General Biology Exam Study Guide: Chemistry of Life, Macromolecules, and Water

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Chemistry of Life

Concepts of Matter

The study of biology begins with understanding the basic chemical principles that govern living systems. Matter is anything that has mass and occupies space, and it is composed of elements and compounds.

Element: A pure substance consisting of only one type of atom (e.g., Carbon, Oxygen).
Compound: A substance formed when two or more elements are chemically bonded (e.g., Water - H2O).
Atomic Structure: Atoms consist of protons, neutrons, and electrons. The atomic number is the number of protons, and atomic mass is the sum of protons and neutrons.
Isotopes: Atoms of the same element with different numbers of neutrons. Some isotopes are radioactive and have applications in medicine and research.

Example: Carbon-12 and Carbon-14 are isotopes of carbon; Carbon-14 is radioactive and used in radiometric dating.

Chemical Reactions in Atoms

Chemical reactions involve the making and breaking of chemical bonds, leading to changes in the composition of matter.

Octet Rule: Atoms tend to gain, lose, or share electrons to achieve a full set of eight valence electrons.
Ions: Charged particles formed when atoms gain or lose electrons.
Covalent Bond: A chemical bond formed by the sharing of electron pairs between atoms.
Polar Covalent Bond: Electrons are shared unequally, resulting in partial charges (e.g., in water molecules).

Example: Water (H2O) has polar covalent bonds, making it an excellent solvent.

Water and Its Properties

Water Molecule Structure and Hydrogen Bonding

Water is essential for life due to its unique chemical and physical properties.

Hydrogen Bond: A weak bond between a hydrogen atom and an electronegative atom (such as oxygen or nitrogen).
Hydrophilic: Substances that dissolve easily in water (water-loving).
Hydrophobic: Substances that do not dissolve in water (water-fearing).

Example: Salt (NaCl) is hydrophilic, while oil is hydrophobic.

Water as a Solvent

Water's polarity allows it to dissolve many substances, making it a universal solvent.
Hydrogen bonding contributes to water's high specific heat, surface tension, and ability to moderate temperature.

Additional info: Water's ability to form hydrogen bonds is crucial for the structure of proteins and nucleic acids.

Carbon Chemistry and Macromolecules

Covalent Bonds and Carbon's Versatility

Carbon forms the backbone of biological molecules due to its ability to form four covalent bonds.

Dynamic Molecules: Carbon can form chains, rings, and complex structures.
Functional Groups: Specific groups of atoms that confer particular chemical properties (e.g., hydroxyl, carboxyl, amino, phosphate, methyl).

Example: The carboxyl group (-COOH) is acidic and found in amino acids.

Macromolecules: Monomers and Polymers

Macromolecules are large molecules essential for life, formed by joining smaller units called monomers.

Monomer: A single subunit (e.g., glucose, amino acid).
Polymer: A chain of monomers (e.g., starch, protein).
Dehydration Reaction: Joins monomers by removing water.
Hydrolysis Reaction: Breaks polymers into monomers by adding water.

Example: Proteins are polymers of amino acids; starch is a polymer of glucose.

Carbohydrates

Monosaccharides and Disaccharides

Carbohydrates are energy-rich organic compounds made of carbon, hydrogen, and oxygen.

Monosaccharide: Simple sugar (e.g., glucose, fructose).
Disaccharide: Two monosaccharides joined by a glycosidic bond (e.g., sucrose).
Aldose vs. Ketose: Aldoses have an aldehyde group; ketoses have a ketone group.

Example: Glucose is an aldose; fructose is a ketose.

Polysaccharides

Polysaccharides are long chains of monosaccharides and serve as energy storage or structural materials.

Starch: Energy storage in plants.
Glycogen: Energy storage in animals.
Cellulose: Structural component in plant cell walls.

Polysaccharide	Function	Organism
Starch	Energy storage	Plants
Glycogen	Energy storage	Animals
Cellulose	Structure	Plants

Additional info: Chitin is a structural polysaccharide found in fungi and arthropods.

Lipids

Structure and Function

Lipids are hydrophobic molecules important for energy storage, membrane structure, and signaling.

Fatty Acid: Long hydrocarbon chain with a carboxyl group.
Triglyceride: Three fatty acids bonded to glycerol.
Saturated vs. Unsaturated: Saturated fatty acids have no double bonds; unsaturated have one or more double bonds.

Example: Butter contains saturated fats; olive oil contains unsaturated fats.

Phospholipids

Phospholipids are major components of cell membranes, forming a bilayer due to their hydrophilic heads and hydrophobic tails.

Phospholipid Bilayer: Structure of biological membranes.
Hydrophilic Head: Interacts with water.
Hydrophobic Tail: Repels water.

Component	Property
Head	Hydrophilic
Tail	Hydrophobic

Additional info: Cholesterol is a lipid that stabilizes membrane fluidity.

Proteins

Amino Acids and Protein Structure

Proteins are polymers of amino acids and perform a wide range of functions in cells.

Amino Acid: Contains an amino group, carboxyl group, and a unique side chain (R group).
Peptide Bond: Covalent bond joining amino acids.
Primary Structure: Sequence of amino acids.
Secondary Structure: Alpha helices and beta sheets formed by hydrogen bonding.
Tertiary Structure: Overall 3D shape of a protein.
Quaternary Structure: Association of multiple polypeptide chains.

Example: Hemoglobin is a protein with quaternary structure.

Protein Denaturation

Denaturation is the loss of protein structure due to changes in temperature, pH, or chemicals.

Denatured proteins lose their function.
Factors causing denaturation include heat, acids, and solvents.

Additional info: Enzymes are proteins that catalyze biochemical reactions and are sensitive to denaturation.

Nucleic Acids

DNA and RNA Structure

Nucleic acids store and transmit genetic information.

Nucleotide: Monomer of nucleic acids, consisting of a sugar, phosphate, and nitrogenous base.
DNA: Double-stranded, contains deoxyribose sugar, bases A, T, C, G.
RNA: Single-stranded, contains ribose sugar, bases A, U, C, G.
Phosphodiester Bond: Links nucleotides in a chain.

Type	Sugar	Bases	Strands
DNA	Deoxyribose	A, T, C, G	Double
RNA	Ribose	A, U, C, G	Single

Example: Messenger RNA (mRNA) carries genetic information from DNA to ribosomes for protein synthesis.

Base Pairing and Function

Adenine pairs with Thymine (DNA) or Uracil (RNA).
Cytosine pairs with Guanine.
Base pairing is essential for DNA replication and RNA transcription.

Additional info: Hydrogen bonds stabilize the double helix structure of DNA.

Key Equations and Concepts

General formula for carbohydrates:
Peptide bond formation:
Phosphodiester bond formation: