Prokaryotes: Structure and Function PDF

LORIE MAE V. VILORIA,RN,LPT, MEd,Ph.D (in progress)  Diversity & Classification 2 branches ▪Archebacteria ► Confined to extreme environments ► Similar to early earth ► More closely related to eukaryotes than to modern bacteria Only a few genera: ► Extremophiles- PY...

LORIE MAE V. VILORIA,RN,LPT, MEd,Ph.D (in progress)  Diversity & Classification 2 branches ▪Archebacteria ► Confined to extreme environments ► Similar to early earth ► More closely related to eukaryotes than to modern bacteria Only a few genera: ► Extremophiles- PYROLOBUS FUMARII ► Extreme halophiles - salt loving ► Thermoacidophiles ▪Eubacteria ► most modern bacteria ► very diverse Bacterial Shapes Mesosome Mesosomes - invagination of the plasma membrane that increases the surfaces area of the plasma membrane during binary fission. The mesosome also serves as a site for the attachment and distribution of genetic material during binary fission.  The Bacterial Cell Wall ►Instead of cellulose, contain peptidoglycan ▪A polymer of modified sugars cross- linked with amino acids that forms a mesh layer in the plasma membrane ►The gram stain distinguishes many disease causing bacteria based on the type of cell wall ►Many antibiotics work by attacking the bacterial cell wall  The Gram Stain ► A valuable tool for distinguishing types of bacteria based on the cell wall ► Gram (+) ► accept gram stain ► have simpler cell walls with large amounts of peptidoglycan ► Gram (-) ► do not stain ► have more complex cell walls with less peptidoglycan ► cell walls contain lipopolysaccharides ► are more likely to be pathogenic (cause disease) ► more resistant to antibiotics  Antibiotics ►Many antibiotics work on the cell wall ►Common antibiotics (e.g. penicillin) work by preventing cross-linking of peptidoglycan ►Therefore bacteria can’t form new cell walls. Therefore no new bacteria are formed ►Explains added resistance of gram (-) bacteria to these antibiotics External Structures of Prokaryotic Cells Slime Layer The Capsule ►Many bacteria secrete a sticky substance that forms another protective layer, the capsule ►Outside the cell wall ►Helps them stick to things ►Provides protection Capsule Stain  Bacterial DNA – a circular chromosome plus plasmids The DNA of most bacteria is contained in a single circular molecule, called the bacterial chromosome. The chromosome, along with several proteins and RNA molecules, forms an irregularly shaped structure called the nucleoid. This sits in the cytoplasm of the bacterial cell. Inclusion Bodies Plasmid - small fragments of self-replicating extrachromosomal DNA that codes for the resistance to antibiotics or for the productions of a specific metabolite.  Plasmids (functions) ►Bacteria may also have smaller rings of DNA called plasmids ►Plasmids carry non-essential genes such as antibiotic resistance, metabolism of special nutrients, etc. ►Plasmids replicate independently ►Can be transferred when bacteria conjugate Plasmids help bacteria to survive stress Structures of Movement Bacterial Appendages Flagella Axial Filaments Pili (Fimbriae) Bacterial Appendages Flagella Structures of locomotion Originate in the plasma membrane In bacteria rotate like a propellar Many different arrangements Bacterial Appendages Axial filament (endoflagella) ENDOFLAGELLUM External Structures of Prokaryotic Cells Fimbriae ►Sticky, bristlelike projections ►Used by bacteria to adhere to one another, to hosts, and to substances in environment  External Structures of Prokaryotic Cells ► Pili ► Also known as conjugation pili ► Longer than fimbriae but shorter than flagella ► Mediate the transfer of DNA from one cell to another (conjugation) THANK YOU!!