Cell Theory and Structure J. R. Jones Fall 2007

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. 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. http://www.smithlifescience.com/cork2.GIF

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…… Eukaryotes Nucleus Many organelles Large in size Ex: Humans, plants, fungi, etc. Prokaryotes No nucleus Few organelles Small in size Ex: Bacteria 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.harlem-school.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%26safe%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 protiens 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. One 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. Among multicellular animals, nearly all of the mtDNA in a fertilized egg is inherited from only the mother. One mechanism for this is simple dilution: an egg contains 100,000 to 1,000,000 mitochondria, whereas a sperm contains only 10 to 100.

http://micro. magnet. fsu http://micro.magnet.fsu.edu/cells/chloroplasts/images/chloroplastsfigure1.jpg http://en.citizendium.org/images/c/c7/MitochondriaSMALL2.jpg