Mod2: Chemical Basis of Life

Atomic Numbers & Symbols:
- Carbon (C):
- Atomic Number: 6
- Atomic Weight: 12.01
- Hydrogen (H):
- Atomic Number: 1
- Atomic Weight: 1.008
- Oxygen (O):
- Atomic Number: 8
- Atomic Weight: 16.00
- Nitrogen (N):
- Atomic Number: 7
- Atomic Weight: 14.01
- Phosphorus (P):
- Atomic Number: 15
- Atomic Weight: 30.97
- Sulfur (S):
- Atomic Number: 16
- Atomic Weight: 32.07
- Trace Elements (less than 0.01%): Boron (B), Chromium (Cr), Cobalt (Co), Copper (Cu), Fluorine (F), Iodine (I), Iron (Fe), Manganese (Mn), Molybdenum (Mo), Selenium (Se), Silicon (Si), Tin (Sn), Vanadium (V), Zinc (Zn).

Niels Bohr's Model of 1913: The atomic nucleus is composed of protons and neutrons, with electrons orbiting around it.

Definition: Atoms with the same number of protons but different numbers of neutrons.
Example: Carbon isotopes (C-12, C-13, C-14).
Half-life of carbon-14: 5,730 years – used for dating dead tissues (fossils).
- After 5,730 years, the amount of C-14 is reduced to 50%.
- Organisms dead for 5,730 years have 50% less C-14 than living organisms.
- The C-14 supply is not replenished in dead tissues.

Carbon-14 Dating:
- Living organisms absorb all three isotopes of carbon. After death, C-14 decays to nitrogen-14.
  | Years After Death | C-14 Percentage |
  |-------------------|-----------------|
  | 0 | 100% |
  | 5,730 | 50% |
  | 11,460 | 25% |
  | 17,190 | 12.5% |

Chemical bonds are physical attractions between atoms due to electron transfer, sharing, or differences in atomic charge.
Atoms form bonds to fill their outermost (valence) shell of electrons.

Ionic Bonds:
- Formed by the complete transfer of electrons between atoms, resulting in oppositely charged ions that are electrostatically attracted to one another.
Covalent Bonds:
- Non-polar Covalent Bonds: Equal sharing of electrons between atoms.
- Polar Covalent Bonds: Unequal sharing of electrons, resulting in charged parts of the molecule.
- Example: Water (H₂O) is a polar molecule.
Hydrogen Bonds:
- Electrostatic attractions between polar molecules (e.g., water).

Nucleic Acids: Composed of nucleotides (sugar, phosphate, base).
Proteins: Composed of amino acids.
Carbohydrates: Composed of monosaccharides (short-term and long-term energy storage).
Lipids: Composed primarily of fatty acids (non-polar and insoluble in water).

Building blocks of proteins, with 20 common amino acids encoded by the human genetic code.
- Essential Amino Acids: Obtained from the diet.
- Non-Essential Amino Acids: Synthesized in the body.
Each amino acid has a basic structure: amine (amino), carboxyl, hydrogen, α-carbon, and R group.

Primary Structure: Linear sequence of amino acids linked by covalent peptide bonds.
Secondary Structure: Stabilized by hydrogen bonds, leading to structures like α-helices and β-pleated sheets.

Monosaccharides: Examples include glucose, which serves as a short-term energy source.
Disaccharides: Composed of two monosaccharides for short-term energy storage (e.g., lactose).
Polysaccharides: Long-term energy storage (e.g., starch in plants, glycogen in animals) and structural components (e.g., cellulose in plants, chitin in animals).

Triglycerides: Composed of three fatty acids; long-term energy storage.
Phospholipids: Form cellular membranes; have hydrophobic fatty acid tails and polar heads.
Steroids: Made of sterol rings; serve as signaling molecules regulating organismal functions.