Lecture 13 - Bacteria Overview Flashcards
How are bacteria phylogeny categorized?
Similarity of 16s RNA
What are the main differences between prokaryotic and eukaryotic cells?
Unicellular vs multicellular
No nucleus or membrane bound organelles in prokaryotic
ciruclar DNA vs linear
Cell division via binary fission vs meiosis/mitosis
Prokaryotes always asexual
Huge variety of metabolic pathways vs common metabolic pathways
Explain how Gram staining works?
Crystal violet used to stain bacteria, then iodine to form complex. If gram positive it has thick peptidoglycan cell wall and one membrane, the cell wall maintains the stain colour even after wash whereas the gram negative bacteria have a OM which is what is stained - washes away with EtOH. Counter stain with saffranin to view gram negative bacteria
What is a monoderm and a diderm?
Monoderm - one membrane - gram positive
Diderm - two membranes - gram negative
What are components of cell envelope?
Membrane(s), peptidoglycan cell wall, periplasmic space
What are differences in the membrane proteins of gram positive and gram negative bacteria?
Positive - WTA, LTA
Negative - LPS (Lipid A, endotoxin)
What is the difference between the OM and IM of Gram negative bacteria?
OM made of Lipid A and IM made of phospholipids
How are LTA and LPS bound to cell envelope? What are components of LPS? Which PRR’s do LTA and LPS bind to?
LTA covalently bound to cell wall, LPS bound to OM via Lipid A. O-Antigen, core saccharide and Lipid A. TLR2 and TLR4, respectively.
What is the structure of the cell wall?
Peptidoglycan. NAM + NAG monomers that contain peptide chain from the NAM which are then bound via pentaglycine bridge in Gram positive and direct covalent linkage in Gram negative.
List the different motility strategies used by bacteria?
Polar and perisplasmic flagella, contractile cytoskeleton, gliding motility
What are the main ways that horizontal gene transfer can occur?
Transformation - Donor DNA released into the cytoplasm or extracellular space, taken up by recipient
Transduction – Bacteriophage injects donor DNA (could be from another bacterium or phage DNA) into recipient
Conjugation - Plasmid transfer via conjugation bridge and Type IV pilus
How is iron sequestered in the host cells? How do bacteria extract this iron?
In molecules: ferritin, hemoglobin, lactoferrin, transferrin. Bacteria release toxins that cause lysis releasing Fn, Hg, Lf. They also release siderophores and use receptors specific to each molecule which uptake these complexes and iron extracted within the bacterial cell.
3 major types of toxins?
AB toxins - Catalytic A subunit and one or more “binding” B subunits
membrane-disrupting toxins - pore forming
superantigens - activate Th cells and induce cytokine storm
How are endotoxins released compared to exotoxins?
Endotoxins released during bacterial lysis vs exotoxins which are secreted
How does the Sec pathway work to secrete proteins from the bacteria? What other Sec-dependent pathways are there and how to they differ? How do these secretion pathways differ between Gram positive and Gram negative bacteria? How are Gram negative proteins transported across the OM?
SecB chaperone binds to peptide with a Sec signal sequence and transports it to SecA. This ATPase then threads the peptide through the SecYEG translocon through the membrane into the extracellular space or perisplasm. Signal sequence is degraded in cytoplasm.SRP/Sec and TAT. SRP/Sec pathway transports peptide cotranslationally vs Sec which is post-translational. TAT is also post-translational however it is after folding vs Sec and SRP/Sec which are before folding. In gram negative, these pathways transport to the periplasm vs in gram positive the protein is transported to the extracellular space. Second set of secretion channels.