General Biology: Molecular and Cellular Foundations Study Guide

Lecture 2: Chemical Bonds and Water

2.1 How Atoms Interact to Form Bonds and Make Molecules

Atoms interact through various types of chemical bonds to form molecules essential for life. Understanding these bonds is fundamental to studying biological molecules.

• Covalent Bond: A strong bond formed when two atoms share one or more pairs of electrons.

• Nonpolar Covalent Bond: Electrons are shared equally between atoms (e.g., O2).

• Polar Covalent Bond: Electrons are shared unequally, resulting in partial charges (e.g., H2O).

• Ionic Bond: Formed when one atom donates an electron to another, creating ions (e.g., NaCl).

• Hydrogen Bond: A weak bond between a hydrogen atom and an electronegative atom (often oxygen or nitrogen).

• Van der Waals Interactions: Weak attractions between molecules due to transient local partial charges.

2.2 Properties of Water and Their Biological Importance

Water's unique properties make it essential for life. These properties arise from its polarity and ability to form hydrogen bonds.

• Cohesion: Water molecules stick together due to hydrogen bonding.

• Adhesion: Water molecules stick to other substances.

• High Specific Heat: Water can absorb a lot of heat before changing temperature.

• High Heat of Vaporization: Water requires significant energy to evaporate.

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

Example: Water's high specific heat helps organisms maintain stable internal temperatures.

2.5 Types of Interactions/Bonds in Biological Molecules

• Functional Groups: Specific groups of atoms within molecules that have characteristic properties (e.g., hydroxyl, carboxyl, amino).

• Hydrolysis: Breaking bonds by adding water.

• Condensation (Dehydration Synthesis): Forming bonds by removing water.

Lecture 3: Proteins and Nucleic Acids

3.1 Proteins: Monomers and Bonds

Proteins are polymers made of amino acid monomers linked by peptide bonds. Their structure determines their function.

• Amino Acids: Building blocks of proteins, each with a central carbon, amino group, carboxyl group, hydrogen, and R group (side chain).

• Peptide Bond: Covalent bond linking amino acids in a protein.

• R Group: Determines the properties and function of each amino acid.

Example: The R group of glutamic acid is acidic, while that of lysine is basic.

3.2 Protein Structure

• Primary Structure: Sequence of amino acids.

• Secondary Structure: Local folding (α-helix, β-sheet) stabilized by hydrogen bonds.

• Tertiary Structure: Overall 3D shape of a single polypeptide.

• Quaternary Structure: Association of multiple polypeptide chains.

Example: Hemoglobin has quaternary structure with four polypeptide subunits.

3.3 Protein Folding and Chaperones

• Chaperones: Proteins that assist in the proper folding of other proteins.

• Proper folding is essential for protein function; misfolded proteins can cause disease.

3.4 Nucleic Acids: Structure and Function

Nucleic acids (DNA and RNA) store and transmit genetic information. They are polymers of nucleotide monomers.

• Nucleotide: Consists of a sugar, phosphate group, and nitrogenous base.

• Phosphodiester Bond: Links nucleotides in a chain.

• Base Pairing: A-T (or A-U in RNA), G-C via hydrogen bonds.

3.5 DNA and RNA: Structure and Differences

• DNA: Double-stranded, deoxyribose sugar, stores genetic information.

• RNA: Single-stranded, ribose sugar, involved in protein synthesis and regulation.

Feature	DNA	RNA
Sugar	Deoxyribose	Ribose
Strands	Double	Single
Bases	A, T, G, C	A, U, G, C
Function	Genetic storage	Protein synthesis, regulation

Lecture 4: Carbohydrates

4.1 Carbohydrate Monomers and Bonds

Carbohydrates are energy-rich molecules made of carbon, hydrogen, and oxygen. They are classified by the number of sugar units.

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

• Disaccharides: Two monosaccharides linked by glycosidic bonds (e.g., sucrose).

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

4.2 Glycosidic Bonds and Polysaccharide Structure

• Glycosidic Bond: Covalent bond joining two monosaccharides.

• Structural Polysaccharides: Cellulose (plants), chitin (fungi, exoskeletons).

• Storage Polysaccharides: Starch (plants), glycogen (animals).

4.3 Structure-Function Relationships in Carbohydrates

• Branching and bond type affect digestibility and function.

• Cellulose's β(1→4) bonds make it rigid and indigestible to humans.

• Starch's α(1→4) and α(1→6) bonds make it digestible and a good energy source.

Lecture 5: Lipids and Membranes

5.1 Lipid Structure and Function

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

• Fats (Triglycerides): Glycerol + 3 fatty acids; energy storage.

• Phospholipids: Glycerol + 2 fatty acids + phosphate group; main component of cell membranes.

• Steroids: Four fused carbon rings (e.g., cholesterol).

5.2 Phospholipid Bilayer and Membrane Structure

• Phospholipid Bilayer: Double layer with hydrophilic heads facing out and hydrophobic tails facing in.

• Membrane fluidity is affected by fatty acid saturation and cholesterol content.

5.3 Membrane Proteins and Transport

• Integral (Transmembrane) Proteins: Span the membrane.

• Peripheral Proteins: Attached to membrane surface.

• Channel Proteins: Allow specific molecules to pass through.

• Carrier Proteins: Bind and transport substances across the membrane.

• Pumps: Use energy to move substances against their gradient (e.g., Na+/K+ ATPase).

5.4 Passive and Active Transport

• Passive Transport: Movement of substances down their concentration gradient (no energy required).

• Active Transport: Movement against the gradient, requiring energy (usually ATP).

Example: The Na+/K+ ATPase pump maintains ion gradients in animal cells.

5.5 Aquaporins and Other Membrane Proteins

• Aquaporins: Channel proteins that facilitate water transport.

• GLUT: Glucose transporter.

• Ion Channels: Allow passage of ions (e.g., Na+, K+).

Additional info:

• Standard error bars, p-values, and statistical significance are important for interpreting experimental data.

• Gel electrophoresis is used to separate DNA, RNA, and proteins by size and charge.