Introduction to Medical Biochemistry

Medical biochemistry is a cornerstone in the education of healthcare professionals, forming a vital component of their curriculum. In modern medical science, biochemistry is indispensable, providing a deep understanding of metabolic pathways, cellular communication, molecular mechanisms, and diseases linked to biochemical imbalances. Its relevance spans everything from the action of biomolecules in health and disease to the underlying mechanisms of cellular signaling.

This lecture note on medical biochemistry aims to integrate and simplify the core principles, making them accessible for graduate-level health science students. The content is designed to cover key areas of the subject, ensuring a comprehensive grasp of the fundamental biochemistry necessary for healthcare professionals. The topics are grouped around the following core themes:

Conformation and Structure of Biomolecules: Understanding how the shape and structure of biomolecules dictate their biological functions.

Metabolic Synthesis and Degradation: Delving into how major metabolites are formed and broken down in the body.

Energy Production and Storage: Exploring how the body produces, stores, and utilizes energy at the molecular level.

Biocatalysts: Examining the role of enzymes in catalyzing biochemical reactions, and their practical applications.

Hormonal Intercellular Communication: Understanding how hormones act as messengers between cells, regulating various physiological processes.

Molecular Genetics and Gene Expression: Investigating the molecular processes that control gene expression and regulation.

Enzymes: The Biological Catalysts

Proteins within the body perform an array of crucial functions, one of the most important being their role as biological catalysts, known as enzymes. Enzymes facilitate highly specific biochemical reactions, directing metabolic processes and maintaining the regulation of the entire body’s metabolism. They are pivotal in the synthesis and breakdown of nutrients and biomolecules, and their activity is central to maintaining health.

Enzyme assays play a key role in diagnostics, allowing for the identification of tissue damage, the extent of disease progression, and the monitoring of therapeutic interventions. By analyzing enzyme levels, medical professionals can detect and track the presence of various diseases.

Amino Acids and Proteins: The Building Blocks of Life

Proteins are the fundamental molecules that constitute living systems. These complex molecules are polymers made from amino acids, linked by peptide bonds. Proteins are central to the expression of genetic information, functioning as enzymes, hormones, antibodies, transporters, structural components, and more. They serve as molecular tools that carry out countless physiological tasks, from forming the structural framework of tissues to mediating biological processes.

Though there are over 300 amino acids, only 20 are encoded by the DNA of higher organisms. The acid-base properties of amino acids significantly affect the physical and chemical characteristics of proteins. Proteins are organized into four structural levels: primary, secondary, tertiary, and quaternary. It is their three-dimensional structure that determines their biological activity, with denaturation (the unfolding or disorganization of proteins) often resulting in the loss of function.

Amino acid-derived peptides also play critical roles in the body, and their specialized products are essential for normal physiological function.

This introduction is designed to engage students with an interest in medical biochemistry by presenting complex concepts in an accessible, structured manner, while emphasizing the real-world relevance of biochemistry in healthcare

Carbohydrates

Carbohydrates are essential biomolecules found in living organisms. These molecules are typically composed of multiple hydroxyl groups and either an aldehyde or ketone group, giving rise to polyhydroxy aldoses or ketoses. Carbohydrates are classified into three main categories: monosaccharides, disaccharides, and polysaccharides. Monosaccharides represent the smallest sugar unit, while disaccharides consist of two monosaccharides connected by glycosidic bonds, which can be either α or β types. Polysaccharides are larger molecules made up of more than 10 monosaccharide units.

Carbohydrates play a wide variety of roles in organisms, including providing energy, acting as storage molecules for energy, serving as components of cell membranes, and mediating communication between cells. A deficiency in enzymes such as lactase can result in discomfort and diarrhea, while impaired metabolism of galactose and fructose can lead to cataracts due to lens protein turbidity. Blood glucose levels are tightly regulated by hormones like insulin, and malfunction in insulin production or function can lead to conditions like diabetes, increasing the risk of vascular diseases, atherosclerosis, and renal failure.

In the process of integrative metabolism and bioenergetics, glucose is converted to pyruvate in the presence of oxygen. Pyruvate can also be derived from amino acids, proteins, and other precursors such as glycerol and propionate. Pyruvate is further broken down into acetyl-CoA, a key intermediate in the metabolism of carbohydrates, lipids, and amino acids. Acetyl-CoA enters the citric acid cycle in the mitochondria, where it is oxidized to produce carbon dioxide, water, and reduced coenzymes (NADH, FADH2). These reduced nucleotides are used in oxidative phosphorylation to generate ATP, the cell's primary energy currency.

Lipids

Lipids, another major class of biomolecules, are primarily hydrophobic and water-insoluble. They can be extracted using non-polar solvents such as benzene, methanol, or ether. Some lipids, like triglycerides, serve as energy storage molecules, while others, like lipoproteins, are involved in the transport of lipids in the body. Cholesterol, although lacking fatty acids, is a lipid-like molecule and plays a crucial role in cell membrane structure, acting as a hydrophobic barrier that regulates the entry and exit of molecules. Imbalances in lipids can result in conditions such as obesity and atherosclerosis. The breakdown of fatty acids provides energy, but excessive breakdown can lead to ketosis, ketoacidosis, and potentially life-threatening conditions such as coma and death. Cholesterol levels are regulated by complex mechanisms, and understanding these processes is important in treating conditions involving high cholesterol.

Vitamins

Vitamins and minerals are organic compounds and elements required in small amounts for proper body functioning. Vitamins cannot be synthesized by the body and must be obtained from the diet. While they do not directly provide energy, they are vital for maintaining health and preventing chronic diseases. Vitamins are generally divided into water-soluble (such as Vitamin B-complex and C) and fat-soluble (Vitamins A, D, E, and K) groups. Minerals, including elements like calcium, phosphorus, magnesium, sodium, potassium, chlorine, and sulfur, are required in large amounts and are termed macroelements. Trace elements like iron, iodine, and zinc are required in smaller amounts but are also essential for health. Deficiencies in specific minerals, such as fluorine, can result in issues like tooth decay, while excess fluorine can lead to fluorosis.

For individuals with gastrointestinal disorders, vitamins and trace elements are particularly important, as those with these conditions may rely on artificial diets or parenteral nutrition, where the correct intake of these nutrients is vital for overall health and recovery.