Fundamental Concepts in General Biology: Cell Structure, Chemical Bonds, and Biological Molecules

Study Guide - Smart Notes

Tailored notes based on your materials, expanded with key definitions, examples, and context.

Cell Structure and Classification

Eukaryotic vs. Prokaryotic Cells

Cells are the basic units of life and are classified into two major types: eukaryotic and prokaryotic. Understanding their differences is essential for studying biological systems.

Eukaryotic cells have membrane-enclosed organelles, with the nucleus being the largest and most prominent.
Prokaryotic cells are simpler, usually smaller, and do not contain a nucleus or other membrane-enclosed organelles.
Bacteria are prokaryotic; plants, animals, fungi, and all other forms of life are eukaryotic.

Atoms, Elements, and Isotopes

Atomic Structure

Atoms are the fundamental units of matter, and elements differ in their atomic structure.

Atomic number: The number of protons in the nucleus (denoted as left subscript).
Mass number: The sum of protons plus neutrons in the nucleus (denoted as left superscript).
Isotopes: Two atoms of an element that differ in the number of neutrons.

Electron Shells

First shell (e.g., H and He): Can hold no more than 2 electrons.
Second and third shells: Hold a maximum of 8 electrons each.
Valence: The number of electrons required to complete the outermost shell, or valence shell.

Chemical Bonds and Interactions

Types of Chemical Bonds

Atoms with incomplete valence shells can share or transfer electrons, resulting in chemical bonds that hold atoms together.

Covalent bonds: Sharing of a pair of valence electrons between two atoms.
Ionic bonds: Transfer of electrons from one atom to another, resulting in charged atoms called ions.
Hydrogen bonds: Form when a hydrogen atom covalently bonded to one electronegative atom is also attracted to another electronegative atom.

Covalent Bonds

In a covalent bond, shared electrons count as part of each atom's valence shell.
Nonpolar covalent bond: Atoms share electrons equally.
Polar covalent bond: One atom is more electronegative, and atoms do not share electrons equally, resulting in partial charges.

Ionic Bonds

Atoms may strip electrons from their bonding partners (e.g., sodium transfers an electron to chlorine).
After electron transfer, both atoms become ions with opposite charges.

Hydrogen Bonds

Common in biological molecules, especially between water molecules and between oxygen or nitrogen atoms.
Water is a polar molecule, allowing it to form hydrogen bonds.

Properties of Water and Related Substances

Hydrophilic, Hydrophobic, and Amphipathic Substances

Water's polarity influences how substances interact with it.

Hydrophilic: Substances with an affinity for water (usually polar molecules).
Hydrophobic: Substances that do not have an affinity for water.
Amphipathic: Substances containing both hydrophilic and hydrophobic regions.

Acids, Bases, and pH

Definitions and the pH Scale

Acids and bases are defined by their effect on hydrogen ion concentration in solution.

Acid: Increases the H+ concentration of a solution.
Base: Reduces the H+ concentration of a solution.
pH scale: Used to describe whether a solution is acidic (pH < 7), neutral (pH = 7), or basic (pH > 7).

Organic Molecules and Functional Groups

Functional Groups in Organic Chemistry

Organic molecules contain specific groups of atoms called functional groups that determine their chemical properties.

Hydroxyl group
Carboxyl group
Carbonyl group
Amino group
Sulfhydryl group
Phosphate group
Methyl group

Biological Macromolecules

Classes of Biological Molecules

All living things are made up of four major classes of large biological molecules:

Carbohydrates
Lipids
Proteins
Nucleic acids

Polymer Formation and Breakdown

Condensation (dehydration) reaction: Two monomers bond together through the loss of a water molecule.
Hydrolysis: Polymers are disassembled to monomers by adding water, essentially the reverse of dehydration.

Carbohydrates

Starch and glycogen: Storage polysaccharides.
Cellulose and chitin: Structural polysaccharides.

Lipids

Saturated fatty acids: Maximum number of hydrogen atoms, no double bonds, solid at room temperature, more common in animals, contribute to atherosclerosis.
Unsaturated fatty acids: One or more double bonds, liquid at room temperature, more common in plants.

Proteins

Amino acids: Organic molecules with carboxyl and amino groups; differ in properties due to side chains (R groups).
Peptide bond: Covalent bond between amino acids formed by dehydration reaction.
Protein structure can be affected by pH, salt concentration, temperature, and other environmental factors, leading to denaturation (loss of function).

Nucleic Acids

DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) are the two types of nucleic acids.
DNA directs synthesis of messenger RNA (mRNA), which controls protein synthesis.

Cellular Components and Functions

Basic Features of All Cells

Plasma membrane: Encloses the cell, controlling movement of substances in and out.
Cytosol: Semifluid substance inside the cell.
Chromosomes: Carry genetic information (genes).
Ribosomes: Synthesize proteins.

Summary Table: Cell Types and Features

Feature	Eukaryotic Cell	Prokaryotic Cell
Nucleus	Present	Absent
Membrane-bound organelles	Present	Absent
Size	Usually larger	Usually smaller
Examples	Plants, animals, fungi	Bacteria

Summary Table: Types of Chemical Bonds

Bond Type	Description	Example
Covalent	Sharing of electron pairs	H2O, O2
Ionic	Transfer of electrons, formation of ions	NaCl
Hydrogen	Attraction between H and electronegative atom	Between water molecules

Key Equations

Mass number:
pH:

Example: Water Molecule Polarity

The water molecule (H2O) is polar because oxygen is more electronegative than hydrogen, resulting in partial negative and positive charges at opposite ends. This allows water molecules to form hydrogen bonds, which are critical for many biological processes.

Example: Formation of Peptide Bond

A peptide bond forms between the carboxyl group of one amino acid and the amino group of another, releasing a molecule of water in a dehydration reaction.

Additional info: Tables and diagrams have been described in text for clarity and completeness. All major topics from the notes have been expanded with academic context for self-contained study.