Enzyme cofactors, coenzymes and prosthetic groups

what do cofactors and coenzymes do?

• they may transfer atoms pr groups from one reaction to another in a multi-step pathway or they may actually form part of the active site of an enzyme

what is the difference between a cofactor and a coenzyme?

• they both have the same role but if the cofactor is an organic molecule is it called a coenzyme

how are inorganic cofactors obtained?

• via the diet as minerals

• such as iron, calcium, chloride and zinc ions

• e.g. the enzyme that catalyses the breakdown of starch contains a chloride ion that is necessary for the formation of a correctly shaped active site

how are coenzymes obtained?

• via the diet as vitamins

• e.g. vitamin B3 is used to synthesis NAD, a coenzyme is responsible for the transfer of hydrogen atoms between molecules involved in respiration

what are prosthetic groups?

• cofactors required by some enzymes for catalytic activity

what is something that is different between cofactors and prosthetic groups?

• some cofactors bind loosely or temporarily but prosthetic groups are tightly bound and form a permanent part of the protein

what is an example of a prosthetic group?

iron ion in haemoglobin is a prosthetic group

what is a precursor enzyme?

• when some enzymes are produced in a longer, inactive form

what can precursor enzymes also be called?

zymogens

why are some enzymes produced as precursor enzymes?

• it prevents the enzyme from causing damage to the cells that produce them or ensures that they only activate under certain specific conditions

how does activation of precursor enzymes happen?

• activation occurs by proteolytic cleavage

• the removal of the peptide causes a permanent change in tertiary structure

• the new shape exposes or completes the active site, turning the enzyme active

what is an inactive enzyme without it’s cofactor called?

apoenzyme

what is an apoenzyme?

the inactive protein part of an enzyme that lacks its cofactor

what happens when the cofactor binds to the apoenzyme?

• it activates it

• it becomes a holoenzyme

what is proteolytic cleavage?

• the removal of part of the polypeptide chain

what carries out the proteolytic cleavage?

• another enzyme, often a protease

what is blood clotting triggered by?

tissue damage and platelet aggregation

what is the blood clotting mechanism?

• Platelets release clotting factors, including factor X.

• Factor X requires the cofactor vitamin K to function.

• Activated factor X converts prothrombin to thrombin by cleaving bonds and changing its tertiary structure.

• Thrombin converts fibrinogen to fibrin, forming insoluble fibres.

• Fibrin + platelets = blood clot.

• The clotting process involves a cascade of enzyme activations, ensuring rapid and controlled clot formation

how do cofactors increase activity of enzymes?

• completes the enzyme's shape

• helps bind the substrate

• or participates in the reaction

how do coenzymes increase activity of enzymes?

• Bind temporarily to the enzyme

• Help transfer atoms or chemical groups during reactions

• are not permanently attached — they come and go

how do prosthetic groups increase the activity of enzymes?

• Help the enzyme bind to the molecule it’s working on,

• Help carry electrons or atoms,

• Or help stabilize the reaction.