Unit 1: English Summary – Biochemistry and Physiology

1. Carbohydrates: Structure and Biological Importance

Carbohydrates are organic molecules composed of carbon (C), hydrogen (H), and oxygen (O), typically in a 1:2:1 ratio. They serve as primary energy sources and structural components in organisms. Based on their complexity, carbohydrates are classified into monosaccharides, disaccharides, polysaccharides, and glycoconjugates.

1.1 Monosaccharides (Simple Sugars)

Monosaccharides are the simplest form of carbohydrates, consisting of a single sugar unit. They serve as the fundamental building blocks for more complex carbohydrates.

• Structure: Composed of three to seven carbon atoms, classified based on the number of carbon atoms:

·       Triose (3C): Glyceraldehyde

·       Tetrose (4C): Erythrose

·       Pentose (5C): Ribose, Deoxyribose

·       Hexose (6C): Glucose, Fructose, Galactose

• Biological Importance:

·       Glucose is the primary energy source in cellular metabolism.

·       Ribose and deoxyribose are integral to nucleic acids (RNA and DNA).

1.2 Disaccharides

Disaccharides consist of two monosaccharide units linked by a glycosidic bond.

·       Examples and Functions:

·       Sucrose (Glucose + Fructose): Common table sugar; primary transport sugar in plants.

·       Lactose (Glucose + Galactose): Found in milk; essential for infant nutrition.

·       Maltose (Glucose + Glucose): Produced during starch digestion.

1.3 Polysaccharides

Polysaccharides are complex carbohydrates formed by polymerizing monosaccharides through glycosidic bonds.

• Structural Polysaccharides:

·       Cellulose: Provides structural integrity in plant cell walls; indigestible to humans.

·       Chitin: A structural component in fungal cell walls and arthropod exoskeletons.

• Storage Polysaccharides:

·       Starch: The main energy reserve in plants.

·       Glycogen: The primary energy storage in animals, stored mainly in the liver and muscles.

1.4 Glycoconjugates

Glycoconjugates are carbohydrates covalently linked to proteins or lipids, playing essential roles in cell communication and immune response.

·       Glycoproteins: Found in cell membranes, influencing cell recognition.

·       Glycolipids: Crucial in cell signaling and immune response.

2. Lipids: Structure and Biological Importance

Lipids are hydrophobic biomolecules that play key roles in energy storage, membrane structure, and signaling.

2.1 Fatty Acids

Fatty acids are hydrocarbon chains terminating in a carboxyl (-COOH) group. They are classified into saturated and unsaturated fatty acids.

·       Saturated Fatty Acids: No double bonds; found in animal fats (e.g., stearic acid, palmitic acid).

·       Unsaturated Fatty Acids: Contain one or more double bonds; found in plant oils (e.g., oleic acid, linoleic acid).

2.2 Triacylglycerols (Triglycerides)

Triglycerides are composed of three fatty acids esterified to a glycerol backbone. They serve as energy reserves in adipose tissues.

·       Biological Importance:

·       Energy storage, providing twice the energy yield of carbohydrates.

·       Insulation and protection of vital organs.

2.3 Phospholipids

Phospholipids consist of two fatty acids, a glycerol molecule, and a phosphate group. They form the fundamental structure of biological membranes.

·       Example: Phosphatidylcholine (lecithin), a key component of cell membranes.

2.4 Glycolipids

Glycolipids are lipids with carbohydrate groups attached. They contribute to cellular recognition and signaling.

·       Example: Cerebrosides and gangliosides in the nervous system.

2.5 Steroids

Steroids are lipid molecules with a characteristic four-ring structure.

·       Examples:

·       Cholesterol: Maintains membrane fluidity and serves as a precursor for steroid hormones.

·       Hormones: Estrogen, testosterone, cortisol, involved in various physiological functions.

3. Proteins: Structure, Classification, and General Properties

Proteins are essential biomolecules composed of amino acids linked by peptide bonds. They perform a vast array of functions, from catalyzing reactions to providing structural support.

3.1 Amino Acids: Structure and Classification

Amino acids contain an amino (-NH₂) group, a carboxyl (-COOH) group, a hydrogen atom, and a unique R-group attached to a central carbon.

·       Essential Amino Acids: Must be obtained from the diet (e.g., lysine, tryptophan, valine).

·       Non-essential Amino Acids: Can be synthesized by the body (e.g., alanine, serine).

3.2 Levels of Protein Organization

Proteins exhibit multiple structural levels that determine their function.

1.        Primary Structure: Linear sequence of amino acids.

2.      Secondary Structure: Local folding patterns (α-helix, β-sheet) stabilized by hydrogen bonds.

3.      Tertiary Structure: The 3D shape formed by interactions between side chains.

4.      Quaternary Structure: Multi-subunit complexes (e.g., hemoglobin).

3.3 Types of Proteins

·       Simple Proteins: Composed entirely of amino acids (e.g., albumin).

·       Conjugate Proteins: Contain a non-protein group (e.g., hemoglobin with a heme group).

4. Learning Outcomes and Broader Perspectives

Understanding biomolecules is foundational to biochemistry and physiology. Key learning outcomes include:

4.1 How Simple Molecules Form Complex Macromolecules

·       Monosaccharides combine to form polysaccharides.

·       Fatty acids and glycerol assemble into triglycerides and phospholipids.

·       Amino acids link together to form complex proteins.

4.2 Thermodynamics of Enzyme-Catalyzed Reactions

·       Enzymes lower activation energy, facilitating biochemical reactions.

·       ATP hydrolysis provides energy for cellular processes.

4.3 Mechanisms of Energy Production

·       Glycolysis: Breakdown of glucose to generate ATP.

·       Krebs Cycle: Produces electron carriers for oxidative phosphorylation.

·       Electron Transport Chain: Drives ATP synthesis via chemiosmosis.

4.4 Systems Biology and Functional Components of an Organism

·       Biomolecules function as part of integrated biological systems.

·       Metabolic pathways interconnect to maintain homeostasis.

4.5 Regulatory Mechanisms for Function Maintenance

·       Hormonal control (e.g., insulin in glucose metabolism).

·       Feedback inhibition in enzymatic pathways.

Conclusion

Biomolecules form the foundation of life, facilitating essential physiological processes. Carbohydrates provide energy and structural support, lipids contribute to membrane integrity and signaling, and proteins drive metabolic reactions. Their intricate interactions underscore the complexity of biological systems. Mastering their structure and function equips students with a deep understanding of life at the molecular level.

By integrating biochemical knowledge with physiological insights, students can appreciate the dynamic nature of life and its regulatory mechanisms, fostering a holistic view of biological sciences.