Bio Unit 3

Water's Properties and Roles in Life

• Water is the medium for most life processes, enabling chemical reactions between dissolved molecules.
• Water's polar covalent bonds create partial charges, leading to hydrogen bonding. These bonds give water unique properties like cohesion and adhesion.
• Cohesion: Water molecules stick together, crucial for transpiration (water movement in plants). Evaporation from leaves creates tension pulling water up the xylem, forming a continuous column. Cohesion creates surface tension, vital for aquatic habitats.
• Adhesion: Water sticks to solid surfaces like xylem walls, enabling capillary action—water's upward movement against gravity. Capillary action transports water from soil through plants.
• Water is a good solvent due to its polarity, dissolving hydrophilic (polar) solutes and ions, but not hydrophobic (non-polar) substances. Metabolism relies on aqueous solutions. Water acts as an excellent transport medium in plants (xylem for water and minerals, phloem for sugars) and animals (blood plasma).
• Buoyancy: Water exerts an upward force against gravity (floating). Aquatic organisms often have equal density to water.
• Viscosity: Water's resistance to flow. Motion through water requires overcoming this property.
• Thermal Conductivity: Water readily transmits heat, helpful for dissipating heat from metabolic processes.
• Specific Heat Capacity: Water needs a significant energy change to alter its temperature, acting as a buffer against large temperature fluctuations. This property is vital for aquatic organisms and maintains relatively stable body temperatures in animals through blood plasma and cell water.

Carbohydrates: Structure and Function

• Carbohydrates are carbon-based molecules forming branched or unbranched chains or rings.
• Macromolecules are built from small monomers (monosaccharides) through condensation reactions, removing water to create bonds.
• Glycosidic bonds: Bonds formed between monosaccharides during condensation reactions, creating disaccharides and polysaccharides. 1-4 and 1-6 linkages distinguish different polysaccharide structures like amylose and amylopectin (starch) and glycogen.
• Hydrolysis: Adding water to break glycosidic bonds; essential for digestion.
• Monosaccharides: Simple sugars (e.g., glucose). Trioses, pentoses, and hexoses are classified by carbon number.
• Polysaccharides: Complex carbohydrates; important for structural support and energy storage.
• Cellulose: a structural polysaccharide in plant cell walls. Beta-glucose forms linear chains. Hydrogen bonds between chains provide strength.
• Starch: energy storage in plants; composed of amylose (linear) and amylopectin (branched).
• Glycogen: energy storage in animals; highly branched, more readily broken down.
• Glycoproteins and glycolipids: Proteins and lipids with attached carbohydrate chains. These structures play key roles in cell recognition.
• Blood type antigens are glycoproteins, unique carbohydrate patterns enabling cell recognition and response.

Lipids: Diverse Structures

• Lipids are hydrophobic (non-polar) molecules dissolving in non-polar solvents.
• Fatty acids: Long hydrocarbon chains with a carboxyl group.
• Triglycerides: Glycerol + 3 fatty acids, crucial for long-term energy storage and thermal insulation in adipose tissue.
• Phospholipids: Glycerol + 2 fatty acids + phosphate group. The hydrophilic phosphate head and hydrophobic fatty acid tails arrange in a bilayer, forming cell membranes.
• Saturated fatty acids: Straight chains, solid at room temperature.
• Unsaturated fatty acids: Contain double bonds; Cis-unsaturated acids are bent, while trans-unsaturated acids are straight. The shape affects the melting point and, indirectly, the properties of materials like oils and fats.
• Phospholipids form a bilayer in water where polar "heads" face outwards and nonpolar "tails" face inwards, creating a barrier.
• Steroids have a unique four-ring structure; these non-polar molecules can easily pass through cell membranes.

Proteins: Diverse Functional Molecules

• Proteins are long chains of amino acids connected by peptide bonds formed in condensation reactions.
• Amino acids: 20 different types; Plants can manufacture all, while animals must obtain from diet.
• Polypeptides: Chains of amino acids.
• Proteins fold into specific 3D shapes crucial for their function.
• Denaturation: Loss of protein structure due to heat or pH changes; this can significantly alter a protein's function.
• Proteome: an organism's complete set of proteins.

Cell Membranes: Structure and Function

• Cell membranes consist of a lipid bilayer (phospholipids) and proteins (integral and peripheral).
• Selectively permeable barrier: Cell membranes control what enters and leaves the cell, based on size and charge of molecules.
• Diffusion: Passive movement of molecules from high to low concentration. Small, non-polar molecules diffuse directly through the membrane.
• Osmosis: Passive movement of water across a membrane from low to high solute concentration.
• Facilitated diffusion: Passive movement of molecules through channel proteins.
• Active transport: Movement of molecules against their concentration gradient, requiring energy (ATP).
• Fluid mosaic model: A dynamic representation of the membrane structure, with components moving around.
• Glycoproteins and glycolipids on the cell surface play roles in cell recognition and interactions.