Unit 1 covers water, hydrogen bonding, elements of life, and four biomolecule families: carbohydrates, lipids, proteins, and nucleic acids. Water is a polar molecule due to unequal electron sharing between oxygen and hydrogen, resulting in a partial negative charge on oxygen and partial positive charges on hydrogen.

Hydrogen bonds are intermolecular bonds, unlike covalent or ionic bonds which are intramolecular. These hydrogen bonds are much weaker than covalent and ionic bonds. They are crucial for the structure of DNA, RNA, and proteins. Key properties of water, such as cohesion, adhesion, and surface tension, arise from hydrogen bonding.

• ★Water is a polar molecule with unequal electron sharing.0:15
• ★Hydrogen bonds are weak intermolecular bonds.0:30
• ★Hydrogen bonds are key to DNA, RNA, and protein structure.1:15
• ★Cohesion, adhesion, and surface tension result from hydrogen bonding.2:00

Example: Hydrogen bonds form between nitrogen and hydrogen in DNA, such as between adenine and thymine.1:30

Cohesion is the hydrogen bonds between water molecules. This property contributes to water's unique characteristics, such as a high heat of vaporization, meaning it takes a lot of energy for water to evaporate. Water also has a high specific heat, allowing it to hold a significant amount of heat.

Adhesion refers to water's ability to stick to other substances, like cellulose in plant xylem. This property is crucial for transpiration, where water is pulled up through plants due to cohesion and adhesion. Surface tension arises from hydrogen bonds creating a 'net' that can support objects, such as a paper clip floating on water.

• ★Cohesion is hydrogen bonds between water molecules.2:13
• ★Adhesion is water sticking to other substances.2:25
• ★Acidic solutions have more hydrogen ions, pH < 7.4:05
• ★Basic solutions have more hydroxide ions, pH > 7.4:15

Example: Dissolving hydrochloric acid in water increases hydrogen ions, lowering pH.4:05

The elements of life are carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur, abbreviated as CHOPS. Carbon is the central element in all biological molecules. Hydrogen is involved in energy exchange, particularly in cellular respiration through NAD and NADH, where NAD+ is the low energy form and NADH is the high energy form.

Monomers are the smaller building blocks of biomolecules, while polymers are larger structures made from these monomers. Three of the four groups of biomolecules—carbohydrates, proteins, and nucleic acids—are built from these monomers. Think of monomers like Legos; you can combine them to create various structures, which are the polymers.

• ★The elements of life are CHOPS: C, H, N, O, P, S.4:36
• ★NAD+ is the low energy form; NADH is the high energy form.4:36
• ★Monomers are building blocks; polymers are larger structures.4:36
• ★Monomers are like Legos, combined to form polymers.4:36

Example: An analogy for monomers is Legos, which can be combined to create various structures (polymers).4:36

Every unspecified angle vertex in a molecular structure represents a carbon atom. For example, in the formula $C_6{H}_{12}{O}_6$, there are six carbon atoms.

Dehydration synthesis combines monomers to form polymers by removing water. Enzymes facilitate this process by removing a hydroxyl group from one monomer and a hydrogen from another, resulting in the release of water: $Monome{r}_1+Monome{r}_2\to Polymer+H_{2}O$. Hydrolysis is the reverse process, where water is added to break down polymers into monomers.

• ★Dehydration synthesis combines monomers by removing water.6:35
• ★Hydrolysis breaks down polymers by adding water.6:40
• ★Lactose can be hydrolyzed into galactose and glucose.6:50
• ★Functional groups help decode molecular interactions in biology.7:20

Example: Lactose, a disaccharide, is hydrolyzed into galactose and glucose.6:50

Key polar functional groups include the hydroxyl group, carbonyl group, carboxyl group, amino group, sulfhydryl group, and acetyl group. The hydroxyl and carbonyl groups make molecules hydrophilic or water soluble. The carboxyl group is found in amino acids, which contain both amino and carboxyl groups. The sulfhydryl group stabilizes protein structure by forming bonds that maintain a specific three-dimensional shape. The acetyl group activates DNA through acetylation, contrasting with the methyl group.

The four types of macromolecules in living organisms are carbohydrates, lipids, proteins, and nucleic acids. Carbohydrates consist of monosaccharides, with glucose being a key example. Disaccharides, such as lactose, are composed of two linked monosaccharides. Polysaccharides serve as energy storage (like starch in plants and glycogen in animals) and have structural roles (like cellulose in plant cell walls). Humans cannot digest cellulose, while some animals, like ruminants and termites, can.

• ★Hydroxyl and carbonyl groups make molecules hydrophilic.9:02
• ★Carbohydrates are made of monosaccharides; glucose is a key example.9:02
• ★Humans cannot digest cellulose; some animals can.9:02
• ★The four macromolecules are carbohydrates, lipids, proteins, and nucleic acids.9:02

Example: Lactose is a disaccharide composed of two linked monosaccharides.9:02

Ruminants like cows, sheep, goats, and deer have symbiotic relationships with microorganisms that hydrolyze carbohydrates, releasing glucose monomers for energy. Lactose, the sugar in milk, is a disaccharide that requires the enzyme lactase for hydrolysis into monosaccharides.

Most mammals produce lactase only during infancy. In human evolution, some pastoralist herders developed a mutation allowing lactase production into adulthood, leading to lactase persistence in regions like Africa, Europe, Saudi Arabia, and the Indian subcontinent. However, the majority of humans are lactose intolerant as adults. Lactade is a product containing lactase that can help lactose intolerant individuals digest lactose.

• ★Ruminants have microorganisms that hydrolyze carbohydrates.11:53
• ★Lactose is a disaccharide; lactase hydrolyzes it into monosaccharides.12:00
• ★Lactase persistence evolved in some human populations due to dairy consumption.12:20
• ★Lactade helps lactose intolerant individuals digest lactose.13:20

Example: Lactade can be used by lactose intolerant individuals to help digest lactose.13:20

Lipids are non-polar molecules that do not dissolve in water, making them hydrophobic. Unlike carbohydrates, proteins, and nucleic acids, lipids are not composed of repeating monomers. Triglycerides serve as energy storage in both animals (solid) and plants (liquid, called oils). Waxes are utilized for waterproofing.

Phospholipids are key components of cell membranes. They consist of a hydrophobic tail and a hydrophilic head, connected by glycerol. In water, phospholipids spontaneously arrange themselves to form a bilayer structure, with hydrophilic heads interacting with water and hydrophobic tails avoiding it.

• ★Lipids are non-polar and hydrophobic.14:46
• ★Triglycerides are used for energy storage in animals and plants.14:55
• ★Phospholipids form a bilayer in cell membranes.15:05
• ★Waxes provide waterproofing.14:55

Example: Phospholipids arrange in a bilayer with hydrophilic heads facing water and hydrophobic tails facing away.15:05

Amino acids are the monomers of proteins. Each amino acid has a central carbon connected to an amine group, a carboxyl group, a hydrogen atom, and a variable R group. The R group can be polar, non-polar, acidic, or basic. There are 20 different amino acids that make up all life.

Proteins have four levels of structure. The primary structure is the linear sequence of amino acids, which is genetically determined. The secondary structure involves interactions in the polypeptide backbone. The tertiary structure involves interactions between the R groups of amino acids.

• ★Amino acids consist of a central carbon, amine group, carboxyl group, hydrogen atom, and R group.16:55
• ★There are 20 different amino acids in all life.17:05
• ★Proteins have four levels of structure: primary, secondary, tertiary, and quaternary.17:15
• ★Primary structure is the linear sequence of amino acids, genetically determined.17:25

Example: The R group can vary in properties, being polar, non-polar, acidic, or basic.17:00

Quaternary structure involves interactions between multiple folded tertiary peptides. Primary structure is the sequence of amino acids in a polypeptide. Proteins are synthesized by ribosomes, not enzymes. Amino acids are linked together by peptide bonds, forming a polypeptide backbone.

Secondary structure arises from interactions between carbonyl and amine groups in the polypeptide backbone. Hydrogen bonds stabilize the shapes of secondary structures like alpha helices and pleated sheets. An alpha helix is a corkscrew-shaped structure formed by hydrogen bonding. Pleated sheets form when polypeptide chains are parallel or antiparallel, allowing for hydrogen bonding.

• ★Quaternary structure involves multiple folded tertiary peptides.18:49
• ★Primary structure is the sequence of amino acids in a polypeptide.18:55
• ★Proteins are synthesized by ribosomes, not enzymes.19:00
• ★Secondary structure arises from hydrogen bonds between carbonyl and amine groups.19:10

Example: An alpha helix is stabilized by hydrogen bonds, forming a corkscrew shape.19:15

Tertiary protein structure involves interactions between side chains or R groups. Key types of bonds include hydrogen bonds, ionic bonds, covalent bonds, and hydrophobic clustering. Covalent bonds, especially between sulfhydryl groups, are crucial for maintaining the protein's specific shape. Myoglobin is an example of a tertiary protein that stores oxygen in muscle tissue.

Quaternary structure consists of multiple polypeptides interacting to form a functional protein. Hemoglobin, a quaternary protein, transports oxygen in red blood cells and is composed of four polypeptide chains. Sickle cell disease is caused by a recessive mutation that substitutes valine for glutamic acid in hemoglobin, affecting the amino acid's polarity and leading to disease symptoms.

• ★Tertiary structure involves R group interactions.20:50
• ★Quaternary structure consists of multiple polypeptides.21:00
• ★Sickle cell disease results from a mutation in hemoglobin.21:15
• ★Valine substitution for glutamic acid affects hemoglobin function.21:20

Example: Hemoglobin's structure includes four polypeptide chains, crucial for oxygen transport.21:10

Deoxygenated blood occurs when blood gives off oxygen to muscle tissue during exercise. This process leads to mutated hemoglobin molecules forming hydrophobic bonds, which causes fibers to develop within the cells. These mutant cells clump in smaller arteries, resulting in pain crises and tissue damage, characteristic of sickle cell anemia.

Sickle cell disease has evolved from a childhood disease to a manageable condition with proper medical care, allowing individuals to live into their 50s, 60s, and beyond. Having one copy of the sickle cell gene offers resistance to malaria, showcasing an evolutionary advantage. DNA is the molecule of heredity, passing genetic information from generation to generation, while RNA serves as the hereditary molecule in some viruses and plays a key role in information transfer. RNA can take various forms and can act as an enzyme, unlike the double helix structure of DNA.

• ★Deoxygenated blood occurs when blood gives off oxygen to muscle tissue during exercise.23:37
• ★Mutated hemoglobin forms hydrophobic bonds, leading to sickle-shaped cells.23:45
• ★Sickle cell disease is manageable with good medical care, allowing longer lifespans.23:55
• ★DNA is the molecule of heredity; RNA transfers genetic information and can act as an enzyme.24:10

Example: Sickle cell disease provides resistance to malaria, illustrating an evolutionary advantage.24:05

Ribosomes are catalytic RNA. They are involved in protein synthesis. ATP is a monomer of RNA and serves as the energy molecule of life. Nucleotides, the monomers of nucleic acids, consist of a five-carbon sugar, a phosphate group, and a nitrogenous base.

In DNA, the sugar is deoxyribose, while in RNA, it is ribose. DNA has four bases: adenine (A), thymine (T), cytosine (C), and guanine (G). RNA contains adenine (A), uracil (U), cytosine (C), and guanine (G). DNA consists of two nucleotide strands connected by sugar-phosphate bonds and hydrogen bonds between bases. A pairs with T, and C pairs with G.

• ★Ribosomes are catalytic RNA involved in protein synthesis.26:21
• ★Nucleotides consist of a five-carbon sugar, a phosphate group, and a nitrogenous base.26:21
• ★In DNA, the sugar is deoxyribose; in RNA, it is ribose.26:21
• ★DNA strands are anti-parallel and bonded by hydrogen bonds between complementary bases.26:21

Example: Adenine (A) pairs with thymine (T) in DNA, while cytosine (C) pairs with guanine (G).26:21

DNA is directional. Nucleotides consist of a sugar and phosphate backbone. DNA polymerase is the enzyme that builds DNA strands. It has an active site and can only add new nucleotides at the three prime (3') end of a growing strand.

All nucleic acids are synthesized in the five prime (5') to three prime (3') direction. This directionality is crucial for DNA replication.

• ★DNA is directional, with specific orientation.28:54
• ★DNA polymerase adds nucleotides at the 3' end.28:54
• ★Nucleic acids are synthesized from 5' to 3'.28:54

Example: DNA synthesis involves adding nucleotides in the 5' to 3' direction by DNA polymerase.28:54