BIOC3021 #1 - Molecules & Cell + Water, pH, and Buffers

Covalent Bond

• hold atoms together to form molecules (share electrons to fill outer electron shell)

  • Particularly bonds between carbon atoms

Non-covalent Bonds

• weak chemical forces that maintain biological structure and determine molecular interactions

  • Allow for changes in structure (Ex. DNA replication)

Types of Non-covalent Bonds

1. Ionic Interactions

2. Hydrogen Bonds

3. Hydrophobic Interactions

4. Van der Waals Interactions

Prokaryotic Cells

Small, single-celled organisms with a simple structure

Eukaryotic Cells

Complex cell containing a “true” nucleus and other organelles

Biomolecules

1. Amino Acids

2. Monosaccharides (carbohydrates)

3. Nucleotides

4. Lipids

Amino Acids Definition

• Contain an amino group (-NH2) and a carboxylic acid group (-COOH)

  • Ionized groups are: (-NH3+) and (-COO-)

Carbohydrates Definition

• Contain C, H, and O

  • Simple carbohydrates (monosaccharides) contain one sugar, following the formula (CH2O)n

Nucleotides Definition

Contain a five-carbon sugar (pentose), a nitrogenous ring (base), and a phosphate group

Lipids Definition

Group of insoluble, naturally occurring molecules (C, H, O)

Biopolymers

1. Proteins

2. Polysaccharides (carbohydrates)

3. Nucleic Acid

Proteins Definition

Polymers of amino acids linked by amide bonds (also called peptide bonds)

Nucleic Acids Definition

Polymers of nucleotides linked by phosphodiester bonds

Polysaccharides (carbohydrates)

Polymer of carbohydrates containing multiple monosaccharides linked by glycosidic bonds

Water has an unusually _ _ _

High boiling point

Properties of Water

• Polar Molecule

  • Partial charges form a dipole (polar covalent bond)

• Hydrogen-bonded Network

  • Molecules in liquid water interact to form rapidly changing, random hydrogen bonds

The average lifetime of a hydrogen bond between 2 H2O molecules is

9.5 picoseconds

H2O in liquid water forms an average of _ hydrogen bonds

3.4

H2O in solid ice forms _ hydrogen bonds

4

Solvent Properties of Water

1. Forms hydrogen-bonds with polar solutes

2. Forms hydration shells around charged ions

3. Forms clathrate (cage-like) structures around non-polar solute molecules (hydrophobic solutes)

4. Produces micelles with amphiphilic molecules

Micelle

Single-layer, spherical structures formed by amphiphilic molecules in water

Lipid Bilayer

Bilayers (two-layer sheets) formed by amphiphilic molecules in water

Colligative Properties of Water

Properties that depend only on the number of solute particles per unit volume, NOT on the chemical nature of the solute

Examples of Colligative Properties of Water

Osmotic pressure effects, freezing point depression, boiling point elevation, and vapor pressure lowering

High concentration of solutes could result in

Swelling and eventual rupture of the cell

pH

A measure of hydrogen ion concentration

pH Formulas

pH = -log₁₀[H⁺] and [H⁺] = 10^-pH

What relationship does [H+] and [OH-] have?

Inverse relationship

Ionization Constant Equation

K_w = [H⁺][OH^-} = 10^-14

Buffer Systems

1. Phosphate System: buffers the intracellular fluid of cells

2. Carbonate System: buffers the blood plasma

Phosphate System consists of:

• H2PO4- ➡ dihydrogen phosphate ion that neutralizes excess hydroxide (OH-) ion

• HPO42- ➡ monohydrogen phosphate ion that neutralizes excess hydrogen (H+) ion

Carbonate System consists of:

• HCO3- ➡ bicarbonate ion that neutralizes excess hydrogen (H+) ion

• H2CO3 ➡ carbonic acid that neutralizes excess hydroxide (OH-) ion