Bacterial Structure, Function, Growth and Taxonomy Flashcards
What are Bacteria?
Unicellular, ubiquitous host dependent organisms.
What are the 6 main parts of a typical bacterial cell?
1.Outer membrane (not present in all bacteria)
2. Cell wall: Made of peptidoglycan with varying thickness between gram positive and gram negative bacteria
3.Cytoplasmic Membrane composed of a protein matrix similar to a phospholipid bilayer
4. Pili: external structures essential for the adhesion step in the invasion process.
5. Flagellum: appendages important for motility. There may be multiple flagella present on a bacterial cell on the poles ore laterally around the cell. Anchored in the cytoplasmic membrane to access ATP
6. Genome: bundles of genetic information in a circular conformation known as cccDNA containing histone like proteins
What is the mesosome?
This is an invagination in the cytoplasmic membrane though to be important in the division and thus replication of bacterial cells but it is also thought to be an artifact of electron microscopy.
What is the importance of gram staining?
This is a key diagnosis method which differentiates between gram negative and gram positive bacteria based on the thickness of their cell wall. Gram negative bacteria with a thin cell wall and gram positive with a thicker cell wall
What is the overall process used when conducting a gram stain?
- Heat fix over a flame
- Stain bacteria by flooding the slide with a dye like crystal violet
- Fix stain on cell wall using a mordent like Gram’s Iodine
- Decolorise with alcohol/acetone
- Counter stain with a dye like Safranin Red
The result would be pink (Gram neg) or purple (Gram pos) colonies observed using light microscopy
Give 4 examples of a Gram negative bacillus
- Escherichia coli
- Klebsiella pneumoniae
- Pseudomonas aeruginosa
- Haemophilus Influenzae
Give two examples of a gram positive coccus
- Staphylococcus aureus
- Streptococcus pyogenes
Give two examples of a gram negative diplococcus
- Neisseria meningitidis
2.Neisseria gonorrhea
What are the three components of the cell envelope of a bacterial cell?
- The outer membrane if present
- Cell wall
- Inner/Cytoplasmic membrane
What are the 4 major functions of the cell wall?
- Maintain rigidity and cell structure/shape
- Maintain osmolarity: prevents osmotic lysis
- Survival: The cell wall interacts with host membranes
- Cell Division: Forms cross-wall separating two daughter cells in replication
Explain how bacterial synthesis comes about.
-The peptidoglycan precursor is synthesized within the bacterial cell
-It is then exported across the cell membrane, this step may be interrupted by antibiotic bacitracin
-If uninterrupted a site is created in the existing cell wall by enzymatic action of PBPs
-The new nucleotide minus terminal D-ala is incorporated into the precursor and the cell proliferates
What are PBPs
penicillin-binding proteins the are responsible for the modification and polymerization of peptidoglycan
Which two species of bacteria have shown different cell wall morphologies?
- Mycobacterium
2.Mycoplasma
What makes mycoplasma’s cell wall morphology different?
-No cell wall is present
- the cell membrane contains steroids
What makes mycobacterium’s cell wall morphology different?
-They have a modified peptidoglycan layer
-Poor gram stain
-Acid fast needed (carbolfuchsin) as
-They are covalently attached to arabinogalactan polymer
-resulting in a mycolic waxy coat