IB Biology Topic B1.1.1: Chemical Properties of a Carbon Atom Notes

Carbon's Bonding: Why One Element Underpins All of Life

1. Carbon forms the foundation of every biological molecule, from the DNA in your cells to the food you eat.
2. Carbon is the element of life, even though oxygen and nitrogen are more common.

The answer lies in carbon's bonding ability, versatility, and role in molecular diversity.

Covalent Bonding: Carbon Shares Electrons to Build Stable Molecules

1. A covalent bond forms when two atoms share a pair of electrons.
   1. Covalent bonds are the strongest type of bond in biological systems, which is why they build durable molecules like DNA and proteins.
   2. Carbon has four electrons in its outer shell but needs eight for stability.
   3. This allows carbon to form four covalent bonds, which gives rise to complex structures.

Carbon's Bonding Potential: One Element Builds Countless Structures

Carbon can form a variety of structures, ranging from simple chains to complex rings, making life's molecular diversity possible.

1. Single bonds create long chains
   1. Straight chains form fatty acids in cell membranes.
   2. Branched chains form molecules like isobutane, which changes how a molecule interacts and functions.
2. Double and triple bonds add rigidity and reactivity
   1. Double bonds introduce kinks into molecules, as seen in unsaturated fatty acids, which changes membrane fluidity.
   2. Triple bonds are less common but extremely strong, and they alter a molecule's properties.
3. Carbon rings form the basis of life's chemistry
   1. Single rings, like glucose, are soluble, which makes them ideal for energy transport in the body.
   2. Multiple rings, like cholesterol, strengthen cell membranes and act as a precursor for hormones.

Ethene vs Ethane: Bond Type in Action

Functional Groups: Small Attachments Control a Molecule's Chemistry

While the carbon backbone provides structure, functional groups determine a molecule's reactivity and interactions.

1. There are three key functional groups in biological molecules.
   1. Hydroxyl (-OH) is found in sugars and alcohols, making molecules polar and water-soluble.
   2. Carboxyl (-COOH) is found in amino acids and fatty acids, making them acidic and reactive.
   3. Amino (-NH2) is found in proteins, where it is essential for forming peptide bonds.

Why Carbon Is the Foundation of Life: Four Bonds Build Every Major Biomolecule

1. Carbon's ability to form four covalent bonds allows for complex, three-dimensional molecules.
   1. Three-dimensional molecular structures are crucial for DNA's double helix.
   2. Complex interactions are essential for enzyme function and signalling pathways.
2. This versatility builds every major class of biological molecule
   1. Carbohydrates (sugars) store and provide energy.
   2. Lipids (fats) form membranes and store energy long-term.
   3. Proteins enable structural support and enzymatic reactions.
   4. Nucleic acids (DNA and RNA) carry genetic information.

Nature of Science: Standard Units Keep Carbon Measurements Consistent

1. Scientists use SI units to measure carbon-based molecules consistently.
2. SI prefixes simplify how very large or very small measurements are written.
   1. kilo- (k) equals 10 to the power of 3.
   2. centi- (c) equals 10 to the power of minus 2.
   3. milli- (m) equals 10 to the power of minus 3.
   4. micro- (μ) equals 10 to the power of minus 6.
   5. nano- (n) equals 10 to the power of minus 9.