Introduction to Biochemistry: Biomolecules and Metabolism

Enzyme activity follows saturation kinetics where reaction velocity increases with substrate concentration until reaching Vmax. The Michaelis constant (Km) represents substrate concentration at half-maximal velocity. Competitive inhibition involves inhibitors competing with substrates for the active center, increasing Km without changing Vmax. Non-competitive inhibition reduces Vmax while keeping Km unchanged. Allosteric inhibition involves reversible structural changes at regulatory sites. These mechanisms allow cells to precisely control metabolic pathways through feedback regulation.

Enzyme activity is measured by reaction velocity, which depends on substrate concentration following Michaelis-Menten kinetics where Km represents the substrate concentration at half Vmax and reflects catalytic power; enzymes can be regulated through specific inhibition (competitive, non-competitive, and mixed types), allosteric modulation with cooperativity between T and R states, covalent modification (phosphorylation, acetylation), proteolytic activation of zymogens, and genetic control of enzyme quantity.

Enzyme activity is regulated through multiple mechanisms. Covalent modification (like phosphorylation) adds/removes chemical groups to activate/inactivate enzymes. Allosteric regulation involves regulatory molecules binding to allosteric sites, changing enzyme shape and activity. Irreversible inhibition permanently stops enzymes through denaturation (heat, acids, bases), freezing-thawing cycles, or oxidation of critical amino acid groups. Competitive inhibition occurs when inhibitors compete with substrates for the active site, overcome by increasing substrate concentration. Non-competitive inhibition binds to allosteric sites, changing enzyme shape so substrates cannot bind.

Enzyme activity is regulated through multiple mechanisms: (1) Active site and regulatory site interaction where regulatory molecules bind to control enzyme function, (2) Feedback inhibition where end products inhibit earlier enzymes in metabolic pathways, (3) Irreversible inhibition that permanently disables enzymes, and (4) Phosphorylation/dephosphorylation cycles that activate or deactivate enzymes. These mechanisms allow cells to precisely control metabolic pathways and maintain homeostasis.

Enzymes are biological catalysts that accelerate chemical reactions by lowering activation energy, enabling reactions to proceed under cellular conditions. They follow the lock-and-key principle, binding specifically to substrates at active sites. Key characteristics include substrate specificity (binding only to precise molecules) and group specificity (acting on similar molecular types). Enzyme activity is regulated by multiple factors: temperature, substrate concentration, pH, and inhibitors. Two main inhibition mechanisms exist: competitive inhibition (inhibitors compete for active sites) and non-competitive inhibition (inhibitors alter enzyme conformation). Additionally, end-product inhibition provides feedback regulation in metabolic pathways, where the final product inhibits upstream enzymes to prevent overproduction.

DNA replication is the semi-conservative process where DNA polymerase synthesizes new DNA strands using the original strands as templates, involving enzymes like helicase, topoisomerase, primase, and ligase; transcription is the process where RNA polymerase synthesizes mRNA from DNA template following base-pairing rules (A-U, G-C), occurring in the nucleus; and translation is the process where ribosomes synthesize proteins from mRNA using tRNA to deliver amino acids, occurring in the cytoplasm. These three processes form the central dogma of molecular biology, with DNA replication being the foundation for genetic inheritance, transcription enabling gene expression, and translation producing functional proteins.

The central dogma of molecular biology describes the flow of genetic information in cells: DNA replication is the process where DNA makes copies of itself before cell division; transcription is the process where DNA is copied into messenger RNA (mRNA); and translation is the process where mRNA is used by ribosomes to synthesize proteins. These three processes form the fundamental framework for understanding how genetic information is stored, copied, and expressed in living organisms.

The central dogma of molecular biology describes how genetic information flows from DNA to RNA to protein through three key processes: DNA replication creates two identical DNA copies from one original strand by separating the double helix and adding complementary nucleotides (adenine-thymine, guanine-cytosine); transcription transfers DNA information to messenger RNA (mRNA) using RNA polymerase, where uracil replaces thymine; and translation occurs in ribosomes where mRNA codons (three nitrogenous bases) are read by transfer RNA molecules carrying specific amino acids, which join together to form proteins.

Transcription converts DNA into mRNA through RNA polymerase binding to the promoter region (TATA box), synthesizing mRNA complementary to the template strand with uracil replacing thymine; pre-mRNA undergoes splicing to remove introns before leaving the nucleus. Translation occurs at ribosomes where mRNA codons (sets of three nucleotides) are read by tRNA anticodons, with amino acids joined at the ribosome's A, P, and E sites to form polypeptide chains, terminating when stop codons (UAA, UAG, UGA) signal release factors to disassemble the ribosome.

Key molecular processes: (1) Replication (DNA to DNA synthesis) occurs in the nucleus and requires energy, (2) Transcription (DNA to RNA synthesis) occurs in the nucleus and involves dehydration synthesis (water release), (3) Translation (protein synthesis) occurs at ribosomes (on rough ER or in cytoplasm) and requires energy. All three processes involve energy consumption and dehydration synthesis.

Clinical biochemistry encompasses errors in carbohydrate metabolism (diabetes mellitus, hypoglycemia), lipid metabolism (hypercholesterolemia, lipoprotein disorders), and amino acid/nucleic acid metabolism (cystinuria, urea cycle disorders, porphyrias). These disorders arise from enzyme or receptor defects in metabolic pathways. The paper covers diagnostic tests including liver, kidney, pancreatic, and gastric function tests to identify metabolic abnormalities. Understanding metabolic pathways (glycolysis, gluconeogenesis, oxidation pathways) is essential for correlating metabolic errors with clinical findings.

Clinical Biochemistry deals with the laboratory applications of biochemistry to find out the causes of diseases. It involves analyzing body fluids such as blood, urine, and other body fluids to determine their chemical composition and identify abnormalities. The field determines the chemical account statement of body fluids and is used for the diagnosis of various clinical conditions including diabetes mellitus, heart disease, and other metabolic disorders. Clinical Biochemistry performs various tests to determine the function of different organs in the body, such as liver function tests, kidney function tests, and electrolyte tests. These tests are essential for diagnosing organ-specific diseases and monitoring overall body health.

This section covers metabolic disorders and clinical biochemistry concepts. Glycogen storage diseases result from enzyme deficiencies in glycogen metabolism. Gaucher disease involves glucocerebrosidase deficiency causing glucocerebroside accumulation. Fabry disease involves alpha-galactosidase A deficiency causing globotriaosylceramide accumulation. The oxygen-hemoglobin dissociation curve shows how temperature and 2,3-BPG levels affect oxygen affinity. Glycemic index is calculated as (test food area/reference food area) × 100, with high-glycemic foods (>70) causing rapid blood glucose spikes.

Defects in normal biochemical processes lead to specific diseases: amino acid deficiencies cause genetic diseases; defective protein production causes conditions like sickle cell anemia; lipid defects result in atherosclerosis from excessive lipid deposition in blood vessels; and carbohydrate metabolism disturbances lead to diabetes mellitus. Studying normal processes is essential for diagnosing and curing patients.

This section bridges biochemical theory with clinical practice: (1) Metabolic disorders resulting from enzymatic defects (e.g., phenylketonuria, gout), (2) Immune system function and antibody classification (IgG, IgM, IgA, IgE), (3) Lipid classification and biological roles in membranes and signaling, (4) Clinical laboratory investigations including blood chemistry, urine analysis, and diagnostic testing. These concepts enable healthcare professionals to diagnose diseases, monitor treatment efficacy, and understand the molecular basis of pathological conditions affecting patients.

James Black pioneered rational drug design by starting with a medical problem (angina), studying underlying physiology (adrenaline's role in increasing cardiac oxygen demand), and then designing a chemical solution (beta blockers that block adrenaline receptors). This contrasts with earlier pharmaceutical approaches where companies simply tweaked existing drugs to find new uses. Rational drug design involves identifying biological targets first, then finding or creating chemicals that match those targets, becoming a central principle in modern pharmacology.

The third unit covers rational drug design: (1) Definition, principles, and methods of rational drug design compared to traditional drug design; (2) Structure-based vs ligand-based drug design - two fundamental approaches with different strategies; (3) Virtual screening - computational methods for screening large compound libraries; (4) Drug-likeness screening and Lipinski's Rule of Five - guidelines for evaluating drug candidates; (5) Pharmacophore modeling - identifying essential features for drug activity; (6) Pharmacophore-based screening with examples.

Rational drug design involves creating drugs specifically targeted to bind to particular proteins involved in disease. A landmark example is imatinib (Gleevec), developed in the 1990s for treating leukemia. Scientists knew this leukemia protein binds ATP (the cell's energy molecule), so they created a library of ATP-like chemicals and tested them to find one that could inhibit the protein's function, demonstrating successful targeted therapy.

Rational drug design is an approach where drugs are designed based on understanding the molecular structure and function of their targets. This requires three key pieces of information: (1) identification of a malfunctioning protein driving disease pathology, (2) assessment that the protein's function is druggable (can be inhibited effectively), and (3) knowledge of the protein's detailed molecular structure to enable computer-aided design of molecules that fit precisely into the target's binding site.

Rational drug design creates medications specifically targeting biological molecules. The process involves designing small molecules that act as ligands (molecules binding to larger molecules) complementary in shape and charge to target proteins or enzymes. These molecules bind to active sites of enzymes, blocking substrate binding and inhibiting function. This approach produces highly specific drugs targeting particular pathogen components.