Exam 1: Ch 3: Prokaryotes Flashcards
3 characteristics that help differentiate prokaryotes from eukaryotes:
− The way their DNA is packaged (lack of nucleus and histones) (have way less DNA b/c histones help eukaryotes pack DNA tightly)
− The makeup of their cell wall (peptidoglycan and other unique chemicals)
− Their internal structure (lack of membrane bound organelles)
Bacterial chromosome
has all the DNA that makes the bacteria functional
Actin cytoskeleton
helps w/structure and movement
Fimbriae
can attack/will make bacteria more pathogenic
Plasmid
luxury DNA
Prokaryotic cell contents
− All bacteria have: membrane, bacterial chromosome, ribosomes, actin cytoskeleton, cytoplasm
− Some bacteria have: fimbriae, outer membrane, cell wall, pilus, capsule, inclusion, plasmid, flagellum, endospore, intracellular membranes ← all of these things (except inclusions) have the ability to make bacteria more pathogenic
Prokaryotic cell size
most are very small (0.5-2.0 um in diameter); large surface to volume ratio for nutrients to enter cell quickly → can release things much faster (use diffusion)
Prokaryotic cell shape
coccus (sphere), bacillus (rod), spirillum, spirochete, vibrio (spiral)
Prokaryotic cell arrangement
diplo- (pairs), strepto- ( strip), staphylo- (cluster like ppl at a staff meeting)
Prokaryotic cell organization
− External o Appendages: flagella, pili, fimbriae o Glycocalyx: capsule, slime layer − Cell envelope o Cell wall o Membranes − Internal o Cytoplasm o Ribosome o Inclusions o Nucleoid/chromosome o Endospore o Plasmid
Flagella
bacterial locomotion; comprised mainly of proteins; 360 degrees rotation
− ~50% of bacteria have it
− Function: motility, chemotaxis – can chemotax toward or away from substances or cells (like WBCs) using “run and tumble motions”
Testing for flagella
− Testing for flagella: semi solid media, staining the flagella, hanging drop
o Hanging drop method – drop of liquid w/specimen hanging upside down from undersurface of coverslip
• Bacteria are alive so we can see motility; difficult to visualize since microbes are not stained
• Motile bacteria will flit and dart around in the drop
• Non-motile bacteria will wobble back and forth but make no progress away from a stop
Pili
allow bacteria to attach to surfaces or to other bacteria
two types: conjugation pili & fimbriae (attachment pili)
Conjugation pili
bacteria attach to each other w/conjugation pili and transfer plasmids (mini chromosomes) down the pilus
Fimbriae
(attachment pili) – facilitates attachment to other bacteria, surfaces and other types of cells (such as RBCs)
o Can be involved w/formation of a biofilm
Glycocalyces
“sugar coat” comprised of polysaccharides and protein; varies in thickness
− Used to: avoid phagocytosis and for adhesion (biofilms)
− Two varieties:
slime layer & capsule
Slime layer
unorganized loose thin glycocalyx; promote adherence to surfaces; protects cells from drying out, traps nutrients & binds cells together; important in biofilm production
Capsule
organized, tightly packed, thick glycocalyx; prevents phagocytosis of bacteria by WBCs; cloaking device – hides the bacteria from the immune system → more likely to infect
• Capsid: bound more tightly to the cell, denser and thicker than slime layer; visible by negative staining; produces a sticky (mucoid) character to colonies
o Encapsulated bacterial cells generally have higher pathogenicity b/c they can hide from the host’s immune system
Biofilms
glycocalyces (slime) and fimbriae (attachment)
− Formation: First colonists stick to surface → as cells divide, they form a dense mat bound together by sticky extracellular deposits and sometimes fimbriae
− Fimbriae also act to attach bacteria together in a biofilm
− Once they attach → start making genes to make slime → create their own environment → building apartment complex → make it livable for other bacteria → layers of different environments form
Cell membrane
forms a boundary btwn inside and outside of cell
− Highly selectively permeable – regulates chemicals that enter and exit the cell
− Contains respiratory enzymes which enable the membrane to capture or harness cellular energy in the form of ATP
− Structure: similar to eukaryotic cells; fluid mosaic model w/phospholipids in a “fluid” dynamic bilayer and proteins arranged in “mosaic” model
Fluid mosaic model (cell membrane)
described as fluid b/c molecules are able to move; described as mosaic b/c it is made up of many different kinds of components