1 Chemistry Of Life

Water contains polar covalent bonds because oxygen is more electronegative than hydrogen, creating partial charges within each molecule. The partially positive hydrogen of one water molecule is attracted to the partially negative oxygen of a neighboring water molecule, forming a hydrogen bond.

The polarity of water enables hydrogen bonding not only between water molecules but also between and within biological molecules. For example, polar regions of proteins and nucleic acids can form hydrogen bonds with water or with other polar regions within the same molecule, which influences molecular structure and function.

Water’s high specific heat capacity means that a large amount of heat energy must be absorbed or released to change its temperature. Because organisms contain a high proportion of water, their internal temperatures remain relatively stable despite fluctuations in the external environment, supporting homeostasis.

If water’s heat of vaporization were significantly lower, each gram of sweat that evaporated would carry away less heat energy from the body. The organism would need to produce much more sweat to achieve the same cooling effect, making thermoregulation less efficient and potentially leading to overheating in warm environments.

Water molecules in the liquid phase are connected by an extensive network of hydrogen bonds. To vaporize, individual molecules must break free from these bonds, which requires substantial energy input. Therefore, the strength and number of hydrogen bonds directly account for water’s high heat of vaporization.

Adhesion pulls water molecules along the polar walls of xylem vessels, while cohesion holds the water molecules together as a continuous column. Together, these properties allow water to move upward from roots to leaves against the force of gravity during transpiration.

At the surface of a body of water, molecules lack hydrogen-bonding partners above them and therefore form stronger hydrogen bonds with neighboring molecules beside and below them. This creates a net inward pull that makes the surface behave like an elastic film, resisting disruption.

A substance that disrupts hydrogen bonding would reduce surface tension. Surface tension depends on the net inward hydrogen bonding among surface water molecules; weakening these bonds would decrease the cohesive force at the surface, making it easier for objects to break through the water’s surface layer.

Carbon, hydrogen, and oxygen are the three most prevalent elements used to build carbohydrates, proteins, lipids, and nucleic acids.

The plant would be unable to synthesize adequate phospholipids and nucleic acids because both require phosphorus — phospholipids need phosphate in their head group, and nucleic acids need phosphate in their sugar-phosphate backbone. Carbohydrate and most other lipid synthesis would remain unaffected because those molecules do not contain phosphorus.

Sulfur is incorporated into certain amino acids that form proteins, so a lack of sulfur would prevent proper protein assembly. Carbohydrates are composed only of carbon, hydrogen, and oxygen, so their synthesis does not depend on sulfur availability.

During dehydration synthesis, a hydrogen ion is removed from one monomer and a hydroxyl group is removed from the other, resulting in the release of a water molecule. A covalent bond forms between the two monomers, linking them together. Repeating this process produces a polymer through polymerization.

Hydrolysis breaks the covalent bond between monomers by adding water across the bond. The hydrogen ion from the water molecule attaches to one monomer, and the hydroxyl group attaches to the adjacent monomer, separating them and restoring each to its individual form.

The cell would be unable to form new polymers because dehydration synthesis is the reaction that creates the covalent bonds linking monomers together. Without this reaction, monomers would remain unlinked, and essential macromolecules such as proteins and polysaccharides could not be assembled, impairing growth and repair.

Monosaccharides are linked by covalent bonds through dehydration synthesis, which removes a water molecule each time a new monomer is added, producing a polysaccharide chain. Polysaccharides are broken down by hydrolysis, which adds a water molecule across each covalent bond to release individual monosaccharides.

Glycogen is highly branched, providing many free ends where enzymes can simultaneously cleave glucose monomers, allowing rapid energy release. Cellulose has a rigid, linear structure suited for structural support rather than quick enzymatic breakdown, so it cannot be mobilized as an energy source efficiently.

The degree of branching in a polysaccharide determines whether it functions primarily in energy storage or structural support. Starch and glycogen are branched to varying degrees, enabling enzymes to access glucose monomers for energy, with glycogen's greater branching allowing faster mobilization. Cellulose is linear and unbranched, forming rigid fibers that provide structural integrity to plant cell walls rather than serving as an energy reserve.

Double bonds cause kinks in the hydrocarbon chain, which prevent unsaturated fatty acid molecules from packing tightly together. The weaker intermolecular interactions mean less energy is needed to separate the molecules, so unsaturated lipids tend to be liquid at room temperature rather than solid.

The melting point would decrease. The polyunsaturated tail introduces multiple kinks, which disrupts the tight packing of the fatty acid chains. With less orderly packing and weaker intermolecular interactions, the fat transitions from solid to liquid at a lower temperature.

Fats store energy in their many carbon–hydrogen bonds, providing a concentrated fuel reserve for the organism. In some mammals, subcutaneous fat also provides insulation that helps maintain body temperature in cold environments.