Biology 1: Water Properties Quiz

Biology 1 "BIO131"

• Course taught by Dr. Ahmed Deghidy
• PhD in Molecular Biology
• At Alex U, Alexandria, Egypt

Water: A Vital Compound

• Water molecules are composed of one oxygen atom and two hydrogen atoms.
• Oxygen shares an electron with each hydrogen atom.
• Water's polarity results from oxygen's greater electronegativity.
• This creates partial negative charges near oxygen and partial positives near hydrogen.
• Water has a simple molecular structure.

Water molecules are cohesive

• Cohesion is water's tendency to adhere to other water molecules due to hydrogen bonding.
• Cohesion is responsible for water's surface tension.
• Surface tension is the force that allows insects to glide on water.
• High surface tension is due to hydrogen bonding between water molecules.

Water molecules are adhesive

• Water's polarity allows it to adhere to other polar molecules.
• Adhesion is the attraction of water to other substances.
• Water adheres to surfaces like glass, causing water to rise in narrow tubes (capillary action).
• Adhesion strength is greater than gravity in narrow tubes.

Properties of Water

• Cohesion: Hydrogen bonds hold water molecules together.
• High specific heat: Water absorbs or releases heat when bonds break or form, minimizing temperature changes.
• High heat of vaporization: Many hydrogen bonds must break for water to evaporate, cooling body surfaces.
• Lower density of ice: Water molecules in ice are spaced further apart due to hydrogen bonding, making ice less dense than liquid water.
• Solubility: Polar water molecules attract ions and polar compounds, making them soluble.

The Chemical Building Blocks of Life

• Biological molecules are primarily composed of carbon atoms bonded to other carbon atoms or atoms of oxygen, nitrogen, sulfur, phosphorus, or hydrogen.
• Carbon atoms can form up to four covalent bonds.
• This allows for diverse structures in biological molecules.
• Molecules consisting only of carbon and hydrogen are hydrocarbons (e.g., gasoline).
• Hydrocarbons make good fuels due to high energy stored in C-H bonds.

Functional groups

• Differences in molecular properties of biological molecules are primarily due to functional groups.
• Functional groups give specific chemical properties to molecules.
  • Ex1: Amino groups make molecules more basic.
  • Ex2: Carboxyl groups make molecules more acidic.
    • Hydroxyl
    • Carbonyl
    • Carboxyl
    • Amino
    • Sulfhydryl
    • Phosphate

Biological macromolecules

• Macromolecules include carbohydrates, lipids, nucleic acids, and proteins.
• Polymers are large molecules made from repeating subunits (monomers).
• Polymers are built via dehydration reactions (water is lost).
• Polymers are broken down via hydrolysis reactions (water is added).
• Lipids are macromolecules that don't strictly follow monomer-polymer relationships, forming through dehydration reactions linking fatty acids to glycerol.

Carbohydrates

• Carbohydrates contain carbon, hydrogen, and oxygen in a 1:2:1 ratio.

• Their empirical formula is (CH₂O)ₙ.

• They're excellent energy storage molecules due to numerous C-H bonds.

• Simplest carbohydrates are monosaccharides (e.g., glucose, fructose, galactose).

• Disaccharides are formed from two monosaccharides bonded together (e.g., sucrose, lactose).

• Polysaccharides are long chains of monosaccharides (e.g., starch, cellulose, glycogen).

• Starch: A storage polysaccharide consisting of unbranched chains of α-glucose monomers.

• Cellulose: A structural polysaccharide consisting of unbranched chains of β-glucose monomers. Cellulose is difficult for most animals to digest.

• Glycogen: An animal storage polysaccharide, branched, with more branches than plant starch.