BIO101: Introduction to Molecular and Cellular Biology

Read this chapter to learn about the four unique properties of water. After you read, you should be able to explain why water is an excellent solvent, describe water molecules that are polar and capable of hydrogen bonding with four neighboring water molecules, and distinguish between a solute, solvent, and solution.

Watch this lecture, which reviews the special chemical properties of the water molecule.

Watch this lecture to learn how the pH scale affects biological systems. Remember that acids are proton donors, while bases are proton acceptors.

As you review this section, notice the difference between a strong and weak acid and base. How do the pH measurements of acidic and basic solutions affect living organisms? Different foods have different amounts of hydrogen ions, which is also known as proton concentration.

Watch this lecture, which describes how acids and bases relate to the concentration of hydrogen ions in a solution. You should be able to explain how acids and bases alter the hydrogen ion concentration of a solution directly and indirectly.

A polymer is a particular category of macromolecule that is built by connecting many smaller subunits called monomers (poly- means many). Of the four biological macromolecules that you have been studying, only three are polymers. Lipids are not polymers, but the others are.

• Polysaccharides are macromolecular carbohydrates. Be careful with the words polysaccharide and carbohydrate. They are sometimes used interchangeably but should not be. Carbohydrates include both small molecules and large molecules (macromolecules). Polysaccharides are a type of carbohydrate, but not all carbohydrates are polysaccharides. As the name implies, polysaccharides are polymers made up of multiple monosaccharides. Monosaccharides are monomers, and they can be connected in a linear or branched arrangement.
  
  
• Proteins are polymers that are made up of monomers called amino acids. Unlike polysaccharides, which may be branched, a protein must be a linear (or end-to-end) arrangement of amino acids. Organisms use 20 different kinds of amino acids (in an unlimited number of combinations and orders) to construct their proteins.
  
  
• We can also call a nucleic acid a polynucleotide. That alternative name indicates it is a polymer made up of many nucleotides. In the case of DNA, the monomers are nucleotides containing the pentose (five-carbon sugar) called deoxyribose. For RNA, the nucleotides contain ribose instead of deoxyribose. Although there are only four commonly used DNA nucleotides (and four commonly used RNA nucleotides), a typical DNA molecule contains millions of nucleotides, so there is an unlimited number of sequences of such nucleotides.

Be sure you can match each type of monomer to the type of polymer that can be made from such monomers. You should also know how polymers are constructed using dehydration reactions and deconstructed using hydrolysis reactions.

Watch this lecture to review biological macromolecules and their role in biological organisms. Identify their building blocks and how they form polymers. Also, understand the structures and how they relate to the function of each macromolecule's role in organisms. After watching, you should be able to list the four major classes of macromolecules, distinguish between monomers and polymers, and define the terms dehydration synthesis and hydrolysis.

Carbohydrates are classified into three subtypes: monosaccharides, disaccharides, and polysaccharides. Some polysaccharides (like cellulose and chitin) are important for their structural strength, whereas other polysaccharides (like starch and glycogen) are important for storing energy. Polysaccharides also serve as important identity markers on the surfaces of cells, so they play a role in immunity.

A carbohydrate is an organic compound such as sugar or starch, which plants use to store energy. Read this text, which discusses the role of carbohydrates in cells and in the extracellular materials of animals and plants. When you finish, make sure you can describe the function and structure of carbohydrates.

Lipids are important for storing energy, thermal insulation, and providing protective padding. Phospholipids form the infrastructure of all cell membranes. Lipids also make up natural waxes and oils and many hormones. Read this section to learn more about lipids. When you have finished reading this section, make sure you can describe the function and structure of lipids.

Proteins perform an impressively long list of biological functions. They function as enzymes, structural elements, chemical signals, transporters, and receptors. They also play important roles in cell-to-cell adhesion and immunity. As you read this section, make sure you can describe the four levels of protein structure.

Nucleic acids include various DNA and RNA molecules. They serve informational purposes. DNA stores the genetic code, and various types of RNA help in the process of interpreting that code to build proteins. Certain RNAs can also function as catalysts.

After you have read this section, try to respond to the following review questions:

1. Why are biological macromolecules considered organic?
2. What role do electrons play in dehydration synthesis and hydrolysis?
3. Describe the similarities and differences between glycogen and starch.
4. Why is it impossible for humans to digest food that contains cellulose?
5. Explain at least three functions that lipids serve in plants and/or animals.
6. Why have trans fats been banned from some restaurants? How are they created?
7. Explain what happens if even one amino acid is substituted for another in a polypeptide chain. Provide a specific example.
8. Describe the differences in the four protein structures.
9. What are the structural differences between RNA and DNA?
10. What are the four types of RNA, and how do they function?