Microbiolog to Introduction y - Weebly

Introduction to

Microbiology

Anas Abu-HumaidanM.D. Ph.D.

Lecture 2

1. Nucleolus2. Nucleus3. Ribosome (80S)4. Vesicle5. Rough endoplasmic reticulum6. Golgi apparatus (or "Golgi body")7. Cytoskeleton8. Smooth endoplasmic reticulum9. Mitochondrion

10. Vacuole11. Cytosol12. Lysosome13. Centriole

Cell structure / Eukaryotes

Cell structure / Eukaryotes / Nucleus

• The nucleus contains the genome, andis surrounded by a porus membrane totraffic proteins.

• The nucleolus is important in ribosomebiogenesis.

• DNA wraps around histones formingnucleosomes, which coil to form fiberscalled chromatin which coils and loopsto form chromosomes.

Cell structure / Prokaryotes /Nucleoid• The nucleoid (meaning nucleus-like) is

an irregularly-shaped region within thecell of a prokaryote that contains all ormost of the genetic material. Incontrast to the nucleus of a eukaryoticcell, it is not surrounded by a nuclearmembrane.

• The genome of prokaryotic organismsgenerally is a circular, double-strandedpiece of DNA, of which multiple copiesmay exist at any time. The length of agenome varies widely, but is generallyat least a few million base pairs.

Top Adenine thymidine(A-T) pairing; bottom: guanine-cytosine (G-C) pair

Prokaryotes vs Eukaryotes DNA

Prokaryotic DNA:

• Is found freely in the cytoplasm (withina region called the nucleoid)

• Is naked (i.e. not bound with proteinsand therefore doesn’t form chromatin)

• Genomes are compact (contain littlerepetitive DNA and no introns)

• Contains extra-chromosomal plasmids

• Is circular in shape

Eukaryotic DNA:

• Is contained within a nucleus

• Is bound to histone proteins

• Genomes contain large amounts ofnon-coding and repetitive DNA(including introns)

• Do not contain plasmids (butorganelles such as the mitochondriamay contain their own chromosomes)

• Are linear in shape

Prokaryotes vs Eukaryotes ribosomes

• Prokaryotes have smallerribosomes, this property isused to target bacterialprotein synthesis withantibiotics.

Transcription and translation

• Prokaryotes couple transcription withtranslation, because of no nuclear membrane.

Cell structure / Eukaryotes / Vesicles

• A lipid bilayer, similar to the cellmembrane, that functions incompartmentalizing cellular processesand substances.

• Involved in metabolism, transport andstorage of molecules, as well as reactionchambers.

• Include: Vacuoles, lysosomes, transportvesicles and secretory vesicles.

• Prokaryotes DO NOT contain organellessurrounded by a membrane.

1. Nucleolus2. Nucleus3. Ribosome4. Vesicle5. Rough endoplasmic reticulum6. Golgi apparatus (or "Golgi body")7. Cytoskeleton8. Smooth endoplasmic reticulum9. Mitochondrion



Cell structure / Eukaryotes and prokaryotes / Cytoskeleton

• The cytoskeleton is a scaffold thatholds the structure of the cell, andfacilitates transport in the cell, as wellas motility and migration.

• Microfilaments are polymers of theprotein actin.

• Cillia and flagella are made ofmicrotubules (protein cylinders madeof tubulin) enclosed in a membrane.

• Not only eukaryotes, but alsoprokaryotes possess a cytoskeleton,with actin and tubulin - like proteins.

Actin Tubulin

Cell structure / Prokaryotes

• Circular DNA is packaged in nucleoid.More than one nucleoid can be found,but all are similar (haploid).

• Cytoplasm contains smaller ribosomes(70S), and inclusion bodies thatfunction in the storage of energy or asa reservoir of structural building blocks(e.g. Glycogen, PHB, polyphosphate).

• Cell membrane have high proteindensity, and lacks sterols found ineukaryotes.

Cell structure / Eukaryotes/ Cell membrane functions

The plasma membrane (also calledthe cell membrane) is a phospholipidbilayer with embedded proteins thatencloses every living cell. Thismembrane blocks uncontrolledmovements of water-solublematerials into or out of the cell. Thevarious proteins embedded in thephospholipid bilayer penetrate intoand through the bilayer three-dimensionally.

Cell structure / Prokaryotes/ Cell membrane functions

1. Permeability and transport (activeand passive).

2. Electron transport and oxidativephosphorylation

3. Excretion of hydrolyticexoenzymes and pathogenicityproteins.

4. Biosynthetic functions

5. Chemotactic systems

Cell structure / Prokaryotes/Gram (+) Cell wall

• High tensile strength owing toPeptidoglycans.

• Plays a role in cell division andits own synthesis and is anantigenic determinant.

• Teichoic acid is found inGram(+) bacteria andcontributes to tensile strengh,porousity and antiginicity.

Cell structure / Prokaryotes/Gram (-) Cell wall

• Smaller peptidoglycan layer, but an extra outermembrane, with Lipopolysaccharide (LPS) outerleaflet.

• LPS is an antigenic determinant.

• Antibiotics pass slowly through the outermembrane contributing to the high antibioticres. of Gram (-)s.

• Permiplasm contains transporters anddetoxifiers (e.g. β-lactamase, important inantibiotic resistance).

Scanning electron microscopy experiments performed on E. coli (K12 MG1655), S. haemolyticus (MTCC 3383), and S. haemolyticus protoplasts.

Computational antimicrobial peptide design and evaluation against multidrug-resistant clinical isolates of bacteria• December 2017• Journal of Biological Chemistry 293(10):jbc.M117.805499

Cell structure / Prokaryotes/ staining

Cell structure / Prokaryotes/ staining / Gram staining

Cell structure / Prokaryotes/ Cell wall

• Mycoplasmas lack a cell wall,leading to variability in shape, andresistance to antibiotics that attackthe cell wall.

• Some bacteria form an externallayer of polysaccharides called acapsule when rigid, or a slime layerwhen loose, which contributes toinvasiveness and resistance tophagocytosis.

Conclusion

• Differences exist between prokaryotic and human eukaryotic cell structure,mainly in the nucleus, lipid bilayer organelles, and cell wall.

• Bacteria can be divided on the basis of their cell wall differences into grampositive and gram negative bacteria.

Further reading:

• Sherris Medical Microbiology, sixth editionChapter 21: Bacteria—Basic Concepts

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