Download Chromatin Nucleolus Pore Nucleus Two

Chapter 4:
Cells and Organelles
Categorizing Cells
Eukaryotes vs. Prokaryotes
Is this the best way to classify cells?
Current View
Cell Size
Three factors that limit cell size:
1. Adequate surface area to volume ratio
2. Diffusion rates of molecules
3. Need for adequate concentrations of
reactants and catalysts
Surface area is important
Cell Differences
There are several areas where Bacteria,
Archaea, and Eukaryotic cells differ:
1. Nucleus
2. Internal Membranes
3. Cytoskeleton
4. Exocytosis and Endocytosis
5. DNA organization
6. DNA packing
7. Segregation of genetic information
8. Gene expression
Nucleus
Eukaryote
Prokaryote
(Bacteria and Archaea)
Cell Differences
There are several areas where Bacteria,
Archaea, and Eukaryotic cells differ:
1. Nucleus
2. Internal Membranes
3. Cytoskeleton
4. Exocytosis and Endocytosis
5. DNA organization
6. DNA packing
7. Segregation of genetic information
8. Gene expression
Internal Membranes
(compartmentalization)
Three advantages of having internal membranes:
1. Maintain necessary concentrations
2. No interference between processes
3. Keep “good” molecules from “bad”
Cell Differences
There are several areas where Bacteria,
Archaea, and Eukaryotic cells differ:
1. Nucleus
2. Internal Membranes
3. Cytoskeleton
4. Exocytosis and Endocytosis
5. DNA organization
6. DNA packing
7. Segregation of genetic information
8. Gene expression
Cytoskeleton
• Bacteria = poorly developed/non-existent
• Archaea = poorly developed/non-existent
• Eukaryotes = well developed and important to
cellular function
Cell Differences
There are several areas where Bacteria,
Archaea, and Eukaryotic cells differ:
1. Nucleus
2. Internal Membranes
3. Cytoskeleton
4. Exocytosis and Endocytosis
5. DNA organization
6. DNA packing
7. Segregation of genetic information
8. Gene expression
Endocytosis and Exocytosis
Fluid outside cell
Vesicle
Protein
Cytoplasm
Vesicle forming
Cell Differences
There are several areas where Bacteria,
Archaea, and Eukaryotic cells differ:
1. Nucleus
2. Internal Membranes
3. Cytoskeleton
4. Exocytosis and Endocytosis
5. DNA organization
6. DNA packing
7. Segregation of genetic information
8. Gene expression
DNA organization
• Bacteria = Small, circular, few proteins
• Archaea = Small, circular, moderate amount of
proteins
• Eukaryotes = Large, linear, lots of proteins
Cell Differences
There are several areas where Bacteria,
Archaea, and Eukaryotic cells differ:
1. Nucleus
2. Internal Membranes
3. Cytoskeleton
4. Exocytosis and Endocytosis
5. DNA organization
6. DNA packing
7. Segregation of genetic information
8. Gene expression
DNA Packing
• Bacteria and Archaea = highly folded
• Eukaryotes = wrapped around proteins in
chromosomes
Cell Differences
There are several areas where Bacteria,
Archaea, and Eukaryotic cells differ:
1. Nucleus
2. Internal Membranes
3. Cytoskeleton
4. Exocytosis and Endocytosis
5. DNA organization
6. DNA packing
7. Segregation of genetic information
8. Gene expression
Segregation of Genetic Information
• Bacteria and Archaea = replicate genome, pass
it on to daughter cells
• Eukaryotes = mitosis and meiosis
Cell Differences
There are several areas where Bacteria,
Archaea, and Eukaryotic cells differ:
1. Nucleus
2. Internal Membranes
3. Cytoskeleton
4. Exocytosis and Endocytosis
5. DNA organization
6. DNA packing
7. Segregation of genetic information
8. Gene expression
Gene expression (Bacteria and Archaea)
Bacteria and Archaea
• Transcribe very specific segment of RNA
• RNA may contain information for more than one
polypeptide
• No RNA processing
• Not compartmentalized
Gene expression (Eukaryotes)
Eukaryotes
• Transcribe large molecules of RNA
• RNA is processed before translation
• 1 RNA = 1 polypeptide
• Compartmentalized
Unity vs. Diversity in Cells
• Unity = cells resemble one another in several
fundamental ways
• Diversity = cells are different from each other in
specific ways
Unity in Cells
Virtually all cells:
• Oxidize sugars for energy
• Transport ions across membranes
• Undergo division
• Have a plasma membrane
• Have ribosomes
• Have double stranded DNA as genetic info
Diversity in Cells
Diversity among cells arises from specialization
Plasma Membrane
Nucleus
Nucleus
Chromatin
Nucleolus
Two membranes
of nuclear envelope
Pore
Rough
endoplasmic
reticulum
Ribosomes
Nucleus (cont.)
Mitochondrion
Chloroplast
Endosymbiont Theory
Theory stating that mitochondria and chloroplasts
arose as symbiotic relationship with ancient,
single celled organisms
• Both contain own DNA and ribosomes
• Both can make their own RNA and proteins
• Resemble bacteria in size and shape
Endoplasmic Reticulum (ER)
Golgi Apparatus
Secretory Vesicles
Lysosome
Lysosome (cont.)
Mitochondrion fragment
Peroxisome fragment
TEM 42,500 
Lysosome containing
two damaged organelles
Peroxisome
Vacuoles
Ribosome
Cytoplasm
Contains organelles and cytosol
Cytoskeleton
• Microfilaments – thinnest
• Intermediate filaments
• Microtubules – thickest
Cytoskeleton
Extracellular Matrix
• Found in animal cells
• Provides physical support to cells in tissues
• Made of collagen and proteoglycans
• Keeps tissues elastic
Cell Wall
Plants:
• Function – keep the cell rigid
• Composition – cellulose
Bacteria
• Function – protect from hypotonic environments
• Composition – amino sugars and proteins
Archaea
• Function – protect from hypotonic environments
• Compostion – proteins and peptidoglycans
Cell Junctions
Plants:
• Plasmodesmata
Animal:
• Gap
• Tight
• Adhesive
Tight junctions
Adhesive junctions
Gap junctions
Extracellular matrix
Space between cells
Plasma membranes of adjacent cells
Viruses
• Non-cellular
• Reproduce by taking over cellular machinery
• Absent: Ribosomes, cytoplasm, organelles,
enzymes (few exceptions)
• Structure: capsid, core, maybe some
membrane
Structure
• No metabolism
• No response to environmental stimuli
• Can’t reproduce itself
Are viruses alive?
• No metabolism
• No response to environmental stimuli
• Can’t reproduce itself
Viroids
• Smallest known infectious agent
• Circular piece of RNA that infects plant cells
• Not known to code for any proteins
• Transmission?
• Mechanisms of infection?
Prions
• Infectious proteins (proteins misfolded)
• Causes several diseases: scrapie, mad-cow,
kuru
• Mechanism?