Define and give examples of polysaccharides, triacylglycerols, nucleotides, and nucleosides. Explain how to name nucleosides.

1. Polysaccharides are complex carbohydrates formed by many monosaccharide units linked together. Homopolysaccharides are composed of only one type of monosaccharide unit. Examples include starch, glycogen, and cellulose* (all made of glucose units). Heteropolysaccharides are composed of two or more different types of monosaccharide units. Examples include hyaluronic acid and heparin*. 2. TAG stands for Triacylglycerol (also known as triglyceride). It is a lipid molecule composed of a glycerol backbone esterified to three fatty acid molecules. TAGs serve as the primary form of energy storage in animals and plants. 3. A nucleotide is the basic building block of nucleic acids (DNA and RNA). It consists of three components: a nitrogenous base (adenine, guanine, cytosine, thymine, or uracil), a pentose sugar (deoxyribose in DNA or ribose in RNA), and one or more phosphate groups. 4. A nucleoside is a part of a nucleotide, consisting of a nitrogenous base covalently linked to a pentose sugar (deoxyribose or ribose), but without any phosphate groups. 5. Naming Nucleosides: The nitrogenous base's name is modified. For purine bases (Adenine, Guanine), the suffix "-osine" is added: Adenine becomes Adenosine, Guanine becomes Guanosine*. For pyrimidine bases (Cytosine, Thymine, Uracil), the suffix "-idine" is added: Cytosine becomes Cytidine, Thymine becomes Thymidine, Uracil becomes Uridine*. Naming Nucleotides: Nucleotides are named by adding "monophosphate," "diphosphate," or "triphosphate" to the corresponding nucleoside name, indicating the number of phosphate groups attached. Example: Adenine → Adenosine (nucleoside) → Adenosine monophosphate (AMP), Adenosine diphosphate (ADP), Adenosine triphosphate* (ATP). Similarly: Guanine → Guanosine → Guanosine monophosphate* (GMP). Cytosine → Cytidine → Cytidine monophosphate* (CMP). Thymine → Thymidine → Thymidine monophosphate* (TMP). Uracil → Uridine → Uridine monophosphate* (UMP). 6. A peptide bond is formed between two amino acids through a dehydration synthesis (or condensation) reaction. The carboxyl group (-COOH) of one amino acid reacts with the amino group (-NH_2) of another amino acid. A molecule of water is removed, and a covalent bond forms between the carbon atom of the carboxyl group and the nitrogen atom of the amino group, resulting in a -CO-NH- linkage. What's next?