Key Concepts in Biology: From Molecules to Cellular Processes

Posted on Feb 8, 2025 in Chemistry

Pasteur’s Experiment and Spontaneous Generation

Pasteur’s experiment disproved the theory of spontaneous generation. It was a testable and repeatable experiment.

Chemical Bonds and Interactions

Polar vs. Non-Polar Molecules

• Polar: Not balanced.
• Non-Polar: Balanced.

Types of Chemical Bonds

• Covalent Bond: A bond where two atoms share electrons to achieve stability. An atom can share up to four electrons.
• Hydrogen Bond: A weak connection between a hydrogen atom and another atom, such as oxygen or nitrogen (in polar molecules).
• Ionic Bond: A bond formed when an atom donates an electron to another, creating a bond between a positively charged ion (cation) and a negatively charged ion (anion). Electrostatic attraction holds the ions together. Example: NaCl.
• Van der Waals Interactions: Weak, temporary attractions between molecules due to small, momentary shifts in electron positions. They occur when electrons are not symmetrically distributed in a molecule.

Water and Its Properties

A water molecule can form up to four hydrogen bonds. These bonds are weaker than covalent bonds. Water is neutral overall. Oxygen and nitrogen can form hydrogen bonds, as can hydrogen attached to oxygen or nitrogen. Ionization can break water into two particles:

• OH^–: Hydroxide ion
• H⁺: Hydrogen ion

Water requires more energy to heat. Substances can be:

• Hydrophilic: Polar
• Hydrophobic: Non-polar

Macromolecules: Carbohydrates, Lipids, Proteins, and Nucleic Acids

Carbohydrates

Condensation: The removal of a water molecule during the linking of monomers.
Hydrolysis: A chemical process in which water breaks down a compound. Water molecules split into hydrogen and hydroxide ions.
Carbohydrate: Simple sugars, such as glycogen, starch, and cellulose.

Monosaccharides are the simplest form of carbohydrates (C_nH_2nO_n, where n = 3 to 7):

• Glucose: C₆H₁₂O₆
• Fructose: C₆H₁₂O₆ (different structure)
• Galactose: C₆H₁₂O₆ (same formula as glucose)
• Ribose: C₅H₁₀O₅
• Deoxyribose: C₅H₁₀O₄

Peptidoglycan: A polysaccharide found only in bacteria, containing a modified monosaccharide.
Amylose: Formed from β-1,4-glycosidic linkages of glucose; spiral structure; 25% of starch.
Amylopectin: α-linkages; 75% of starch. Starch is composed of branched amylopectin and unbranched amylose.
Polymers containing sugars: Store genetic information and energy, and protect cells.
Chitin: An important component in the structure of many animal and fungal cells.

Lipids

Lipids include steroids, waxes, and phospholipids.

• Saturated Fats: Tightly packed, less fluid, contain more hydrogen than unsaturated fats with the same number of carbon atoms.
• Unsaturated Fats: Have kinks in their tails, are more fluid, and have double bonds in their fatty acid chains (e.g., olive oil).

Cholesterol is a component of animal cell membranes.

Proteins

Proteins are made of amino acids linked by peptide bonds. When two amino acid monomers are positioned so that the carboxyl group of one is adjacent to the amino group of the other, they can be joined through a dehydration reaction.

• The secondary structure of a protein results from hydrogen bonds; some regions of a polypeptide may coil or fold, held in place by hydrogen bonds.
• Tertiary structure is NOT directly dependent on peptide bonds.
• R groups (side groups) are found on the inside of the folded chain, away from water.
• Stabilized by covalent bonds: Primary, tertiary, and quaternary levels of protein structure.

Nucleic Acids

Nucleic acids are made of nucleotides.

Cellular Processes: Osmosis, Diffusion, and Transport

Osmosis: The movement of water from an area of low solute concentration to an area of high solute concentration.
Hypo: Less solute.
Hyper: More solute.
Diffusion: A passive process where molecules move from higher to lower concentration.
Transport:

• Passive Transport: Includes diffusion and osmosis.
• Active Transport: Requires energy (e.g., ATP).