Key Concepts in Cell Biology and Macromolecules

Essential Biological Macromolecules

Properties: Hydrophilic vs. Hydrophobic

• Hydrophilic (water-loving): Nucleic Acids, Carbohydrates, Starch, Chitin. Glucose is hydrophilic because it contains many hydroxyl functional groups.
• Hydrophobic (water-fearing): Lipids.

Key Molecules and Building Blocks

• Organic Molecules: Examples include Methane (CH4) and Glucose.
• Creating Polymers: Polymers are created from monomers through a Dehydration Reaction.

Types of Macromolecules

Carbohydrates

• Monosaccharides: Simple sugars like glucose, fructose, and galactose.
• Disaccharides: Maltose is formed from two glucose molecules.

Lipids

• Unsaturated Fats & Oils: These contain carbon-carbon double bonds in their fatty acids.

Proteins

• Proteins are unique in that they contain Nitrogen.
• Protein Structure Levels:
  • Primary: Formed by peptide bonds.
  • Secondary: Formed by hydrogen bonds.
  • Tertiary: Also involves hydrogen bonds and other interactions.
  • Quaternary: The arrangement of multiple polypeptide chains.
• Protein Function: A primary function of proteins is not for immediate energy. Enzymatic proteins, for example, carry out chemical reactions in a cell.
• Prions: These are infectious proteins that cause disease by inducing other proteins to misfold.

Nucleic Acids

• Base Differences: RNA contains Uracil, while DNA contains Thymine.
• Nucleic acids are not a component of the plasma membrane.

Cell Structure and Function

The Cytoskeleton

• The cytoskeleton is a network of protein filaments.
• Centrioles: Organize microtubules.
• Basal Bodies: These structures anchor cilia.

Organelles and Cellular Components

• Vacuoles: Primarily used for storage.
• Vesicles: Act like 'moving vans' to transport materials within the cell.
• Fimbriae: Bristle-like structures that help with adhesion.
• Sex Pilus: A hollow tube that allows bacteria to transfer DNA.

The Endomembrane System

This is a series of membrane-bound organelles that work together. It is not found in prokaryotes.

• Import Pathway: The plasma membrane pinches off to create vesicles containing a substance.
• Secretion Process (Export): Proteins made in the rough ER are transported to the smooth ER by a vesicle.

Endosymbiotic Theory

This theory suggests that mitochondria and chloroplasts were once free-living prokaryotes. Evidence includes that they reproduce by dividing, just like prokaryotes.

Techniques for Studying Cells

Microscopy Comparison

• Light Microscope: Inexpensive and can be used to observe living cells. Stains are often required to see details, and it has low resolution.
• Phase-Contrast Microscope: Can be used to study living cells without staining, but the resolution is slightly low.
• Electron Microscope: Provides very high resolution but is expensive, time-intensive, and cannot be used to study living cells.

Cell Separation Methods

• Freeze-Fracture: Cells are frozen in liquid nitrogen and then fractured along their plasma membrane.
• Cell Fractionation: Cells are taken apart and their components are separated by spinning them at high speeds.

The Plasma Membrane and Transport

The Fluid Mosaic Model

The membrane is a fluid phospholipid bilayer in which proteins are either wholly or partially embedded.

Passive Transport

This process does not require energy as molecules move down their concentration gradient.

• Diffusion: The movement of molecules down their concentration gradient.
• Osmosis: The diffusion of water across a selectively permeable membrane. When a cell is placed in a hypertonic solution, it shrivels as water moves out.
• Facilitated Transport: This process is specific, does not require energy, and uses a channel or carrier protein to help molecules cross the membrane.

Active Transport

Active transport requires energy because molecules are moved up (against) their concentration gradient.

• Carrier Proteins: Used in both active transport and facilitated transport.
• Sodium-Potassium Pump: An example of active transport that maintains a high concentration of sodium outside the cell and a high concentration of potassium inside the cell.

Bulk Transport

• Pinocytosis: The importation of liquids into the cell, often involving clathrin-coated pits.

Cellular Connections

The Extracellular Matrix (ECM)

Components of the ECM include Fibronectin and Elastin. Desmosomes are not part of the ECM itself, but a type of cell junction.

Types of Cell Junctions

• Tight Junctions: Prevent leaking between cells.
• Junctions Not Found in Plants: Plant cells do not have tight junctions, desmosomes, or gap junctions; they have plasmodesmata instead.