Unit 1 Essential Content

This first unit sets the foundation for students to understand the chemical basis of life, which is needed for mastery of future areas of focus and provides students with a survey of the elements necessary for carbon-based systems to function. Students learn that water and the properties of water play a vital role in the survival of individuals and biological systems. They also learn that living systems exist in a highly complex organization that requires input of energy and the exchange of macromolecules. This unit also addresses in detail how and in what conformations molecules called monomers bond together to form polymers. The structure of monomers and polymers determines their function. In the units that follow, students will need to understand and explain the interaction and bonding of atoms to form molecules.

1. The subcomponents of biological molecules and their sequence determine the properties of that molecule.

2. Living systems depend on properties of water that result from its polarity and hydrogen bonding.

3. The hydrogen bonds between water molecules result in cohesion, adhesion, and surface tension.

4. Organisms must exchange matter with the environment to grow, reproduce, and maintain organization.

5.  Atoms and molecules from the environment are necessary to build new molecules—

   1. Carbon is used to build biological molecules such as carbohydrates, proteins, lipids, and nucleic acids. Carbon is used in storage compounds and cell formation in all organisms.

   2. Nitrogen is used to build proteins and nucleic acids. Phosphorus is used to build nucleic acids and certain lipids.

6. Hydrolysis and dehydration synthesis are used to cleave and form covalent bonds between monomers.

   1. Structure and function of polymers are derived from the way their monomers are assembled— 

      1. In nucleic acids, biological information is encoded in sequences of nucleotide monomers. Each nucleotide has structural components: a five-carbon sugar (deoxyribose or ribose), a phosphate, and a nitrogen base (adenine, thymine, guanine, cytosine, or uracil). DNA and RNA differ in structure and function. 

      2.  In proteins, the specific order of amino acids in a polypeptide (primary structure) determines the overall shape of the protein. Amino acids have directionality, with an amino (NH2) terminus and a carboxyl (COOH) terminus. The R group of an amino acid can be categorized by chemical properties (hydrophobic, hydrophilic, or ionic), and the interactions of these R groups determine structure and function of that region of the protein. 

      3. Complex carbohydrates comprise sugar monomers whose structures determine the properties and functions of the molecules. 

      4. Lipids are nonpolar macromolecules

         1. Differences in saturation determine the structure and function of lipids. 

         2. Phospholipids contain polar regions that interact with other polar molecules, such as water, and with nonpolar

         3. Directionality of the subcomponents influences structure and function of the polymer

      5. Nucleic acids have a linear sequence of nucleotides that have ends, defined by the 3’ hydroxyl and 5’ phosphates of the sugar in the nucleotide. 

         1. During DNA and RNA synthesis, nucleotides are added to the 3’ end of the growing strand, resulting in the formation of a covalent bond between nucleotides.

         2. DNA is structured as an antiparallel double helix, with each strand running in opposite 5’ to 3’ orientation. Adenine nucleotides pair with thymine nucleotides via two hydrogen bonds. Cytosine nucleotides pair with guanine nucleotides by three hydrogen bonds.

      6. Proteins comprise linear chains of amino acids, connected by the formation of covalent bonds at the carboxyl terminus of the growing peptide chain. 

         1. Proteins have primary structure determined by the sequence order of their constituent amino acids, secondary structure that arises through local folding of the amino acid chain into elements such as alpha-helices and beta-sheets, tertiary structure that is the overall three-dimensional shape of the protein and often minimizes free energy, and quaternary structure that arises from interactions between multiple polypeptide units. The four elements of protein structure determine the function of a protein.

      7. Carbohydrates comprise linear chains of sugar monomers connected by covalent bonds. Carbohydrate polymers may be linear or branched.  

      8. DNA and RNA molecules have structural similarities and differences related to their function

         1. Both DNA and RNA have three components—sugar, a phosphate group, and a nitrogenous base—that form nucleotide units that are connected by covalent bonds to form a linear molecule with 5’ and 3’ ends, with the nitrogenous bases perpendicular to the sugar-phosphate backbone.

         2. The basic structural differences between DNA and RNA include the following:

            1. DNA contains deoxyribose and RNA contains ribose.

            2. RNA contains uracil and DNA contains thymine. 

            3. DNA is usually double stranded; RNA is usually single stranded

            4. The two DNA strands in double-stranded DNA are antiparallel in directionality.