General Biology: Chemical Foundations, Macromolecules, and Nucleic Acids Study Guide

Chemical Bonds and Properties of Water

Types of Chemical Bonds

Chemical bonds are the forces that hold atoms together in molecules and compounds. The main types are:

• Covalent Bonds: Atoms share electrons. Can be polar (unequal sharing) or nonpolar (equal sharing).

• Ionic Bonds: Electrons are transferred from one atom to another, creating charged ions that attract each other.

Example: Water (H2O) is formed by polar covalent bonds between hydrogen and oxygen.

Hydrogen Bonds

Hydrogen bonds are weak attractions between a hydrogen atom (attached to an electronegative atom like oxygen or nitrogen) and another electronegative atom. They are crucial in stabilizing biological molecules.

• Responsible for many properties of water.

• Play a role in the structure of DNA and proteins.

Polarity of Water

Water is a polar covalent molecule because oxygen is more electronegative than hydrogen, causing an unequal sharing of electrons.

• Leads to partial positive and negative charges on hydrogen and oxygen, respectively.

• Allows water molecules to form hydrogen bonds with each other.

Properties of Water Due to Hydrogen Bonds

Hydrogen bonding gives water unique properties essential for life:

• Cohesion and Adhesion: Water molecules stick to each other (cohesion) and to other surfaces (adhesion).

• Surface Tension: Water has a high surface tension, allowing small objects to float.

• High Specific Heat: Water absorbs a lot of heat before its temperature rises, helping regulate climate and body temperature.

• High Heat of Vaporization: Water requires significant energy to change from liquid to gas, aiding in cooling mechanisms like sweating.

• Density of Water: Ice is less dense than liquid water, so it floats, providing insulation for aquatic life.

pH, Buffers, and Functional Groups

pH and Buffers

pH measures the concentration of hydrogen ions in a solution. It ranges from 0 (acidic) to 14 (basic), with 7 being neutral.

• Buffers are substances that help maintain a stable pH in biological systems by neutralizing excess acids or bases.

• Example: Blood contains bicarbonate buffer to maintain pH around 7.4.

Functional Groups

Functional groups are specific groups of atoms within molecules that determine the chemical properties and reactions of those molecules.

• Examples: Hydroxyl (-OH), carboxyl (-COOH), amino (-NH2), phosphate (-PO4).

• Functional groups influence polarity and reactivity.

Atoms, Elements, and Macromolecules

Atoms and Elements

Atoms are the basic units of matter, composed of protons, neutrons, and electrons. Elements are pure substances made of only one type of atom.

• Valence Electrons: Electrons in the outermost shell, important for chemical bonding.

• Major Elements in Macromolecules: Carbon, hydrogen, oxygen, nitrogen, phosphorus, sulfur.

Dehydration and Hydrolysis Reactions

Macromolecules are formed and broken down by specific chemical reactions:

• Dehydration (Condensation) Reaction: Joins monomers by removing water.

• Hydrolysis Reaction: Breaks polymers into monomers by adding water.

Carbohydrates

Structure and Types

Carbohydrates are organic molecules made of carbon, hydrogen, and oxygen. They serve as energy sources and structural components.

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

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

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

Alpha and Beta Glucose

• Alpha Glucose: Forms starch and glycogen (energy storage).

• Beta Glucose: Forms cellulose (structural component in plants).

Linkages and Isomers

• Glycosidic Linkages: Bonds between sugar monomers.

• Isomers: Molecules with the same formula but different structures (e.g., glucose and galactose).

Comparison of Starch, Cellulose, and Glycogen

Polymer	Function	Type of Bond	Found In
Starch	Energy storage	Alpha 1,4 glycosidic	Plants
Cellulose	Structural support	Beta 1,4 glycosidic	Plants
Glycogen	Energy storage	Alpha 1,4 and 1,6 glycosidic	Animals

Lipids

Structure and Function

Lipids are hydrophobic molecules, including fats, oils, and steroids. They are important for energy storage, insulation, and cell membranes.

• Fatty Acids: Long hydrocarbon chains with a carboxyl group.

• Triglycerides: Three fatty acids linked to glycerol.

• Phospholipids: Major component of cell membranes.

Type of Linkage: Ester linkage between fatty acids and glycerol.

Proteins

Structure and Levels of Folding

Proteins are polymers of amino acids, folded into specific shapes for diverse functions.

Level of Folding	Description	Types of Bonds
Primary	Sequence of amino acids	Peptide bonds
Secondary	Local folding (alpha helix, beta sheet)	Hydrogen bonds
Tertiary	Overall 3D shape	Hydrogen, ionic, disulfide, hydrophobic interactions
Quaternary	Multiple polypeptides assembled	Same as tertiary

• Peptide Bond: Covalent bond between amino acids.

• Denaturation: Loss of protein structure due to environmental changes.

• Renaturation: Regaining native structure under suitable conditions.

Protein Synthesis and Folding

• Proteins are synthesized by ribosomes using mRNA templates.

• Folding is influenced by amino acid sequence and cellular environment.

Nucleic Acids

Structure and Components

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

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

• DNA: Deoxyribonucleic acid; double-stranded; stores genetic information.

• RNA: Ribonucleic acid; single-stranded; involved in protein synthesis.

DNA vs. RNA Comparison

Feature	DNA	RNA
Pentose Sugar	Deoxyribose	Ribose
Nitrogenous Bases	A, T, C, G	A, U, C, G
Strandedness	Double-stranded	Single-stranded
Traditionally	Genetic storage	Protein synthesis
Directionality	5' to 3'	5' to 3'

Additional Key Points

• Chargaff's Rule: In DNA, the amount of adenine (A) equals thymine (T), and cytosine (C) equals guanine (G).

• Hydrogen Bonds: Hold base pairs together (A-T: 2 bonds, C-G: 3 bonds).

• Melting Temperature: DNA with more C-G pairs has a higher melting temperature due to more hydrogen bonds.

• Experiments: Griffith, Avery, Hershey-Chase, and Watson-Crick contributed to understanding DNA structure.

Additional info: Some explanations and examples have been expanded for clarity and completeness.