Coenzyme Structure and Biological Functions

Flashcards covering coenzyme definitions, vitamin B-complex derivatives, non-vitamin coenzymes, and their specific biological functions from the lecture notes.

Coenzyme

A non-protein, organic, low molecular weight, and dialysable substance associated with enzyme function.

Apoenzyme

The protein part of an enzyme that, on its own, is not always adequate to bring about catalytic activity.

Holoenzyme

The active functional enzyme made up of a protein part (apoenzyme) and a non-protein part (coenzyme or cofactor).

Cofactors

Non-protein, small additional factors collectively required by many enzymes for catalytic activity.

Nicotinamide Adenine Dinucleotide (NAD+) and NADP control

Hydrogen- and electron-transferring coenzymes derived from Nicotinic acid (Vitamin B) that participate in biological oxidation-reduction reactions across carbohydrate, lipid, and protein metabolism.

Flavin Mononucleotide (FMN) and Flavin Adenine Dinucleotide (FAD)

Coenzymes commonly called flavoproteins that are associated with dehydrogenases and function as hydrogen transferrers in redox reactions within the electron transport chain.

Isoalloxazine Ring

The functional unit of FMN and FAD coenzymes that serves as the acceptor for two hydrogen atoms with electrons.

Coenzyme A (CoA)

A thiol coenzyme synthesized from pantothenate (Vitamin B) that transfers acyl groups, forms thioesters with carboxylic acids, and aids in transferring fatty acids from cytosol to mitochondria.

Thiamine Pyrophosphate (TPP)

A coenzyme involved in the transfer of aldehyde groups, essential for the irreversible conversion of pyruvate to acetyl-CoA, the $\alpha$-ketoglutarate dehydrogenase reaction in the TCA cycle, and transmission of nerve impulses.

Pyridoxal Phosphate (PLP)

A coenzyme associated with transaminases that accepts an amino group from an amino acid to convert into pyridoxamine phosphate (PAMP) and transfers it to a keto acid.

Non-Vitamin Coenzymes

Organic substances that have no relation to vitamins but function as coenzymes, such as ATP, CDP, UDP, SAM, and PAPS.

Cytidine Diphosphate (CDP)

A non-vitamin coenzyme required in phospholipid synthesis that acts as a carrier of choline and ethanolamine.

Uridine Diphosphate (UDP)

A non-vitamin coenzyme that acts as a carrier of monosaccharides.

S-Adenosylmethionine (SAM)

A non-vitamin coenzyme that donates a methyl group in biosynthetic reactions.

Phosphoadenosine Phosphosulfate (PAPS)

A non-vitamin coenzyme that donates a sulfate group for the synthesis of mucopolysaccharides.