Microbiology - Outcome 1 Flashcards
what are bacteria?
prokaryotes
what are prokaryotes?
unicellular (single celled) organisms that lack a defined nucleus or other organelles
what are the 2 categories of bacteria?
eubacteria and ancient bacteria
what are eubacteria?
true bacteria
what are ancient bacteria?
they inhabit extreme environments and carry out unusual metabolic reactions
what is the morphology of a bacterial cell?
its shape and size
what are the three main groups that bacteria morphology can be divided in to?
- cocci
- bacilli
- vibrio and spirillum
what is the shape of a bacterium if it has a cocci shape?
spherical or oval
if a bacteria name has the prefix diplo- what would its arrangement look like?
it would be in pairs
if a bacteria has the prefix strepto- what would its arrangement look like?
it would be in an arrangement of chains
if a bacteria has the prefix staphylo- what would its arrangement be?
it would be in an arrangement of clusters
what is the shape of a bacterium if it is rod shaped?
bacilli
what is the shape of a bacterium if it is curved or has comma-shaped rods?
vibrio
what is the shape of a bacterium if it has thick rigid spirals (in wave shapes)?
spirillum
what are the common structural components that all bacteria have?
- a genome (DNA)
- ribosomes
- cell membrane
- cell wall
what is a bacterial cell wall composed of?
peptidoglycan
what are the two groups bacteria are divided into based on their reaction to the Gram Stain?
gram positive and gram negative
describe a gram positive cell wall
- are thick (20-80 nm)
- contain several layers of peptidoglycan
- contain teichoic acids
describe a gram negative cell wall
- are thinner (1-3 cm)
- contain less peptidoglycan
- have an outer membrane which surrounds peptidoglycan layer of gram negative cell walls
- outer membrane contains a unique component called lipopolysaccharide (LPS)
- LPS is known as an endotoxin - plays a role in infection
- lipid A is the toxic component of endotoxin
- the space between the outer membrane and the cell membrane is called the periplasmic space
describe what happens to a gram positive cell wall when it undergoes the gram stain
retain purple colour of grams crystal violet dye and so appear purple when viewed under microscope
describe what happens to a gram negative cell wall when it undergoes the gram stain
they do not contain crystal violet dye and instead stain the pink colour of the counterstain safranin
what is peptidoglycan and what is its structure?
- a large polymer
- it has a backbone of alternating sugar molecules known as NAG and NAM
- it has some short lengths of protein used as cross linkers
what does the cross-linking of proteins in peptidoglycan result in?
- very large peptidoglycan sac whose units are interconnected
- the sacs are very strong yet also elastic
- also porous - allows molecules to pass through sturcture
what can peptidoglycan be attacked by?
antibiotics and enzymes
how does penicillin attack peptidoglycan?
inhibits formation of protein cross linkers, so cell walls are weaker and easily damaged
how does the enzyme lysozyme attack peptidoglycan?
cuts sugar backbone of peptidoglycan molecule, so it damages cell wall and lyses bacterial cells (ie kills them)
what cell wall type is more susceptible to damage from enzymes and antibiotics and why?
a gram positive cell wall is more susceptible to damage because it contains more peptidoglycan than a gram negative cell wall does
the structure of peptidoglycan in a gram positive wall is similar to that of a gram negative cell wall except what?
there is a greater variety of peptide arrangements and cross-linking
what is the function of the cell wall?
- gives bacterial cell shape and provides protection from osmotic lysis
- pathogenic bacteria have components which contribute to their ability to cause disease ie. pathogenicity
what is the function of teichoic acids?
- gives gram positive cells a negative charge and contributes to they ability to cause the production of antibodies (antigenicity)
- also aids in attachment of bacterial cells to tissues
what is the function of LPS (endotoxin?)
- confers toxicity
-determines virulence ie ability to infect body
what us the function of an outer membrane?
- presents outer surface with strong negative charge which helps bacterial cell evade phagocytosis
- needs to allow passage of nutrients through porins (special protein channels)
what do bacterial cell membranes consist of?
mainly of lipids with saturated fatty acids and do not normally contain sterols such as cholesterol
what does the bacterial cell membrane do due to the cell not containing any organelles?
- the cell membrane takes on all the functions for which a double membrane is required in eukaryote cells
- eg site of respiration and in photosynthetic bacteria it is the site of photosynthesis
- site of biosynthesis of lipids and cell wall component eg peptidoglycan
- thought to be involved in coordination of DNA replication during cell division
what does selectively permeable barrier mean?
- regulates the passage of substances into and out of the cell
- allows free passage of water and small uncharged molecules
-larger molecules and charged molecules require transport systems
what receptors do bacterial cell membranes contain and what does this allow?
they contain receptors which allow the bacterial cell to respond to chemicals in the environment in chemotaxis
what are mesosomes and where are they observed and what is their role?
- in-foldings of the bacterial cell membrane
- observed in both gram positive and gram negative bacteria
- they are artefacts
what is the bacterial chromosome?
one large circular molecule of DNA which lies free in the cytoplasm in an area called the nucleoid
what are plasmids?
smaller, circular extra chromosomal pieces of DNA
what is the genome?
the total DNA content of the prokaryotic cell
what are inclusion bodies?
- distinct granules of organic or inorganic material contained in the cytoplasm
- usually reserve materials
what can some inclusion bodies be?
membrane bound vesicles in the cytoplasm containing photosynthetic pigments or enzymes
what are examples of cytoplasmic inclusion bodies and their functions?
glycogen granules
- reserve carbon and energy source
gas vesicles
- buoyancy in water
what group of bacteria notably form endospores?
gram positive bacteria
what are endospores?
highly resistant structures which enable bacteria to survive periods when the environment is hostile to growth eg exhaustion of an essential nutrient
they are NOT reproductive structures
what are flagella and what Is it composed of?
filamentous structures composed of the protein flagellin which are attached to the cell surface
what is the function of flagella?
to allow a swimming cell movement or motility
how do bacterial flagella move?
they rotate like a propeller
what are the 3 structures that a flagellum is composed of?
- the filament
- the hook
- the basal body
what is the function of the filament in a flagellum?
- largest part of flagellum
- extends from the cell surface to the tip of the flagellum
what is the function of the hook in a flagellum?
short curved segment linking the basal body to the filament
what is the function of the basal body in a flagellum?
anchors the flagellum and is composed of a system of rings
what are the two patterns of flagella distribution in bacteria and how is it determined?
- flagella distributed over the whole surface
- flagella arising from one or both poles of the cell
the pattern distribution is genetically determined and can be used to distinguish between bacteria
what are pili and what are they composed of?
- short, fine, hair like structures on the surface of bacterial cells
- shorter and more rigid than flagella
- composed of proteins called pilins