Chapter 19 · Biochemistry
19.2The Cell and Its Main Chemical Components
8 min · two checks
Predict
Which four families account for most of the dry mass of a cell, besides salts and small metabolites?
The idea
- Name the major classes of biomolecules.
- Place water and membranes in the picture.
A cell is a watery solution and a set of compartments, wrapped in a membrane. Water is both solvent and reactant. Ions — Na⁺, K⁺, Ca²⁺, Cl⁻ — carry signals and charge. The large molecules fall into four families. Proteins do chemistry and structure. Nucleic acids store and transmit sequence. Carbohydrates store energy and mark surfaces. Lipids form membranes and long-term energy stores.
The membrane is a bilayer of phospholipids: hydrophilic heads toward water, hydrophobic tails inward. That arrangement is the intermolecular-force chapter applied to a cell. Proteins embedded in the bilayer move specific ions and molecules, because the tails themselves will not let polar solutes wander through. Everything in this chapter happens in that context, not in a dry flask.
Keep these
- Water is the main component. The big four are proteins, nucleic acids, carbohydrates, and lipids.
- A phospholipid bilayer makes the membrane.
- Embedded proteins control traffic the bilayer would block.