Plasmids

Question 1

Where are plasmids mainly found?

Answer 1

They are mainly found in Bacteria.

Question 2

What are plasmids?

Answer 2

They’re small, circular, double stranded DNA molecule which is distinct from the a cell’s chromosomal DNA.
It’s an extrachromosomal DNA element, which isn’t connected to the chromosomal DNA and can replicate independently.

Question 3

Are the genes carried on the plasmid crucial for the survival of the bacterium?

Answer 3

No, they’re not crucial under normal environmental conditions. Where they may be gained or lost without harming the cell.

Question 4

Mention the genetic advantages that the plasmids give.

Answer 4

Plasmids may carry genes for antibiotic resistance, tolerance to toxic metals, production of toxins, and the synthesis of enzymes.

Question 5

Where are plasmids found in human?

Answer 5

They’re not found in the nucleus but they are found in the mitochondria.

Question 6

What are R factors ? (Restriction factors)

Answer 6

R factors are plasmids that carry genes that give their host cell resistance to antibiotics, heavy metals, or cellular toxins. Which give the plasmids a significant medical importance.

Question 7

How many groups of genes do R factors contain?

Answer 7

They contain two groups of genes.

Question 8

Mention two examples of antibiotic resistant bacteria.

Answer 8

(1) Dysentery epidemic infectious agent.

(2) Normal bacteria from the patients such as E. coli.

Question 9

When were resistance factors first discovered?

Answer 9

They were first discovered in Japan in the late 1950s after several dysentery epidemics.

Question 10

How did the antibiotic resistance spread?

Answer 10

The bacteria acquired resistance through the spread of genes from one organism to another. The plasmids mediated this transfer are R factors.

Question 11

Why are plasmids an important tool for genetic engineering?

Answer 11

Due to the presence of synthetic plasmids (vectors) whose most important property is self-replication, so they serve as vehicles for the replication of desired DNA sequences.

Question 12

What is a vector (synthetic plasmids) in molecular biology?

Answer 12

A vector, refers to a plasmid that is engineered to make it a more useful tool for molecular biologists.

Question 13

When can a vector be capable of replicating?

Answer 13

A vector must be capable of replicating once in a cell.

Question 14

Why do vectors serve as vehicles for the replication of desired DNA sequences?

Answer 14

Because any DNA that is inserted in the vector will be replicated in the process.

Question 15

Mention an example of synthetic plasmids and its length.

Answer 15

pBR322, its length is 4361 bp.

Question 16

What are the characteristics which have to be found in a synthetic plasmid?

Answer 16

(1) Origin of replication
(2) Multiple cloning site
(3) Resistance gene
(4) Marker genes

Question 17

What is an origin of replication?

Answer 17

This is the specific sequence of nucleotides where DNA replication begins.

Question 18

What is a multiple cloning site?

Answer 18

This site contains recognition sites for specific restriction enzymes. These restriction enzymes can be used to cut the plasmid so foreign DNA can be pasted in by ligation.

Question 19

What is a resistance gene?

Answer 19

This gene codes for a protein the bacteria need in order to survive in a particular growth medium, for example, when a specific antibiotic is present.

Question 20

What are marker genes ? What do we mean by selectable marker?

Answer 20

They are common selectable marker genes (It protects the organism from a selective agent to identify it) are for antibiotic resistance or for an enzyme that carries out an easily identified reaction.

Question 21

Mention a plasmid vector used for cloning in the bacterium E. coli .

Answer 21

A plasmid vector used for cloning in the bacterium E. coli is pUC19. (Identify the different sites of pUC19 in the original lecture)

Question 22

What are shuttle vectors?

Answer 22

They are plasmids which are capable of existing in several different species.

Question 23

What is the importance of a shuttle vector? Mention some examples.

Answer 23

It can be used to move cloned DNA sequences among organisms, such as among bacterial, yeast, mammalian cells, or among fungal, and plant cells. Shuttle vectors can be very useful in the process of genetically modifying multicellular organisms.

Question 24

Mention an example for when shuttle vectors can be very useful in the process of genetically modifying multicellular organisms.

Answer 24

For example, trying to insert herbicide resistance genes into plants.

Question 25

What is the difference between cloning and expression vectors?

Answer 25

1) Cloning vectors are vectors are used to make many copies of a specific target gene.
2) Expression vectors are used for expression (production) of protein of a specific target gene which is inserted.