AP Bio Unit 1 (Chemistry of Life) Review. Crush your unit test!

Water is a polar molecule with unequal electron sharing, leading to partial charges and the formation of weak intermolecular hydrogen bonds. These bonds are crucial in biology, stabilizing structures like DNA, RNA, and proteins, and give water its unique properties such as cohesion, adhesion, and high surface tension. Understanding pH, including acidic and basic solutions based on hydrogen and hydroxide ion concentrations, is also covered.

The essential elements of life are carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur (CHNOPS). Carbon is central to biomolecules, while hydrogen is vital for energy exchange and gradients. Monomers are building blocks that combine to form polymers through dehydration synthesis (removing water) and can be broken down by hydrolysis (adding water). Various functional groups (phosphate, methyl, hydroxyl, carbonyl, carboxyl, amino, sulfhydryl, acetyl) are critical for molecule function, such as energy transfer, gene regulation, and structural stability.

Carbohydrates are composed of monosaccharide monomers (simple sugars like glucose). Disaccharides are two linked monosaccharides (e.g., lactose), and polysaccharides are large chains used for energy storage (starch, glycogen) or structural roles (cellulose). The video explains why humans can digest starch but not cellulose, and discusses the evolution of lactose tolerance/intolerance in humans, linking it to the lactase enzyme and its production through adulthood.

Lipids are characterized by being wholly or partially nonpolar and are not made of repeating monomers. They serve various functions: triglycerides for energy storage, waxes for waterproofing, phospholipids as key components of cell membranes, and steroid hormones for signaling. Phospholipids, with their hydrophilic heads and hydrophobic tails, spontaneously form bilayers in water, forming the structural basis of cell membranes.

Proteins are made of amino acid monomers, each with a central carbon, an amine group, a carboxyl group, a hydrogen atom, and a variable R-group. There are 20 variations of R-groups causing differences in polarity and acidity. Protein structure has four levels: primary (linear sequence of amino acids), secondary (alpha helices and beta-pleated sheets formed by hydrogen bonds in the polypeptide backbone), tertiary (3D shape from interactions between R-groups), and quaternary (interactions between multiple folded polypeptide chains). The video uses hemoglobin and sickle cell disease as an example to illustrate these concepts.

Nucleic acids, DNA and RNA, carry genetic information. DNA is the hereditary molecule, while RNA has diverse functions including information transfer (mRNA) and catalytic activity (ribozymes). ATP, a nucleotide monomer, is the energy currency of cells. Nucleotides consist of a five-carbon sugar, a phosphate group, and one of four nitrogenous bases. DNA uses deoxyribose and bases A, T, C, G; RNA uses ribose and bases A, U, C, G. DNA is a double helix with two antiparallel nucleotide strands connected by hydrogen bonds between complementary base pairs (A-T, C-G). The directionality (5' to 3') is crucial for DNA replication by enzymes.