Chapter 5: The Principles of Polymers

Major Classes of Macromolecules

Macromolecules are large, complex molecules essential for life. They are typically polymers, made from repeating subunits called monomers.

• Carbohydrates

• Lipids

• Proteins

• Nucleic Acids

Monomers and Polymers

• Monomer: A small molecule that serves as a building block for polymers.

• Polymer: A large molecule consisting of many similar or identical monomers linked together.

• Example: Glucose is a monomer; starch is a polymer made of glucose units.

Condensation (Dehydration) and Hydrolysis Reactions

These are chemical reactions involved in the synthesis and breakdown of polymers.

• Condensation (Dehydration) Reaction: Joins two monomers by removing a water molecule, forming a new bond.

• Hydrolysis Reaction: Breaks a bond between monomers by adding a water molecule.

• Example: Formation of a peptide bond between amino acids (dehydration); digestion of starch into glucose (hydrolysis).

Carbohydrates: Structure and Function

Carbohydrates serve as fuel and building material. They include monosaccharides, disaccharides, and polysaccharides.

• Monosaccharides: Simple sugars (e.g., glucose, fructose). Major fuel for cells and raw material for building molecules.

• Disaccharides: Formed when a dehydration reaction joins two monosaccharides. The bond is called a glycosidic linkage.

• Polysaccharides: Polymers composed of many sugar building blocks. Examples: starch, glycogen, cellulose.

Comparison of Starch and Cellulose:

• Starch: Has α(1→4) linkages; helical and easy to digest for energy.

• Cellulose: Has β(1→4) linkages; straight and strong for structure. Most animals cannot digest cellulose due to lack of enzymes for β-linkages.

Lipids: Structure and Types

Lipids are hydrophobic molecules, including fats, phospholipids, and steroids.

• Fats: Made of glycerol and three fatty acids. Store energy, cushion organs, and insulate the body.

• Phospholipids: Two fatty acids and a phosphate group attached to glycerol. Major component of cell membranes; form bilayers in water.

• Steroids: Lipids with four fused carbon rings. Include cholesterol and hormones (e.g., estrogen, testosterone).

Saturated vs. Unsaturated Fats:

• Saturated fatty acids: Maximum number of hydrogen atoms, no double bonds; solid at room temperature.

• Unsaturated fatty acids: One or more double bonds; liquid at room temperature.

Proteins: Structure and Function

Proteins are polymers of amino acids and perform many functions in the cell.

• Polypeptide: A polymer of amino acids linked by peptide bonds.

• Protein: One or more polypeptides folded into a specific shape.

• Peptide Bond Formation: Dehydration reaction between amino group (–NH2) and carboxyl group (–COOH) of two amino acids.

Amino Acid Structure:

• Amino group (–NH2)

• Carboxyl group (–COOH)

• Hydrogen atom

• R group (side chain): Determines properties and function

Protein Structure Levels:

• Primary: Sequence of amino acids

• Secondary: Alpha helix and beta sheet, stabilized by hydrogen bonds

• Tertiary: 3D shape stabilized by interactions among R groups (hydrogen bonds, ionic bonds, hydrophobic interactions, disulfide bridges)

• Quaternary: Association of multiple polypeptides

Protein Denaturation: Loss of structure due to heat, pH, or chemicals; results in loss of function.

Nucleic Acids: Structure and Function

Nucleic acids (DNA and RNA) store and transmit hereditary information.

• Nucleotide: Monomer of nucleic acids; consists of a nitrogenous base, a pentose sugar, and a phosphate group.

• Nucleoside: Nitrogenous base + sugar (no phosphate)

• DNA: Deoxyribonucleic acid; double helix; deoxyribose sugar; bases A, T, C, G

• RNA: Ribonucleic acid; single-stranded; ribose sugar; bases A, U, C, G

Nitrogenous Bases:

• Pyrimidines: Single ring (C, T, U)

• Purines: Double ring (A, G)

DNA Structure: Double helix with sugar-phosphate backbone on the outside and nitrogenous bases paired in the center (A-T, G-C) via hydrogen bonds. Strands are antiparallel.

Chapter 6: How We Study Cells

Microscopy: Principles, Advantages, and Limitations

Microscopes are essential tools for studying cell structure and function. There are several types, each with unique features.

• Light Microscope (LM): Uses visible light to magnify images of specimens.

• Transmission Electron Microscope (TEM): Sends a beam of electrons through a specimen; provides detailed images of internal structures.

• Scanning Electron Microscope (SEM): Scans the surface with electrons; provides 3D images of the specimen's surface.

Comparison Table: Types of Microscopes

Additional info:

• Other topics in the original notes (e.g., cell fractionation, organelle structure) are not fully visible in the provided images but are typically covered in this chapter.