BACTERIA

Miss. Pierre

nucleoid

DNA in the bacterial cell is generally confined to this central region. Though it isn't bounded by a membrane, it is visibly distinct (by transmission microscopy) from the rest of the cell interior.

ribosomes

Ribosomes give the cytoplasm of bacteria a granular appearance in electron micrographs. Though smaller than the ribosomes in eukaryotic cells, these inclusions have a similar function in translating the genetic message in messenger RNA into the production of peptide sequences (proteins).

storage granules(not shown) Nutrients and reserves may be stored in the cytoplasm in the form of glycogen, lipids, polyphosphate, or in some cases, sulfur or nitrogen.

endospore

(not shown) Some bacteria, like Clostridium botulinum, form spores that are highly resistant to drought, high temperature and other environmental hazards. Once the hazard is removed, the spore germinates to create a new population

capsuleThis layer of polysaccharide (sometimes proteins) protects the bacterial cell and is often associated with pathogenic bacteria because it serves as a barrier against phagocytosis by white blood cells.

outer membrane

(not shown) This lipid bilayer is found in Gram negative bacteria and is the source of lipopolysaccharide (LPS) in these bacteria. LPS is toxic and turns on the immune system of , but not in Gram positive bacteria.

cell wall

Composed of peptidoglycan (polysaccharides + protein), the cell wall maintains the overall shape of a bacterial cell. The three primary shapes in bacteria are coccus (spherical), bacillus (rod-shaped) and spirillum (spiral). Mycoplasma are bacteria that have no cell wall and therefore have no definite shape.

periplasmic space

(not shown) This cellular compartment is found only in those bacteria that have both an outer membrane and plasma membrane (e.g. Gram negative bacteria). In the space are enzymes and other proteins that help digest and move nutrients into the cell.

plasma membrane

This is a lipid bilayer much like the cytoplasmic (plasma) membrane of other cells. There are numerous proteins moving within or upon this layer that are primarily responsible for transport of ions, nutrients and waste across the membrane

pili

These hollow, hairlike structures made of protein allow bacteria to attach to other cells. A specialized pilus, the sex pilus, allows the transfer of plasmid DNA from one bacterial cell to another. Pili (sing., pilus) are also called fimbriae (sing., fimbria).

flagella

The purpose of flagella (sing., flagellum) is motility. Flagella are long appendages which rotate by means of a "motor" located just under the cytoplasmic membrane. Bacteria may have one, a few, or many flagella in different positions on the cell.

Shapes of bacteria

Ref (Pg 14 Taylor and Green) & (550 Clegg)

http://www.britannica.com/EBchecked/media/83721/Most-bacteria-multiply-by-an-asexual-reproductive-process-called-binary

Please take notes.

Sexual reproduction

Figure 4 : Schematic drawing of bacterial conjugation.1.Chromosomal DNA.2.Plasmids.3.Pilus.

Structure of a virus

Viruses have double-stranded DNA, double-stranded RNA, single-stranded DNA or single-stranded RNA. The genetic material is not typically exposed but covered by a protein coat.

Bacteriophage

Bacteria that attack bacteria are called bacteriophages.They have 2 types of life cycles

LyticLysogenic

Ref (pg 20-23;793;834) Taylor and GreenPg 549 Clegg.

Bacteriophage

Gene technology

Refers to the procedures involving the manipulation of DNA. The terms genetic engineering and recombinant DNA technology often means the same thingOften the application involves changing the genetic make up and thus the properties of an organism.Uses of gene technology include genetic finger printing.

Recombinant DNA

Genes from two different sources - often different species - are combined into the same molecule.

Example: E.coli and the gene for human insulin

two

Biotechnology• Biotechnology is the manipulation of organisms

to make useful products.

• Practices that go back centuries:

-- Bacteria to make wine and cheese

-- Selective breeding of livestock

DNA cloning

Gene cloning enable scientists to prepare multiple identical copies of gene-sized pieces of DNA.

• A foreign gene is inserted into a bacterial DNA and this molecule is returned to a bacterial cell.

• Every time this cell reproduces, the foreign DNA is copied as well.

• In the end, the bacterial clone will make the protein encoded by the foreign gene.

• Bacteria are most commonly used as host cells for gene cloning because DNA can be easily isolated and reintroduced into their cells.

• Bacteria cultures also grow quickly, rapidlyreplicating the foreign genes.

Recap

ENZYME NATURAL SOURCES APPLICATION IN RECOMBINANT DNA TECHNOLOGY

Restriction enzymes (restriction endo nucleases)

Cytoplasm of bacteria-combats viral infection by breaking up viral DNA

Application in recombinant DNA technology

DNA ligase With nucleic acid in the nuclei the cells of all organisms

Breaks the DNA molecules into shorter segments at specific nucleotide sequences

Polymerase With nucleic acid in the nuclei the cells of all organisms

Synthesises nucleic acid strands from nucleotides, guided by a template strand of nucleic acid.

Reverse transcriptase Found in particular types of RNA viruses called retro viruses.

Synthesises a DNA strand complementary to an existing RNA strand

Application.1.

Production of human bacteria by Insulin “Shot gun” approach

• Gene cloning and genetic engineering were made possible by the discovery of restriction enzymes that cut DNA molecules at specific locations.

• The sequence recognised may be 4,6or 8 bases long.

• Most restrictions enzymes are very specific, recognizing short DNA sequences and cutting at specific point in these sequences.

Restriction enzymes are used to make recombinant DNA

•Eg:

• BamHI recognises GGATCC

• BblII recognises AGATCT

• San 3A recognises GATC

Application.2.Use of Reverse Trancription

Reverse transcription –is the reverse of normal transcription. A particular sequence of DNA is copied from a messenger RNA template

Reverse transcriptase- is an enzyme which catalyses reverse transcription.

Questions.

Define the term genome?Why do we say DNA double stranded?What property of DNA is exploited in joining sticky ends?What feature of prokaryotes (bacteria0make then appropriate for recombinant DNA technology rather than eukaryotes?Given just one restriction endonuclease enzyme explain why it cant be used to cut all the genes on a chromosome.