L3-Bacterial cell structure and function PDF

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Bacterial cell structure and function

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Flagella- tail (tend to be in one place) Pili- shorter than flagella and tend to be in all different directions around the cell Capsule- provides a sticky adhesive surface Cell wall- protects bacterium. Phospholipid bilayer, can be gram negative or positive - Peptidoglycan - Surface lipids/sugars Cytoplasmic membrane Cytoplasm – contains naked DNA (one long circle of DNA) - Ribosomes

Cellular structures Capsule  ‘the slime layer”  It is polysaccharide and polypeptide rich and sticky adhesive layer that not all bacteria have  Can provide protection: o Desiccation -(environment) i.e. presence to the air where it has drying conditions, slime layer keeps hydration o Phagocytosis- bypass/ mask biomarkers that can be identified by immune cells which will trigger phagocytosis  Allows attachment to surfaces  Steptocossus mutans o Lives on our teeth (plaque) o Catheters

o Central venous line o strep mutans forms plaque via a biofilm on our teeth using the slime layer to help the bacteria to stick together biofilms o big problem clinically  tend to form on surfaces that are clean such as plastic or our teeth.  Big problem when using catheters to connect to out central venous line for administering medicines etc, at the site at which the catheter penetrates the skin, there is an interaction b/w microbes on the skin and the plastic, whereby there is an environment where bacteria can grow.  We must use sterile wound dressings and disinfect the area before using the catheter to reduce the formation of these biofilms. o complex communities  it is harder to get at the bacteria in the middlethere is a titration/ decrease in permeability of the drugs through the biofilm

cell wall  complex, semi-rigid structure o characteristic shape of the cell o surrounds the fragile cell membrane o strong and flexible, like a chain linked fence- peptidoglycan layer so prevents osmotic rupture o contributes to disease mechanisms  almost all have a cell wall o mycoplasma is the only one without a cell wall

Gram- negative cell wall  periplasm- peptidoglycan (NAG + NAM)  lipopolysaccharide (LPS) massively contributes to how we treat bacterial infections otherwise patients can get LPS toxic shock

gram positive 

thick peptidoglycan layer which is leafleted with teichoic acid on the exterior

gram negatives  have cytoplasmic membrane and have thin layer of peptidoglycan  have inner and outer membrane o exterior leafleted with many lipids  proteins that cover the whole span of the cell wall- protein channels called efflux pumps which help to regulate homeostasis o nutrient conc o antibiotic resistance go from the cytoplasmic membrane to the outer most surface

Gram- positive cell wall  Much smoother/ more simple  Peptidoglycan layer leafleted with Lipoteichoic acid  Proteins dotted around Cell (cytoplasmic) membrane   

 peptidoglycan (PG)  composed of N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) o alternating molecules that form the ‘chain links’ o between these we have crossing links formed by peptide cross bridges o this forms a carbohydrate backbone (NAG + NAM) and amino acid side chain

Encloses cytoplasm of the cell Mainly phospholipids (amphipathic) Lipid bi-layer (fluid mosaic model) o Polar head (hydrophilic) o Non-polar tail (hydrophobic) Protein channels through membrane

What does it do?  Permeability barrier o Prevents the leakage and functions as a gateway for transport of nutrients in and out of the cell  Protein anchor o Anchor for proteins that are important for transport o Bio energetics- electron transport chain  Production of ATP for survival o Important for chemotaxis- where are Flagel proteins are anchored o Energy conservation- site of proton motive force This makes it very valuable as a drug target- make holes in bacterial cell membrane Cytoplasm  Internal matrix of the cell o 80% water

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o Proteins, carbs, lipids Contained within the cytoplasm o DNA o Ribosomes o inclusion bodies  storerooms within the cell, that can contain protein, fat or carbs  energy reserves to ensure long term survival

Flagella  provides motility  4 possible arrangements relating to poles 1) Monotrichous (mono=one)  Single polar 2) Lopotrichous (lopho=tufted)  Two or more at one/both ends 3) Amphitrichous (amphi=both)  Single polar flagellum at each end 4) Peritrichous (peri=around)  Distributed over the entire cell flagellum structure in Gram- negative bacteria  Driven by proton motive force that causes ring to turn

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4 rings- C ring + MS ring present within the cytoplasmic membrane, P ring- small and present within the periplasm and anchored within the peptidoglycan, L ringpresent within the outer membrane

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Hook protein- creates a kink in the tail which means that the tail (made of flagellin) whips when the ring rotates o As the rings turn due to the proton motive force (proton translocation across the membrane) causes the whipping movement

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In Gram positive bacteria there is no L ring and there is a much larger P ring One of the ways that bacteria maintain homeostasis is by pumping things in and out- efflux pumps o One of the things that can be pumped out is antibiotics i.e. E. coli is a really good pathogen because it can pump antibiotics back out again

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Bacterial motility 

There are a series of runs and tumbles  If the bacterium is monotrichous (polar flagellum),you get a counter clockwise rotation of the flagellum causing the bacterium to run  the organism will then tumble within the matrix/liquid etc. and when it stabilises again, the flagella will be reactivated leading to another run.

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Peritrichous bacteria- flagella bundle together while running as they all whip in the counter clockwise rotation  Then as the electrochemical gradient resets + recover, they tumble (due to browning and motion)

Chemotaxis  Chemotaxis in response to chemical stimulus (also phototaxis, aerotaxis, osmotaxis and hydrotaxis)  If there is no stimulant, then movement is random  Positive/negative chemotaxis  Series of runs and tumbles wherein runs are extended if in direction of a chemical attractant (chemoreceptors)

Fimbrae and pili

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Fimbrae (Fimbril) Protein hooks on the outside  Allow adherence e.g. enteric bacteria (salmonella etc from food)  Pathogenicity determinant  E. coli

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Pili (Pilus) o Pillin o 1-2 per cell o Join bacterial cells during transfer of DNA (bacterial sex - HGT)

Bacterial Genome  Chromosome o Single long circular molecule of dsDNA o No envelope (Prokaryotic cell)  Plasmid(mobile genetic elements) o Can exist in multiple copies o Replicate independently o Not critical for bacterial survivalbut can contain genes that are advantageous i.e. antibiotic resistance o Transferable (via bacterial sex) Conjugation (Bacterial sex)

genetic infomation into becteria that can transform them into other things or change the way they work

Horizontal gene transfer (HGT)  Another way bacteria can take up genetic information 3 types  Transformation o Do things chemically which disrupt the cell wall allowing for DNA present in the environment to be taken up by the bacteria

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Ribosomes Involved in protein synthesis 2 subunits  30S  50S  =70S  Eukaryotes 80S Target for antibiotics  Streptomycin  Neomycin  Tetracyclines  Macrolides

Inclusion Bodies  Reserve deposits  Volutin  Phosphate store  Glycogen  Polysaccharide store  Lipids Bacterial Endospores 

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o This can be done by heat shock Conjugation (bacterial sex) Transduction o Can occur by viruses/ bacteriophages which insert

Gram positive bacteria  Clostridium  Bacillus These 2 are the most common that sporulate readily Position  Terminally (at one end)  Sub-terminally (near one end)  Centrally  Size - can be bigger (Clostridium) or smaller (Bacillis) than bacteria Not a reproductive process

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1 spore - 1 vegetative cell

Germination- “out of spore’ - Going from the spore back to the vegetative cell

 Releases botulinum toxin (botulism)  Inhibits release of acetylcholine  Flaccid paralysis  Clostridium tetani  Inhibits removal of acetylcholine Spasmic paralysis Endotoxins  Outer cell wall of Gram negative bacteria  Lipid portion of LPS  Lipid A  Released upon cell lysis  Symptoms  Same regardless of species  Severity variable  Fever, weakness, general aches, LPS toxic shock

Toxins 2 types: 

Exotoxins o Mostly produced by Gram positive bacteria o Produced inside bacteria as part of growth o Then release them

• endotoxins o Constituent if cell wall of Gramnegative microbes o Toxin is released after the bacterium has been killed Exotoxins  Protein molecules o Active (A) subunit o Binging (B) subunit  Mainly produced by Gram positives  Highly specific  Soluble in blood o Rapid transmission  Rapid onset of symptoms Classic exotoxin producers  Clostridium botulinum...