prokaryotic cell structure Flashcards
(36 cards)
what is a microorganism
microorganisms are living things which in general, are too small to be seen with the naked eye and can be viewed only with the aid of a microscope
morphology of bacteria
cocci - spherical
bacilli - rod shaped
spirals/curves
coccoid bacteria
spherical shaped
monococci - single cocci
diplococcus - paired cocci
sarcina - cubically packed cocci
staphylococcus - grouped cocci
streptococcus - chained cocci
bacilli
ROD SHAPED
short, long, curved, and chained rods
filamentous bacteria
colony characteristics
diameter
edge
colour
rise
bacteria components
must be able to give structure and function
- genome
- ribosomes
- cell membrane
- cell wall
- surface layer
what is the structure of the bacterial genome?
the bacterial genome is composed of DNA or RNA arranged within the cytoplasm of the cell.
bacterial genomes contain a singular chromosome, with additional pieces of small circular DNA called plasmids.
what is the function of the bacterial genome?
the bacterial genome controls all the activities of the cell.
the bacterial genome is essential for reproduction and directing protein synthesis.
what is the structure of the ribosome?
ribosomes are found free in the cytoplasm of bacteria.
ribosomes are composed of two subunits - the large and the small subunit, which are both needed for translation.
the small subunit decodes the genetic message.
the large subunit catalyses peptide bond formation.
what is the function of the ribosome?
the ribosome is a cell organelle responsible for protein synthesis and are the site of translation.
what is the structure of the bacterial cell membrane?
the bacterial cell membrane is a thin (5-10nm) phospholipid bilayer, which does not typically contain steroids.
what is a phospholipid?
a phospholipid is an amphipathic molecule with a hydrophilic phosphate head group and hydrophobic saturated or monounsaturated fatty acid tails.
what is the function of the bacterial cell membrane?
the bacterial cell membrane is a selectively permeable barrier that separates the cytoplasm from the bulk environment.
the bacterial cell membrane contains integral membrane proteins
what is a mesosome?
a mesosome is an infolding or invaginations of the cell membrane that is involved with DNA replication and segregation as well as being involved with cell wall synthesis.
mesosomes have a role in respiration and photosynthesis.
what is the structure of the bacterial cell wall?
the bacterial cell wall is a rigid structure that contains the cell membrane.
the structure of the cell wall is categorised as Gram positive and Gram negative, which is decided based on the colour of the cells following Gram staining.
the cell wall contains peptidoglycan.
what are characteristics of Gram positive cell walls?
Gram positive cell walls stain purple.
Gram positive cells have thick cell walls as they contain several layers of peptidoglycan.
in Gram positive cells, the periplasmic space is usually absent or very small as there is more peptidoglycan present.
Gram positive cell walls contain teichoic acids.
what are teichoic acids?
teichoic acids extend to the surface of peptidoglycan and give the cell wall a negative charge since teichoic acids are negatively charged.
occassionaly teichoic acids are anchored to the plasma membrane - these are called lipoteichoic acids.
teichoic acids aid attachment of bacterial cells to tissues.
examples of Gram positive bacteria.
bacillus
streptococcus
clostridium botulinum
lactobacillus
what are the characteristics of Gram negative cell walls?
Gram negative cell walls stain pink, as their cell wall structure is unable to retain the crystal violet stain instead being stained by the safranin counterstain.
Gram negative cells have thin walls as they contain very little peptidoglycan. Gram negative cell walls have an outer membrane and periplasmic space as there is less peptidoglycan present.
Gram positive cell walls lack teichoic acids but contain lipopolysaccharides (LPS)
what are lipopolysaccharides (LPS)?
LPS are located mainly on the outer surface of the outer membrane.
LPS is known as an endotoxin which plays a role in infection by Gram negative bacteria.
Lipid A is the toxic component of endotoxin.
LPS determines virulence.
examples of Gram negative bacteria.
E.coli
salmonella typhi
shigella boydii
helicobacter
what are the properties of peptidoglycan?
peptidoglycan is a cross linked sac-like network that is strong, elastic and porous.
peptidoglycan is involved in shape and integrity.
the basic structure of peptidoglycan is the same in both Gram positive and Gram negative cell walls the only difference is the quantity of peptidoglycan present.
antibiotics such as penicilin and enzymes such as lysozyme can break down peptidoglycan - breakdown of peptidoglycan causes cell lysis as the peptidoglycan prevents over expansion of the cell membrane - Gram positive cells are more susceptible to this as they contain a greater amount of peptidoglycan.
bacteria without cell walls
mycoplasms are a group of bacteria that lack a cell wall, they have sterol-like molecules incorporated into their membranes and usually inhabit osmotically-protected environments.
sometimes under the pressure of antibiotic therapy, pathogenic streptococci stop growing their cell wall - when antibiotic therapy is withdrawn the can regrow their cell wall and reinfect unprotected tissues.
what is the function of the bacterial cell wall?
the bacterial cell wall give the bacterial cell shape.
the bacterial cell wall provides protection from osmotic lysis and toxic substances.
the bacterial cell wall plays a role in cell division and motility.
the bacterial cell wall of pathogenic bacteria have components which contribute to pathogenicity.
the bacterial cell wall is the site of action of many antibiotics.
