Medical Biochemistry

1. Biomolecules in the Human Body

Biomolecules are essential for the body’s structure, function, and regulation. Here’s a breakdown of the major categories of biomolecules:

• Proteins: Proteins are large, complex molecules that perform a variety of functions in the body. They act as enzymes (which catalyze biochemical reactions), hormones (which regulate physiological processes), and structural components (like collagen in connective tissues). Proteins are made of amino acids linked by peptide bonds. The shape of a protein is critical for its function, and any structural abnormalities can lead to diseases such as sickle cell anemia.
• Carbohydrates: These include sugars (monosaccharides like glucose) and complex molecules (polysaccharides like starch and glycogen). Carbohydrates provide energy for cellular processes, and excess glucose is stored as glycogen in the liver and muscles. Glycogen breakdown into glucose provides energy when needed, especially in the brain and muscles.
• Lipids: Lipids are fats, oils, and related molecules that serve as energy storage molecules (e.g., triglycerides) and important components of cell membranes (e.g., phospholipids and cholesterol). Cholesterol, for example, is crucial for the synthesis of steroid hormones (like cortisol and estrogen), and phospholipids form the lipid bilayer of cell membranes, regulating what enters and leaves the cell.
• Nucleic Acids: DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) are the genetic materials in all living organisms. DNA stores genetic information, while RNA helps with the expression of that information by guiding protein synthesis. Mutations in DNA can lead to genetic disorders, such as cystic fibrosis, where a mutation in the CFTR gene affects lung function.

2. Metabolism

Metabolism refers to all the chemical reactions occurring in the body to maintain life. These reactions can be categorized into two types:

• Catabolism: This refers to the breakdown of larger molecules into smaller ones, often releasing energy. For example, glycolysis is the breakdown of glucose into pyruvate, releasing energy stored in glucose.
  • Citric Acid Cycle: This is a key pathway that occurs in the mitochondria, further breaking down products from glycolysis to produce ATP (the body’s energy currency).
  • Fatty Acid Oxidation: This process involves breaking down fatty acids into smaller molecules to produce energy, particularly during fasting or long-duration exercise.
• Anabolism: Anabolic processes build larger molecules from smaller ones, requiring energy. Examples include:
  • Protein Synthesis: Amino acids are linked together to form proteins.
  • DNA Replication: Nucleotides are joined to form DNA strands during cell division.

Metabolic disorders arise when there is a dysfunction in these processes. For example:

• Diabetes occurs when insulin (a hormone that helps regulate glucose metabolism) is deficient or ineffective, leading to high blood sugar levels.
• Phenylketonuria (PKU) is a genetic disorder where the enzyme that breaks down phenylalanine (an amino acid) is deficient, causing a buildup of phenylalanine which can harm the brain.

3. Enzymes and Enzyme Regulation

Enzymes are proteins that speed up biochemical reactions by lowering the activation energy needed for those reactions to occur. They are crucial in almost all physiological processes, including digestion, energy production, and the synthesis of cellular components.

• Enzyme Catalysis: Enzymes work by binding to substrates (reactants) at their active sites, converting them into products, and releasing them.
• Regulation: Enzymes can be regulated in several ways:
  • Allosteric Regulation: This occurs when a molecule binds to a site other than the enzyme’s active site, altering its activity.
  • Feedback Inhibition: This is a mechanism where the end product of a metabolic pathway inhibits an enzyme that acts earlier in the pathway, thus regulating the pathway’s activity.
  Abnormal enzyme activity can result in diseases such as lactose intolerance, where the enzyme lactase is insufficient, or galactosemia, where the enzyme responsible for metabolizing galactose is deficient.

4. Clinical Biochemistry and Diagnostics

Medical biochemistry is heavily used in clinical diagnostics to monitor health and diagnose diseases. Various biochemical tests are used to evaluate the levels of substances in the blood, urine, or other body fluids. Common tests include:

• Blood Tests:
  • Glucose Levels: Used to diagnose and manage diabetes.
  • Lipid Profile: Measures cholesterol and triglyceride levels to assess cardiovascular risk.
  • Liver Function Tests: Include enzymes like ALT and AST, which are released when the liver is damaged.
• Urine Tests:
  • Creatinine and Urea: Used to assess kidney function.
  • Urinalysis: Looks for abnormalities such as proteins, glucose, or blood in the urine.
• Genetic Testing: Identifies mutations in DNA that may predispose an individual to specific diseases, such as BRCA mutations for breast cancer or CFTR mutations for cystic fibrosis.

5. Hormones and Signal Transduction

Hormones are chemical messengers that regulate physiological functions. They bind to specific receptors on target cells, triggering a cascade of biochemical events inside the cell (signal transduction). Key examples include:

• Insulin: Regulates glucose metabolism. When blood sugar is high, insulin helps cells take up glucose from the blood.
• Thyroid Hormones (T3 and T4): Regulate metabolism, growth, and development.
• Cortisol: A stress hormone that helps regulate the body’s response to stress, including increasing glucose levels and reducing inflammation.

Signal transduction involves molecules inside the cell, often proteins that work in a cascade, such as kinases (enzymes that add phosphate groups to other proteins). For example, the MAPK pathway is involved in cell growth and differentiation.

6. Genetic Disorders

Medical biochemistry studies genetic disorders, which occur when there is a mutation in the genes that encode enzymes or other proteins necessary for normal body function. Some examples include:

• Phenylketonuria (PKU): Caused by a mutation in the gene that encodes the enzyme phenylalanine hydroxylase, leading to the accumulation of phenylalanine in the blood, which can damage the brain.
• Cystic Fibrosis: Caused by mutations in the CFTR gene that results in thick mucus buildup in the lungs and digestive tract, leading to respiratory and digestive problems.
• Sickle Cell Anemia: A mutation in the hemoglobin gene causes red blood cells to assume a sickle shape, leading to blockages in blood vessels and reduced oxygen delivery to tissues.

7. Therapeutic Interventions

Medical biochemistry helps in understanding how drugs interact with the body at the molecular level. There are two main areas to focus on:

• Pharmacodynamics: This studies the effects of a drug on the body. For example, aspirin inhibits cyclooxygenase enzymes to reduce inflammation and pain.
• Pharmacokinetics: This studies how the body processes drugs, including absorption, distribution, metabolism, and excretion (ADME). This helps determine the right dosage and frequency for a drug.

Chemotherapeutic agents for cancer or antiviral drugs for infections are developed by targeting specific biochemical pathways or molecules (e.g., inhibiting viral enzymes like protease or reverse transcriptase).

8. Nutritional Biochemistry

Nutritional biochemistry focuses on how nutrients are used in metabolic processes. It involves the study of:

• Vitamins and Minerals: Essential for enzyme function. For example, Vitamin C is crucial for collagen synthesis, and iron is required for hemoglobin production.
• Energy Metabolism: Carbohydrates, fats, and proteins are metabolized to generate ATP. Deficiencies or excesses in nutrients can lead to conditions like scurvy (Vitamin C deficiency) or rickets (Vitamin D deficiency).

9. Cancer Biochemistry

Cancer involves genetic mutations that alter normal cell function, such as uncontrolled growth or the ability to avoid cell death. Some key aspects include:

• Oncogenes: These are mutated genes that promote cancer. For example, the ras gene can lead to uncontrollable cell division.
• Tumor Suppressor Genes: These genes normally inhibit cell growth or induce apoptosis. Mutations in tumor suppressor genes like p53 can lead to cancer.
• Warburg Effect: Cancer cells often rely on glycolysis (even when oxygen is available) for energy production, a phenomenon known as the Warburg effect. This is a hallmark of cancer metabolism.

10. Research and Advances

Medical biochemistry is an evolving field, with cutting-edge technologies providing deeper insights into health and disease. Notable advancements include:

• Genomics and Proteomics: These fields focus on studying the entire genome (all genes) and proteome (all proteins) of an organism. This information is used to understand disease mechanisms and identify new therapeutic targets.
• Biomarker Discovery: New biochemical markers are being discovered to diagnose diseases earlier or monitor the effectiveness of treatments.

11. Role in Healthcare and Education

Medical biochemists play a crucial role in healthcare:

• Clinical Laboratories: Perform diagnostic tests on blood, urine, and tissue samples.
• Research: Medical biochemists conduct research to discover new treatments, identify disease mechanisms, and develop diagnostic tools.
• Education: They teach medical students, lab technicians, and healthcare professionals, providing the knowledge necessary for diagnosing and treating diseases.