Week 4 Lecture Notes

Week 4

Four major macromolecules are the building blocks of the cell:
- Proteins
- Lipids
- Nucleic Acids
- Carbohydrates

Nucleic acids store, transmit, and help express hereditary information.
The amino acid sequence of a polypeptide is programmed by a unit of inheritance called a gene.
Genes consist of DNA, a nucleic acid made of monomers called nucleotides.
Only certain bases in DNA pair up and form hydrogen bonds: adenine (A) always with thymine (T), and guanine (G) always with cytosine (C).
This is called complementary base pairing.
Purines: Adenine (A) and Guanine (G)
Pyrimidines: Thymine (T, in DNA) and Cytosine (C)
Structure of RNA Molecules
- RNA also has a sugar-phosphate backbone; however, it is different from DNA.
- The sugar in the backbone is a ribose sugar.
- There is also a difference in the nitrogenous bases (T-U).
- RNA is a single strand and is highly unordered.

Carbohydrates serve as fuel and building material.
Carbohydrates include sugars and the polymers of sugars.
The simplest carbohydrates are monosaccharides, or simple sugars.
Monosaccharides have molecular formulas that are usually multiples of CH2O.
Glucose (C6H12O6) is the most common monosaccharide.
A disaccharide is formed when a dehydration reaction joins two monosaccharides.
- This covalent bond is called a glycosidic linkage.
Many monosaccharides linked together to form long polymers.
- Examples:
  - Energy storage – starch, glycogen
    - Starch: Amylose (unbranched), Amylopectin (somewhat branched)
  - Structural – cellulose, chitin
    - Cellulose molecule (unbranched)
Why is cellulose a structural polysaccharide while starch serves as energy storage?
- The difference is based on two ring forms for glucose: alpha (a) and beta (b)