General Biology Study Notes: Water, Macromolecules, and Protein Structure

Water Characteristics

Hydrogen Bonds

Hydrogen bonds are a type of non-covalent interaction that occurs between a partially positive hydrogen atom and a partially negative atom, such as oxygen or nitrogen. These bonds are crucial for the properties of water and biological molecules.

• Definition: A hydrogen bond is an electrostatic interaction between a partial positive hydrogen atom and a partial negative atom.

• Strength: Hydrogen bonds are generally weaker than covalent bonds but stronger than ionic bonds in aqueous environments.

• Example: Water molecules form hydrogen bonds with each other, contributing to water's high boiling point and surface tension.

Ionic and Covalent Bonds

Covalent bonds involve the sharing of electron pairs between atoms, while ionic bonds involve the transfer of electrons and the attraction between oppositely charged ions.

• Covalent Bonds: Strongest in an aqueous environment; electrons are shared between atoms.

• Ionic Bonds: Electrostatic interactions between full charges; weaker in water due to dissociation.

• Hydrogen Bonds: Electrostatic interactions between partial charges; weaker than covalent and ionic bonds.

Hydrophobic and Hydrophilic Substances

Hydrophilic substances are polar or charged and can interact with water, while hydrophobic substances are nonpolar and do not interact favorably with water.

• Hydrophilic: Water-loving; typically polar or charged molecules.

• Hydrophobic: Water-fearing; typically nonpolar molecules.

• Example: Hydrocarbons are hydrophobic, while salts and sugars are hydrophilic.

Acids and Bases in Water

Acids donate protons (H+) to the solution, while bases accept protons. The strength of acids and bases is determined by their ability to dissociate in water.

• Acid: Donates a proton to the solution and becomes negatively charged, thus decreasing the pH.

• Base: Accepts a proton from the solution and becomes positively charged, thus increasing the pH.

• pH Equation: $pH = -\log[H^+]$

Macromolecules

Types of Macromolecules

Macromolecules are large, complex molecules essential for life. The four major types are carbohydrates, proteins, nucleic acids, and lipids.

• Carbohydrates: Energy storage and structural support.

• Proteins: Catalysis, structure, movement, signaling.

• Nucleic Acids: Genetic information storage and transfer.

• Lipids: Membranes, energy storage.

Functional Groups

Functional groups are specific groups of atoms within molecules that determine their chemical properties and reactivity.

• Amino: Basic, can accept a proton.

• Carboxyl: Acidic, can donate a proton.

• Hydroxyl: Polar, can form hydrogen bonds.

• Methyl: Nonpolar, hydrophobic.

• Sulfhydryl: Can form disulfide bonds, important in protein structure.

Classification of Functional Groups

Functional groups can be classified as acidic, basic, polar, or nonpolar, which affects their behavior in biological systems.

• Acidic: Carboxyl group (-COOH)

• Basic: Amino group (-NH2)

• Polar: Hydroxyl group (-OH), carbonyl group (C=O)

• Nonpolar: Methyl group (-CH3), hydrocarbon chains

Amino Acids and Proteins

Amino Acid Structure

Amino acids are the building blocks of proteins, each containing an amino group, a carboxyl group, a hydrogen atom, and a unique side chain (R group).

• General Structure: $\text{H}_2\text{N}-\text{CHR}-\text{COOH}$

• Classification: Based on side chain properties: nonpolar, polar, acidic, basic.

• Peptide Bond: Covalent bond formed between the amino group of one amino acid and the carboxyl group of another.

Polypeptides and Proteins

Polypeptides are chains of amino acids linked by peptide bonds. Proteins are functional polypeptides that have folded into specific three-dimensional structures.

• Primary Structure: Sequence of amino acids.

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

• Tertiary Structure: Overall three-dimensional shape formed by interactions between side chains.

• Quaternary Structure: Association of multiple polypeptide chains.

Protein Folding and Function

Protein function is determined by its structure, which is stabilized by various interactions, including hydrogen bonds, ionic bonds, hydrophobic interactions, and disulfide bridges.

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

• Denaturation: Loss of protein structure due to heat, pH changes, or chemicals.

• Example: Enzymes are proteins whose function depends on their three-dimensional structure.

Protein Separation and Visualization

Gel Electrophoresis

Gel electrophoresis is a technique used to separate proteins or nucleic acids based on size and charge.

• Principle: Molecules are loaded into a gel and an electric field is applied; smaller molecules move faster.

• SDS-PAGE: Proteins are coated with SDS to give them a uniform negative charge, allowing separation by size.

• Case Study: In SDS-PAGE, the largest protein subunit migrates the least, while the smallest migrates the farthest.

Protein Subunit	Migration Distance
Alpha	Least
Beta	Most
Full-length	Intermediate

Nucleic Acids

Structure of Nucleotides

Nucleotides are the building blocks of nucleic acids, composed of a phosphate group, a five-carbon sugar (ribose or deoxyribose), and a nitrogenous base.

• Components: Phosphate group, pentose sugar, nitrogenous base (A, T, C, G, U)

• Example: DNA contains deoxyribose; RNA contains ribose.

• Base Pairing: $A-T$, $C-G$ in DNA; $A-U$, $C-G$ in RNA

Summary Table: Types of Macromolecules

Macromolecule	Monomer	Function
Carbohydrate	Monosaccharide	Energy, structure
Protein	Amino acid	Catalysis, structure, movement
Nucleic Acid	Nucleotide	Genetic information
Lipid	Fatty acid (not a true polymer)	Membranes, energy storage

Additional info: Some explanations and examples have been expanded for clarity and completeness, including definitions and context for functional groups, protein folding, and gel electrophoresis.