lecture 03 - cell structure and function1

8/11/2019 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)


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 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

lecture 03 - cell structure and function1

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