Lecture 5 - Comprehensive Study Notes on Carbohydrates and Biological Polymers

All living things are made up of four classes of large biological molecules:
- Carbohydrates
- Lipids
- Proteins
- Nucleic acids
Macromolecules are large molecules and are complex in structure.
Large biological molecules possess unique properties that arise directly from the orderly arrangement of their atoms.
Polymer definition:
- A polymer is a long molecule consisting of many similar building blocks.
Monomer definition:
- Monomers are the repeating units that serve as building blocks for polymers.
Three of the four classes of life's organic molecules are polymers.

Dehydration Reaction:
- Occurs when two monomers bond together through the loss of a water molecule.
- Serves as the chemical process for building polymers from monomers.
Hydrolysis:
- Polymers are disassembled to monomers by hydrolysis.
- Hydrolysis is a reaction that is essentially the reverse of the dehydration reaction.
Enzymes:
- Specialized macromolecules that speed up chemical reactions.
- Facilitate reactions such as those that make polymers or break down polymers.

Carbohydrates Overview:
- Carbohydrates include sugars and the polymers of sugars.
- Monosaccharides, or simple sugars, represent the simplest carbohydrates.
Molecular Characteristics:
- Monosaccharides have molecular formulas that are usually multiples of $CH_2O$ .
- Glucose ( $C_6H_{12}O_6$ ) is the most common monosaccharide.
Cellular Functions:
- Monosaccharides serve as a major fuel for cells.
- Monosaccharides act as raw material for building molecules.
Monosaccharide Classification:
- Location of the carbonyl group: Classified either as an aldose or a ketose.
- Carbon skeleton size: Classified by the number of carbons in the carbon skeleton.
Spatial Arrangement:
- Monosaccharides exhibit diverse spatial arrangement around asymmetric carbons.
- Spatial variations impart distinctive shapes, binding properties, and behaviors.

Disaccharide Formation:
- A disaccharide is formed when a dehydration reaction joins two monosaccharides.
- The covalent bond that holds the two monosaccharides together is called a glycosidic linkage.
Glucose Ring Orientations:
- Glucose rings can be formed in two different orientations: alpha ( $\alpha$ ) and beta ( $\beta$ ).
- The specific orientation of the glucose molecules determines the type of bond formed.
Linkage Types:
- An $\alpha\text{ 1-4}$ bond connects the two glucose rings from below the respective planes of the glucose molecules.
- A $\beta\text{ 1-4}$ bond connects the two glucose rings from across their respective planes.

Polysaccharides Overview:
- Polysaccharides are the polymers of sugars and fulfill storage and structural roles.
- The architecture and function of a polysaccharide are determined by its sugar monomers and the positions of its glycosidic linkages.
Starch:
- Starch is a storage polysaccharide of plants.
- Consists entirely of glucose monomers.
- Amylose is the simplest form of starch.
Glycogen:
- Glycogen is a storage polysaccharide in animals.
- Glycogen is stored mainly in liver and muscle cells.
- Hydrolysis of glycogen in liver and muscle cells releases glucose when the cellular demand for sugar increases.

Cellulose:
- Cellulose is a structural polysaccharide and a major component of the tough wall of plant cells.
- Cellulose ( $\beta\text{ 1-4}$ ) is a polymer of glucose with glycosidic linkages that differ from that of starch ( $\alpha\text{ 1-4}$ ).
- Some hydroxyl groups on the monomers of cellulose can hydrogen bond with hydroxyls of parallel cellulose molecules.
Chitin:
- Chitin is another structural polysaccharide found in the exoskeleton of arthropods.
- Chitin provides structural support for the cell walls of many fungi.