MICROBIOLOGY LEC. 3

MICROBIOLOGY LEC. 3

Question Answer
Some distinctions of a Prokaryote: One circular chromosome, not in a membrane. No histones, no organelles, Bacteria: peptidoglycan cell wallsArchaea: pseudomurein cell walls. Divides by binary fission.
Some distinctions of a Eukaryote: Paired chromosomes, in nuclear membrane, histones, organelles, polysaccharide walls, when present. Divides by mitosis.
Structure of Prokaryotes: Appendages on outside: flagella and Pili (fimbriae)Capsule and envelope: outer membrane (G-only). Periplasm (G-) between two membranes. Contains a cytoplasm consisting of a nucleoid, ribosomes and storage granules.
Shapes of Bacteria: Determined by heredity.
Most are monomophic: they maintain a single shape.
What are pleomophic: have many different shapes due to environmental factors changing the shape of them.
definition of diplcocci: cocci that remain in pairs after dividing.
definition of streptococci: Divide and attach and chain like structure.
definition of tetrad: divide in two groups and remain in groups of 4.
definition of Sarcinae: divide in three planes and remain in cube like structure.
definition of Staphylococci: Divide in grapelike structures and form clusters.
Cell Wall general information: prevents osmotic lysis, determines shape, and made of peptidoglycan.
Glycocalyx: Secreted on the surface. sticky polymer that is external to the cell wall and is composed of polysaccharide and peptide. Made inside cell, and secreted to outside. If firmly attached we call it a capsule.
How to determine if a capsule is present? gram staining.
what if the glycocalyx is loosely attached? we call it the slime layer.
Peptidoglycan information: a sugar, Polymer of Disaccharide N acetyglucosamine (NAG) and N acetylmuramic acid (NAM). Cross linked by short chain of aa (peptide). Forms dynamic, mesh like girdle around the cell.
Describe Gram Positive cell walls: Gram positive: Thick peptidoglycan wall. Contains Teichoic Acids (alcohol and phosphate), in acid fast cells, contains mycolic acids which is a waxy substance
Describe Gram negative cell walls: Thin peptidoglycan (as mono layer), no teichoic acids, outer membrane (LPS layer). Contains periplasm: psychical volume between the membrane. Periplasm is a gel like fluid in the perplasmic space that sits between the plasma membrane and the outer membr.
Why doesn't gram negative cells have a periplasm? cell walls of gram negative bacteria contain only a small amount of peptidoglycan and are more susceptable to mechanical breakage.
Describe outer membrane of gram negative cell wall: Lipopolysaccharides, lipoproteins and phospholipids . Specialized function. Its strong negative charge is important in preventing phagocytosis. E Coli 0157:H7.
Negative cell wall Lipid A: Endotoxin which when released upon cell death causes edema, and septic shoc.
Gram staining positive mechanisms: Crystal violet idoine crystals form in cell. Alcohol dehydrates thick peptidoglycan and CV I2 crystals leave, making it more permeable to crystal violet iodine. Pink color is masked by the remaining crystal violet left.
Gram staining negative mechanisms: Gram negative: Alcohol dissolves outer membrane and leaves holes in the peptidoglycan. CV I2 washers out. Making the cell pink when safranin is added as counter stain.
What are some examples of Atypical cell walls?Mycoplasms and Archaea and Lysozymes. Mycoplasmas: Lack cell walls (genetic), sterol in plasma membrane provide stability. Smallest known bacteria that can grow and reproduce outisde living cells. Archaea: Wall less or walls of pseudomurein (lack NAM and D amino acids.) Appear gram negative
Define Flagella: Long filamentous appendages that propel bacteria. Can be at one end or throughout entire cell. peritrichous (throughout) and polar (at one end.)
Structure of Flagella: 1) long outermost region, filament: constant in diameter and contains protein flagellin arranged in chains.2) Hook: attached to filament, consisting of a different protein.3) Basal body: anchors the flagellum to the cell wall and plasma mb.
Flagella in mobility: the bacteria can change the speed or mobility of the flagellum depending on the situation.
Flagella in Taxis: a bacteria moving toward or away from a particular stimuli.
Fimbriae: shorter, straighter, and thinner than flagella. Consist of protein called pilin arranged helically around core. Fimbrae can occur at the poles of bacteria or evenly distributed. Adhere to each other or other surfaces. looked at gonorrhoeae as example.
What happens without fimbriae? the bacteria cannot pile together, thus resulting in no disease.
Pili: usually longer than fimbraie. one or two per cell. motility and DNA transfer. gliding motility causes a smooth gliding of the bacteria.
cojugation pili: bring bacteria together allowing the transfer of DNA.
Motile Cells: Combine to form larger propeller. Bacteria runing and tumble. Direction of flagellar rotaition determines which of these movements occurs.
Prokaryotes: movement:Chemotaxis, phototaxis, aerotaxis, magnetotaxis chemotaxis: sense chemicalsphototaxis: sense light intensityaerotaxis: favorable oxygen concentrationsmagnetotaxis: move along magnetic lines.
Explain bacterial motility: running: counterclockwise (CCW) spin=swimming motion for a few seconds. propelled by flogella working unison.tumble: clockwise (CW) spin=cell stops and tumbles in place <1 second. flagella loosen apart and flail about then run resumes in new direction.
Chemotaxis: Biased, random walk. Motile cell senses favorable nutrients or chemical, receptor proteins on cell membrane. Run toward higher concentration–>tuble is delayed for a few seconds. (longer run). move away from higher conc=norm
Chemotaxis continued: cells accumlate in area of higher concentrations=chemotaxis. Repellants cause longer runs away from concentration.
Chemotactic Bacteria: Detect chemicals (sensory cells like taste or smell). Can detect change in gradient during time of run.
Axial Filaments: Endoflagella, in spirochetes/ anchored at one end of a cell, rotation causes cell to move.
Cytoplasmic membrane: Surrounds the cytoplasm, regulates passage into and out of the cell (transport). Components consist of phospholipid bilayer, proteins and membranec fluid.
Cytoplasm: 85% water but no flfuid as in eukaryotes, more gel like. Nucleoid: no histone proteins, region contains circular dsDNA, Ribosomes: 70s. Site of protein synthesis.Inclusion bodies:Internal storage. Store for later when needed.
Ribosomes: prokaryotic ribosomes are called 70s ribosomes. small subunit 30s + large subunit 50s = complete 70s ribosome
Inclusion types: metachromatic granules: phosphate reservespolysaccharide granules: energy reserve such as glycogenLipid inclusion: energy reserves (oil)Sulfur granules: energy reserves.gas vacuole: buoyancy – protein covered in cylindersmagnetosomes–>iron oxid
Endospores: result of deplete gram positive bacteria. resting cells. Endospores can survive extreme condition such as heat, lack of water, and exposure to chemicals and radiation.
sporulation: endospore formation. begins when carbon or other nutrient becomes scarce. Can survive for over 100 years.
germination: returns to vegetative state. occurs after exposure to heat or chemicals and occurs only in good growth conditions.

Leave a Reply

Your email address will not be published. Required fields are marked *