Biomolecules: Structure and Function

Carbohydrates, Lipids, Proteins, and Nucleic Acids

Biomolecules are essential organic compounds that play critical roles in cellular structure and function. The four major classes are carbohydrates, lipids, proteins, and nucleic acids.

• Carbohydrates: Composed of carbon, hydrogen, and oxygen. Classified as monosaccharides (simple sugars), disaccharides (two sugars), and polysaccharides (many sugars). Functions: Energy source (e.g., glucose), energy storage (e.g., glycogen), and structural support (e.g., cellulose in plants).

• Lipids: Hydrophobic molecules including fats, oils, phospholipids, and steroids. Functions: Long-term energy storage, membrane structure (phospholipids), insulation, and hormone synthesis (steroids).

• Proteins: Polymers of amino acids. Functions: Enzymatic catalysis, structural support, transport, signaling, and immune defense. Denaturation is the loss of protein structure due to heat, pH, or chemicals, resulting in loss of function.

• Nucleic Acids: DNA and RNA, composed of nucleotides. Functions: Storage and transmission of genetic information, protein synthesis.

Example: Hemoglobin (protein) transports oxygen; glycogen (carbohydrate) stores energy in animals.

Dehydration Synthesis and Hydrolysis

• Dehydration Synthesis: Chemical reaction that joins two molecules by removing a water molecule. Used to build polymers from monomers.

• Hydrolysis: Chemical reaction that breaks down polymers into monomers by adding water.

Equation:

• Dehydration synthesis:

• Hydrolysis:

pH Scale and Human Blood pH

• pH Scale: Measures hydrogen ion concentration; ranges from 0 (acidic) to 14 (basic), with 7 as neutral.

• Human Blood pH: Normally maintained between 7.35 and 7.45 (slightly basic).

Equation:

Cell Structure and Function

Cell Theory

• All living things are composed of cells.

• The cell is the basic unit of life.

• All cells arise from pre-existing cells.

Plasma (Cell) Membrane: Composition and Structure

• Composed primarily of a phospholipid bilayer with embedded proteins, cholesterol, and carbohydrates.

• Functions: Selective barrier, communication, and structural support.

Membrane Proteins: Categories and Functions

• Integral (transmembrane) proteins: Span the membrane; involved in transport and signaling.

• Peripheral proteins: Attached to membrane surface; involved in signaling and structural support.

• Functions: Transport, enzymatic activity, cell recognition, intercellular joining, and attachment to cytoskeleton.

Membrane Structures: Glycocalyx, Microvilli, and Cilia

• Glycocalyx: Carbohydrate-rich area on cell surface; involved in cell recognition and protection.

• Microvilli: Finger-like projections that increase surface area for absorption (e.g., intestinal cells).

• Cilia: Hair-like structures that move substances across cell surfaces (e.g., respiratory tract).

Cell Junctions

• Tight Junctions: Seal adjacent cells to prevent leakage of extracellular fluid.

• Desmosomes: Anchor cells together, providing mechanical strength.

• Gap Junctions: Allow direct communication between cells via channels.

Function of Tight Junctions: Maintain cell polarity and barrier function in epithelial tissues.

Membrane Transport Mechanisms

Types of Transport

• Passive Transport: Movement of substances down their concentration gradient without energy input. Includes diffusion, facilitated diffusion, and osmosis.

• Active Transport: Movement of substances against their concentration gradient using energy (ATP). Includes primary and secondary active transport.

• Vesicular Transport: Movement of large particles via vesicles (endocytosis, exocytosis).

Osmosis and Tonicity

• Osmosis: Diffusion of water across a selectively permeable membrane.

• Tonicity: The ability of a solution to cause a cell to gain or lose water.

• Isotonic: No net water movement; cell volume remains stable.

• Hypotonic: Water enters the cell; cell may swell and burst.

• Hypertonic: Water leaves the cell; cell shrinks (crenation).

Example: Placing red blood cells in a hypotonic solution causes them to swell.

Water Balance in Cells

• Water balance is determined by the relative concentrations of solutes inside and outside the cell.

• In a hypotonic environment, water enters the cell; in a hypertonic environment, water leaves the cell.

Cell Structures and Organelles

Functions of Cell Structures

Example: Mitochondria are abundant in muscle cells due to high energy demand.

Summary Table: Types of Membrane Transport

Additional info: Some details, such as specific examples and expanded definitions, were inferred from standard Anatomy & Physiology curriculum to ensure completeness and clarity.