prokaryotic cell structure

Question 1

what is a microorganism

Answer 1

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

Question 2

morphology of bacteria

Answer 2

cocci - spherical
bacilli - rod shaped
spirals/curves

Question 3

coccoid bacteria

Answer 3

spherical shaped
monococci - single cocci
diplococcus - paired cocci
sarcina - cubically packed cocci
staphylococcus - grouped cocci
streptococcus - chained cocci

Question 4

bacilli

Answer 4

ROD SHAPED
short, long, curved, and chained rods
filamentous bacteria

Question 5

colony characteristics

Answer 5

diameter
edge
colour
rise

Question 6

bacteria components

must be able to give structure and function

Answer 6

1. genome
2. ribosomes
3. cell membrane
4. cell wall
5. surface layer

Question 7

what is the structure of the bacterial genome?

Answer 7

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.

Question 8

what is the function of the bacterial genome?

Answer 8

the bacterial genome controls all the activities of the cell.
the bacterial genome is essential for reproduction and directing protein synthesis.

Question 9

what is the structure of the ribosome?

Answer 9

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.

Question 10

what is the function of the ribosome?

Answer 10

the ribosome is a cell organelle responsible for protein synthesis and are the site of translation.

Question 11

what is the structure of the bacterial cell membrane?

Answer 11

the bacterial cell membrane is a thin (5-10nm) phospholipid bilayer, which does not typically contain steroids.

Question 12

what is a phospholipid?

Answer 12

a phospholipid is an amphipathic molecule with a hydrophilic phosphate head group and hydrophobic saturated or monounsaturated fatty acid tails.

Question 13

what is the function of the bacterial cell membrane?

Answer 13

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

Question 14

what is a mesosome?

Answer 14

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.

Question 15

what is the structure of the bacterial cell wall?

Answer 15

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.

Question 16

what are characteristics of Gram positive cell walls?

Answer 16

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.

Question 17

what are teichoic acids?

Answer 17

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.

Question 18

examples of Gram positive bacteria.

Answer 18

bacillus
streptococcus
clostridium botulinum
lactobacillus

Question 19

what are the characteristics of Gram negative cell walls?

Answer 19

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)

Question 20

what are lipopolysaccharides (LPS)?

Answer 20

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.

Question 21

examples of Gram negative bacteria.

Answer 21

E.coli
salmonella typhi
shigella boydii
helicobacter

Question 22

what are the properties of peptidoglycan?

Answer 22

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.

Question 23

bacteria without cell walls

Answer 23

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.

Question 24

what is the function of the bacterial cell wall?

Answer 24

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.

Question 25

what is the function of the outer membrane of bacteria?

Answer 25

the outer membrane of bacteria presents an outer surface with a strong negative charge to help evade phagocytosis.
the outer membrane of bacteria is a permeability barrier that allows passage of nutrients via porins.
the outer membrane of bacteria is a receptor for the F pilus and is an attachment site for viruses.

Question 26

what are bacterial endospores?

Answer 26

bacterial endospores are formed by a few groups of bacteria - bacillus and clostridium.
bacterial endospores are not reproductive structures, they are highly resistant structures which enable bacteria to survive periods when the environment is hostile to growth.

Question 27

what is flagella?

Answer 27

flagella are filamentous structures composed of the protein flagellin that are attached to the cell surface.
flagella are 20nm in diameter and allow a swimming cell movement or motility.
flagella can rotate at up to 40-60 revolutions per second.

Question 28

what is the structure of flagella?

Answer 28

flagella are composed of three parts: the filament, the basal body and the hook.
the filament is the largest part of the flagellum which extends from the cell surface to the tip of the flagellum.
the basal body anchors the flagellum in the cell via the plasma membrane and peptidoglycan, and is composed of a system of rings.
the hook is a short curved segment linking the basal body to the filament.

Question 29

what is the arrangement of flagella?

Answer 29

1. polar
   one or more flagella arising from one or both poles of the cell.
2. peritrichous
   lateral flagella distributed over the whole surface of the cell.

Question 30

what is the structure of pilli?

Answer 30

pilli is a short, fine, hair-like structure on the surface of bacterial cells, that is about 3-10nm in diameter.
pilli are composed of proteins called pilins.

Question 31

what is the function of pilli?

Answer 31

the common pilli is involved in attachment.
the F/sex pilus is involved in bacterial conjugation, which is the transferring of genetic information from one prokaryotic cell to another prokaryotic cell, through direct contact

Question 32

what is a capsule?

Answer 32

a capsule is a discrete detectable layer of polysaccharides outside the bacterial cell wall.
a capsule is well organised and is not easily washed off.

Question 33

what is a slime layer (bio-film)?

Answer 33

a slime layer is less discrete, diffuse and unorganised layer easily removed from the cell.
a slime layer extends some distance beyond the cell wall.

Question 34

what is the function of capsules and slime layers?

Answer 34

capsules and slime layers aid in attachment of bacterial cells to surfaces and to protect bacterial cells from engulfment by protozoa and by white blood cells (phagocytosis) aiding pathogenicity.
capsules and slime layers protect against attack by antimicrobial agents and protect bacterial cells against desication (drying out).
capsules and slime layers exclude viruses and other toxic materials, e.g. detergents.

Question 35

what are inclusion bodies?

Answer 35

inclusion bodies are distinct granules of organic or inorganic material contained in the cytoplasm- these are usually reserve materials, e.g. glycogen granules that reserve carbon as an energy source.
some inclusion bodies are membrane bound vesicles into the cytoplasm containing photosynthetic pigments or enzymes.

Question 36

heterotrophic bacteria

Answer 36

bacteria that obtain their energy source from elsewhere
bacteria that depend on organic substances for growth.