Lecture 03 - Cell Structure and Function1
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Transcript of Lecture 03 - Cell Structure and Function1
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The Functional Anatomy ofProkaryotic & Eukaryotic Cells
Outline
To introduce the major structural features ofprokaryotic cells:
shape and size
the cell membrane and cell wall
appendages
genetic material
other inclusions in the cytoplasm .
The prokaryotic cell
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Spherical (coccus) Rod (bacillus)
spirochete Pleomorphic (multiple shapes)
Being small has its advantages
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Prokaryotic Structure:
1. The outer envelope2. Flagella3. Genetic Information4. Intracellular Structures
The Outer Envelope
The Plasma Membrane
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The Cell Wall
Cell Wall Protects Bacteria from the Affects of Osmosis
Cell Wall Protects Bacteria from the Affects of Osmosis
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The Cell Wall - Structure
G = N-acetylgluosamine M = N-aceylmuramic acid(sugar derivatives, i.e. glycans)
The Cell Wall - Structure
Peptidoglycan sheet structure Glycan backbone Pepide cross-links
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Archaea have cell walls made ofmaterials other than peptodiglycan, ifthey have them at all. pseudopeptidoglycan polysaccharides glycoproteins
proteins
The Cell Wall - Structure
The Cell Wall - Structure
the paracrystaline surface layer (S-layer)
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The cell wall is clinically important because:
1. It is a barrier contributes to the ability of somespecies to cause disease
Action of some antibiotics is on the cell wall (e.g.penicillin).
3. Chemical composition of the cell wall is used todifferentiate the major types of bacteria
The Cell Wall
The Outer Envelope:The outer membrane of gram negative bacteria
A second phospholipid membrane relatively permeable due to porins Contains not only protein andphospholipids, but also a largequantity of polysaccharides Lipids and polysaccharides are linkedto form lipopolysaccharide (LPS)
The Outer Envelope Glycocalyx(Capsule / Slime layer)
Ususally composed ofpolysaccharides (sugars), butsometimes protein or both.
Chemical composition varieswidely between prokaryotes
Structured and firmly attached = capsule. Unorganized and only loosely attached = referred
to as a slime layer
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Capsules may contribute to bacterial virulence:
by protecting the bacteria from being recognized andphagocytosed by the immune cells of the host by serving to attach the bacteria to tissue surfaces
Also allow attachment to other surfaces in nature formation of biofilms
Help prevent water loss and desiccation
The Outer Envelope Glycocalyx(Capsule / Slime layer)
Bacterial AppendagesFlagella - motilityFimbriae - attachment to surfacesPili - genetic conjugation
Bacterial AppendagesFlagella - motilityFimbriae - attachment to surfacesPili - genetic conjugation
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FlagellaSome prokaryotes have flagella, which are long,
helical, filamentous appendage that providemotility for the prokaryote
Motility
Advantage of motility is that it provides bacteriawith a means to move toward a favorable
environment or away from a hostile environment
when bacteria move in one direction for a period oftime, it is referred to as a run or swim
runs often end abruptly in tumbles which arerandom changes in direction
tumbles are the result of a reversal of flagellarotation
then a run resumes
Motility
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TaxisMovement of bacteria towards a stimulus is termed taxis: chemotaxis move towards a chemical phototaxis move towards light
Flagella are composed of 3 parts:1) Filament - flagellin protein2) Hook3) Basal Body (motor)
Flagellum Motor (the basal body)
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Genetic Information : TheNucleoid Region
The nucleoid region contains the single,circular, double-stranded bacterialchromosome
The chromosome is not surrounded by anuclear envelope
The chromosome is attached to theplasma membrane
Plasmids
Plasmids are small circular, double-strandedmolecules
Plasmids are extrachromosomal DNA elements andtypically encode between 5 and 100 genes that are notcrucial for survival
Under certain conditions, plasmids can be
advantageous for survival by encoding genes involvedin antibiotic resistance, tolerance to toxic metals,production of toxins, and synthesis of enzymes
Intracellular StructuresInclusions
Metachromatic Granules (polyphosphate) inorganic phosphate
Polysaccharide Granules consist of glycogen & starch
Lipid Inclusions - acidic carbon chains (fatty acids)
Sulfur Granules sulfur metabolism byproduct
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Intracellular StructuresInclusions
Carboxysomes contain the enzyme ribulose 1,5-
diphosphate carboyxlase which allow prokaryotesto use CO 2 as the sole carbon source
Gas Vacuoles found in aquatic prokaryotes, aid inbuoyancy
Magnetosomes inclusions of iron oxide which actlike magnets
Eukaryotic cell structure vs.prokaryotic structure
Eukaryotic Cells -compare and contrast
Eukaryotes differ from prokaryotes in the followingways:
DNA is found in the nucleus DNA is associated with histones and nonhistone
proteins membrane-enclosed organelles cell wall when present is chemically simple usually divide by mitosis
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Cell Wall & Glycocalyx
Most eukaryotes have a cell wall although it istypically much simpler than in prokaryotic cells
1. Do not contain peptidoglycan
2. Plants and algae - cellulose
2. Fungi - sometimes cellulose or chitin
3. Yeasts - glucan and mannan (polysaccharides)
3. Animal cells - glycoproteins & glycolipids
Plasma Membrane
The plasma membranes of prokaryotes and eukaryotesare similar. One important difference is thateukaryotic cells can actively internalize extracellular material by endocytosis andexpel it by exocytosis.
During endocytosis, the plasmamembrane surrounds an
extracellular molecule andinternalizes it in a vesicle.
Flagella & Cilia
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Flagella & cilia are anchored to the plasma membraneby the basal body
Microtubules are arranged in a 9+2 structure
Flagella & Cilia
QuickTime and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Eukaryotic Cilia & FlagellaMove in a Wave-like Manner
Genetic Information In eukaryotic cells, genetic information is stored in
the cell nucleus complexed with proteins calledhistones & nonhistone proteins
The nucleus is the largest organelle in the cell andis surrounded by a double membrane called thenuclear envelope
Within the nucleus is one or more spherical bodiescalled nucleoli. The nucleolus is the site ofribosomal RNA synthesis
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http://www.steve.gb.com/science/nucleic_acids.html
chromatin =DNA + proteins
Intracellular StructuresWithin eukaryotic cells, there are a variety of organelles that have specific shapes and specializedfunctions.
Eukaryotic organelles include:1. Nucleus2. Endoplasmic reticulum (ER)3. Golgi complex4. Lysosomes Vacuoles Mitochondria
Chloroplasts Peroxisomes Centrosomes
http://www.steve.gb.com/science/nucleic_acids.htmlhttp://www.steve.gb.com/science/nucleic_acids.html