Chemistry of Life and Atomic Structure

Chemical Elements in Life

• 25 elements are essential for life
• Four elements make up 96% of living matter: Carbon (C), Hydrogen (H), Oxygen (O), and Nitrogen (N)
• Four elements make up most of the remaining 4%: Phosphorus (P), Calcium (Ca), Sulfur (S), and Potassium (K)

Atomic Structure and Bonding

• Atoms are the basic building blocks of matter
• The outermost shell of an atom, the valence shell, determines its chemical behavior
• Electrons fill shells from the inside out: 1st shell holds 2 electrons, 2nd shell holds 8, and 3rd shell holds 8
• Elements in the same row of the periodic table have the same number of shells
• Elements in the same column have the same number of valence electrons and similar chemical properties

Chemical Bonds

• Covalent bonds: Two atoms share a pair of electrons, forming molecules
• Hydrogen bonds: Weak attractions between polar molecules, like water molecules, due to the attraction of a positive hydrogen atom to a negative oxygen atom
• Ionic bonds: Transfer of electrons from one atom to another, creating ions

Importance of Water in Biology

• Water is essential for all life, existing both inside and outside cells
• Cohesion: Water molecules are attracted to each other due to hydrogen bonding, leading to surface tension and capillary action
• Adhesion: Water molecules are attracted to other substances, also due to hydrogen bonding.
• Solvent: Water is a good solvent for many molecules, due to its polarity.
• Lower density as a solid: Ice floats because it's less dense than liquid water
• High specific heat: Water can absorb a lot of heat before its temperature changes significantly
• High heat of vaporization: Water requires a lot of energy to evaporate

Hydrophilic and Hydrophobic Interactions

• Hydrophilic: Substances that are attracted to water, often polar molecules
• Hydrophobic: Substances that are not attracted to water, often non-polar molecules

pH and Buffers

• pH scale: Measures the acidity or alkalinity of a solution, ranging from 0 to 14
• Acid: A substance that releases hydrogen ions (H+)
• Base: A substance that accepts hydrogen ions
• Buffer: A solution that resists changes in pH

Functional Groups

• Hydrocarbons: Mostly carbon and hydrogen, relatively unreactive but become more active when functional groups are added

Carbohydrates

• Provide energy and structural support

Proteins

• Perform various functions like enzyme activity, structure, and immune responses

Lipids

• Store energy, form cell membranes, and act as signaling molecules

Nucleic Acids

• Store and transmit genetic information (DNA and RNA)