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
Concentration gradient (cell membrane)
difference in concentration of molecules in one area compared to another; Brownian motion: all the molecules in your body/everywhere are constantly vibrating
Tonicity (cell membrane)
animal always wants an isotonic solution
Selective permeability (cell membrane)
selective about what crosses based on: size, electrical charge, other properties
Osmosis (cell membrane)
type of passive diffusion that moves water across a selectively permeable membrane from an area of lower solute concentration to an area of higher (Brownian motion); does NOT involve movement of solutes
o Maintaining a proper water balance is vital for every cell
Cell wall
supports the shape of the cell and prevents osmotic lysis; external to cell membrane
3 types: gram +, gram -, acid fast/waxy/myobacteria
Peptidoglycan
repeating framework of long glycan (sugar) chains cross-linked by short peptide (protein) fragments; provides cell wall strength to resist rupturing due to osmotic pressure; very strong structure; synthesis inhibited by penicillin (lyses cell)
Gram + cell wall
components: peptidoglycan, membrane proteins, cell membrane, envelope, lipoteichoic acid, wall techoic acid
many layers of peptidoglycan; thick layer of it; one plasma membrane
• Techoic acid – function is unclear; binds w/crystal violet and iodine to form insoluble complex in gram stain (positive = purple)
• Envelope of gram positive bacteria has one cell membrane
• The thick layer of peptidoglycan is what protects the cell from the high level salt in MSA
• The 4 P’s:
1. Positive – gram pos cells
2. Peptidoglycan – have many layers
3. Purple – stain purple in gram stain
4. Penicillin – susceptible to penicillin b/c it targets the many peptide crosslinks in peptidoglycan
Gram - cell wall
components: peptidoglycan, membrane proteins, cell membrane, outer membrane layer, porin proteins, LPS, phospholipids, lipoproteins, periplasmic space
few layers of peptidoglycan; thin layer of it; outer membrane has LPS
• Has 2 membranes: cell membrane (same as gram pos) + an outer membrane → much more resistant to antibiotics and some other chemicals than gram pos b/c of the outer membrane
• Lipopolysaccharides
Lipopolysaccharides
(Lipid A + polysaccharide) –
• Endotoxins - cause fever and shock: O-antigen is recognized by host and initiates immune response
Acid fast/waxy/myobacteria
have cell walls composed of mycolic acid (a waxy lipid); very protective cell walls
• Use the acid fast stain to characterize mycobacteria – the stain requires heating the stain to penetrate thru the cell wall
• Difficult to disinfect and treat due to cell wall composition (Myobacteria tuberculosis, Myobacteriia leprosae)
Cytoplasm
cytosol and all the structures in the cell; site of metabolism (the buildup and breakdown of molecules)
− Cytosol – gel like, water based fluid in cell; ~80% water
Ribosomes
protein synthesis (little protein production factories); composed of rRNA and protein − Bacterial ribosomes similar to eukaryotic except bacteria have 70S ribosomes and eukarya have 80S ribosomes (units for size, eukarya are larger) − Fungus (eukarya) attacl bacteria by going after their ribosomes – inhibit protein synthesis
Inclusions
store viruses; burst open → viruses enter environment
Nuclear region
(b/c there is no nucleus)
− Nucleoid – mostly DNA; contains one circular chromosome
− Plasmid – mini chromosome that contains non essential “luxury” DNA
Endospore
not a cell structure but a cell state…
− Some bacteria have ability to produce endospores, resting stages
− Structure: DNA + spore coat (extremely tough) + small amt of cytoplasm
− Function: allow bacteria to survive adverse conditions (heath, lack of water, disinfectants for thousands of years); difficult to sterilize and present huge problem in hospitals
− Life cycle: vegetative cell (infects the host) → can live in an unlivable environment for awhile in vegetative state → transform into endospore → hangout until it becomes livable enough to infect
o Dormancy period = can be around for a long time
Unique groups of bacteria
intracellular parasites
archaea bacteria
Intracellular bacteria
intracellular bacteria must live IN host cells in order to undergo metabolism and repdroduction (they have their own reproductive ability but need to be inside host cells)
− Chlamydia
− Hard to kill off inside of cell but is still possible
Archaea bacteria
in every habitat on earth, growing in soil, acidic hot springs, radioactive waste, water, deep in the earth’s crust, in organic matter, in live bodies of plants and animals
− Don’t have peptidoglycan in cell walls
− No examples of pathogenic archaea bacteria
− Get nutrients from environmental things
Phenotypic methods of classification
− Microscopic phenotypes (ex. Staphylococcus)
− Cultural phenotypes (yellow, round, convex, mucoid colonies, etc)
− Biochemical tests
Molecular methods of classification
DNA sequence, RNA sequence, protein sequence
Species in prokaryotes
A collection of bacterial cells, all of which share an overall similar pattern of traits and 70-80% of their genes
Members of given species can show variations
Subspecies/strain/type of prokaryotes
terms used to designate bacteria of the same species that have differing characteristics
Serotype of prokaryotes
refers to representatives of a species that stimulate a distinct pattern of antibody (serum) responses in their hosts; distinct immunological pattern; what antibody is being made in the body
5 structures found in all bacterial cells
cell (cytoplasmic) membrane, bacterial chromosome (nucleoid), ribosomes, actin cytoskeleton, cytoplasm — majority have: cell wall and glycocalyx
8 specific structures found in some (not all) bacterial cells
fimbriae, outer membrane, cell wall, pilus, capsule, plasmid, inclusion, flagellum
Life functions that prokaryotic cells accomplish as a single cell
reproduction, metabolism, nutrient processing
Encapsulated bacteria
has greater pathogenicity b/c the capsule protect the bacteria against phagocytes (WBCs); phagocytes would attack and destroy thru phagocytosis, but the coating blocks the mechanisms that phagocytes use → they are free to multiply and infect body tissues
Mycolic acid
found in non typical cell wall (Myobacterium); virulent: thick waxy nature imparted to cell wall makes for a high degree of resistance to certain chemicals and dyes; the resistance is the basis for the acid fast stain used to diagnose TB (Myobacterium tuberculosis)
Mycoplasmas
bacteria that naturally lacks a cell wall; the membrane is stabilized by sterols and resistant to lysis (Mycoplasm pneumonia – walking pneumonia)
Stimulus that causes bacteria to sporulate and form an endospore
− The depletion of nutrients, especially an adequate carbon or nitrogen source
− Once the stimulus is received by the vegetative cell → undergoes conversion into sporangium → endospore
Germination of spores
(return to vegetative state) – in the presence of water and a specific chemical or environmental stimulus (germination agent) ← often an amino acid or inorganic salt
Importance of classification systems
aid in differentiating and identifying unknown species; organized prokaryotes and studying their relationships and origins
