Chapter 5: The Principles of Polymers and Macromolecules

The Principles of Polymers

Polymers are large molecules made by linking together smaller units called monomers. They are essential for the structure and function of living organisms.

• Carbohydrates: Serve as energy sources and structural components. Examples include sugars and starches.

• Lipids: Function as energy storage, insulation, and make up cell membranes. Examples include fats, oils, and steroids.

• Proteins: Perform a wide range of functions, including catalyzing reactions (enzymes), structural support, and transport.

• Nucleic acids: Store and transmit genetic information. DNA and RNA are the main types.

Monomers are the building blocks of polymers. For example, amino acids are the monomers of proteins, and nucleotides are the monomers of nucleic acids.

Carbohydrates: Structure and Function

Carbohydrates are classified based on the number of sugar units:

• Monosaccharides: Single sugar units (e.g., glucose, fructose).

• Disaccharides: Two monosaccharides joined together (e.g., sucrose, lactose).

• Polysaccharides: Long chains of monosaccharides (e.g., starch, glycogen, cellulose).

Glycosidic bonds link monosaccharides together. The orientation of these bonds (alpha or beta) determines the properties of the polysaccharide.

• Starch: Storage polysaccharide in plants; made of alpha-glucose.

• Glycogen: Storage polysaccharide in animals; similar to starch but more branched.

• Cellulose: Structural polysaccharide in plants; made of beta-glucose, forms strong fibers.

Hydrolysis is the process of breaking down polymers into monomers by adding water.

Lipids: An Overview

Lipids are hydrophobic molecules that include fats, phospholipids, and steroids.

• Fats: Composed of glycerol and fatty acids. Used for energy storage.

• Phospholipids: Major component of cell membranes. Have hydrophilic heads and hydrophobic tails.

• Steroids: Include hormones like cholesterol.

Saturated fatty acids have no double bonds; unsaturated fatty acids have one or more double bonds, affecting fluidity.

Proteins: Structure and Function

Proteins are polymers of amino acids. Their function depends on their three-dimensional shape, which is determined by four levels of structure:

• Primary structure: Sequence of amino acids.

• Secondary structure: Local folding (alpha-helix, beta-sheet) stabilized by hydrogen bonds.

• Tertiary structure: Overall 3D shape due to interactions among R groups.

• Quaternary structure: Association of multiple polypeptide chains.

Denaturation is the loss of protein structure (and function) due to changes in temperature, pH, or other factors.

Nucleic Acids: DNA and RNA

Nucleic acids store and transmit hereditary information. They are polymers of nucleotides, each consisting of a sugar, phosphate group, and nitrogenous base.

• DNA: Double-stranded, stores genetic information.

• RNA: Single-stranded, involved in protein synthesis.

Nucleotide structure:

• 5-carbon sugar (deoxyribose in DNA, ribose in RNA)

• Phosphate group

• Nitrogenous base (A, T, C, G in DNA; A, U, C, G in RNA)

DNA forms a double helix with complementary base pairing (A-T, G-C).

Chapter 6: A Panoramic View of the Cell

Prokaryotic vs. Eukaryotic Cells

Cells are classified as prokaryotic or eukaryotic based on their structure.

• Prokaryotic cells: Lack a nucleus and membrane-bound organelles. DNA is in the nucleoid region. Example: bacteria.

• Eukaryotic cells: Have a nucleus and membrane-bound organelles. Examples: plants, animals, fungi, protists.

Key differences:

• Prokaryotes: Simpler, smaller, all functions in one space.

• Eukaryotes: Compartmentalized, larger, specialized organelles.

Cell Organelles and Their Functions

• Nucleus: Contains genetic material (DNA), controls cell activities.

• Ribosomes: Synthesize proteins. Free ribosomes float in cytoplasm; bound ribosomes are attached to the endoplasmic reticulum (ER).

• Endoplasmic Reticulum (ER): Network of membranes. Rough ER has ribosomes and synthesizes proteins; smooth ER synthesizes lipids and detoxifies.

• Golgi apparatus: Modifies, sorts, and packages proteins and lipids.

• Lysosomes: Contain digestive enzymes to break down waste.

• Mitochondria: Site of cellular respiration, produces ATP.

• Chloroplasts (plants): Site of photosynthesis.

• Vacuoles: Storage and support (large central vacuole in plants).

The Endomembrane System

The endomembrane system includes the nuclear envelope, ER, Golgi apparatus, lysosomes, and vesicles. It is involved in the synthesis, modification, and transport of cellular materials.

The Cytoskeleton

The cytoskeleton provides structural support, enables cell movement, and organizes cell contents.

• Microtubules: Hollow tubes, maintain cell shape, help with chromosome movement and organelle transport.

• Microfilaments: Thin rods, involved in muscle contraction and cell movement.

• Intermediate filaments: Provide mechanical support.

Cell Surfaces and Junctions

• Cell wall: Provides support and protection (plants, fungi, some protists).

• Extracellular matrix (ECM): Network of proteins and carbohydrates outside animal cells, provides support and signaling.

• Cell junctions:

  • Tight junctions: Prevent leakage between cells.

  • Desmosomes: Anchor cells together.

  • Gap junctions: Allow communication between cells.

Chapter 7: Membrane Structure and Function

Membrane Structure

Biological membranes are composed of a phospholipid bilayer with embedded proteins. The amphipathic nature of phospholipids (hydrophilic heads, hydrophobic tails) allows the formation of membranes.

• Fluid mosaic model: Describes the membrane as a fluid structure with proteins embedded in or attached to the bilayer.

• Cholesterol: Maintains membrane fluidity.

Membrane Transport

Substances move across membranes by passive or active transport.

• Passive transport: No energy required. Includes diffusion, osmosis, and facilitated diffusion.

• Active transport: Requires energy (ATP). Moves substances against their concentration gradient.

• Osmosis: Diffusion of water across a selectively permeable membrane.

• Isotonic solution: No net movement of water.

• Hypertonic solution: Water leaves the cell; cell shrinks.

• Hypotonic solution: Water enters the cell; cell swells.

Bulk transport includes endocytosis (phagocytosis, pinocytosis) and exocytosis.

Chapter 11: Cell Communication

Cell Signaling

Cells communicate using chemical signals. The process involves three stages:

1. Reception: Signal molecule binds to a receptor.

2. Transduction: Signal is relayed and amplified inside the cell.

3. Response: Cell carries out a specific activity.

• Receptors can be on the cell surface or inside the cell (intracellular).

• Second messengers (e.g., cAMP, Ca2+) relay signals inside the cell.

• Phosphorylation cascades: Series of protein activations by adding phosphate groups.

• Cellular responses include changes in gene expression, metabolism, or cell division.

• Apoptosis: Programmed cell death, important for development and disease prevention.

Tables

Comparison of Prokaryotic and Eukaryotic Cells

Types of Membrane Transport

Levels of Protein Structure

Key Equations

• Osmosis (Water Potential):

• Where is water potential, is solute potential, and is pressure potential.

• ATP Hydrolysis:

• ATP is hydrolyzed to ADP and inorganic phosphate, releasing energy for cellular work.

How We Study Cells

• Light microscope (LM): Uses light to magnify images of living cells.

• Transmission electron microscope (TEM): Slices cells to view internal structures.

• Scanning electron microscope (SEM): Provides 3D images of cell surfaces.

Additional info:

• Some explanations and examples were expanded for clarity and completeness.

• Tables were inferred and constructed based on standard biology content.