prokaryotes- cellular structure Flashcards
what are the components of bacterial cells?
cell wall
cell membrane
ribosomes
genome
surface layer
pilli
flagella
capsules and slime layers
what is the bacterial cell wall?
a rigid structure that contains the cell membrane
contains peptidoglycan
gives bacterial cell shape
provides protection from osmotic lysis and toxic substances
plays a role in cell division and motility
pathogenic bacteria have components which contribute to pathogenicity
site of action of many antibiotics
categorised as Gram-positive or Gram-negative dependent upon the colour retained following Gram-staining
Gram-positive cell walls
stain purple
have thick cell walls as they contain several layers of peptidoglycan
periplasmic space is usually absent or very small.
contain teichoic acids
Gram-negative cell walls
stain pink
have thin cell walls as they contain very little peptidoglycan
have an outer membrane and periplasmic space
contain lipopolysaccharides
peptidoglycan
involved in shape and integrity
teichoic acids
provides negative charge
aid attachment of bacterial cells to tissues
lipopolysaccharides (LPS)
an endotoxin which contributes to infection by Gram-negative bacteria (lipid A)
determines virulence
what is the bacterial cell membrane?
a thin (5-10nm) phospholipid bilayer which does not typically contain steroids.
is a selectively permeable barrier that separates the cytoplasm from the bulk environment
contains integral membrane proteins
phospholipid
an amphipathic molecule with a hydrophilic phosphate head group and hydrophobic saturated or monounsaturated fatty acid tails.
mesosome
infolding of the cell membrane that is involved with:
> DNA replication and segregation
> cell wall synthesis
> respiration
> photosynthesis
bacterial ribosomes
found free in the cytoplasm of bacteria
composed of two subunits (small and large) both of which are needed for translation.
> small subunit - decodes the genetic message
> large subunit - catalyses peptide bond formation
the cell organelle responsible for protein synthesis and are the site of translation
bacterial genome
composed of DNA or RNA arranged within the cytoplasm of the cell
contain a singular chromosome, and, additional pieces of small circular DNA called plasmids
controls all activities of the cell
is essential for reproduction and directing protein synthesis
what is the function of the surface layer/outer membrane of bacteria?
presents an outer surface with a strong negative charge to help evade phagocytosis
is a permeability barrier that allows passage of nutrients via porins
is a receptor for the F-pilus
is an attachment site for viruses
what is pilli?
a short, fine, hair-like structure composed of the protein pilins that are 3-10nm in diameter found on the surface of bacterial cells.
common pilli
involved in attachment
F/sex pilus
involved in bacterial conjugation which is the transfer of genetic information from one prokaryotic cell to another prokaryotic cell through direct contact.
what is flagella?
composed of three parts: the filament, the basal body, and the hook.
allow a swimming cell movement or motility
the filament (flagella)
the largest part of the flagellum which extends from the cell surface to the tip of the flagellum
the basal body (flagella)
anchors the flagellum in the cell via the plasma membrane and peptidoglycan
composed of a system of rings
the hook (flagella)
a short, curved segment linking the basal body to the filament.
what is the function of capsules and slime layers?
aid in attachment of bacterial cells to surfaces
protect bacterial cells from engulfment by protozoa and by white blood cells (phagocytosis) aiding pathogenicity
protect against attack by antimicrobial agents
protect bacterial cells against desiccation
exclude viruses and other toxic materials e.g. detergents.
morphology of bacteria
spherical > cocci
rod-shaped > bacilli
spirals/curves
coccoid bacteria
single cocci > monococci
paired cocci > diplococcus
cubically packed cocci > sarcina
grouped cocci > staphylococcus
chained cocci > streptococcus
