Ch 2 - Chemical Components of Cells

Compare ionic, covalent, hydrogen bonds, and van der waals attraction.

Covalent: atoms share electrons

• strong bond, stable cell, generally doesn’t dissociate in water, main bond holding atoms together within molecules

  • H2, O2, H2O, CO2, N2

Ionic: electrons are transferred from one atom to another

• weaker than covalent bonds; commonly dissociate in water

• one atom loses electron(s) and becomes positively charged; other atom gains electrons are becomes negatively charged (opp charges attract)

  • NaCl, CaCl2, MgCl2

Hydrogen: attraction between a hydrogen atom covalently bonded to an electronegative atom and another electronegative atom

• occur between: water molecules, amino acids in proteins, bases in DNA

Van der waals: weak, short-range attractions between atoms that are close together

Describe electronegativity and polarity in molecules and their importance in biology.

• electronegativity is an atom’s ability to attract electrons toward itself

• nonpolar covalent bond: shared electrons are equally distributed between atoms/ no electronegativity difference (H-H)

• polar covalent bond: electrons are shared unequally (H-O)

  • more electronegative atom = (δ−)

  • least electronegative atom = (δ+)

• polar molecules interact well with water, while nonpolar molecules do not.

Electronegativity of the 4 major atoms, including carbon

F = 4.0

O = 3.4

N = 3.0

H = 2.1

C = 2.5

Explain hydrophilic and hydrophobic molecules and hydrophobic interactions.

Hydrophilic molecules are those that interact well with water due to their polar or charged characteristics, allowing them to form hydrogen bonds. In contrast, hydrophobic molecules do not interact well with water and tend to be nonpolar, often leading to aggregation (clustering) in aqueous environments to minimize exposure to water. Hydrophobic interactions help produce: lipid bilayer, protein folding. they are NOT real bonds

Explain how covalent bonds and weak interactions are critical in assembling biological molecules

covalent bonds create the molecule, weak interactions help the molecule fold and maintain its functional (3D) shape.

Describe the unique properties of water that make it important to life

it’s polar and forms hydrogen bonds, leading to high surface tension, heat of vaporization, specific heat capacity, and solvent properties that support biochemical reactions.

Calculate the pH of a solution given a concentration H+ or OH-

pH = −log[H⁺]

Kᵥ = [H⁺][OH⁻] → At 25°C: Kᵥ = 1 × 10⁻¹⁴

At neutral pH:

[H⁺] = [OH⁻] = 1 × 10⁻⁷ M

Calculate the concentration of H+ or OH- given a pH

To find H+:

[H⁺] = 10⁻ᵖᴴ

to find [OH-]

[H⁺][OH⁻] = 10⁻¹⁴

Therefore:

[OH⁻] = 10⁻¹⁴ / [H⁺]

concept of molarity/calculate the amount of stock solution or dry powder needed to create a specific solution

M = mol/L

Explain acid, base, and buffers and their properties and importance

acids

• donate H+; strong acid almost completely dissociates; weak acid partially dissociates

bases

• increase OH- concentration; strong bases almost completely dissociate, weak bases generally accept H+ from water and increases OH-

buffers

• solution that resists changes in pH when a small amount of acid or base is added

  • weak base + CA; weak acid + CB

Properties of covalent bond: Geometry and rigidity

oxygen: bent

nitrogen: trigonal pyramidal

carbon: tetrahedral

double bonds: C-C double bonds are shorter and more rigid than C-C single bonds

single bonds allow for movement around the bond axis

double bonds prevent rotation

polar vs non-polar biological functional groups

Polar Groups (hydrophilic)

hydroxyl (-OH), carboxyl (-COOH), Carbonyl (C=O), Amino (-NH2), amide (-CONH2), Phosphate (-PO4), sulfhydryl (-SH)

Nonpolar groups (hydrophobic)

methyl (-CH3)