L6 Flashcards
What are prokaryotic cells and what do they contain and what is there function?
Contain free floating genetic material, mesosome (organelle of bacteria) invagination of the plasma membrane functions either in DNA replication and cell division or excretion of exoenzymes.
What do eukaryotic cells contain?
True nucleus, membrane-bound organelles of bacterial ancestry
What are the 3 type of shapes of prokaryotic cells?
Spherical, rod, spiral
What are the 4 type of shapes of archaeal cells?
Bacillus or rod, A branched, coccus, square shape
What is the structure of the prokaryotic envelope?
Cell membrane, cell wall, outer membrane (only in gram-negative bacteria)
What is the function of the prokaryotic envelope?
Maintain shape, provide protection, prevent bursting/rupture in hypotonic environment
Prokaryotic cell envelope - what is the cell membrane?
Bacterial phospholipid bilayer - a glycerol-phosphate head is attached to a fatty acid. The cell membrane is not enough protection for prokaryotes however. It is vulnerable to chemical due to lipid nature. So prokaryotes surrounds the cell membrane with a cell wall. And in gram-negative bacteria with an additional outer membrane.
Prokaryotic cell envelope - what is the cell wall?
Consists of murein, a type of peptidoglycan. Glycan chains are made of alternative units of N-acetylglucosamine and N-acetyl muramic acid connected by a beta 1-4 glycosylic bond. Glycan chains are cross linked together via a small peptide attached to each N-acetyl muramic acid unit. Lysosomes break the beta 1-4 linkages between N-acetyl muramic acid and N-acetyl-D-glucosamine.
Prokaryotic cell envelope - what is the gram positive cell?
Bacteria can be grouped as gram-positive. The cell wall of a gram-positive cell is surrounded by a thick cell wall made up of peptidoglycan/murein. Techoic acids give the cell wall rigidity and helps gram-positive bacteria adhere to surfaces. The thick cell wall of peptidoglycan is not as secure a defense for the gram-positive as you might think.
Prokaryotic cell envelope - what effect do b-lactams have on the gram positive cell?
B-lactams are a class of antibiotics that inhibit peptidoglycan synthesis. They bind and inactivate the enzyme that assembles peptidoglycan chains and bonds the peptides of the peptide Glycan layers to each other. Without an active enzyme the cell wall cannot be remodelled as the cell grows, the cell wall weakens so much that the internal osmotic pressure eventually causes the cell to burst.
Prokaryotic cell envelope - what is the gram negative cell?
Cell membrane is surrounded by a thin cell wall and also am outer membrane.
Prokaryotic cell envelope - how are gram positive and gram negative differentiated?
Staining of cells. Thickness of cells as well as gram-positive stain purple and gram-negative stain red.
How to complete a gram stain?
Application of crystal violet dye, application of iodine, alcohol wash (dehydrates peptidoglycan layer), application of safranin (counter stain to visualise decoloirised gram negative).
Prokaryotic cell envelope - what is the outer membrane?
Only in gram-negative, asymmetric bilayer with a lipolysaccharide (LPS) outer layer and a phospholipid inner layer. LPS is lipid modified with sugars. Each LPS - one glycolipid, polysaccharide core, long carbohydrate chain (o antigen) confers hydrophobicity to the membrane.
Prokaryotic cell envelope - what is the outer membrane O antigen?
Very immunogenic, elicits a strong antigenic response in in vertebrates. Made up of varying numbers of repeating units. Not all gram-negative bacteria have O antigen. Even without the O antigen the outer membrane of gram-negative bacteria is an effective barrier. However this can make nutritent uptake difficult.
What are porins?
Protein channels in the membrane of gram-negative bacteria. Mediate the diffusion of hydrophilic compounds.
What is the periplasm?
Aqueous/gel-like space between the cell membrane and the outer membrane. The murein layer is found within this space.
What does the periplasm contain?
Degradative enzymes that break down molecules so they can be transported across the inner membrane. Proteins with affinity for sugars and amino acids that equip the cell to soak nutrients from the growth medium. B-lactamases which protect the cells by inactivating antibiotics.
What is the other kind of outer membrane (bacteria)?
Some bacteria do not have an outer membrane made of LPS. Instead they have waxes called mycolic acids. These mycolic acids orient themselves in lipid bilayers. Porins are embedded in the mycolic acid bilayer. Mycolic acid bilayers are attached to peptidoglycan cell wall via complex sugars.
What are acid-fast bacteria?
Bacteria with an outer membrane of mycolic acids. Mycolic acids make mycobacterium tuberculosis colonies looks like yellowish lumps of wax. Myco = fungus because of the way colonies grow. These bacteria are resistant to harsh chemical as the outer membrane is hydrophobic. They cannot be studied with gram stain.
How do you stain acid-fast bacteria?
Stain with carbon fuchsin in the presence of heat. Any bacteria can be stained with it. Wash with a mixture of acid and alcohol to decolorise all but acid fast cells. Counterstain with methylene blue to show cells that are not acid-fast. Acid-fast bacteria remain red. Non-acid-fast bacteria turn clear then are stained blue.
What are mycoplasmas?
Some bacteria do not have a cell wall, only a cell membrane. Mycoplasmas have sterols in their cell membranes to make them more rigid and tougher. Because mycoplasmas do not have peptidoglycan, B lactam antibiotics do not affect them
What are additional exterior layers and appendages that some bacteria and archaea can make?
Capsules and slime layers, flagella, Pili.
What are capsules/slime layers?
Many prokaryotes surround themselves with a coat of slime. This layer is made up of high-molecular polysaccharides or polymers of amino acids. When the coat is attached to the cell it’s called capsule and when it is loose it is called slime layer. Only produced in response to certain environmental cues. Helps microbes retain water and nutrients and resistant to diffusion of chemicals. Also helps adhesion to surfaces and build multicellular communities = biofilms. Which acts as a line of defence against WBCs.
What is the flagellum/a?
Many prokaryotes are propelled through liquids and wet surfaces by the action of extracellular filaments, flagella. Mobility is important for virulence and biofilm formation. The flagellum have : a long filament, connecting hook, basal body.
What is the flagellum/a filament?
Helical, rigid, hollow and composed of a single protein flagellin. Flagellin is very antigenic.
What is the flagellum/a hook?
Joint between the filament and the basal body. Made of a single protein, hook protein.
What is the flagellum/a basal body?
Is a rod with attached rings, the rings anchor the structure to the cell envelope while allowing the rod to rotate. Consists of different proteins.
What is the pilus/pili?
Hair. Allow the cell to attach to hosts and other surfaces, transfer proteins and nucleic acids, and move. Most commonly mediate attachment via adhesins to surfaces such as mucosa. Help cells to escape attack by WBCs, resist engulfment phagocytosis. Very antigenic, made of pilins, Pili common in gram-negative bacteria.
How does the Pili twitching mobility work?
Pili extend and retract by adding or removing a pilin to the base of the pilus. The tip of the pilis touches the surface, the adhesins at the tip of the pilus adhere the cell to the surface. The Pilus depolymerises its bases the shortening of the pilus drags the cell forward.
