BIOL Chapter 6: A Tour of the Cell
Introduction to Cells
Discovery: Cells were discovered in 1665 by Robert Hooke.
Cell Theory:
All organisms are composed of cells.
Cells are the smallest living things.
Cells arise only from pre-existing cells.
Size Considerations:
Most cells are relatively small due to their reliance on diffusion.
Smaller cells have advantages over larger ones in nutrient uptake and waste removal.
Limitations of Cell Size
As a cell increases in size, its volume grows faster than its surface area.
Neurons overcome size limitations by being long and skinny for better nutrient and waste transport.
Comparing Prokaryotic and Eukaryotic Cells
Basic Features of All Cells:
Plasma membrane
Semifluid substance called cytosol
Chromosomes (carry genes)
Ribosomes (make proteins)
Prokaryotic Cells
Simplest organisms, lack a membrane-bound nucleus.
DNA present in nucleoid region.
Have a cell wall outside the plasma membrane for protection and shape.
Do contain ribosomes, which are not membrane-bound.
Two domains: Archaea and Bacteria.
Eukaryotic Cells
Possess a membrane-bound nucleus, more complex than prokaryotic cells.
Characterized by compartmentalization through membrane-bound organelles and the endomembrane system.
Contain a cytoskeleton.
Check for Understanding Questions
Major cause of cell size limits includes:
C. Small cells have sufficient surface area for efficient functioning.
Cellular Structures and Their Functions
Endoplasmic Reticulum (ER)
Types of ER:
Rough ER: Contains ribosomes, synthesizes proteins for secretion, lysosomes, or plasma membrane.
Smooth ER: Lacks ribosomes, involved in lipid synthesis, calcium storage, and detoxification.
Golgi Apparatus
Flattened stacks of membranes for packaging and distributing molecules.
Contains cis and trans faces; vesicles transport molecules to their destinations.
Lysosomes
Membrane-bound digestive vesicles arising from Golgi apparatus.
Contain enzymes for macromolecule breakdown and destroying engulfed material through phagocytosis.
Vacuoles
Membrane-bound storage structures in plants, serve various functions.
Types: Central vacuole (plants), contractile (some protists), and storage vacuoles.
Mitochondria
Found in all eukaryotic cells, involved in ATP production through oxidative metabolism.
Structure: Outer membrane, intermembrane space, inner membrane with cristae, and matrix.
Mitochondria contain their own DNA.
Chloroplasts
Present in plant and some eukaryotic cells, contain chlorophyll for photosynthesis.
Surrounded by two membranes with thylakoids inside and contain their own DNA.
Endosymbiosis Theory
Eukaryotic organelles originated by symbiosis between free-living cells.
Prokaryotes were engulfed by ancestral eukaryotes leading to mitochondria and chloroplasts.
Cytoskeleton and Cell Motility
Cytoskeleton
Composed of protein fibers, supports cell shape, and positions organelles.
Three types of fibers:
Microtubules (thickest)
Microfilaments (actin filaments, thinnest)
Intermediate filaments (medium thickness).
Microtubules
Composed of tubulin polymers, involved in maintaining cell shape, motility, and chromosome movement.
Form cilia and flagella (9 + 2 arrangement).
Microfilaments
Comprised of actin, aid in maintaining cell shape, and contribute to muscle contraction and cell motility.
Intermediate Filaments
Composed of keratin proteins, maintain cell shape and anchor organelles.
Extracellular Components
Cell Walls of Plants
Cell wall distinguishes plant cells from animal cells, providing protection, shape maintenance, and water regulation.
Composed of cellulose fibers embedded in polysaccharides and proteins.
Extracellular Matrix (ECM)
Found in animal cells, provides a protective layer, with collagen as a notable component.
Integrins link ECM to the cytoskeleton.
Intercellular Junctions
Facilitate adhesion, interaction, and communication between cells through physical contact.
Types of junctions include tight junctions, desmosomes, and gap junctions.