viruses and bacteria Flashcards
how are viruses compared to bacteria in terms of size?
tiny
what are viruses made of?
nucleid acid - DNA/RNA
enclosed in a protein coat called a capsid
what so some viruses have?
viral envelope that helps them infect their host
from where are the viral envelopes derived from? why?
from the host cell to help the virus be unnoticed by the immune system
what are viral envelopes made of?
made up of phospholipids and glycoproteins
what do some viruses carry?
enzymes in their capsids
shapes of viruses?
may be rod shaped or more complex in structure
complex viruses
bacteriophages that infect bacteria
where can viruses reproduce?
only within a host cell
when a person sneezes, when are the released viruses activated?
until a host gets the virus into their own body
why arent viruses activated until they go into a body?
they lack enzymes for metabolism and cannot make their own proteins
*why some scientists classify viruses as nonliving
host range
each type of virus can only infect a limited range of host cells
*some are so small that it only includes 1 species
how are viruses able to identify their hosts?
by protein receptors in the surface of the host cells that form a lock and key first with the receptors on the surface of the virus
example of a virus with a big host range?
rabies - can infect raccoons, skunks, dogs, and humans
most viruses can infect eukaryotes that are?
tissue specific
what do cold viruses infect?
only the cells of the respiratory tract
what does HIV infect?
only helper T cells - type of WBC
what happens once a virus is inside of a host?
they start taking control of the host?
what does a virus do to the host?
reprogram it to make copies of the viral RNA/DNA (DNA replication) and viral proteins (protein synthesis)
what does the host cell provide for the virus?
nucleotides, enzymes, ribosomes, RNA, amino acids, ATP, for the making of viral part
what is the lytic cycle?
a viral cycle during the last stage of infection
what happens during the lytic cycle?
lytic cycle first destroys the host’s DNA and eventually the host
then viruses are free to go infect other healthy cells
what is a virus that reproduces by the lytic cycle called?
virulent virus
what does virulent mean?
very infectious
how long does it take a virulent virus to destruct its host?
20-30 minutes
steps of lytic cycle (5)
- phage stick to receptor on outer surface of cell
- sheath of tail contracts, making a hole through the cell wall and membrane. phage injects DNA
- empty capsid is left as ghost. cell’s DNA is destroyed (hydrolyzed)
- phage’s DNA is replicated
- cell lyses
when happens when a cell lyses?
100-1000 of viruses bursts free from the host cell
how have host cells evolved to protect themselves?
some have mutated their surface receptors and are no longer recognized by a particular bacteriophage
some have enzymes that are bale to break down viral DNA/RNA (Eco RI)
what is the lysogenic cycle?
when a virus infects a host cell but doesnt destroy the host and doesnt destroy the hosts’s DNA
what happens to the viral DNA in lysogenic cycle?
it becomes incorporated into the hosts DNA
what is the viral DNA called when it is part of the host’s DNA?
provirus - general term
prophage - only for bacteria
what does a provirus not do?
it does not interfere with the normal functioning of the host cell
what happens every time a host cell duplicated in a lysogenic cycle?
the viral DNA gets copied as well
when does a lysogenic cell get triggered to switch to the lytic cycle?
can go on for years until triggered by physical/emotional stress
do viruses go undetected in lysogenic cycles?
most of the time - some can alter the host’s phenotype
ex. scarlet fever causes red rashed on skin since the host cell makes toxins (proteins) and the body reacts to it
most viruses have what nucleic acid?
RNA as their genetic material
what type of virus causes AIDS?
retro viruses - viruses that have RNA ns use an enzyme within the virus itself called reverse transcriptase to make DNA
what happens when DNA is created by reverse transcriptase?
DNA is integrated into the host’s DNA as a provirus which will be replicated over and over in a lysogenic cycle
why are HIV infected individuals appear unaffected for so long?
lysogenic cycle
some HIV viruses can bud off from the host cell and go infect other helper T cells an d then destroy the helper T cells when it switches to a lytic cycle
what happens when the HIV infected cell lyses?
helper T cells are destroyed by the HIV virus and there is a total loss of immunity and now has AIDS
why is HIV a difficult antigen for the body to destroy?
it keeps mutating and the immune system cannot keep up with it
why are all mutations of RNA viruses?
they do not have the proofreading steps of DNA replication
what is the common drug to control HIV?
AZT - interferes with the action of reverse transcriptase
what are vaccines?
dead/weakened forms of pathogens
what are pathogens?
viruses or bacteria
what do vaccines do?
since the cannot cause the disease because they are weakened, they stimulate the immune system to mount a defense in the event of a “live” attack.
who made the first vaccine?
Dr Edward Jenner
what did Jenner notice?
milkmaids who contracted cowpox were resistant to smallpox
cowpox
a mild disease that usually infects cows
smallpox
a disease that often resulted in death
what did Jenner do?
he scratched James with a needle containing fluid from the sore of a milkmaid who had cowpox
what happened to James?
when he was later exposed to smallpox, he didnt get sick
why didnt James get sick?
cowpox and smallpox viruses are so similar that the immune system cannot distinguish them
What can vaccines be used for?
a viral or bacterial infection
what can antibiotics not be used on?
viral infections
when are vaccines usually given?
before an infection
when are antibiotics used?
after one gets a bacterial infection
why cant antibiotics be used for viral infections?
antibiotics kill bacteria by inhibiting enzymes, but viruses lack enzymes
exception - AZT is used to stop the action of reverse transcriptase in HIV
what does penicillin do?
interfere with the enzymes that build cell wall.
viruses dont have cell walls while bacteria do
who found penicllin?
alexander fleming
how frequent do RNA viruses mutate?
often
* flu shot for every year for RNA influenza virus
what happens to viral diseases are viruses increase their host range?
new ones come about
*Hanta- spread from deer mice to humans who inhaled dust containing traces of urine and feces from mice
what increases viral diseases?
increased travel
sexual promiscuity
intravenous drug use
isolated plants, animals, tribes discovered
how can plant viruses be spread?
insects that act as carriers and by farmers who inadvertently transmit the viruses on their gardening tools
how are scientists trying to stop the increase in viral diseases in terms of agriculture?
breeding viral resistant crops
what are prions
misfolded protein normally present in brain cells
when did prions hit the news?
in 90s when they plagued the british beef industry causing madcow disease
what happens when a prion gets into a cell containing the normal form of the protein?
the prion converts the normal protein to a prion version causing degenerative brain disease
what type of cells are bacteria?
prokaryote
how do bacteria divide?
asexually and divide by binary fission every 20 minutes
when bacteria divide, how are the resulting cells compared to the parent?
identical
what does the short generation time creating large number of bacteria arise?
new mutations that bring about genetic variety
layers of bacteria
capsule/slime layer
cell wall
cell membrane
what is genetic recombination?
combining DNA from two individuals into the genome of a single individual
what are the three ways genetic recombination occurs?
transformation
transduction
conjugation
transformation
alteration of a bacterial cell’s genome by the uptake of foreign DNA from the environment
example of transformation
Griffith’s experiment where R cells took up a piece of DNA from heat killed Smooth cells enabling to get a capsule that transformed them into pathogenic pneumonia
how can bacteria be stimulated to pick up DNA?
heat shock and calcium ions
what is stimulating bacteria to uptake used for?
incorporate foreign/naked DNA that code for protein such as insulin for diabetics
transduction?
bacteriophages carry bacterial genes from one host to another
2 types of transduction
generalized transduction that involves lytic cycle
specialized transduction which involves lysogenic cycle
steps of generalized transduction
always starts with bacteriophage that infects bacterial cell
host DNA is hydrolyzed into pieces and phage DNA and proteins are made
phage accidentally picks up bacterial DNA
crossing over occurs when transducing phages infect new host cells
recombinant bacteria at the end
steps of specialized transduction
bacterial cell has prophage integrated between it’s own DNA
prophage DNA exits incorrectly taking adjoining bacterial DNA with it, switching to lytic
bit of bacterial DNA in viral DNA phage
crossing over
recombinant bacteria
conjugation (Horizontal Gene Transfer)
bacterial version of sex in which one bacterial cell transfers DNA to another bacterial cell
what happens in conjugation?
one way process in which the “male” makes a sex pilus and transfers some DNA from plasmid to “female”
sex pilus
temporary cytoplasmic bridge
how does “maleness” come about?
presence of special piece of DNA called F plasmid (F= fertility)
what does having the F factor enable?
enables the bacteria to be the donner of DNA
what are plasmids?
small pieces of self-replicating DNA in bacteria are separate from the nucleoid
if the f factor is in the plasmid, what is it called?
F plasmid
can the F factor be a part of the nucleoid?
yes
what does the F plasmid consist of?
25 genes, most of which are required to make a sex pilus
how to denote whether a bacteria has F plasmid or not?
male - F+
female - F-
when does a F- become F+?
when two cells conjugate
step of normal conjugation?
DNA replication of F plasmid in F+ is sent to F- through sex pilus
now both cells are F+
what happens when an F+ incorporates the F plasmid into its own nucleoid?
Hfr cell - high frequency recombination cell
conjugation where F plasmid is in nuceloid
male Hfr will undergo DNA replication and accidentally transfer part of the DNA that contains a part of F plasmid and some genes of nucleoid to the F- cell
crossing over between homologous regions of the newly transferred genes and bacterial chromosomes of F- cell
R plasmids
plasmids that carry genes that make them resistant to antibiotics
what do R plasmids code for?
enzymes that are able to break down antibiotics such as penicillin or a ampicillin
due to natural selection, what happens when more bacteria have a R plasmid?
increasing number of bacteria become resistant to antibiotics making it difficult to treat bacterial infections
superbug
MRSA - multiple resistant staphylococcus aureus
what is a transposon?
transposable piece of DNA that can move from one location to another
where do transposons move in bacterial cells?
within the nucleoid between the nucleoid and plasmids or from one plasmid to another plasmid``
what are transposons also sometimes called? why is this misleading?
jumping genes
some transposons “jump” from one location to another, while others make a copy and that copy gets inserted elsewhere
who was the first to identify transposons?
Barbara McClintok - breeding experiments with Indian Corn
what did Barbaba notice?
changes in color of corn kernels that could only be explained by “mobile” elements capable of moving from one location to another in the genome
who had transposons?
both eukaryotes and prokaryotes
what are operons?
a way to control transcription in bacteria aka turn on/off
what is a metabolic pathway?
the making or breaking of molecules
if Trp accumulates in a cell, how does the cell stop its creation?
it shuts down the making of the amino acid by negative feedback inhibition as it is maintaining homeostasis
if E coli is deprived of one of the aa Trp from its environment, what does it do?
regulate the number of specific enzymes made to create Trp through a metabolic pathway
the blocking of this metabolic pathway takes place at the level of stopping where?
stopping transcription of mRNA coding for these enzymes in the pathway
the 5 genes that are translated into tryptophan are where?
grouped together on a chromosome
the segment of DNA that codes for Trp is transcribed by?
one promoter where RNA polymerase an bind to and begin trascription
operator
a segment of DNA after the promotor that controls the making of enzymes- switching them on or off
what does the operator control?
the access of RNA polymerase to the genese
operon=
promotor + operator + genes they control
2 types of operons
repressible
inducible
repressible operons
turned off when a small molecule binds to its regulatory protein
inducible operons
turned on when a small molecule binds to its regulatory protein
what type of operon is trp operon?
repressible since it is turned off by an allosterically binding molecule
what is located upstream of an operon?
regulatory gene that makes a regulatory protein
what does the cell do when there is too much of trp?
cell activates the repressor which then binds to the operator and the operon is off
What type of operon is the lac operon?
Inducible as it is turned on when small molecule binds allows Teri calls to its regulatory protein removing it from the operator
What does the lac operon do?
Make enzymes that hydrolyze lactose
What happens when a bacterium is exposed to milk?
Signals the bacterium it needs to make enzymes to break it down
Repressible operons usually function in what type of pathway?
Anabolic - the making of something
Inducible operons usually function in what type of pathways?
Catabolic - the breaking of something
DNA exists in its loose form during interphase called
Chromatin
What happens to DNA during prophase?
Chromatin condenses into replicated chromosome
What is eukaryotic DNA combined with?
Large amount of proteins called histones
How many types of positive charges histone that the negative charged DNA molecule wraps itself around?
5
Why is DNA negative?
Phosphate groups
Combination of DNA wound around histone
Nucleosome
appearance of nucleosome
Beads on a string
