SUMMARY

• 1.1 Living Systems Require a Limited Variety of Atoms and Molecules

  Oxygen, hydrogen, and carbon make upw 98% of the atoms in living organisms. Hydrogen and oxygen are prevalent because of the abundance of water, and carbon is the most common atom in all biomolecules.

• 1.2 There Are Four Major Classes of Biomolecules

  Proteins, nucleic acids, lipids, and carbohydrates constitute the four major classes of biomolecules. Proteins are the most versatile with an especially prominent role as enzymes. Nucleic acids are primarily information molecules: DNA is the genetic information in most organisms, whereas RNA plays a variety of roles, including serving as a link between DNA and proteins. Lipids serve as fuels and as membranes. Carbohydrates are key fuel molecules that also play a role in cell-to-cell interactions.

• 1.3 The Central Dogma Describes the Basic Principles of Biological Information Transfer

  The central dogma of biology states that DNA is replicated to form new DNA molecules. DNA can also be transcribed to form RNA. Some information in the form of RNA, called messenger RNA, can be translated into proteins.

• 1.4 Membranes Define the Cell and Carry Out Cellular Functions

  Membranes, formed of lipid bilayers, are crucial for establishing boundaries between cells and their environment and for establishing boundaries within internal regions of many cells. There are two structurally distinct types of cells: eukaryotic cells and prokaryotic cells. Eukaryotic cells are characterized by a complex array of intracellular membrane-bounded compartments called organelles. The nucleus is the largest organelle and houses the genetic information of the cell. Other organelles play roles in energy transformation, in protein processing and secretion, and in digestion. In contrast, prokaryotic cells are smaller and less complex, and they lack membrane-bounded compartments.