Biology IB 2.2

Cell Wall

Made of murein (not cellulose), which is a protein/carbohydrate complex (peptidoglycan)

Plasma Membrane

Controls the entry and exit of substances, pumping some of them in by active transport

Cytoplasm

Contains all the enzymes needed for all metabolic reactions, since there are no organelles.

Ribosome

The smaller (70 S) type are all free in the cytoplasm, not attached to membranes (like RER). They are used in protein synthesis which is part of gene expression.

Nucleoid

Is the region of the cytoplasm that contains DNA. It is not surrounded by a nuclear membrane. DNA is always a closed loop (i.e. a circular), and not associated with any proteins to form chromatin.

Flagella

These long thread like attachments are generally considered to be for movement. They have an internal protein structure that allows the flagella to be actively moved as a form of propulsion. The presence of flagella tends to be associated with the pathogenicity of the bacterium. The flagella is about 20nm in diameter. This structure should not be confused with the Eukaryotic flagella seen in protoctista.

Pilli

These thread like projections are usually more numerous than the flagella. They are associated with different types of attachment. In some cases they are involved in the transfer of DNA in a process called conjugation or alternatively as a means of preventing phagocytosis.

Slime Capsule

A thick polysaccharide layer outside of the cell wall, like the glycocalyx of eukaryotes. Used for sticking cells together, as a food reserve, as protection against desiccation and chemicals, and as protection against phagocytosis. In some species the capsules of many cells in a colony fuse together forming a mass of sticky cells called a biofilm. Dental plaque is an example of a biofilm.

Plasmids

Extra-nucleoid DNA of up to 400 kilobase pairs. Plasmids can self-replicate particularly before binary fission.They are associated with conjunction which is horizontal gene transfer.

Conjunction

Direct contact between bacterial cells in which plasmid DNA is transferred between a donor cell and a recipient cell. There is no equal contribution to this process, no fertilisation and no zygote formation. It cannot therefore be regarded as sexual reproduction.