Chapter 4: A Tour of the Cell - Lecture Notes

Introduction

• Chapter 4 covers cell biology and organelles.
• Cells are the basic unit of life.
• All living things are made of one or more cells.
• Cells come from pre-existing cells.

Microscopes

• Light Microscopes: Use lenses and light to magnify samples up to about 1000 times. Can see cells, chromosomes, chloroplasts, etc.
• Electron Microscopes: Use electron beams, create computer images, not for living cells.
  • Scanning Electron Microscopes
  • Transmission Electron Microscopes

Cell Fractionation

• Process of separating cellular components by spinning in a centrifuge.
• Heavier components like the nucleus separate first.

Prokaryotes vs Eukaryotes

• Prokaryotic Cells: No nucleus, include bacteria and archaea.
  • Lack membrane-bound organelles.
  • Have one circular chromosome in nucleoid region.
• Eukaryotic Cells: Have a nucleus, found in protists, fungi, plants, and animals.
  • Contain membrane-bound organelles.

Common Features of All Cells

• Plasma Membrane: Selectively permeable.
• Cytosol: Semi-liquid substance.
• Chromosomes: At least one in every cell.
• Ribosomes: Make proteins, not membrane-bound.

Eukaryotic Cell Components

• Nucleus: Contains DNA, double-membraned.
  • Nucleolus: Region where ribosomes are made.
• Endoplasmic Reticulum (ER)
  • Rough ER: Has ribosomes, makes glycoproteins.
  • Smooth ER: No ribosomes, detoxifies substances, makes lipids.
• Golgi Apparatus: Processes and packages proteins.
• Lysosomes: Contain digestive enzymes, involved in apoptosis.
• Vacuoles: Storage, large central vacuole in plants.
• Mitochondria: ATP production, have their own DNA and ribosomes.
• Chloroplasts: Photosynthesis, found in plants, also have own DNA and ribosomes.

Importance of Cell Size

• Cells remain small to maintain a favorable surface area-to-volume ratio for efficient nutrient and gas exchange.

Cytoskeleton

• Provides structural support to the cell.
• Components:
  • Microtubules
  • Microfilaments
  • Intermediate filaments

Cell Walls and Extracellular Structures

• Plant Cell Walls: Made of cellulose.
• Animal Extracellular Matrix: Contains collagen and other fibers.

Intercellular Junctions

• Plant Cells: Plasmodesmata allow movement of substances between cells.
• Animal Cells: Tight junctions, desmosomes, gap junctions.

Endosymbiotic Theory

• Suggests mitochondria and chloroplasts were once free-living bacteria engulfed by ancestral eukaryotic cells.

Summary

• Cells are highly organized systems with emergent properties.
• All organelles work together to provide cell functionality.