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Structure of prokaryotic cells and of viruses

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Prokaryotic cells

Prokaryotes do not have a nucleus like eukaryotes do. Their DNA is not membrane-bound, just free in the cytoplasm. The extra features of prokaryotic cells vs. eukaryotic cells you must learn are:

-the cytoplasm overall does not contain membrane-bound organelles such as mitochondria and endoplasmic reticulum

-prokaryotic ribosomes are smaller than their eukaryotic counterparts

-as previously covered, and their primary defining element, they lack a nucleus; instead, their DNA is a single circular molecule freely present in the cytoplasm and not associated with any proteins such as histones in eukaryotes

-they have a cell wall which contains a special glycoprotein called murein (also known as peptidoglycan)

Some prokaryotes also go further to have some specialised parts, some seen in the diagram:

-one or more plasmids which are also circular DNA loops but much smaller; these can be exchanged between cells or even between different species as they can carry genes for antibiotic resistance

-a capsule made of polysaccharides as their outermost layer (on top of the cell wall on top of the plasma membrane)

-one or more flagella which aid in locomotion


Viruses do not have a cell. They are also not alive in the absence of a living carrier they can invade. Essentially, they are just genetic code inside a protein vessel with an attachment component for invading cells whether prokaryotic or eukaryotic (there is a huge variety of viruses specialised for different host organisms).

Once inside their target cell, their genetic code is ejected and starts being unwittingly translated by the invaded cell. The code instructs the creation of more viruses. During the time it takes the invaded cell to recognise the foreign DNA and destructive activity (as the viruses spread and use up the host organism's resources before tearing the cells apart), the virus has replicated and can spread further, whether its host has survived the invasion or not. Savage.

In their endless variety, viruses do have conserved elements illustrated in the diagram of a bacteriophage ("bacteria eater" specialised in invading bacteria which are prokaryotes) next to influenza which causes flu:

-the genetic material whether DNA or RNA 

-a capsid (protein coat) which contains the genetic material

-attachment proteins which direct its invasion of the host cell; in the bacteriophage these are the tail fibers at the bottom resembling spider legs, while in influenza it's the ball-like protrusions covering the membrane envelope (these act as antigens that a host organism may have antibodies for, or develop the antibodies and thus immunity as a result of the invasion)

Ok byeeeeeeeeeeee

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