lecture 4 - prokaryotic cell structure Flashcards
cell
fundamental unit of life
cell characteristics
- spherical or cylindrical
- cytoplasmic membrane
- chromosomes (DNA)
- ribosomes for protein synthesis
- reproduce to form progeny cells
- obtain energy from environment
Bacterial cell structures
all: cell membrane, cytoplasm, ribosomes, chromosomes
most: cell wall, surface coating (glycocalyx)
some: flagella, pili, fimbriae, capsules, slime layers, endospores
what is the cytoplasm
Gelatinous solution (proteins)
Site for many metabolic activities
70%-80% water
Also contains large cell masses (ex: chromatin, ribosomes, granules)
how do chromosomes fit into cell
lots of DNA is packed into cell, some are “lysed” to let DNA escape out of cell so it isn’t so cramped
-it is compacted by twisting (supercoiling) and protein binding
characteristics of bacterial chromosomes
-single circular DNA strand located in the nucleotide (dense area of cell)
what s the cell envelope?
combination of cell membrane and wall
- protects cell and contains cytoplasm
- site of metabolic processes
- gram - bacteria have two
what are the functions of the cell membrane
- Energy reactions (ATP synthesis; proton and ion gradients)
- Regulates transport (selectively permeable membrane)
- Secretion
gram + bacteria structure
2layers
Cell membrane
Thick cell wall (peptidoglycan)
-Cell wall anchored to membrane and covered with sugar on the outside used to repelle water, and things you don’t want, helps with infection
Gram - bacteria structure
3 layers
- outter membrane
- -Long sugar filaments extend from outside (lipopolysaccharides)
- inside is phospholipid layer which is anchored to peptidoglycan layer by lipoproteins
- has porin proteins for access into cell
- only small molecules to penetrate
- extra layer of protection that substances have to get through - Thin cell wall (peptidoglycan)
- Cell membrane
characteristics of lipopolysaccharides
-located on Outer layer of the outer membrane
Three domains:
- Lipid A (endotoxin - signals infection)
- Core polysaccharide
- O Antigen
what is the significants of the o antigen of lipopolysaccharides?
O antigen is the dominant antigen of Gram negative cells
V. cholerae O139
Caused epidemic in india in 90’s
O1 pandemic strain
E. coli O157
what does the cell wall do?
determines shape, provides structural support
-made of 1 cell peptidoglycan = sugar (glycan) and protein (peptide)
-when antibiotics target this cells pop because no structure or support - “lysis”
what is a flagellum?
- propeller for swimming
- driven by proton motive force
- +/- chemotaxis and phototaxis
- rotates rapidly
- three parts: Filament (tail), hook (where it attaches), and basal body (motor)
- vary in number and arrangement
how do bacteria move?
Flagellum can only propel when rotating counterclockwise
Tumbles (stops)
Runs (moves)
Speed:
Spin rate
Spin duration
“steering” is accomplished by running more than tumbling when it gets close to attraction
fimbriae
used for attachment
- allow to stick to things
- smaller than flagellum - short pills
- can be 1000/ cell
-stick to one another to form bridge in HGT conjugation
pili
used for:
- attachment
- genetic exchange (plasmids)
- Motility (slow spiderman webgrab/ swing)
- Very important for infection and interactions with host
glycocalyx slime layer
a loose shield that protects some bacteria from loss of water and nutrients
glycocalyx capsule
when the glycocalyx is bound more tightly to the cell and is denser and thicker
Ex) staphoccocus psnmonia has capsule to invade
in general what types of bacteria usually have glycocalyx and why?
- pathogenic bacteria
- Capsule protects bacteria against phagocytosis by immune cells
-slimyness can determine pathogenicity
virulence
Ability of a microbe to cause disease in another organism
virulence factor
Microbial components that contribute to the ability to cause disease in a susceptible host
- what is virulence factor for one organism may be a colonization factor for another (good vs bad bacteria)
example: fili, fimbriae, capsules, flagella are used by commensals and pathogens
how do bacteria survive in hosts
-Blocked phagocytic response: Bacteria escape and persist ***CAPSULES
Immune system can subsequently overreact when body can’t clear the bacteria
how do microbes get into host cells?
Exoenzymes: break down and inflict damage on tissues OR dissolve host defence barriers
Examples Mucinase Keratinase Collagenase Hyaluronidase
toxigenicity
ability to produce toxins
-weaken host, damage tissue
toxinoses
a variety of diseases caused by toxigenicity
toxemias
toxinoses in which the toxin is spread by the blood from the site of infection (ex: tetanus and diphtheria)
intoxications
toxinoses caused by ingestion of toxins (botulism)
- Not infected
- Toxins can be very species specific in target
what is the difference between exotoxins and endotoxins?
Eco - excreted by bacterium, target organs are damaged
endo: accidental ;not produced by bacteria. LPS (gram -)
how do antimicrobials work?
- drugs Disrupt the cell processes or structures of bacteria, fungi, and protozoa / stop viral replication
-interfere with the function of enzymes required to synthesize and assemble macromolecules
or, destroy structures already formed in the cell
selectively toxic
GOAL
drugs kill or inhibit microbial cells without damaging host tissues
where do antibiotics come from?
metabolic product of aerobic bacteria and fungi
-chemists alter structure of natural antibiotics to form new antibiotics
how do antibiotics target cells?
cell wall inhibitors cell membrane inhibitors metabolic inhibitors DNA replication inhibitors RNA Polymerase inhibitors protein synthesis inhibitors
minimum inhibitory concentration (MIC)
The lowest concentration of antibiotic at which a species can’t grow
-when antibiotics are used at incorrect MIC levels that bacteria isn’t killed results in evolution of resistance
