Enzymes: Biological Catalysts

Enzymes: Biological Catalysts

• Enzymes act as biological catalysts, accelerating reaction rates within living cells.
• Enzymes are critical for metabolism and life processes within cells.
• Enzymes exhibit specificity, enhancing reaction rates without being consumed.
• Specificity results from complementary shapes, charges, and characteristics between the enzyme and its substrates.

Enzyme-Substrate Interaction

• Enzymes bind substrates at the active site to form an enzyme-substrate complex.
• The active site is a pocket formed by the enzyme's tertiary and quaternary structure.
• Specificity is explained by the "Lock and Key" and "Induced-fit" theories.

Enzyme Classification

• Enzyme names usually indicate their function with the suffix "-ase".
• Enzymes are classified using an EC (Enzyme Commission) number into main classes based on reaction type.
• EC 1: Oxidoreductases catalyze oxidation/reduction reactions.
• EC 2: Transferases transfer chemical groups.
• EC 3: Hydrolases catalyze the hydrolysis of chemical bonds.
• EC 4: Lyases catalyze the cleavage of chemical bonds (excluding oxidation or hydrolysis).
• EC 5: Isomerases catalyze geometric and structural changes between isomers.
• EC 6: Ligases join two compounds utilizing ATP hydrolysis.
• EC 7: Translocases transport substances across membranes (added in 2018).
• The EC number has four digits indicating class, subclass, sub-subclass, and serial number.

Enzyme Properties and Regulation

• Enzymes are excellent catalysts, accelerating reactions significantly.
• Activity is regulated by temperature, pH, and additives.
• Enzymes lower activation energy by forcing molecules through a different transition state.
• Activity is affected by pH and temperature, with enzymes functioning best at specific levels.
• Enzyme activity can be affected by inhibitors, which decrease activity, and activators, which increase activity.

Enzyme Inhibition

• Enzyme activity can be modulated by inhibitors.
• Reversible inhibition involves non-covalent binding, without any chemical changes, and is reversible.
• Irreversible inhibition involves covalent bond, preventing catalytic activity, and is irreversible.
• Competitive inhibitors bind to the active site.
• Non-competitive inhibitors bind elsewhere and alter the enzyme's shape.

Enzyme Activation

• Enzymes are activated by ions (Ca2+, Mg2+), cofactors, coenzymes, or proenzyme conversion.
• Enzyme activation converts an inactive enzyme molecule into a metabolically active form.
• Activators bind to enzyme molecules and boost their metabolic activity.

Cofactors and Coenzymes

• Some enzymes need cofactors or coenzymes to function.
• Cofactors are inorganic ions or organic molecules that assist enzymes.
• Coenzymes are organic molecules that function as cofactors, often derived from vitamins.
• Metalloproteins are enzymes containing tightly bound metal ions at their active sites.

Water-Soluble Vitamins as Coenzyme Precursors

• Water-soluble vitamins are precursors to coenzymes.
• B vitamins (Thiamin, Riboflavin, Niacin, Pantothenic Acid, Pyridoxine, Biotin, Folic Acid, Cobalamin) and Vitamin C are included.
• Thiamin (Vitamin B1) is part of thiamin pyrophosphate (TPP) and is involved in decarboxylation.
• Riboflavin (Vitamin B2) constitutes flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN), for redox reactions.
• Niacin (Vitamin B3) is part of nicotinamide adenine dinucleotide (NAD+) and NADP+, for redox reactions.
• Pantothenic Acid (Vitamin B5) is part of coenzyme A (CoA), involved in energy production and lipid/amino acid metabolism.
• Pyridoxine (Vitamin B6) is converted to pyridoxal phosphate (PLP), involved in amino acid transamination and decarboxylation.
• Biotin is involved in carboxyl-group transfer reactions.
• Folic Acid (B9) constitutes tetrahydrofolate (THFA), for nucleic acid synthesis.
• Cobalamin (Vitamin B12) is involved in methyl group transfer.
• Vitamin C (Ascorbic Acid) acts as an antioxidant and participates in collagen synthesis and biogenic amine biosynthesis.

Heterocyclic Compounds

• Heterocyclic compounds are organic with one or more carbon atoms replaced by heteroatoms in a ring structure.
• They are classified by the number of atoms in the ring, type of heteroatoms, and number of rings.
• Pyrrole derivatives (Porphyrins) are building blocks of compounds that are biologically important.
• Heme, an iron-porphyrin complex, is responsible for the red color of arterial blood and is found in hemoglobin.
• Indole is a fused-ring system in tryptophan and serotonin derivatives.
• Pyrimidines (Cytosine, Thymine, Uracil) and Purines (Adenine, Guanine) are bases found in nucleic acids.

Nucleosides and Nucleotides

• Nucleosides consist of a nitrogenous base linked to a sugar (ribose or deoxyribose) via a glycosidic bond.
• Nucleotides are nucleosides with one or more phosphate groups attached to the sugar.
• Nucleotides are building blocks for DNA and RNA, sources of energy (ATP), second messengers, and intracellular signaling switches.

Nucleic Acids: DNA and RNA

• Nucleic acids (DNA and RNA) are polymers of nucleotides linked by phosphodiester bonds.
• Important molecules store information that is crucial for cellular growth and reproduction.
• Two types of nucleic acids: deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).

DNA

• DNA (Deoxyribonucleic Acid) has a double-stranded helix.
• Contains deoxyribose sugar, and the bases are Adenine (A), Guanine (G), Cytosine (C), Thymine (T).
• Base pairing follows A-T and G-C.
• Primary structure includes alternating 2-deoxy-ribose and phosphate units in the backbone.

RNA

• RNA (Ribonucleic Acid) is single-stranded and contains ribose sugar.
• Bases: Adenine (A), Guanine (G), Cytosine (C), Uracil (U).
• mRNA (messenger), rRNA (ribosomal), and tRNA (transfer) are included in functions.

Key Differences Between DNA and RNA

• RNA is single-stranded and shorter, while DNA is double-stranded and very long.
• DNA nucleotides contain Deoxyribose, Phosphate, and one of four nitrogenous bases (Adenine, Guanine, Thymine, Cytosine).
• RNA nucleotides contain Ribose, Phosphate, and one of four nitrogenous bases (Adenine, Guanine, Uracil, Cytosine).

Conclusion

• Enzymes, cofactors, heterocyclic compounds, nucleotides, and nucleic acids are vital components of life.
• Grasping structure, function, and interactions is essential to understand biological processes.