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A > microbes: the good, the bad and the ugly > Flashcards

microbes: the good, the bad and the ugly Flashcards

1
Q

how do viruses differ in structure and size from eukaryotes and prokaryotes

A

viruses are much smaller and simpler in structure

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2
Q

can viruses reproduce or carry out metabolic activities outside of a host cell

A

no - they rely on their hosts to carry out these processes

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3
Q

Do biologists think that viruses are alive

A

Most would say that they lie in an area between life forms and chemicals

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4
Q

what does a virus consist of

A

a nucleic acid surrounded by a protein coat

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5
Q

can viruses be cultivated on nutrient media in test tubes or petri dishes

A

no

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6
Q

are viruses visible under light microscopes

A

no - the largest ones are nearly visible but generally an electron microscope is required to visualise them a they are so small

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7
Q

what is a virus

A

an infectious particle consisting of a nucleic acid enclosed in a protein coat and in some cases surrounded by a membranous envelope

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8
Q

what do the genomes of viruses consist of

A 
they may consist of:
double stranded DNA
single stranded DNA
double stranded RNA
single stranded RNA
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9
Q

what are the two classes of virus with regards to genome type

A

RNA virus

DNA virus

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10
Q

how is the genome of a virus usually organised

A

it is usually organised into a single linear or circular molecule of nucleic acid (some viruses have multiple molecules of nucleic acid)

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11
Q

What is the proteins shell surrounding the viral genome called

A

a capsid

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12
Q

what are capsids made from

A

a large number of protein subunits called capsomeres

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13
Q

give 2 examples of the shape of a capsid

A

rod, polyhedral

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14
Q

what part of an organism does a adenovirus infect

A

the respiratory tract

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15
Q

what are the viral envelopes that some viruses have derived from

A

the membrane of their host cell (they contain host cell phospholipids and membrane proteins). they also contain proteins and glycoproteins of viral origin

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16
Q

what are glycoproteins

A

they are proteins that have a carbohydrate covalently attached to them

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17
Q

what are viruses called that infect bacteria

A

bacteriophages or simple phages

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18
Q

what does viruses being obligate intracellular parasites mean

A

they can replicate only within a host cell

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19
Q

what is the host range of a virus

A

the different host species that a virus can infect

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20
Q

how do viruses identify host cells

A

by a lock and key fit between the viral surface proteins and the receptor molecule on the host cell surface

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21
Q

in general is a virus host range usually narrow or wide

A

It can be either:
west nile virus infects multiple hosts
measles can only infect humans

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22
Q

true/false Viral infections in multicellular eukaryotes is usually limited to particular tissue

A

true - e.g. the cold virus infects only the cells that line the upper respiratory tract

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23
Q

when does a viral infection begin

A

when the virus binds to the host cell and the viral genome can make its way inside the cell

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24
Q

what are the 3 ways that the viral genome can insert into the cell

A
  1. tail apparatus injects DNA into a bacterium
  2. taken up by endocytosis
  3. fusion of the viral envelope with the host cell plasma membrane
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25
Q

once the viral genome is in the cell what happens

A

the viral proteins encoded results in reprogramming of the cell to copy the viral genome and make more viral proteins

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26
Q

what does the host provide for the virus for replication

A 
nucleotides
enzymes
ribosome 
tRNA
amino acids 
ATP
DNA polymerase (DNA virus)
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27
Q

RNA viruses can encode for what to be synthesised in the host cell that wouldn’t be made in an uninfected cell

A

RNA polymerase

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28
Q

once the viral DNA and capsid proteins have been replicated in the cell, what do they do

A

they self assemble into new virus particles that exit the cell

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29
Q

can the new virus particle that exit the host cell go on to infect other cell

A

yes - in exactly the same way - this is how viruses spread

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30
Q

what are the two alternative mechanisms that double stranded DNA viruses can replicate by

A

lytic cycle

lysogenic cycle

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31
Q

what is the lytic cycle

A

a phage replicative cycle that culminates (ends) in death of the host cell

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32
Q

what is a phage that only replicates by the lytic cycle called

A

virulent phage

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33
Q

what are the steps in the lytic cycle

A

example of T4 phage and E.coli (host)

  1. the phage uses its tail fibres to bind to specific surface proteins (receptors) on E.coli
  2. tail sheath contracts, injecting DNA into the cell leaving an empty capsid outside. The host cell DNA is hydrolysed
  3. the phage DNA directs production of phage proteins and copies of the phage genome by host and viral enzymes using components within the cell
  4. the virus reforms
  5. the phages exit the cell (host dies) phage directs production of enzyme to damage the cell wall (cell bursts
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34
Q

what is the lysogenic cycle

A

a phage replicative cycle that replicates the phage genome without killing the host cell

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35
Q

what is a phage called that is able to use both the lytic and lysogenic cycles

A

temperate phage

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36
Q

when does the lysogenic cycle sometime change to a lytic cycle

A

when an environmental signal is encountered such as a chemical or radiation

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37
Q

what are the steps in the lysogenic cycle

A
  1. the phage attaches to the host cell and injects DNA
  2. the phage DNA circularizes
  3. the phage DNA integrates into the bacterial chromosome, becoming a prophage
  4. the bacterium reproduces normally, copying the prophage and transmitting it to daughter cells
  5. many cell divisions produce a large population of bacteria infected with a prophage
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38
Q

if a prophage exits the bacterial chromosome what process can be initiated

A

lytic cycle

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39
Q

Why have bacteria not become extinct by the lytic cycle

A
  1. lysogeny
  2. natural selection favours bacterial mutants who’s surface proteins are no longer recognised by the phages
  3. when phage DNA does enter the bacterium it is often cut up by restriction enzymes and it can no longer replicate
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40
Q

what are viral envelopes used for

A

to enter the host cell

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41
Q

what protrudes the outer surface of a viral envelope

A

glycoproteins that bind the specific receptor molecules on the host cell surface

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42
Q

what are the ribosomes in the endoplasmic reticulum of the host cell responsible for

A
  1. making the protein parts of the envelope glycoprotein

2. making cellular enzymes inside the endoplasmic reticulum and Golgi apparatus

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43
Q

are herpes viruses envelopes derived from their host plasma membrane

A

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

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44
Q

what is endocytosis

A

cellular uptake of biological molecules and particulate matter via formation of vesicles from the plasma membrane

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45
Q

what is the replicative cycle of an enveloped RNA virus

A
  1. Glycoproteins of the envelope bind to specific receptor molecules on the host, promoting viral uptake by the cell
  2. capsid + viral genome enter host. digestion of capsid by cellular enzymes releases the viral genome
  3. viral genome functions as a template for synthesis of complementary RNA strands by RNA polymerase
  4. copies of viral genome are made using complementary RNA strands as templates
  5. 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)
  6. vesicles transport glycoproteins to the plasma membrane
  7. capsid assembles around each viral genome molecule
  8. each new virus buds from the cell, its envelope studded with viral glycoproteins embedded in the membrane derived from the host cell.
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46
Q

which RNA animal viruses have the most complicated replicative cycles

A

retroviruses (class VI) e.g. HIV

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47
Q

retroviruses have enzymes that transcribe RNA to DNA called what

A

reverse transcriptase

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48
Q

the retrovirus HIV causes what immunodeficiency disease

A

AIDS

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49
Q

do retroviruses have viral envelopes

A

yes

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50
Q

what is integrated (incorporated into host chromosomes) viral DNA called

A

provirus

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51
Q

Do proviruses leave the host cell

A

no they become a permanent resident

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52
Q

what is the difference between a prophage in the lytic cycle compared to a provirus

A

prophage leaves the host cell

provirus stays in the host cell

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53
Q

give some reasons why a virus may not be classed as non living

A

a isolated virus is biologically inert, unable to replicate its genes or generate ATP

54
Q

give some reasons why a virus may be classed as living

A

it has the genetic programming like all other living organisms

55
Q

what are the steps in the replicative cycle of HIV

A
  1. envelope glycoproteins enable the virus to bind to specific receptors on white blood cells
  2. virus fuses with host plasma membrane. capsid proteins are removed releasing viral proteins and RNA
  3. reverse transcriptase catalyses the of a DNA strand complementary to the RNA
  4. reverse transcriptase catalyses the synthesis of a second DNA strand complementary to the first
  5. double stranded DNA incorporated as a provirus into the cell’s DNA
  6. 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
  7. the viral proteins from translation include capsid proteins and reverse transcriptase (made in the cytosol) and envelope glycoproteins (made in the ER)
  8. vesicles transport the glycoproteins to the plasma membrane
  9. capsids are assembled around viral genomes and reverse transcriptase molecules
  10. new viruses with viral envelope glycoproteins bud from the host cell
56
Q

what are plasmids

A

small circular DNA found in bacteria and yeast. they are independent from the bacterial chromosome and can be transferred between cells

57
Q

what are transposons

A

DNA segments that can move from one location to another within a cells genome

58
Q

what feature do viruses, plasmids and transposons share

A

they are all mobile genetic elements

59
Q

what is a prion

A

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

60
Q

what are emerging viruses

A

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

61
Q

what is an epidemic

A

wide spread outbreak of a disease

62
Q

what is a pandemic

A

a global epidemic

63
Q

how do viruses burst on the scene giving rise to diseases that were previously rare or unknown

A
  1. mutation of existing viruses (RNA has high mutation rate) e.g. development of new strains
  2. dissemination (spreading) of a viral disease from a small isolated human population e.g. AIDs
  3. spread of viruses from other animals e.g. swine flu
64
Q

prions have caused a number of degenerative brain diseases in various animal species. name some diseases

A

scrapie in sheep

mad cow disease

65
Q

can prions be transmitted in food

A

yes - eating beef from a cow with mad cow disease causes Creutzfedt-Jakob disease

66
Q

do prions act fast or slow

A

very slow - incubation period of 10 years before symptoms occur. This prevents the source of infection being identified

67
Q

can prions be destroyed

A

no they are virtually indestructible

68
Q

how do prions multiply

A

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

69
Q

what were the first organisms to inhabit earth

A

prokaryotes

70
Q

are most prokaryotes unicellular or multicellular

A

unicellular

71
Q

are prokaryotes smaller or larger than eukaryotes

A

smaller

72
Q

what are the 3 most common shapes of prokaryotes

A

cocci - spherical
bacilli - rod
spiral - coils

73
Q

what are the main functions of a prokaryotic cell wall

A

maintains cell shape
protects the cell
prevents the cell form bursting in a hypertonic environment

74
Q

what are the cell walls of eukaryotes made of

A

cellulose

75
Q

what are the cell walls of bacteria made from

A

peptidoglycan

76
Q

what is peptidoglycan

A

a polymer of modified sugars cross linked by short polypeptides.

77
Q

what is the technique called that categorizes bacterial species based on differences in cell wall composition

A

gram stain

78
Q

what are the steps of a gram stain

A

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

79
Q

what are the characteristics of the cell wall of a gram positive bacteria

A

simple walls composed of a thick layer of peptidoglycan

80
Q

what are the characteristics of the cell wall of a gram negative bacteria

A

structurally more complex walls that have less peptidoglycan. they have an outer membrane that contains lipopolysaccharides

81
Q

what about gram negative bacteria makes them more resistant to antibiotics

A

the lipopolysaccharide layer protect the bacterium from the body’s defences and also impedes the entry of drugs

82
Q

many prokaryotes are surrounded by a sticky layer of proteins, what is this called

A

a capsule if it is dense and well defined

a slime layer if its not as well organised

83
Q

what are the 2 domains of prokaryotes

A

bacteria and archaea

84
Q

gram positive stains have virulent strains that are resistant to what

A

antibiotics

85
Q

what is symbiosis

A

an ecological relationship between organisms of two different species that live together in direct and intimate contact

86
Q

what is mutualism

A

ecological interaction that benefits each of the interacting species

87
Q

what is parasitism

A

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

88
Q

what is commensalism

A

ecological interaction in which one organism benefits but the other is neither helped or harmed

89
Q

what poisons obligate anaerobes

A

oxygen

90
Q

what do obligate aerobes require

A

oxygen

91
Q

do facultative anaerobes need oxygen to survive

A

they can survive with or without oxygen

92
Q

prokaryotes play a major role in recycling what

A

chemical elements between living and non-living ecosystem components i.e. they are nitrogen fixers

93
Q

what industry are microbes involved in

A

food, biotechnology, agriculture, sewage works

94
Q

what are the differences between prokaryotes and eukaryotes

A

eukaryotes are larger
eukaryotes contain a nucleus - only have chromosomes and sometimes plasmids
eukaryotes have membrane bound organelles - prokaryotes lack

95
Q

what do most bacteria propel themselves by

A

flagella

96
Q

what do fimbriae allow prokaryotes to do

A

stick to a substance or others in their colony

97
Q

what do sex pili allow prokaryotes to do

A

exchange DNA

98
Q

what colour do gram negative bacteria stain

A

pink

99
Q

what colour do gram positive bacteria stain

A

purple

100
Q

do bacteria reproduce sexually or asexually

A

asexually

101
Q

are viruses cells

A

no

102
Q

what are the 2 major surface antigens of the influenza virus

A

hemagglutinin and neuraminidase

103
Q

what type of genome does the influenza virus have

A

RNA

104
Q

what do high mutation rates and frequent genetic assortment lead to in influenza

A

variability in its antigens: hemagglutinin and neuraminidase
causes outbreaks by evading the immune system

105
Q

what are viroids

A

single circular RNA molecule - doesn’t encode proteins - mostly affect plant growth

106
Q

which infection is thought to have originated from a viroid

A

hepatitis B

107
Q

which 2 ecological relationships are standard of normal microbiota

A

mutualism

commensalism

108
Q

which ecological relationship is standard of pathogens

A

parasitism

109
Q

which factors are constant in a microbe niche

A

growth factors

110
Q

what parts of the body offer a good habitat for microbes

A

skin
respiratory tract
GI tract
armpits

111
Q

what is the role of normal microbiota

A

protect surfaces form physical colonisation by pathogenic bacteria

112
Q

what is the microbiome

A

microbes, their genomes and environmental interactions in a defined environment
it includes viruses

113
Q

are changes in the microbiome associated with human health and disease

A

yes

114
Q

the ecological relationship between the gut microbiome and host is mostly what

A

mutualism
host - provides food, warmth etc
microbes prevent colonisation by pathogenic bacteria, train the developing host immune system, regulate gut development etc

115
Q

how are microbes passed between people

A 
saliva 
sneezing- aerosol transmission 
not washing hands
insect bites wounds 
sex
116
Q

what is pathogenesis

A

the manner of development of a disease

117
Q

what are pathogens

A

any disease causing organism

118
Q

name some bacterial infections

A

cholera

septicaemia

119
Q

name 2 different ways to prevent infection

A

hygiene

vaccination - stimulate defences and generate memory response

120
Q

how ca a bacterial infection be treated

A

with antibiotics - resistance can be a problem

121
Q

how can viruses be treated

A

there are few treatments available - the drug must inhibit multiplication but not the infected host cell e.g. Influenza A - neuraminidase inhibitor

122
Q

list some foods that microbes are key in the production of

A

bread, cheese, chocolate, yoghurt, vinegar, beer and wine

123
Q

what microbe is involved in beer production

A

yeast

124
Q

how is vinegar made

A

ethanol produced by yeast

converted to acetic acid by addition of acetobacter

125
Q

what is bioremediation

A

the use of microbes to break down dangerous chemicals

126
Q

can bacteria be used to make plastic

A

yes - and its biodegradable

127
Q

what is an exogenous molecule

A

a non native molecule

128
Q

what are endotoxins

A

lipopolysaccharide components of the outer membrane of a gram negative bacteria
salmonella produce endotoxins that cause typhoid fever

129
Q

what are exotoxins

A

proteins secreted by certain bacteria and other organisms

cholera is caused by exotoxins

130
Q

what is human gene therapy

A

inserting RNA functional gene into retrovirus
let retrovirus infect bone marrow cells
insert the bone marrow cells into the patient

131
Q

what are issues with gene therapy

A

efficacy
DNA can be short lived
immune response to virus

A (17 decks)

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