Ch. 19, 20, & 27.2

Question 1

Explain why viruses are obligate intracellular parasites

Answer 1

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.

Question 2

Explain how a virus identifies its host cell

Answer 2

A virus identifies its host by fitting its surface proteins to receptor molecules on the surface of the host cell

Question 3

Describe bacterial defenses against phages

Answer 3

m

Question 4

Define virulent phage

Answer 4

A phage that reproduces only through the lytic cycle

Question 5

Define prophage

Answer 5

A prophage is the viral DNA that is integrated into the host DNA during the lysogenic cycle

Question 6

Define temperate prophages

Answer 6

Temperate prophages use both the lytic and lysogenic cycle to reproduce

Question 7

True or false: occasionally, a prophage
exits the bacterial chromosome,
initiating a lytic cycle.

Answer 7

True

Question 8

Explain the lytic cycle

Answer 8

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.

Question 9

Explain the lysogenic cycle

Answer 9

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.

Question 10

How do retroviruses reproduce

Answer 10

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.

Question 11

Define provirus

Answer 11

A provirus is the viral DNA that is incorporated into the host’s genome during a retrovirus’ reproduction cycle

Question 12

What is the difference between a provirus and a prophage

Answer 12

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.

Question 13

Explain why viruses do not fit the normal definition of life

Answer 13

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.

Question 14

What characteristics do virus’ share with living organisms

Answer 14

Similar to living organisms, viruses can evolve, react to stimuli, and have genetic material.

Question 15

Describe the evidence that viruses probably evolved from fragments of cellular nucleic acids.

Answer 15

Viruses cannot reproduce without a host cell, virus sequences are similar

Question 16

What is a mobile genetic element

Answer 16

A mobile genetic element is a type of DNA that can move around with the genome
candidates for the original sources of viral genomes

Question 17

Give three examples of a mobile genetic element

Answer 17

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

Question 18

Explain how viruses can increase the genetic variation of the host cell

Answer 18

• 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

Question 19

How do vaccines protect against viral infection

Answer 19

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.

Question 20

Define vaccines

Answer 20

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

Question 21

What is an emerging virus

Answer 21

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

Question 22

What is a prion

Answer 22

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

Question 23

Describe the prokaryotic chromosome (based off bacteria)

Answer 23

• 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

Question 24

Explain binary fission

Answer 24

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

Question 25

Compare the sources of genetic variation in bacteria and humans

Answer 25

• 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

Question 26

Describe transformation

Answer 26

Transformation is the alteration of a bacterial cell’s genotype and phenotype by the uptake of naked, foreign DNA from the surrounding environment

Question 27

Describe transduction

Answer 27

In transduction, phages carry bacterial genes from one host cell to another

Question 28

Describe conjugation

Answer 28

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

Question 29

Define “maleness”

Answer 29

• 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

Question 30

Explain how the F plasmid controls conjugation in bacteria

Answer 30

If a cell has an F+ plasmid (donator) then they are able to donate to an F- plasmid (recipient) during conjugation

Question 31

What is an a high frequency recombination cell (HFR)

Answer 31

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

Question 32

Describe the significance of R plasmids

Answer 32

R plasmids offer resistance to various antibiotics

Question 33

Explain how the widespread use of antibiotics contributes to R plasmid-related disease

Answer 33

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

Question 34

What is recombinant DNA

Answer 34

Recombinant DNA is where nucleotide sequences from two different
sources, often two species, are combined in vitro into the same DNA molecule