Ch. 19, 20, & 27.2 Flashcards
Explain why viruses are obligate intracellular parasites
Viruses are obligate intracellular parasites because they cannot reproduce or live separately from a host cell. They cannot do this because they lack most cell organelles like the Golgi complex, mitochondria, ribosomes, etc. and thus have to rely on the host cell’s machinery to reproduce.
Explain how a virus identifies its host cell
A virus identifies its host by fitting its surface proteins to receptor molecules on the surface of the host cell
Describe bacterial defenses against phages
m
Define virulent phage
A phage that reproduces only through the lytic cycle
Define prophage
A prophage is the viral DNA that is integrated into the host DNA during the lysogenic cycle
Define temperate prophages
Temperate prophages use both the lytic and lysogenic cycle to reproduce
True or false: occasionally, a prophage
exits the bacterial chromosome,
initiating a lytic cycle.
True
Explain the lytic cycle
The lytic cycle will result in the death of the host cell. Virus attaches to receptor molecules on surface of host cell, phage DNA is injected and circularizes as host DNA degrades, the viral genomes and proteins (tail sheath and fibers) are synthesized, virus’ are assembled (they come together), new phages digest the host’s cell wall and bursts from the cell - releasing the created viruses.
Explain the lysogenic cycle
The lysogenic cycle keeps the host cell alive. Virus attaches to receptor molecules on surface of host cell, phage DNA is injected and circularizes as host DNA degrades, the phage DNA adds into bacterial chromosomes becoming a prophage, as the bacterium reproduce normally the prophage is copied and transmitted to the daughter cell(s), then the cycle starts again as the prophage in the daughter cell circularizes.
How do retroviruses reproduce
Retrovirus enters the host cell through endocytosis, the viral RNA is released and Reverse Transcriptase converts it to viral DNA, viral DNA enters the nucleus and integrates with the host DNA, the integrated DNA undergoes transcription and produces viral RNA, the viral RNA is then used as mRNA to make the viral proteins and as the viral genome as the new retrovirus particles are assembled, the new retrovirus particles exit the cell through endocytosis to infect more cells. Retroviruses essentially use host cells as a permanent factory.
Define provirus
A provirus is the viral DNA that is incorporated into the host’s genome during a retrovirus’ reproduction cycle
What is the difference between a provirus and a prophage
A prophage is involved in the lysogenic cycle can leave the host cell. A provirus is involved in a retrovirus’ reproduction cycle and is a permanent resident of the host cell.
Explain why viruses do not fit the normal definition of life
Viruses cannot be considered alive because they cannot reproduce independently and only use energy when they are inside the host cell, therefore can rarely be considered alive.
What characteristics do virus’ share with living organisms
Similar to living organisms, viruses can evolve, react to stimuli, and have genetic material.
Describe the evidence that viruses probably evolved from fragments of cellular nucleic acids.
Viruses cannot reproduce without a host cell, virus sequences are similar
What is a mobile genetic element
A mobile genetic element is a type of DNA that can move around with the genome
candidates for the original sources of viral genomes
Give three examples of a mobile genetic element
Plasmids: small, circular, DNA molecules found in bacteria and in yeast, replicate independently
Transposons: DNA segments that can move from one location to another within a cell’s genome
Viruses: “poison,” cause diseases
Explain how viruses can increase the genetic variation of the host cell
- mistakes in replication can cause mutations
- ## transduction; the host cell’s DNA is packaged into a virus either with or instead of the viral genome, then when it goes to infect another cell the donor DNA is recombined into the host’s DNA
How do vaccines protect against viral infection
Vaccines spark your immune response, helping your body fight off and remember the germ so it can attack it if the germ ever invades again.
Define vaccines
Vaccines are harmless derivatives of pathogenic microbes that stimulate the immune system to mount defenses against the actual pathogen
aka, very small amounts of weak or dead germs that strengthen immune system
What is an emerging virus
An emerging virus is a virus that has recently made its presence felt by infecting a new host species or by appearing in a new area of the world, has the potential to spread
What is a prion
A prion is a misfolded protein that can transmit its misfolded shape onto normal variants of the same protein - they can cause several transmissible and fatal neurodegenerative diseases in humans and other animals
Describe the prokaryotic chromosome (based off bacteria)
- single or double circular DNA molecule with a few associated proteins, they are not membrane bound and are found in the nucleoid
- also contains plasmids, smaller circular discs of DNA that can replicate independently of the chromosome
Explain binary fission
In binary fission, an organism duplicates its genetic material (DNA) and then divides into two parts (cytokinesis) with each new organism receiving one copy of DNA
Compare the sources of genetic variation in bacteria and humans
- in humans, genetic variation is due to law of segregation and law of independent assortment
- in bacteria, there are three ways to achieve genetic variation: transformation, transduction, and conjugation
Describe transformation
Transformation is the alteration of a bacterial cell’s genotype and phenotype by the uptake of naked, foreign DNA from the surrounding environment
Describe transduction
In transduction, phages carry bacterial genes from one host cell to another
Describe conjugation
Conjugation is the direct transfer of genetic material between bacterial cells that are temporarily joined, the transfer is one-way with one cell donating to its genes to its mate
Define “maleness”
- maleness is the ability to form a sex pilus (appendage to transfer DNA to “female”) and donate DNA
- results from an F (fertility) factor as part of the chromosome or as a plasmid
Explain how the F plasmid controls conjugation in bacteria
If a cell has an F+ plasmid (donator) then they are able to donate to an F- plasmid (recipient) during conjugation
What is an a high frequency recombination cell (HFR)
An HFR cell is a donor cell that has an F factor integrated into the chromosome, allowing for some chromosomal genes to be transferred to the F- cell during conjugation
Describe the significance of R plasmids
R plasmids offer resistance to various antibiotics
Explain how the widespread use of antibiotics contributes to R plasmid-related disease
When a bacterial population is exposed to an antibiotic the individuals with the R plasmid will survive and increase, so if antibiotics are abused then it will only survive to increase the rate at which R plasmid-related diseases evolve to become immune to them
What is recombinant DNA
Recombinant DNA is where nucleotide sequences from two different
sources, often two species, are combined in vitro into the same DNA molecule
