General Biology Exam Review: Key Concepts and Study Guide

Water Chemistry

Hydrogen Bonds and Properties of Water

Water is a unique molecule essential for life, largely due to its ability to form hydrogen bonds. These bonds influence water's physical and chemical properties, making it vital for biological systems.

• Hydrogen Bond: A weak attraction between the hydrogen atom of one water molecule and the oxygen atom of another. This occurs because water is a polar molecule, with partial positive and negative charges.

• Properties of Water:

  • Cohesion: Water molecules stick to each other, allowing for surface tension.

  • Adhesion: Water molecules stick to other substances, aiding in capillary action.

  • High Specific Heat: Water can absorb a lot of heat before changing temperature, helping regulate climate and body temperature.

  • Solvent Abilities: Water dissolves many substances, facilitating chemical reactions in cells.

• Example: Hydrogen bonding allows ice to float, as the bonds create a less dense structure than liquid water.

Phospholipid Bilayers

Structure and Function

Phospholipid bilayers form the fundamental structure of cell membranes, providing a barrier and enabling selective transport.

• Phospholipid: A molecule with a hydrophilic (water-attracting) head and hydrophobic (water-repelling) tails.

• Bilayer Formation: In water, phospholipids arrange themselves so that the hydrophilic heads face outward toward water, and the hydrophobic tails face inward, away from water.

• Function: This arrangement creates a semi-permeable membrane, controlling the movement of substances in and out of the cell.

• Example: The plasma membrane of animal cells is composed of a phospholipid bilayer with embedded proteins.

Carbon Molecules Important for Life

The Four Main Groups: Monomers, Polymers, and Synthesis/Breakdown

Life depends on four major groups of carbon-based molecules, each with specific monomers and polymers, and unique roles in biological systems.

• Carbohydrates:

  • Monomer: Monosaccharides (e.g., glucose)

  • Polymer: Polysaccharides (e.g., starch, cellulose)

  • Function: Energy storage and structural support

• Lipids:

  • Monomer: Fatty acids and glycerol

  • Polymer: Triglycerides, phospholipids

  • Function: Energy storage, membrane structure

• Proteins:

  • Monomer: Amino acids

  • Polymer: Polypeptides

  • Function: Catalysis (enzymes), structure, transport

• Nucleic Acids:

  • Monomer: Nucleotides

  • Polymer: DNA, RNA

  • Function: Information storage and transfer

• Synthesis: Monomers are joined by dehydration synthesis (removal of water).

• Breakdown: Polymers are broken down by hydrolysis (addition of water).

• Example: The enzyme amylase breaks down starch (a polysaccharide) into glucose monomers.

Domains of Life

Classification and Characteristics

All living organisms are classified into three domains based on cellular structure and genetic differences.

• Eukaryotes: Organisms with complex cells containing a nucleus and organelles. Includes:

  • Plants

  • Animals

  • Fungi

• Prokaryotes: Organisms with simple cells lacking a nucleus. Includes:

  • Bacteria

  • Archaea

• Example: Escherichia coli is a bacterium (prokaryote); Homo sapiens is an animal (eukaryote).

RNA vs. DNA

Differences in Structure and Base Pairing

RNA and DNA are nucleic acids that store and transmit genetic information, but they differ in several key ways.

• DNA (Deoxyribonucleic Acid):

  • Double-stranded helix

  • Sugar: Deoxyribose

  • Bases: Adenine (A), Thymine (T), Cytosine (C), Guanine (G)

  • Base pairing: A-T, C-G

• RNA (Ribonucleic Acid):

  • Single-stranded

  • Sugar: Ribose

  • Bases: Adenine (A), Uracil (U), Cytosine (C), Guanine (G)

  • Base pairing: A-U, C-G

• Example: In transcription, DNA's A pairs with RNA's U.

Elements Essential for Life

CHON: The Four Most Abundant Elements

Most living matter is composed of four key elements, which are fundamental to biological molecules and processes.

• Carbon (C): Backbone of organic molecules

• Hydrogen (H): Found in water and organic compounds

• Oxygen (O): Essential for respiration and water

• Nitrogen (N): Key component of amino acids and nucleic acids

• Example: Proteins contain all four elements in their structure.

Summary Table: Key Biological Molecules

Group	Monomer	Polymer	Main Function
Carbohydrates	Monosaccharide	Polysaccharide	Energy, structure
Lipids	Fatty acid, glycerol	Triglyceride, phospholipid	Energy, membranes
Proteins	Amino acid	Polypeptide	Catalysis, structure
Nucleic Acids	Nucleotide	DNA, RNA	Information storage

Additional info: Academic context and examples have been added to expand on the brief points in the original notes.