Enzymes: Biological Catalysts

Enzymes: Biological Catalysts

• Enzymes are biological catalysts accelerating reaction rates in living cells.
• Enzymes exhibit substrate specificity, enhancing reaction rates without being used up.
• This specificity arises from complementary shapes, charges, and hydrophilic/hydrophobic characteristics.
• Enzymes bind substrates at the active site, forming an enzyme-substrate complex, a pocket that is part of the enzyme's tertiary/quaternary structure.
• The "Lock and Key" and "Induced-fit" theories explain enzyme specificity.
• Enzymes are named with the suffix "-ase" and classified with an EC number based on reaction type.
• Enzymes are classified into main classes that include Oxidoreductases (EC 1), Transferases (EC 2), Hydrolases (EC 3), Lyases (EC 4), Isomerases (EC 5), Ligases (EC 6), and Translocases (EC 7).
• The EC number has four digits indicating enzyme class, subclass, sub-subclass, and serial number.
• Enzymes are excellent catalysts regulated by temperature, pH, and additives.
• They lower activation energy by forcing molecules through a different transition state.
• Enzyme activity is affected by pH, temperature, and molecules like inhibitors (decrease activity) and activators (increase activity).
• Enzyme activity can be modulated through inhibition.
• Reversible inhibition involves non-covalent interactions, while irreversible inhibition involves covalent bonds.
• Competitive inhibitors bind to the active site; non-competitive inhibitors bind elsewhere, altering the enzyme's shape and reducing activity.
• Enzymes can be activated by ions (Ca2+, Mg2+), cofactors, coenzymes, or conversion of a proenzyme.

Cofactors and Coenzymes: Enzyme helpers

• Some enzymes need additional molecules to function, referred to as cofactors or coenzymes.
• Cofactors are inorganic ions or organic molecules that assist enzymes.
• Coenzymes are organic molecules functioning as cofactors, often derived from vitamins.
• Metalloproteins are enzymes with tightly bound metal ions at their active sites.
• Water-soluble vitamins are precursors to coenzymes, including B vitamins (Thiamin, Riboflavin, Niacin, Pantothenic Acid, Pyridoxine, Biotin, Folic Acid, Cobalamin) and Vitamin C. -Thiamin (Vitamin B1): Part of thiamin pyrophosphate (TPP), is involved in decarboxylation reactions.
• Riboflavin (Vitamin B2): Forms flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN), used in redox reactions.
• Niacin (Vitamin B3): Part of nicotinamide adenine dinucleotide (NAD+) and NADP+, used in redox reactions.
• Pantothenic Acid (Vitamin B5): Part of coenzyme A (CoA), involved in energy production and lipid/amino acid metabolism.
• Pyridoxine (Vitamin B6): Converted to pyridoxal phosphate (PLP), involved in amino acid transamination and decarboxylation.
• Biotin: Involved in carboxyl-group transfer reactions.
• Folic Acid (B9): Forms tetrahydrofolate (THFA), used in nucleic acid synthesis.
• Cobalamin (Vitamin B12): Involved in methyl group transfer.
• Vitamin C (Ascorbic Acid): Acts as an antioxidant and is involved in collagen synthesis and biogenic amine biosynthesis.

Heterocyclic Compounds: Cyclic structures

• Heterocyclic compounds are organic compounds with one or more carbon atoms in a ring structure replaced by a heteroatom (O, N, or S).
• Heterocycles are classified based on the number of atoms in the ring, type of heteroatoms, and the number of rings (monocyclic/polycyclic).
• Pyrrole derivatives (Porphyrins) form building blocks of biologically important compounds.
• Heme is an iron-porphyrin complex responsible for the red color of arterial blood.
• Indole is a fused-ring system found in tryptophan and its derivatives like serotonin.
• Pyrimidines (Cytosine, Thymine, Uracil) and purines (Adenine, Guanine) are bases found in nucleic acids.

Nucleosides, Nucleotides, and Nucleic Acids: Genetic components

• Nucleosides: A nitrogenous base (purine or pyrimidine) linked to a sugar (ribose or deoxyribose) via a glycosidic bond.
• Nucleotides: A nucleoside with one or more phosphate groups attached to the sugar.
• Nucleotides are building blocks for DNA and RNA, an intracellular energy source (ATP), and function as second messengers and intracellular signaling switches.
• Nucleic acids (DNA and RNA) are polymers of nucleotides linked by phosphodiester bonds and store information for cellular growth and reproduction.
• DNA (Deoxyribonucleic Acid) is a double-stranded helix containing deoxyribose sugar with bases Adenine (A), Guanine (G), Cytosine (C), and Thymine (T), with base pairing A-T and G-C.
• RNA (Ribonucleic Acid) is single-stranded, containing ribose sugar with bases Adenine (A), Guanine (G), Cytosine (C), and Uracil (U).
• RNA functions as mRNA (messenger), rRNA (ribosomal), and tRNA (transfer).

DNA vs. RNA: Key differences

• RNA is single-stranded and shorter, while DNA is double-stranded and very long.
• DNA nucleotides contain deoxyribose, phosphate, and one of the nitrogenous bases Adenine, Guanine, Thymine, or Cytosine; RNA nucleotides contain ribose, phosphate, and one of the nitrogenous bases Adenine, Guanine, Uracil, or Cytosine.