I. Structure, function, and reproduction of prokaryotes A. Most
prokaryotes are unicellular. 1.Some species form aggregates of two
or more individuals. B. Three (3) common shapes: cocci (round);
bacilli (rod); helical (spiral)
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The world of prokaryotes C. Theyre everywhere! Collective
prokaryote biomass outweighs all eukaryotes combined by at least
tenfold. They exist almost everywhere, including places where
eukaryotes cannot. Most prokaryotes are beneficial; we couldnt live
without them. (e.g. Nitrogen-fixing bacteria)
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Lyme disease: Caused by a spirochete
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Some cause illness bubonic plague, diphtheria, salmonella
Approximately 5000 species have been identified. Estimates of
prokaryote diversity range from 400,000 to 4,000,000 species. D.
Bacteria and Achaea are the two main branches of prokaryote
evolution Achaea are thought to be more closely related to
eukaryotes than to bacteria.
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E. Most prokaryotes secrete sticky substances that form a
protective layer and enable them to adhere to substrates. 1. The
sticky protective layer secreted by prokaryotes is called the
capsule. 2. Some prokaryotes adhere to substrates using Pili. (
Pili are thin, protein tubes originating from the cytoplasmic
membrane) a. Some Pili are specialized for DNA transfer. This
process is called conjugation; note for later in class.
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F. Almost all prokaryotes have cell walls external to the
plasma membrane. 1. Cell walls maintain cell shape. 2. Cell walls
are composed of peptidoglycan.( a polymer consisting of sugars and
amino acids that forms a mesh-like layer outside the plasma
membrane of bacteria, forming the cell wall)
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G. Cellular and genomic organization of prokaryotes is
different from that of eukaryotes 1.Prokaryotes have no nucleus. 2.
The nucleoid region in a prokaryotic cell consists of a
concentrated mass of DNA. This mass of DNA is usually one thousand
times less than what is found in a eukaryote.
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Specialized membranes of prokaryotes N nucleoid
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Prokaryotic cells Diagram
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Components of a prokaryote Cytoplasm Ribosomes Nuclear Zone DNA
Plasmid Cell Membrane Mesosome Cell Wall Capsule (or slime layer)
Flagellum
PROCARYOTES Photosynthesis evolved early in prokaryotic life
Cyanobacteria started to produce O 2 about 2.7 billion years ago
Contrasting hypotheses for the taxonomic distribution of
photosynthesis among prokaryotes.
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Heliobacteria: Causes stomach ulcers
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2. Chlamydias - Parasitic; survive only within cells of animals
- Some cause STDs e.g. Chlamydia
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3. Spirochetes - Helical heterotrophs - Some cause STDs e.g.
syphilis
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Mycoplasma shown covering a human cell; some species of
mycoplasmas cause walking pneumonia
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5. Cyanobacteria - Oxygenic photosynthesis, and chloroplasts
evolved from them.
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Ecological impacts of prokaryotes A. Prokaryotes are links in
the recycling of chemical elements B. Many prokaryotes are
symbiotic (2 organisms living in direct contact with each other).
Mutualism both symbiotic organisms benefit - e.g. Nitrogen-fixing
bacteria like Rhizobium: plant obtain organic nitrogen, Rhizobium
gets energy in the form of sugars that the plant produces.
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Are all prokaryotes disease producing germs? Without
prokaryotes ecosystems would collapse! 53.10
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Humans use prokaryotes in research and technology Examples:
Sewage treatment Bioremediation Chemical & Medical production
Research (genetic engineering, etc.)
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Eukaryotic and Prokaryotic Cells Prokaryote = without a nucleus
Eukaryote = with a nucleus
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EUKARYOTE Diagram
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Components of a Eukaryote Cytoplasm Nucleus with Nucleolus
Mitochondria Chloroplast Ribosomes Rough Endoplasmic Reticulum
Smooth Endoplasmic Reticulum Golgi body Vacuoles
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Components of a Eukaryote continued Lysosomes Cytoskeleton
Centriole Cilium and Flagellum Microvillus Cell membrane Cell
Wall
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Comparing Prokaryotic and Eukaryotic Cells
ProkaryotesEukaryotes Have cell wall or membrane Have DNA Have
cytoplasm Have Organelles Have a nucleus Have membranes surrounding
organelles Are mostly bacteriaInclude all plant and animal
cells
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Summary of the differences! Prokaryotic CellsEukaryotic cells
small cells (< 5 mm)larger cells (> 10 mm) always
unicellularoften multicellular no nucleus or any membrane-bound
organelles always have nucleus and other membrane-bound organelles
DNA is circular, without proteinsDNA is linear and associated with
proteins to form chromatin Ribosomes are small (70S)Ribosomes are
large (80S) no cytoskeletonalways has a cytoskeleton cell division
is by binary fissioncell division is by mitosis or meiosis
reproduction is always asexualreproduction is asexual or
sexual