Click4Biology 2.2 Peokaryotes Notes

8/12/2019 Click4Biology 2.2 Peokaryotes Notes

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2.2.1 Structure of a prokaryotic cell2.2.2 Function of the prokaryotic cell parts 2.2.3 Electron micrograph study of E. coli2.2.4 Binary fission in prokaryotes

Prokaryotic Cells

A number of years ago t o !or egian biologistsobtained a sample of soilfrom a nearby piece

oodland. "n returning tothe laboratory they began toidentify kno n species of

prokaryote and also to classify any unkno nspecies in their sample. By the time the t onor egians had finished they had doubled theentire catalogue of kno n prokaryotic species.#he introduction to prokaryotes pro$ided here isho e$er based on perhaps the best kno

prokaryote Escherichia coli (E. coli). !otice thatimage of E. coli to the left sho s a straight rodshaped cell. "ther types of bacteria shodifferent morphology some of these $ariationsare sho n in the table belo .

2.2.1 Draw and label a diagram of the ultrastructure of Escherichia coli (E. coli) as anexam le of a rokaryote (1)

%ra & #o represent by means of pencil lines.

#he general si'e of a prokaryotic cell is about 1(2 um.

!ote the absence of membrane bound organelles

#here is no true nucleus ith a nuclear membrane

#he ribosome)s are smaller than eukaryotic cells

#he slime capsule is used as a means of attachment to asurface

"nly flagellate bacteria ha$e the flagellum

*lasmids are $ery small circular pieces of %!A thatmaybe transferred from one bacteria to another.
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2.2.2 !nnotate the diagram from 2.2.1 with the functions of each named structure.

Annotate& to add brief notes to a diagram or graph.

Cell "all#

+ade of a murein ,not cellulose- hich is a glycoprotein or peptidoglycan ,i.e. a protein/carbohydratecomple0-. #here are t o kinds of bacterial cell all hich are identified by the ram Stain techni ue henobser$ed under the microscope. ram positi$e bacteria stain purple hile ram negati$e bacteria stain pink.#he techni ue is still used today to identify and classify bacteria. e no kno that the different staining is dueto t o types of cell all

Plasma membrane#

ontrols the entry and e0it of substances pumping some of them in by acti$e transport.

Cyto lasm#

ontains all the en'ymes needed for all metabolic reactions since there are no organelles.

$ibosome#

#he smaller ,56 S- type are all free in the cytoplasm not attached to membranes ,like 7E7-. #hey are used in protein synthesis hich is part of gene e0pression.

%ucleoid#

8s the region of the cytoplasm that contains %!A. 8t is not surrounded by a nuclear membrane. %!A is al ays aclosed loop ,i.e. a circular- and not associated ith any proteins to form chromatin.

&lagella#

#hese long thread like attachments are generally considered to be for mo$ement. #hey ha$e an internal proteinstructure that allo s the flagella to be acti$ely mo$ed as a form of propulsion. #he presence of flagella tends to

be associated ith the pathogenicity of the bacterium. #he flagella is about 26nm in diameter. #his structureshould not be confused ith the e9karyotic flagella seen in protoctista.

Pilli#

#hese thread like pro:ections are usually more numerous than the flagella. #hey are associated ith differenttypes of attachment. 8n some cases they are in$ol$ed in the transfer of %!A in a process called con:ugation oralternati$ely as a means of pre$enting phagocytosis.

'lime Ca sule#

A thick polysaccharide layer outside of the cell all like the glycocaly0 of eukaryotes. 9sed for sticking cellstogether as a food reser$e as protection against desiccation and chemicals and as protection against

phagocytosis. 8n some species the capsules of many cells in a colony fuse together forming a mass of stickycells called a biofilm. %ental pla ue is an e0ample of a biofilm.


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Plasmids#

E0tra(nucleoid %!A of up to 466 kilobase pairs. *lasmids can self(replicate particularly before binaryfission.

#hey are associated ith con:unction hich is hori'ontal gene transfer.

8t is normal to find at least one anti(biotic resistance gene ithin a plasmid. #his should not be confusedith medical phenomena but rather is an ecological response to other antibacterial compounds produced

by other microbes. ommonly fungi ill produce anti(bacterial compounds hich ill pre$ent the bacteria replicating and competing ith the bacteria for a resource.

con ugation

%irect contact bet een bacterial cells in hich plasmid %!A is transferred bet een a donor cell and arecipient cell.

#here is no e ual contribution to this process no fertilisation and no 'ygote formation. 8t cannottherefore be regarded as se0ual reproduction.

2.2. *dentify structures from 2.2.1 in electron m icrogra hs of E. coli (2).

8dentify& #o find an ans er from a gi$en number of possibilities.

1. !ote the double membrane of this E. coli .

#his feature means that the cells do not retain the dark bluestain used in microscopy. #hey are therefore kno n as ram(negati$e this contrast ith ram(positi$e single membrane

bacteria.

2. #here is some e$idence in the image of pilli hich are thesurrounding light grey masses.

3. 8n the cytoplasm of the bacterium there are no $isibleorganelles hich is consistent ith ho e e0pect a

prokaryote cell to appear.

4. #he nucleoid region is not seen ell in this particular image but is clearer in the ne0t image.

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2.2.+ 'tate that rokaryotic cells di,ide by binary fission (1).

State&means to gi$e a specific name $alue or other brief answer ithout e0planation or calculation.

*rokaryotic cells di$ide by binary fission. #his is an ase0ual method of reproduction in hich a

)parental) cell di$ides into t o smaller but e ually si'edcells.

#he cells are genetically identical and form the basis of areproducti$e clone.

a little e0tra information for the interested reader.

#he process of binary fission takes place in four stage&

(a). $e roduction signa l& #he cell recei$es a signal of internal or e0ternalorigin that initiates the cell di$ision.

E.coli replicates about once e$ery 46 minutes hen incubated at 35 o . 8fho e$er e increase the concentration of carbohydrate nutrients that the cell issupplied ith then the di$ision time can be reduced to 26 minutes. #here is asuggestion here that an e0ternal signal ,nutrient concentration- is acting as thereproducti$e signal.

(b). $e lication of D%! & bacterial cells ha$e a single condensed loop of %!A.#his is copied by a process kno n as semi(conser$ati$e replication to producet o copies of the %!A molecule one for each of the daughter cells

#he replication begins at a single point , ori -on the loop of %!A. #he process proceeds around the loop until t o loop ha$e been produced each a copy ofthe original. #he process finishes at a single point on the loop of %!A calledthe ter position.

(c). 'egregation of D%!# "ne %!A loop ill be pro$ided for each of thedaughter cells.

As the ne loops form the ori site becomes attached to some contractile proteins that pull the t o ori sites and therefore the loops to opposite ends ofthe cell. #his is an acti$e process that re uires the bacteria to use energy for thesegregation.

(d). Cytokinesis# ell separation.


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#his occurs once the %!A loop replication and segregation is complete. #he %!A completes a process ofcondensing hilst the plasma membrane begins to form a ) aist) or constriction in the middle of the cell. As the

plasma membrane begins to pinch and constrict the membrane fuses and seals ith additional ne membranealso being formed.

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Click4Biology 2.2 Peokaryotes Notes