Question

17. The phages can reproduce through lysogenic or lytic cycles. In the lysogenic cycle, the phage DNA inserts into their host genome. The phage DNA remains inactive inside the bacterial genome and get replicated when bacterial DNA replicates. Identify the statement as True or false?

1. A phage is a virus that infects plants.
2. The phage that undergoes a lysogenic cycle is called a virulent phage.
3. An integrated phage is called a prophage.
4. A phage that reproduces strictly through the lytic cycle is called a prophage.
5. Virulent phages form plaques that are clear patches of lysed cells on a lawn of bacteria.

17. Plasmids are very common cloning vectors. They are circular supercoiled, extrachromosomal double-stranded DNA molecules, which naturally occur in bacteria, yeast and some high eukaryotic cells. There sizes range from 4.5 kb to 7,500 kb, and they vary in number from 7 to >50. Identify the statements as true or false.

1. Relaxed plasmids have uncontrolled replication, so they are present in multiple copies in a cell.
2. Stringent plasmids have uncontrolled replication, so only 1-2 copies could be found in a cell.
3. Two plasmids from two different incompatible group cannot co-exist.
4. Episomes are those plasmids that can integrate into their host’s chromosome.
5. Conjugative plasmids can mediate their own transfer into other cells.
6. The plasmid that can replicate in many different genera of bacteria is called *broad* host-range plasmid.

Answer 1

A) Bacteriophage

a. False

A bacteriophage (or phage), is a virus that do not directly interact or infect plants but it infects and replicates in bacteria and archaea.

b. False

Phages replicate only through the lytic cycle are known as virulent phages whereas, the phages that replicate using both lytic and lysogenic cycles are known as temperate phages.

c. True

When the DNA of phage is incorporated or integrated into the host cell genome, it is called a prophage.

d. False

Phage that replicate only by the lytic cycle is known as virulent phage and phage genome that inserted and integrated into the host genome is known as prophage.

e. True

The bacterial lawn is caused by a single phage particle or phage- infected bacterium and the plaques are even visual to the naked eye. Therefore, lytic or virulent phages exhibit clear plaques.

B) Plasmid

a. True

Plasmids that have independent replication of the bacterial chromosome with high copy number are under relaxed control of replication. Relaxed plasmids are not under the control of host genome replication.

b. False

The plasmid that have control replication along with the main bacterial chromosome and is present as a single or few copy in cell.

c. True

Plasmids which are incompatible are unable to coexist with in cell.

d. True

Few plasmids that insert and integrated into the host chromosome, and these integrated plasmids are sometimes referred to as episomes in prokaryotes.

e. True

Conjugative plasmids are circular DNA molecules that contain an origin of replication, genes encoding plasmid maintenance and transfer functions. So, these plasmids can mediate their own transfer one cell to another.

f. True

The broad-host-range (BHR) plasmids are plasmids that can self-transfer themselves and can stably replicate and maintain in bacterial species from at least two subgroups. They replicate in wide range of bacteria.