Vitamins and Co-enzyme

Question 1

Enzyme activity

Answer 1

Catalytic diversity dependant on amino acids in the active site e.g chymotrypsin (catalytic triad: Asp/His/Ser)

Question 2

Cofactors

Answer 2

molecules which participate in catalysis

-needs essential portion of active site of cofactor

Question 3

Apoenzyme

Answer 3

Binding of cofactor into the inactive apoenzyme -> active “haloenzyme”

Question 4

Types of co-factors

Answer 4

Essential ions

• small molecules
• metal ions
• they are LOOSELY or COVALENTLY bound

Coenzymes

• Cosubstrate (LOOSE)
• Presthetic groups (COVALENTLY)

Question 5

Essential ions

Answer 5

Mostly metal ions
essential minerals for organisms

Activator ions:

• reversibly bound
• participate in binding of substrate

Metalloenzyme metal ions:

• tightly bound
• participate directly in reaction

Question 6

Inorganic cations

Answer 6

Required for full catalytic rate of enzymes

deficiency can lead to disease

Question 7

Minerals

Answer 7

Often metal ions

Question 8

Metal-activated enzymes

Answer 8

needs stimulation by metal ions
monocovalent cations : k

e.g ATP needs to form a complex with Mg to form MgATP, which changes its susceptibility to nucleic attack

Question 9

Metalloenzymes

Answer 9

firmly bound metal ions at active site

usually transition metals e.g Fe and Zn

Electrophilic catalyst
-attract e-

Reversible oxidation reduction

Question 10

Carbonic anhydrase

Answer 10

Enzyme that catalyse conversion that occurs naturally, takes C02, dissolves c02 to convert into carbonic acid, protons and bicarbonate ions, increase conversion by million fold.

Key role in pH regulation, fluid balance in body

Too active: glycoma symptoms

Question 11

Polarity of small molecules

Answer 11

Carbonic anyhydrase (zinc)

Uses metal ion Zn2+

Chelated by 3His and 1 H20 sitting in the active site

Zn is electrophilic, water losses a proton, structure change. obtain positive charge zinc and hydroxide(-ve) which attacks the C02

C02 does not have a net dipole, hence the negative charged hydroxide acts as a nucleophile.

This forms a good leaving group, by which the Zn losses the hydroxide group.

Water is then used to regenerate the enzyme.

Question 12

Metal in enzymes - Iron in heme and non heme

Answer 12

Redox reactions
heme uses Iron 2+ chelated in the centre

Heme groups occures in catalase and cytochromes

Non heme: iron sulfur clusters

Question 13

Example of non heme

Answer 13

2Fe-2S and 4Fe-4S most common as iron clusters

These are 1 electron redox reactions

e.g photosynthesis. uses heme and nonheme for C02 fixation

Question 14

Co-enzymes

Answer 14

referred to as group transfer reagents
highly specific for accepting and donating chemical groups, often derived from vitamins

Cosubstrates
-loosely bound

Prosthetic groups
-covalent

Question 15

Cosubstrates

Answer 15

They are actual substrates, they need to move to active site of enzyme.
The product needs to be extracted from the enzyme (regeneration of cosubstrate), this is catalysed by another enzyme.
The co-enzyme is recylcled repeatedly.

Question 16

Prosthetic groups

Answer 16

Remain bound to the enzyme
Can be covalently attatched to apoenzyme
tihghtly bound to many weak interactions to active site
Must return to original structure during each full catalytic cycle.

They are part of the active site of the enzyme

Supply of reactive groups not available on side chains of amino acid residues.

Question 17

Coenzyme biosynthesis and nutrient intake

Answer 17

Most synthesis coenzymes from simple precursors
Animals have lost most of these biosynthetic pathways

Precursor source are obtained from dietary nutrients (vitamins)

Vitamins derived from “vital amine”

Question 18

Vitamins

Answer 18

Can be split in water soluble and fat soluble vitamins

water soluble:
B vitamin
-required in daily amount, they are secreted
-cellular stores of corresponding coenzyme are unstable

fat soluble
vitamin A,D,E,K
-stored in fats
-excessive lead to hypervitaminosis