General Biology Study Guide: Chemistry of Life and Biological Molecules

Unit 1: Chemistry of Life

2.3-2.5 Chemical Bonds and Water Properties

The chemistry of life is based on the interactions between atoms and molecules, which are governed by chemical bonds. Water, a vital molecule for life, exhibits unique properties due to hydrogen bonding.

• Chemical Bonds: Interactions between valence electrons of atoms that hold molecules together. Main types include covalent bonds (sharing electrons), ionic bonds (transfer of electrons), and hydrogen bonds (attraction between polar molecules).

• Polar vs. Nonpolar Covalent Bonds: Polar covalent bonds have unequal sharing of electrons, resulting in partial charges (e.g., H2O). Nonpolar covalent bonds share electrons equally (e.g., O2).

• Hydrogen Bonds: Weak attractions between the partially positive hydrogen atom of one molecule and the partially negative atom (often oxygen or nitrogen) of another. Essential for water's properties and biological molecules.

• Water Properties: Due to hydrogen bonding, water has high cohesion, adhesion, surface tension, and a high specific heat capacity. These properties are crucial for life processes.

• Example: Water's ability to dissolve many substances (universal solvent) supports cellular processes.

2.4 Chemical Reactions

Chemical reactions involve the making and breaking of chemical bonds, transforming substances into new products.

• Reactants and Products: Reactants are substances that undergo change; products are the result of the reaction.

• Equation Example: $2H_2 + O_2 \rightarrow 2H_2O$

• Enzymes: Biological catalysts that speed up chemical reactions by lowering activation energy.

2.5 Hydrogen Bonding and Water's Role in Life

Hydrogen bonding gives water unique properties that are essential for life on Earth.

• Cohesion: Water molecules stick to each other, aiding transport in plants.

• Adhesion: Water molecules stick to other surfaces, important for capillary action.

• High Specific Heat: Water resists temperature changes, stabilizing environments.

• Solvent Properties: Water dissolves polar and ionic substances, facilitating biochemical reactions.

• Example: Water's role in regulating body temperature and transporting nutrients.

3. Macromolecules: Structure and Function

3.1 Carbon Compounds

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

• Organic Compounds: Molecules containing carbon and hydrogen; examples include carbohydrates, lipids, proteins, and nucleic acids.

• Functional Groups: Specific groups of atoms (e.g., hydroxyl, carboxyl, amino) that determine chemical properties.

• Dehydration Synthesis: Formation of polymers by removing water.

• Hydrolysis: Breaking polymers into monomers by adding water.

• Equation Example: $\text{Monomer}_1 + \text{Monomer}_2 \xrightarrow{\text{dehydration}} \text{Polymer} + H_2O$

3.2 Macromolecules

Macromolecules are large polymers formed from monomers. The four major classes are carbohydrates, lipids, proteins, and nucleic acids.

• Carbohydrates: Energy source and structural material. Monosaccharides (glucose), disaccharides (sucrose), polysaccharides (starch, cellulose).

• Lipids: Energy storage, insulation, and cell membrane structure. Includes fats, oils, phospholipids, steroids.

• Proteins: Diverse functions including enzymes, transport, structure, and signaling. Made of amino acids.

• Nucleic Acids: Store and transmit genetic information. DNA and RNA are polymers of nucleotides.

3.3 Carbohydrates

Carbohydrates are composed of carbon, hydrogen, and oxygen. They serve as fuel and building material.

• Monosaccharides: Simple sugars (e.g., glucose, fructose).

• Disaccharides: Two monosaccharides joined (e.g., sucrose).

• Polysaccharides: Long chains (e.g., starch, cellulose, glycogen).

• Alpha vs. Beta Glucose: Structural differences affect properties (e.g., digestibility).

• Example: Starch is digestible by humans; cellulose is not.

3.4 Lipids

Lipids are hydrophobic molecules that include fats, oils, and steroids. They are important for energy storage and membrane structure.

• Fatty Acids: Can be saturated (no double bonds), monounsaturated (one double bond), or polyunsaturated (multiple double bonds).

• Triglycerides: Composed of glycerol and three fatty acids.

• Phospholipids: Major component of cell membranes; have hydrophilic heads and hydrophobic tails.

• Example: Cholesterol is a steroid important for membrane fluidity.

3.5 Proteins

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

• Amino Acids: 20 different types, each with a unique side chain (R group).

• Peptide Bonds: Link amino acids together to form polypeptides.

• Protein Structure:

  • Primary: Sequence of amino acids.

  • Secondary: Alpha helices and beta sheets formed by hydrogen bonding.

  • Tertiary: 3D folding due to interactions among side chains.

  • Quaternary: Association of multiple polypeptide chains.

• Functions: Enzymes, structural support, transport, signaling.

• Example: Hemoglobin transports oxygen in blood.

3.6 Nucleic Acids

Nucleic acids store and transmit hereditary information. DNA and RNA are composed of nucleotide monomers.

• DNA: Double helix structure; bases A, T, C, G. A pairs with T, C pairs with G.

• RNA: Single-stranded; bases A, U, C, G. A pairs with U.

• Function: DNA stores genetic information; RNA helps in protein synthesis.

• Example: mRNA carries genetic code from DNA to ribosomes.

Vocabulary and Key Terms

• Matter: Anything that takes up space and has mass.

• Element: Substance that cannot be broken down by chemical reactions.

• Compound: Substance consisting of two or more elements in a fixed ratio.

• Atom: Smallest unit of an element retaining its properties.

• Isotope: Atoms of the same element with different numbers of neutrons.

Comparison Table: Macromolecules

Macromolecule	Monomer	Main Function	Example
Carbohydrate	Monosaccharide	Energy source, structure	Glucose, starch, cellulose
Lipid	Fatty acid, glycerol	Energy storage, membranes	Triglyceride, phospholipid
Protein	Amino acid	Catalysis, structure, transport	Enzyme, hemoglobin
Nucleic Acid	Nucleotide	Genetic information	DNA, RNA

Short Answer Review Questions

• What is the difference between intramolecular and intermolecular bonds?

• How do hydrogen bonds give water its important properties?

• What are the most important properties of water and why are they important to living things?

• How are carbon atoms able to form diverse molecules?

• What are the four major types of macromolecules and their monomers?

• How do dehydration and hydrolysis reactions differ?

• What are the differences between saturated, monounsaturated, and polyunsaturated fatty acids?

• What are the four levels of protein structure?

• How do DNA and RNA differ in structure and function?

Additional info: Some scientific drawing and molecular structure details are referenced but not included; students should refer to textbook diagrams for visual representations.