Cell Theory and Structure
Discovery of the Cell
• Scientists did not start using simple compound
microscopes until the mid 1600’s.
• Robert Hooke used an early compound microscope to
look at slices of cork.
http://www.smithlifescience.com/cork2.GIF
• Hooke named the ‘seemingly empty’ chambers ‘cells.’
• Around the same time, Anton von Leeuwenhoek was
using a single-lens microscope to observe unicellular
organisms in pond water for the first time.
Cell Theory
• Additional observations of cells in other living
things led scientists to 3 basic conclusions,
known as the cell theory.
• Cell Theory states:
▫ All living things are composed of cells.
▫ Cells are the basic units of structure and function
in living things.
▫ New cells are produced from existing cells.
There are two categories of cells……
• Prokaryotes
▫ No nucleus
▫ Few organelles
▫ Small in size
▫ Ex: Bacteria

Eukaryotes
– Nucleus
– Many organelles
– Large in size
– Ex: Humans,
plants, fungi,
etc.
http://www.cod.edu/people/faculty/fancher/EukaryoticCell.jpg
http://www.cod.edu/people/faculty/fancher/ProkaryoticCell.jpg
Cell Structure
• All cells, both prokaryotes and eukaryotes, have
DNA and a cell membrane.
• Cells also contain organelles – specialized
structures within the cell that perform certain
tasks.
• These organelles float around in the cell’s
cytoplasm, which is mostly made of water.
Prokaryotes…….they’re simple.
• Prokaryotes only have a few
basic structures:
▫
▫
▫
▫
DNA
Cell/plasma membrane
Cell wall
Ribosomes
▫ Some use structures like pili,
cilia, and flagellum to move in
aquatic environments.
http://scienceblogs.com/clock/2006/11/cell_structure.php
….but they come in many varieties.
http://images.google.com/imgres?imgurl=http://www.harlem-school.com/10TH/sci_pdf/graphics/prokaryotic_entities.gif&imgrefurl=http://www.harlemschool.com/10TH/sci_pdf/sci.html&h=396&w=284&sz=32&hl=en&start=12&tbnid=dQsSJBBu88uFiM:&tbnh=124&tbnw=89&prev=/images%3Fq%3Ddifferent%2Bshaped,%2Bprokaryotic%26gbv%3D2%26svnum%3D10%26hl%3Den%26sa
fe%3Dactive
Eukaryotes are more complex.
• Eukaryotes can be multicellular or unicellular.
• Eukaryotes contain many organelles…….
Do you know your Organelles?
Cell (plasma) membrane
• Regulates what materials enter and leave the
cell.
Nucleus
• Controls most cell processes and contains nearly all of
the cell’s DNA
Ribosomes
• assemble proteins.
▫ Some are free floating while others are attached to the
endoplasmic reticulum.
Endoplasmic Reticulum (ER)
• There are two types:
▫ Rough – chemically modifies proteins that are produced by the
ribosomes on its surface.
▫ Smooth – contains specialized enzymes and makes lipid
components for the cell membrane.
Golgi apparatus
• Sorts, modifies, and/or packages proteins and
other materials from the ER for storage or
secretion from the cell.
Lysosomes and peroxisomes
• Lysosomes contain enzymes that are specialized to digest
lipids, carbs, proteins so their monomers can be reused
• Peroxisomess contain enzymes that are specialized to
digest toxic substances
Cytoskeleton
http://scienceblogs.com/clock/2006/11/cell_structure.php
• A network of protein filaments (microtubules
and microfilaments) that help the cell move and
maintain its shape
Mitochondria
• Provides the cell with usable chemical energy
▫ It is the site of cellular respiration.
How are they different?
http://staff.tuhsd.k12.az.us/gfoster/standard/BCELL1_files/image005.jpg
http://scienceblogs.com/clock/2006/11/cell_structure.php
Plant cells have special features…..
• Plants contain:
▫ Chloroplasts – create and store usable energy
through the process of photosynthesis.
▫ Cell wall – provides the cell with rigid structure.
▫ 1 Large vacuole – used for the storage of water and
some other materials
 Animal cells usually have many small vacuoles
Some organelles have their own DNA….
• Only two organelles have their own DNA –
mitochondria and chloroplasts.
• Endosymbiotic Theory – suggests that mitochondria
and chloroplasts are the decendents of ancient
prokaryotes that developed symbiotic relationships
with ancient cells.
http://micro.magnet.fsu.edu/cells/chloroplasts/images/chloroplastsfigure1.jpg
http://en.citizendium.org/images/c/c7/MitochondriaSMALL2.jpg