Chemistry Ionic and Covalent Bonds

Bonds

• Ionic Bonds: Involve the transfer of electrons; typically form between metals and nonmetals (e.g., NaCl); result in cations and anions attracting each other.
• Covalent Bonds: Form through sharing of electrons; can be nonpolar (equal sharing, e.g., H-H) or polar (unequal sharing, e.g., H2O).
• Hydrogen Bonds: Weak attractions between molecules; occur when a partial positive hydrogen atom interacts with electronegative atoms (F, O, N), prominent in water.

Structure and Properties of Water

• Water is a polar covalent molecule composed of two hydrogen atoms and one oxygen atom; oxygen carries a partial negative charge.
• Its polarity allows water to dissolve many substances, making it the universal solvent.

pH and Hydrogen Ion Concentration

• pH indicates acidity or basicity based on hydrogen ion concentration; higher H+ concentration means more acidic, while lower H+ concentration means more basic.
• Key body fluids like spinal fluid, blood, saliva, and water generally have a neutral pH around 7.

Enzyme Catalysis

• Enzymes accelerate chemical reactions without being consumed by lowering the activation energy required for the reaction.
• They bind to substrates (often amino acids) and can be reused in subsequent reactions.

Carbon in Organic Molecules

• Carbon, with six protons, neutrons, and electrons, is stable and forms long chains (C-C bonds), essential for organic compounds.
• Carbon's ability to form single, double, or triple bonds is key to its versatility in biological molecules.

Classes of Organic Molecules

• Lipids: Include fatty acids, triglycerides, and phospholipids; have hydrophilic heads and hydrophobic tails; essential in cell membranes, hormone synthesis, and signaling.
• Carbohydrates: Provide glucose and energy, are polar and hydrophilic; structured as CH2O.
• Nucleic Acids: DNA and RNA, responsible for genetic information; DNA is double-stranded, RNA is single-stranded.
• Proteins: Composed of amino acids; vital for tissue repair, enzyme activity, cellular communication, and immune defense.

ATP Structure and Function

• ATP consists of adenine, ribose sugar, and three phosphate groups; high-energy bonds release energy upon phosphorylation.
• Powers cellular activities, including molecule transport across membranes.

Plasma Membrane Structure

• Comprised of a phospholipid bilayer that regulates substance passage; phospholipids have outward-facing hydrophilic heads and inward-facing hydrophobic tails.
• Contains transmembrane proteins for molecule entry and cholesterol for membrane rigidity, along with carbohydrates (glycocalyx) for cell recognition.

Membrane Proteins and Their Functions

• Transport Proteins: Form channels or pumps to move substances across the membrane.
• Anchor Proteins: Secure the cell by attaching the membrane to the cytoskeleton.
• Receptor Proteins: Bind signals from other cells, triggering a response (e.g., hormones).
• Cell-Cell Junction Proteins: Facilitate binding between adjacent cells.
• Membrane Enzymes: Catalyze reactions on the cell surface.
• Recognition Proteins: Help immune cells distinguish between self and foreign agents.

Regulation of Material Transport

• The cell membrane is selectively permeable, controlling material intake and providing structural flexibility for protein movement.
• Organizes compartments within the cell through cytoplasm and cytoskeleton.

Tonicity Definitions

• Isotonic: Equal solute and water concentration inside and outside the cell; no change in cell shape.
• Hypotonic: Lower solute concentration outside the cell; water enters, potentially causing lysis (bursting).
• Hypertonic: Higher solute concentration outside the cell; water leaves, leading to cell shrinkage.