BIOB 160 Principles of Living Systems · Unit 1: The chemistry of life · on Exam 1
1.4 Carbon and the molecular diversity of life
Study notes for Carbon and the molecular diversity of life in BIOB 160 Principles of Living Systems at Montana State University: the big ideas, a worked example, common mistakes and an exam tip. The same topic has endless practice questions and flashcards in Mathub.
Big ideas
- Carbon has 4 valence electrons, so it forms 4 covalent bonds, building chains, branches, rings and double bonds: the skeletons of organic molecules.
- Isomers have the same formula but different structures: structural isomers (different arrangement of atoms), cis-trans isomers (different arrangement around a double bond) and enantiomers (mirror images; often only one form is active, as with some drugs).
- Seven chemical groups to know: hydroxyl (–OH, polar, alcohols), carbonyl (C=O, ketones and aldehydes), carboxyl (–COOH, acidic), amino (–NH₂, basic), sulfhydryl (–SH, forms disulfide bridges), phosphate (–OPO₃²⁻, stores energy in ATP) and methyl (–CH₃, affects gene expression).
- ATP (adenosine triphosphate) is an organic molecule whose phosphate groups release energy when one is removed.
- Hydrocarbons (only C and H) are nonpolar and hydrophobic; adding polar groups such as –OH makes molecules more soluble in water.
Worked example
A molecule has an –NH₂ group on one end and a –COOH group on the other, attached to the same carbon. What class of molecule is it and how does each group behave in water?
Show the solution
It is an amino acid. The amino group acts as a base (picks up H⁺ to become –NH₃⁺) and the carboxyl group acts as an acid (releases H⁺ to become –COO⁻).
Common mistakes
- Mixing up carbonyl (C=O) and carboxyl (–COOH, which contains a carbonyl plus –OH).
- Thinking enantiomers behave the same in the body. Cells often recognize only one.
- Forgetting that carbon usually makes exactly four bonds when you draw structures.
Exam tipReading: Campbell ch. 4 (pp. 56–65). Make flashcards with the structure, name and property of each of the seven groups.
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