MICROBIOLOGY EXAM 2

What's a lysogenic infection?

"Lysogenic infection" and "latent infection" means the same thing, with regards to bacteriophage.

operons are only found in

bacteria

What's a lysogen?

A type of bacterium that is able to produce another phage.

How do enveloped viruses acquire their envelope?

Enveloped viruses acquire their envelope by budding out of its host cell. During the budding process, the virus takes some of the host cell's membrane with it. This "stolen" membrane becomes the envelope of the virus.

Some cancers are known to be triggered by viral infections.

For example, cervical cancer is known to be triggered by infection with human papillomavirus.

Herpes virus causes acute infection in what type of cells?

Herpes virus causes acute infection in epithelial cells (e.g. skin cells).

What's the function of the polymerase gene found in the genome of bacteriophage?

The polymerase gene encodes for the polymerase enzyme. Polymerases function in producing nucleic acids (i.e. they read the information on one nucleic acid strand to make the complementary nucleic acid strand).

Name and briefly describe three different shapes that viruses may have.

Three: Complex shape - Looks like an insect (head, "body", and "legs"). Only viruses that infect bacteria have this shape.

What is transduction?

Transduction occurs when a virus transfers bacterial DNA from one bacterial cell to another bacterial cell.

Fill in the blank: By definition, all sense (+) RNAs have a ____________ and ______________.

ribosome binding site and start codon

What's a bacteriophage?

Virus that infects bacteria

Describe two different ways that animal viruses gain entry into their host cell.

Animal viruses may enter by either (1) endocytosis (where receptors on the virus's capsid binds to molecules on the host cell surface, causing the host cell to take in the entire virus), or (2) fusion (where the viral envelope fuses together with the host cell's cytoplasmic membrane).

Describe two different ways that animal viruses exit from their host cell.

Animal viruses may leave their host cell by either (1) lysing open the host cell or (2) budding out of the host cell.

What's the relationship between antisense (-) RNA and sense (+) RNA?

Antisense (-) RNA is the complement to sense (+) RNA. For example, if an antisense (-) RNA strand has the sequence UACGAG on it, then you would know that the corresponding sense (+) RNA strand would have the sequence AUGCUC on it.

Describe two different ways that newly constructed bacteriophage can leave their host cell. How are these two ways different from one another?

Bacteriophage can either leave by lysing its host cell open (which kills the host cell), or via extrusion. During extrusion, the viral parts are assembled within the membrane of the host cell. Once assembled, the complete virus is then "pushed" (extruded) out without causing the host cell to die.

What are some basic structural difference between bacteriophage and animal viruses?

Bacteriophage have a complex structure (i.e. they are shaped kind of like insects, with a "body" and "legs"). Animal viruses don't have this complex structure. They have just a "head"; they don't have a "body" and "legs". Another difference: Animal viruses can have an envelope and matrix. Bacteriophage rarely have these structures.

How are viruses similar to bacteria?

Both viruses and bacteria are small, and both are capable of causing disease

When herpes virus is causing persistent infection, describe what it's doing inside its host cell.

Herpes virus causes persistent infection by staying in the nerve cell's cytoplasm without replicating. This is different from other viruses that cause persistent infection, which do so by integrating their genetic material into the DNA of the host (herpes virus does not integrate its genetic material into the host).

Herpes virus causes persistent infection in what type of cells?

Herpes virus causes persistent infection in nerve cells

In bacteriophage, what's the difference between productive infection and latent infection?

In a productive infection, a bacteriophage directs its host cell to make even more bacteriophage. These then leave the host cell to infect other cells. In a latent infection, bacteriophage DNA enters the host cell, but no new bacteriophage are produced. Instead, the bacteriophage DNA is copied and passed on every time its host cell divides.

Suppose that a bacterial cell is infected with Phage A. Would this make it easier or more difficult for another Phage A to infect the same cell? Explain your answer.

It is difficult for two of the same type of phage to infect the same bacterial cell. This is because, after a latent phage infects a bacterial cell, it produces a repressor protein that prevents other viruses from infecting that same cell. This makes it so that phage don't have to share its host cell (and all its resources) with other viruses.

What is lysogenic conversion? Give an example of lysogenic conversion.

Lysogenic conversion happens when a latent phage infects a bacterial cell, resulting in the bacterial cell having new abilities. For example, Corenybacterium diphtheriae is a bacterium that produces a toxin, but only if it's infected with a bacteriophage.

What's the difference between lytic bacteriophage and temperate bacteriophage?

Lytic bacteriophage can only cause productive infections. Temperate bacteriophage can cause latent infections, but then switch to cause productive infections.

Would you normally expect to find viruses that have an envelope, but no matrix?

No, they typically come as a package.

Can a (+) sense DNA strand be used to make another (+) DNA strand? Explain your answer.

Not directly. Sense (+) nucleic acid strands can only be used to build a complementary antisense (-) strand. But, once the antisense (-) strand is made, it can then be used to make a sense (+) strand.

Outline what happens during generalized transduction. As part of your answer, explain the role of nuclease.

One: A bacteriophage enters a host bacterial cell to cause productive infection. Two: As part of the process, the bacteriophage produces nuclease to destroy (cut up) the host cell's DNA. This makes it so that the cell no longer makes bacterial parts; instead, it makes all viral parts. Three: When new viruses are put together, sometimes a phage "accidentally" picks up a fragment of bacterial DNA (made from nuclease activity), instead of viral DNA. Four: When this phage infects a new cell, it transfers this bacterial DNA.

Outline and briefly describe the steps of a productive infection in bacteriophage

One: Attachment of viral receptors to molecules found on the host cell's surface. Two: Penetration of the viral genetic material into the host cell. Three: Biosynthesis of viral components (i.e. viral proteins and viral nucleic acids) Four: Assembly of all the viral components to make new, complete, viruses. Five: Release of newly produced viruses.

Outline what happens when a bacteriophage causes a latent infection.

One: Bacteriophage binds to specific molecule on surface of host cell. Two: Bacteriophage's DNA enters the host cell. Three: Bacteriophage's DNA becomes inserted into the DNA of the host cell. Four: Every time the host cell's DNA becomes replicated, the phage DNA becomes replicated along with it. This allows the phage DNA to be passed on to daughter bacterial cells.

Outline how the CRISPR-Cas system works to protect bacteria against repeat viral infections. As part of your answer, explain the roles of the following: palindromic sequences, Cas 1, Cas 9, crRNA, and spacers

One: Bacteriophage injects its DNA into a host bacterial cell. Two: The Cas1 protein in the bacterial cell takes a piece of the phage DNA, and inserts it into the bacterial DNA. Specifically, it becomes inserted in between two palindromic sequences found on the bacterial DNA. Three: Once inserted, the phage DNA is referred to as a spacer. This spacer can be transcribed to produce a type of RNA called crRNA. Four: When the bacterial cell is attacked by the same type of virus in the future, the crRNA works together with the Cas9 protein to bind to, and cut, the virus's DNA. This prevents the viral DNA from causing destruction to the host cell.

Explain how infection with human papillomavirus (HPV) can trigger cancer. As part of your answer, explain the roles of p53 and Rb proteins.

Rb and p53 are both proteins that are normally found in healthy cells. Their function is to stop cell division, especially if there's a defect in the cell. When HPV infects a cell, it deactivates Rb and p53. This makes it harder for cells to stop cell division. This could lead to tumor formation (tumors are made of cells that divide uncontrollably). If this uncontrolled cell growth spreads to other parts of the body, then that's when cancer occurs.

What's the function of restriction enzymes (in relation to infection with bacteriophage)?

Restriction enzymes are produced by bacterial cells. They cleave (cut up) viral DNA that enters the bacterium.

What's the relationship between sense (+) RNA and antisense (-) DNA?

Sense (+) and antisense (-) nucleic acids are complements of one another.

Fill in the blank: Another term for messenger RNA is _____ RNA.

Sense RNA

Which of these can be directly translated to make a protein? Sense (+) DNA Antisense (-) DNA Sense (+) RNA Antisense (-) RNA ...actually, more than one of the above can be directly translated to make a protein

Sense+ RNA

Describe the ways that viral nucleic acids (genomes) may differ from one another.

Some viral nucleic acids RNA, while others are DNA. Some viral nucleic acids are single-stranded, while others are double-stranded. Some viral nucleic acids are segmented (i.e. spread out over multiple nucleic acid "chunks"), while others are non-segmented (i.e. exist only as a single "chunk"). Some viruses have sense (+) nucleic acid, while others are antisense (-) nucleic acid.

What happens to the capsid of an animal virus once that animal virus has entered its host cell?

The capsid is released/broken down so that the virus's nucleic acid becomes released into the host cell.

What's a prophage?

The genetic material of a bacteriophage and incorporated in the genome of bacteria.

What's the function of the lysozyme gene that's found in the genome of bacteriophage? Your Answer: Lysozyme gene is responsible for breaking down bacterial cell wall so the knew viruses can break down and infect.

The lysozyme gene encodes for the lysozyme enzyme. This enzyme degrades the host (bacterial) cell's cell wall so that the newly formed viruses can become released.

What's the function of the nuclease gene that's found in the genome of bacteriophage?

The nuclease gene encodes for the nuclease enzyme, which degrades the chromosomal DNA of the host cell so that it can no longer be used. This makes it so that the host cell's resources (e.g. the host cell's ribosomes, amino acids, nucleotides, tRNA, ATP, etc.) can be devoted to producing viral (instead of host cell) materials.

What is meant by a viral "early gene"? What are two examples of early genes in bacteriophage?

Viral early genes are those that are expressed first, after the virus gains entry into its host cell (i.e. these are the viral genes that are needed immediately after the virus gains entry). Examples of bacteriophage early genes include the genes that encode for nuclease and polymerase.

How are viruses different from bacteria?

Viruses differ from bacteria in a few different ways; viruses are 100x smaller and because of that, they aren't able to produce ribosomes which results in no protein production. Viruses also contain no plasma membrane and are not able to replicate on their own.

In your own words, explain how damage to the host cell's DNA can trigger a latent bacteriophage to become productive. As part of your answer, explain the roles of the following: viral repressor protein, Rec A, Lex A, UmuD gene.

Whenever the host bacterial cell's DNA is heavily damaged, it tries to repair it by producing a protease called Rec A. Rec A removes a repressor protein (called Lex A) from the DNA of the bacterial cell. Once Lex A is removed, it allows the bacterium's UmuD gene to be turned on. This results in the productive of DNA polymerase V, which can then try to repair the heavily damaged DNA. The latent bacteriophage uses Rec A to escape from its damaged host. Rec A can bind to the viral repressor protein that blocks transcription of the virus's excisase gene. Once Rec A removes this repressor protein, the excisase enzyme can be produced. This enzyme then removes the viral DNA from the host bacterial DNA. Once removed, the viral DNA can then direct the host cell to make more viruses that can infect other cells (i.e. once removed, the viral DNA can then cause a productive infection).

Generally, under what circumstance would a phage "want" to switch from a latent to a productive replication cycle?

Whenever the host cell becomes damaged. In this situation, if a bacteriophage remains latent within the host, then it will probably die along with the host. Switching to a productive infection allows the virus to make more complete copies of itself, leave the damaged host cell, and find a healthy host cell to infect.

With regard to animal viruses, what's the difference between acute infection and persistent infection?

With acute infections, the disease symptoms/signs appear suddenly, but last a relatively short period of time. For example, the viruses that cause the common cold produce acute infections. On the other hand, persistent infections are those where the disease symptoms/signs are less severe (and may not appear at all). Persistent infections last a long time, compared to acute infections. For example, herpes virus can produce persistent infections.

The excisase gene is found on the...

bacteriophage's DNA

Enveloped viruses enter their host cell via _______, and exit their host cell via _______.

fusion; budding

When the excisase gene is turned off, it causes the bacteriophage to undergo _______ infection. When the excisase gene is turned on, it causes the bacteriophage to undergo _______ infection.

latent; productive

What's the purpose of the modification gene in bacteria?

makes something to protect bacteria from getting cut from the outside.