A Tour of the Cell

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A Tour of the Cell

• Chapter 6

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Cell theory

• All organisms are made up of cells
• The cell is the basic living unit of
  organization for all organisms
• All cells come from pre-existing cells

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Activities of life

• Most everything you think of a whole organism
  needing to do, must be done at the cellular level
• Reproduction
• Growth development
• Energy utilization
• Response to the environment
• Homeostasis

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How do we study cells?

• Microscopes opened up the world of cells
• Robert Hooke (1665)
• 1st cytologist

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How do we study cells?

• Microscopes
• Light microscopes
• 0.2 µm resolution
• size of a bacterium
• Visible light passes through specimen
• Can be used to study live cells

Technology advancing science!!
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Electron microscope

• 1950s
• 2.0 nm
• 100 times smaller than light microscope
• Reveals organelles
• Can only be used on dead cells
• TEM SEM

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Transmission Electron Microscope

• TEM
• Used mainly to study internal structure of cells
• Aims an electron beam through thin section of
  specimen

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Scanning Electron Microscope

• SEM
• Studying surface structures
• Sample surface covered with thin film of gold
• Beam excites electrons on surface
• Great depth of fieldan image that seems 3-D

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Isolating organelles

• Cell fractionation
• Separate organelles from cell
• Based on variable density of organelles

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Limits to cell size

• Lower limit
• Smallest bacteria mycoplasmas
• 0.1 to 1.o micron (µmmicrometer)
• Most bacteria
• 1-10 microns
• Upper limit
• Eukaryotic cells
• 10-100 microns
• Micronmicrometer1/1,000,000 meter
• Diameter of human hair20 microns

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Why are cells small?

• Lets investigate
• Compare the water absorption of 3 cell groups
• 1 large cell
• 2 medium cells
• 4 small cells

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Q What limits cell size?

• A High surface area-to-volume ratio

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Limits to cell size

• Metabolic requirements set upper limit
• In large cells, material cannot move in out of
  cell fast enough to support life

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Characteristics of all cells

• Surrounded by plasma membrane
• Have cytosol
• Semi-fluid substance within the membrane
• Cytoplasmcytosol organelles
• Contains chromosomes which have genes in the form
  of DNA
• Have ribosomes
• Tiny organelles that make proteins using
  instructions contained in the genes

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Types of cells

• Prokaryotic vs. Eukaryotic cells
• Location of chromosomes
• Prokaryotic DNA in nucleoid region without a
  membrane separating it from the rest of cell
• Eukaryotic DNA enclosed in membrane enclosed
  nucleus

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Prokaryotic Cells
The prokaryotic cell is much simpler in
structure, lacking a nucleus and the other
membrane-enclosed organelles of the eukaryotic
cell. Play video
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Eukaryotic Cells
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Eukaryotic cells

• Eukaryotic cells are more complex than
  prokaryotic cells
• Within cytoplasm is a variety of membrane bound
  organelles
• Specialized, compartmentalized structures in form
  and function
• Eukaryotic cells are generally bigger than
  prokaryotic cells

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An Animal Cell
Figure 6.9
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A Plant Cell
CYTOSKELETON
Figure 6.9
In plant cells but not animal cells Chloroplasts
Central vacuole and tonoplast Cell
wall Plasmodesmata
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Cell membrane

• Exchange organelle
• Plasma membrane serves as a selective barrier
• Allows passage of O2, nutrients wastes

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Organelles Internal membranes

• Internal membranes
• Partition cell into compartments
• Create different local environments
• Compartmentalize functions
• Membranes for different compartments are
  specialized for their function
• Different structures for specific functions
• Unique combination of lipids and proteins in the
  membrane

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Nucleus

• Function
• Contains eukaryotic cells genetic library
• Most genes are in nucleus
• Some genes located in mitochondria and
  chloroplast
• Size
• 5 microns in diameter

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Nuclear Membrane

• Structure
• Separated from cytoplasm by a double membrane
  (nuclear envelope)
• Double membrane is fused in spots forming pores
• Allows large macromolecules particles to pass
  through
• What kind of molecules need to pass through?

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Chromatin

• DNA organized into chromatin
• In normal cells appears as diffuse mass
• When cell prepares to divide, chromatin fibers
  coil up as separate structures, chromosomes

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Chromatin Under the Microscope
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Nucleolus

• Structure
• Densely stained region within the nucleus
• Function
• Production of ribosomal subunits from rRNA and
  protein
• Pass through nuclear pores to cytoplasm combine
  to form ribosomes

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The Nucleolus Under the Microscope
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Ribosomes
ER
Endoplasmic reticulum (ER)
Figure 6.11
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Ribosomes

• Function
• Protein production
• Structure
• Contains rRNA protein
• Composed of 2 subunits that combine to carry out
  protein synthesis
• Produced by the nucleolus

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Ribosomes

• Type
• Free ribosomes
• Suspended in cytosol
• Synthesize proteins that function within cytosol
• Bound ribosomes
• Attached to outside of endoplasmic reticulum and
  nuclear envelope
• Synthesize proteins for export or for membranes

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Ribosomes

• Type
• Free ribosomes
• Suspended in cytosol
• Synthesize proteins that function within cytosol
• Bound ribosomes
• Attached to outside of endoplasmic reticulum and
  nuclear envelope
• Synthesize proteins for export or for membranes