Key Terms and Concepts in General Biology: Molecular and Cellular Foundations

Biological Molecules and Chemical Bonds

Adhesion and Cohesion

Adhesion and cohesion are fundamental properties of water and other molecules that influence biological processes.

• Adhesion: The clinging of one substance to another, such as water to plant cell walls. This property is essential for processes like capillary action in plants.

• Cohesion: The sticking together of like molecules, such as water molecules to each other via hydrogen bonding. Cohesion contributes to surface tension in water.

Chemical Bonds

Chemical bonds are forces that hold atoms together in molecules and compounds.

• Covalent Bond: A chemical bond formed by the sharing of one or more pairs of electrons between two atoms. Covalent bonds are strong and form the backbone of most biological molecules.

• Ionic Bond: A chemical bond resulting from the complete transfer of electrons from one atom to another, creating oppositely charged ions that attract each other.

• Hydrogen Bond: A weak chemical bond formed when a hydrogen atom covalently bonded to one electronegative atom is attracted to another electronegative atom. Hydrogen bonds are important in stabilizing the structures of proteins and nucleic acids.

Types of Molecules

• Amphipathic: A molecule having both hydrophilic (water-loving) and hydrophobic (water-fearing) regions, such as phospholipids.

• Carbohydrate: A biological macromolecule consisting of sugar units, serving as energy sources and structural components.

• Lipid: A large biological molecule, such as fats, oils, and steroids, that is hydrophobic and serves as energy storage or as a component of cell membranes.

• Protein: A biological macromolecule composed of one or more polypeptide chains, folded into a specific three-dimensional shape, performing a wide range of functions.

• Nucleic Acids: Polymers and macromolecules that retain the organism's chemical identity, consisting of a nucleus (protons and neutrons) and orbiting electrons. DNA and RNA are examples.

Cell Membranes and Transport

Membrane Structure and Function

Cell membranes are selectively permeable barriers that regulate the movement of substances into and out of cells.

• Phospholipid Bilayer: The primary component of cell membranes, consisting of two layers of phospholipids with hydrophilic heads facing outward and hydrophobic tails facing inward.

• Fluid Mosaic Model: The accepted model of the cell membrane, describing it as a mosaic of protein molecules bobbing in a fluid bilayer of phospholipids.

• Peripheral Protein: A membrane protein that binds to specific molecules and changes shape to move them across the membrane.

• Channel Protein: A transmembrane protein that forms a pore allowing specific ions or small molecules to pass through the membrane.

Transport Mechanisms

• Passive Transport: Movement of substances across a cell membrane without energy expenditure, driven by concentration gradients.

• Osmosis: The diffusion of water across a selectively permeable membrane from a region of higher water concentration to a region of lower water concentration.

• Facilitated Diffusion: The passive movement of molecules across a cell membrane with the aid of transport proteins (channels or carriers).

• Active Transport: The movement of substances against their concentration gradient, requiring energy input (usually ATP). Example: sodium-potassium pump.

• Electrochemical Gradient: A gradient of electrical potential and chemical concentration across a membrane, influencing the movement of ions.

• Isotonic Solution: A solution with the same solute concentration as that inside a cell, resulting in no net movement of water.

• Hypertonic Solution: A solution with a higher solute concentration than inside a cell, causing water to leave the cell.

• Hypotonic Solution: A solution with a lower solute concentration than inside a cell, causing water to enter the cell.

Macromolecules: Structure and Function

Carbohydrates

• Monosaccharide: The simplest form of carbohydrate, a single sugar unit (e.g., glucose, fructose).

• Disaccharide: A carbohydrate consisting of two monosaccharides linked together (e.g., sucrose).

• Polysaccharide: A large molecule consisting of many monosaccharide units linked together (e.g., starch, cellulose, glycogen).

• Glycosidic Linkage: The covalent bond joining monosaccharides in a polysaccharide.

Proteins

• Amino Acid: The monomer building block of proteins, characterized by an amino group, a carboxyl group, a hydrogen atom, and a variable R group (side chain) attached to a central carbon atom.

• Primary Structure (Protein): The unique linear sequence of amino acids in a polypeptide chain.

• Secondary Structure (Protein): Coiled (alpha-helix) or folded (beta-sheet) patterns formed by hydrogen bonds between the backbone atoms of a polypeptide.

• Tertiary Structure (Protein): The overall three-dimensional shape of a single polypeptide chain, resulting from interactions between R-groups.

• Quaternary Structure (Protein): The overall protein structure resulting from the aggregation of two or more polypeptide subunits.

• R-group (Side Chain): The variable part of an amino acid that gives it its unique chemical properties.

Nucleic Acids

• Nucleotide: The monomer of nucleic acids, consisting of a phosphate group, a five-carbon sugar, and a nitrogenous base.

• DNA: Deoxyribonucleic acid, the molecule that stores genetic information in cells.

• RNA: Ribonucleic acid, involved in protein synthesis and gene regulation.

Scientific Method and Investigation

Scientific Investigation

The scientific method is a systematic approach to understanding natural phenomena through observation, hypothesis formation, testing, and revision based on evidence.

• Hypothesis: A testable explanation for an observation or set of observations.

• Experiment: A procedure conducted to test a hypothesis.

• Variable: Any factor that can change in an experiment.

Selected Table: Types of Solutions and Their Effects on Cells

This table compares the effects of different types of solutions on cells, based on their solute concentrations.

Solution Type	Solute Concentration (relative to cell)	Effect on Cell
Isotonic	Equal	No net movement of water; cell remains the same size
Hypertonic	Higher outside cell	Water leaves cell; cell shrinks
Hypotonic	Lower outside cell	Water enters cell; cell swells or may burst

Additional Key Terms

• Denaturation: A process in which a protein or nucleic acid loses its native shape due to disruption of weak chemical bonds and interactions, often leading to loss of biological activity.

• Enzyme: A substance that can be broken down into simpler substances by chemical means; defined by its number of protons.

• Monomer: The small molecular unit that is the building block of a polymer.

• Polymer: A large molecule consisting of many similar or identical monomers linked together.

• Simple Diffusion: The passive movement of molecules across cell membranes from an area of higher concentration to an area of lower concentration.

Example: The sodium-potassium pump is an example of active transport, using ATP to move sodium ions out of the cell and potassium ions into the cell against their concentration gradients.