymes