microbes: the good, the bad and the ugly Flashcards
how do viruses differ in structure and size from eukaryotes and prokaryotes
viruses are much smaller and simpler in structure
can viruses reproduce or carry out metabolic activities outside of a host cell
no - they rely on their hosts to carry out these processes
Do biologists think that viruses are alive
Most would say that they lie in an area between life forms and chemicals
what does a virus consist of
a nucleic acid surrounded by a protein coat
can viruses be cultivated on nutrient media in test tubes or petri dishes
no
are viruses visible under light microscopes
no - the largest ones are nearly visible but generally an electron microscope is required to visualise them a they are so small
what is a virus
an infectious particle consisting of a nucleic acid enclosed in a protein coat and in some cases surrounded by a membranous envelope
what do the genomes of viruses consist of
they may consist of: double stranded DNA single stranded DNA double stranded RNA single stranded RNA
what are the two classes of virus with regards to genome type
RNA virus
DNA virus
how is the genome of a virus usually organised
it is usually organised into a single linear or circular molecule of nucleic acid (some viruses have multiple molecules of nucleic acid)
What is the proteins shell surrounding the viral genome called
a capsid
what are capsids made from
a large number of protein subunits called capsomeres
give 2 examples of the shape of a capsid
rod, polyhedral
what part of an organism does a adenovirus infect
the respiratory tract
what are the viral envelopes that some viruses have derived from
the membrane of their host cell (they contain host cell phospholipids and membrane proteins). they also contain proteins and glycoproteins of viral origin
what are glycoproteins
they are proteins that have a carbohydrate covalently attached to them
what are viruses called that infect bacteria
bacteriophages or simple phages
what does viruses being obligate intracellular parasites mean
they can replicate only within a host cell
what is the host range of a virus
the different host species that a virus can infect
how do viruses identify host cells
by a lock and key fit between the viral surface proteins and the receptor molecule on the host cell surface
in general is a virus host range usually narrow or wide
It can be either:
west nile virus infects multiple hosts
measles can only infect humans
true/false Viral infections in multicellular eukaryotes is usually limited to particular tissue
true - e.g. the cold virus infects only the cells that line the upper respiratory tract
when does a viral infection begin
when the virus binds to the host cell and the viral genome can make its way inside the cell
what are the 3 ways that the viral genome can insert into the cell
- tail apparatus injects DNA into a bacterium
- taken up by endocytosis
- fusion of the viral envelope with the host cell plasma membrane
once the viral genome is in the cell what happens
the viral proteins encoded results in reprogramming of the cell to copy the viral genome and make more viral proteins
what does the host provide for the virus for replication
nucleotides enzymes ribosome tRNA amino acids ATP DNA polymerase (DNA virus)
RNA viruses can encode for what to be synthesised in the host cell that wouldn’t be made in an uninfected cell
RNA polymerase
once the viral DNA and capsid proteins have been replicated in the cell, what do they do
they self assemble into new virus particles that exit the cell
can the new virus particle that exit the host cell go on to infect other cell
yes - in exactly the same way - this is how viruses spread
what are the two alternative mechanisms that double stranded DNA viruses can replicate by
lytic cycle
lysogenic cycle
what is the lytic cycle
a phage replicative cycle that culminates (ends) in death of the host cell
what is a phage that only replicates by the lytic cycle called
virulent phage
what are the steps in the lytic cycle
example of T4 phage and E.coli (host)
- the phage uses its tail fibres to bind to specific surface proteins (receptors) on E.coli
- tail sheath contracts, injecting DNA into the cell leaving an empty capsid outside. The host cell DNA is hydrolysed
- the phage DNA directs production of phage proteins and copies of the phage genome by host and viral enzymes using components within the cell
- the virus reforms
- the phages exit the cell (host dies) phage directs production of enzyme to damage the cell wall (cell bursts
what is the lysogenic cycle
a phage replicative cycle that replicates the phage genome without killing the host cell
what is a phage called that is able to use both the lytic and lysogenic cycles
temperate phage
when does the lysogenic cycle sometime change to a lytic cycle
when an environmental signal is encountered such as a chemical or radiation
what are the steps in the lysogenic cycle
- the phage attaches to the host cell and injects DNA
- the phage DNA circularizes
- the phage DNA integrates into the bacterial chromosome, becoming a prophage
- the bacterium reproduces normally, copying the prophage and transmitting it to daughter cells
- many cell divisions produce a large population of bacteria infected with a prophage
if a prophage exits the bacterial chromosome what process can be initiated
lytic cycle
Why have bacteria not become extinct by the lytic cycle
- lysogeny
- natural selection favours bacterial mutants who’s surface proteins are no longer recognised by the phages
- when phage DNA does enter the bacterium it is often cut up by restriction enzymes and it can no longer replicate
what are viral envelopes used for
to enter the host cell
what protrudes the outer surface of a viral envelope
glycoproteins that bind the specific receptor molecules on the host cell surface
what are the ribosomes in the endoplasmic reticulum of the host cell responsible for
- making the protein parts of the envelope glycoprotein
2. making cellular enzymes inside the endoplasmic reticulum and Golgi apparatus
are herpes viruses envelopes derived from their host plasma membrane
no instead they are cloaked in membrane derived from the nuclear membrane of the host. this is then shed in the cytoplasm and a new membrane is made from the Golgi apparatus
what is endocytosis
cellular uptake of biological molecules and particulate matter via formation of vesicles from the plasma membrane
what is the replicative cycle of an enveloped RNA virus
- Glycoproteins of the envelope bind to specific receptor molecules on the host, promoting viral uptake by the cell
- capsid + viral genome enter host. digestion of capsid by cellular enzymes releases the viral genome
- viral genome functions as a template for synthesis of complementary RNA strands by RNA polymerase
- copies of viral genome are made using complementary RNA strands as templates
- complementary RNA also function as mRNA which is translated into capsid proteins (in the cytosol) and glycoproteins for envelope (in the ER and Golgi apparatus)
- vesicles transport glycoproteins to the plasma membrane
- capsid assembles around each viral genome molecule
- each new virus buds from the cell, its envelope studded with viral glycoproteins embedded in the membrane derived from the host cell.
which RNA animal viruses have the most complicated replicative cycles
retroviruses (class VI) e.g. HIV
retroviruses have enzymes that transcribe RNA to DNA called what
reverse transcriptase
the retrovirus HIV causes what immunodeficiency disease
AIDS
do retroviruses have viral envelopes
yes
what is integrated (incorporated into host chromosomes) viral DNA called
provirus
Do proviruses leave the host cell
no they become a permanent resident
what is the difference between a prophage in the lytic cycle compared to a provirus
prophage leaves the host cell
provirus stays in the host cell
give some reasons why a virus may not be classed as non living
a isolated virus is biologically inert, unable to replicate its genes or generate ATP
give some reasons why a virus may be classed as living
it has the genetic programming like all other living organisms
what are the steps in the replicative cycle of HIV
- envelope glycoproteins enable the virus to bind to specific receptors on white blood cells
- virus fuses with host plasma membrane. capsid proteins are removed releasing viral proteins and RNA
- reverse transcriptase catalyses the of a DNA strand complementary to the RNA
- reverse transcriptase catalyses the synthesis of a second DNA strand complementary to the first
- double stranded DNA incorporated as a provirus into the cell’s DNA
- proviral genes are transcribed into RNA which serve as genomes for progeny viruses (viruses to be released from the host) and as mRNA for translation into viral protein
- the viral proteins from translation include capsid proteins and reverse transcriptase (made in the cytosol) and envelope glycoproteins (made in the ER)
- vesicles transport the glycoproteins to the plasma membrane
- capsids are assembled around viral genomes and reverse transcriptase molecules
- new viruses with viral envelope glycoproteins bud from the host cell
what are plasmids
small circular DNA found in bacteria and yeast. they are independent from the bacterial chromosome and can be transferred between cells
what are transposons
DNA segments that can move from one location to another within a cells genome
what feature do viruses, plasmids and transposons share
they are all mobile genetic elements
what is a prion
an infectious agent that is a misfolded version of a normal cellular (brain) protein
prions appear to increase in number by converting correctly folded version of the protein to more prions. they are small and disease causing. AN INFECTIOUS PROTEIN
what are emerging viruses
viruses that have suddenly become apparent e.g. HIV which leads to AIDs and the west nile virus that causes swelling of the brain. ebola is also an example. zika is also an example
what is an epidemic
wide spread outbreak of a disease
what is a pandemic
a global epidemic
how do viruses burst on the scene giving rise to diseases that were previously rare or unknown
- mutation of existing viruses (RNA has high mutation rate) e.g. development of new strains
- dissemination (spreading) of a viral disease from a small isolated human population e.g. AIDs
- spread of viruses from other animals e.g. swine flu
prions have caused a number of degenerative brain diseases in various animal species. name some diseases
scrapie in sheep
mad cow disease
can prions be transmitted in food
yes - eating beef from a cow with mad cow disease causes Creutzfedt-Jakob disease
do prions act fast or slow
very slow - incubation period of 10 years before symptoms occur. This prevents the source of infection being identified
can prions be destroyed
no they are virtually indestructible
how do prions multiply
the can’t replicate but once they get into a cell containing the normal form of their protein they convert them to the prion versions. the prions then aggregate
what were the first organisms to inhabit earth
prokaryotes
are most prokaryotes unicellular or multicellular
unicellular
are prokaryotes smaller or larger than eukaryotes
smaller
what are the 3 most common shapes of prokaryotes
cocci - spherical
bacilli - rod
spiral - coils
what are the main functions of a prokaryotic cell wall
maintains cell shape
protects the cell
prevents the cell form bursting in a hypertonic environment
what are the cell walls of eukaryotes made of
cellulose
what are the cell walls of bacteria made from
peptidoglycan
what is peptidoglycan
a polymer of modified sugars cross linked by short polypeptides.
what is the technique called that categorizes bacterial species based on differences in cell wall composition
gram stain
what are the steps of a gram stain
samples are stained with crystal violet dye and iodine, then rinsed in alcohol
the sample is then stained with red dye that enters the cell and binds to DNA
the structure of the bacterium cell wall determines the response
what are the characteristics of the cell wall of a gram positive bacteria
simple walls composed of a thick layer of peptidoglycan
what are the characteristics of the cell wall of a gram negative bacteria
structurally more complex walls that have less peptidoglycan. they have an outer membrane that contains lipopolysaccharides
what about gram negative bacteria makes them more resistant to antibiotics
the lipopolysaccharide layer protect the bacterium from the body’s defences and also impedes the entry of drugs
many prokaryotes are surrounded by a sticky layer of proteins, what is this called
a capsule if it is dense and well defined
a slime layer if its not as well organised
what are the 2 domains of prokaryotes
bacteria and archaea
gram positive stains have virulent strains that are resistant to what
antibiotics
what is symbiosis
an ecological relationship between organisms of two different species that live together in direct and intimate contact
what is mutualism
ecological interaction that benefits each of the interacting species
what is parasitism
ecological relation ship in which one organism, the parasite, benefits by feeding upon another organism, the host, which is harmed. some parasites live within the host (feeding on its tissues), while others feed on the hosts external surface
what is commensalism
ecological interaction in which one organism benefits but the other is neither helped or harmed
what poisons obligate anaerobes
oxygen
what do obligate aerobes require
oxygen
do facultative anaerobes need oxygen to survive
they can survive with or without oxygen
prokaryotes play a major role in recycling what
chemical elements between living and non-living ecosystem components i.e. they are nitrogen fixers
what industry are microbes involved in
food, biotechnology, agriculture, sewage works
what are the differences between prokaryotes and eukaryotes
eukaryotes are larger
eukaryotes contain a nucleus - only have chromosomes and sometimes plasmids
eukaryotes have membrane bound organelles - prokaryotes lack
what do most bacteria propel themselves by
flagella
what do fimbriae allow prokaryotes to do
stick to a substance or others in their colony
what do sex pili allow prokaryotes to do
exchange DNA
what colour do gram negative bacteria stain
pink
what colour do gram positive bacteria stain
purple
do bacteria reproduce sexually or asexually
asexually
are viruses cells
no
what are the 2 major surface antigens of the influenza virus
hemagglutinin and neuraminidase
what type of genome does the influenza virus have
RNA
what do high mutation rates and frequent genetic assortment lead to in influenza
variability in its antigens: hemagglutinin and neuraminidase
causes outbreaks by evading the immune system
what are viroids
single circular RNA molecule - doesn’t encode proteins - mostly affect plant growth
which infection is thought to have originated from a viroid
hepatitis B
which 2 ecological relationships are standard of normal microbiota
mutualism
commensalism
which ecological relationship is standard of pathogens
parasitism
which factors are constant in a microbe niche
growth factors
what parts of the body offer a good habitat for microbes
skin
respiratory tract
GI tract
armpits
what is the role of normal microbiota
protect surfaces form physical colonisation by pathogenic bacteria
what is the microbiome
microbes, their genomes and environmental interactions in a defined environment
it includes viruses
are changes in the microbiome associated with human health and disease
yes
the ecological relationship between the gut microbiome and host is mostly what
mutualism
host - provides food, warmth etc
microbes prevent colonisation by pathogenic bacteria, train the developing host immune system, regulate gut development etc
how are microbes passed between people
saliva sneezing- aerosol transmission not washing hands insect bites wounds sex
what is pathogenesis
the manner of development of a disease
what are pathogens
any disease causing organism
name some bacterial infections
cholera
septicaemia
name 2 different ways to prevent infection
hygiene
vaccination - stimulate defences and generate memory response
how ca a bacterial infection be treated
with antibiotics - resistance can be a problem
how can viruses be treated
there are few treatments available - the drug must inhibit multiplication but not the infected host cell e.g. Influenza A - neuraminidase inhibitor
list some foods that microbes are key in the production of
bread, cheese, chocolate, yoghurt, vinegar, beer and wine
what microbe is involved in beer production
yeast
how is vinegar made
ethanol produced by yeast
converted to acetic acid by addition of acetobacter
what is bioremediation
the use of microbes to break down dangerous chemicals
can bacteria be used to make plastic
yes - and its biodegradable
what is an exogenous molecule
a non native molecule
what are endotoxins
lipopolysaccharide components of the outer membrane of a gram negative bacteria
salmonella produce endotoxins that cause typhoid fever
what are exotoxins
proteins secreted by certain bacteria and other organisms
cholera is caused by exotoxins
what is human gene therapy
inserting RNA functional gene into retrovirus
let retrovirus infect bone marrow cells
insert the bone marrow cells into the patient
what are issues with gene therapy
efficacy
DNA can be short lived
immune response to virus
