Hydrogen bond: water polar interactions

Cellular classification and basic cell architecture

  • World of living creatures is divided into two classes for bacteria: prokaryotes. They are small.

  • Eukaryotes: us and many other features (referred to as eukaryotes).

  • In eukaryotes, the cell has a nucleus (a structure in the middle of the cell).

  • The outside of the cell is bounded by the plasma membrane.

  • Between the nucleus and the plasma membrane lies the cytoplasm.

  • The cytoplasm is typically divided into two parts: organelles and cytosol.

    • The cytosol is the fluid portion;

    • Organelles are specialized structures that reside within the cytoplasm.

  • The cytoplasm includes both the cytosol and organelles.

Quick biology context and a “factoid” prompt

  • A one-factoid memory from biology: in cells we have water, macromolecules, and small molecules; lipids are sometimes included in discussions of macromolecules, but the speaker notes this inclusion is debatable.

  • The cytoplasm contains all sorts of molecules that contribute to cell function: water, macromolecules, lipids (context-dependent), and small molecules.

Water, bonds, polarity, and hydrogen bonding

  • Water is the solvent in cells; chemical composition is ext{H}_2 ext{O} (two hydrogens covalently bonded to one oxygen).

  • Covalent bond definition: a covalent bond is between two atoms when they share a pair of electrons. For water, the O–H bonds are covalent.

    • Each water molecule has two covalent O–H bonds.

  • Polar covalent bonds and partial charges:

    • In each O–H bond, electrons are not shared equally: electrons spend more time around oxygen, giving oxygen a partial negative charge and the hydrogens partial positive charges.

    • Representations: ext{O}^{ ext{δ-}} and ext{H}^{ ext{δ+}}

    • This unequal sharing creates polarity within the water molecule and allows water to participate in hydrogen bonding.

  • Hydrogen bonds:

    • Hydrogen bonds are attractions between the partial positive charge on a hydrogen atom of one molecule and the partial negative charge on an electronegative atom (like oxygen) in a neighboring molecule.

    • Example: in water, a hydrogen from one water molecule can form a hydrogen bond with the oxygen of another water molecule: $$ ext{H}^{ ext{δ+}} \