Plasmids in Molecular Biology

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Questions and Answers

What is the primary function of a plasmid within a host cell?

To provide structural support to chromosomes

To replicate independently and carry genes (correct)

To degrade unwanted DNA

To serve as a template for RNA synthesis

Which enzyme is primarily responsible for constructing plasmids by joining DNA fragments?

DNA ligase (correct)

Helicase

DNA polymerase

Restriction enzyme

What type of interaction can plasmids have with their host cells?

Only parasitic

Only symbiotic

Either symbiotic or parasitic (correct)

None of the above

What characteristic is most commonly associated with plasmids?

Providing antibiotic resistance Signup and view all the answers

Which type of plasmid integrates into the host's chromosome to replicate?

Episome Signup and view all the answers

What is the maximum size that some plasmids can reach?

Up to 250 kilobases Signup and view all the answers

In which type of cells are plasmids predominantly found?

In bacteria, yeasts, archaea, and some eukaryotic cells Signup and view all the answers

Which scientist is credited with coining the term 'plasmid'?

Joshua Lederberg Signup and view all the answers

Which of the following statements about plasmids is false?

They always remain integrated in the host's chromosome. Signup and view all the answers

What is a key characteristic of restriction enzymes in the context of plasmid construction?

They are used to cut DNA at specific sites. Signup and view all the answers

What is the primary function of the origin of replication (ORI) in plasmids?

To start the replication process of the plasmid Signup and view all the answers

How do non-integrating plasmids replicate within a host cell?

Independently without integrating into the host chromosome Signup and view all the answers

What is a common use of plasmid vectors in biotechnology?

To insert traits such as disease resistance in crops Signup and view all the answers

Which of the following best describes a recombinant plasmid?

A plasmid that carries an inserted gene of interest Signup and view all the answers

In gene therapy, which characteristic of plasmids is specifically utilized?

Their capacity to replicate independently Signup and view all the answers

What role do selectable markers play in plasmid cloning?

To ensure the survival of only genetically modified cells Signup and view all the answers

Which of the following is a characteristic of plasmid vectors compared to naturally occurring plasmids?

They are engineered to have specific traits. Signup and view all the answers

Which plasma example is known to cause severe illness due to its virulence plasmid?

Escherichia coli Signup and view all the answers

What is primarily produced using plasmid vectors in biotechnology?

Large quantities of proteins Signup and view all the answers

Which of the following processes involves inserting a healthy gene into a patient's cells?

Gene therapy Signup and view all the answers

Study Notes

Plasmids

A small, circular DNA molecule separate from the host cell's chromosome.
Replicates independently within a host cell, making it a replicon.
Found naturally in bacteria, yeasts, archaea, and some eukaryotic cells.
Can form symbiotic or parasitic relationships with host cells.
Carries genes responsible for specific characteristics in the host cell, including antibiotic resistance.
Replicates prolifically, creating double-stranded fragments.
Commonly used as cloning vectors to transfer foreign DNA into host cells.

History

Discovered in bacterial cells in the late 1940s.
Named "plasmid" in 1952 by Joshua Lederberg, during studies involving Salmonella and the P22 virus.
Defined as any extra-chromosomal hereditary element.
Understanding of plasmids was refined after the discovery of the double-helix DNA structure in 1952.

Plasmid Construction

Uses restriction enzymes to cut DNA at specific sites called restriction sites.
DNA fragments are joined using DNA ligase.
Plasmids vary in size, ranging from less than 1.0 kilobase to over 250 kilobases.
Smaller plasmids rely on the host cell's DNA replication enzymes for replication.
Larger plasmids may carry genes encoding their own replication enzymes.
Some plasmids integrate into the host chromosome for replication, becoming episomes (especially in bacteria).
Linear plasmids exist, but their replication mechanisms are different.

Origin of Replication (ORI)

A specific DNA sequence within plasmids where replication begins.
Usually composed of 50-100 base pairs.
Enables plasmid replication.
Host cell enzymes bind to the ORI to initiate replication.
Replication proceeds around the circular plasmid, ensuring daughter cells receive a copy.
Plasmid integration into a host bacterium can be non-integrating (replicating independently) or integrating (inserting into the host chromosome).

Plasmid Vectors

Engineered plasmids used in genetics and biotechnology.
Designed to be smaller than naturally occurring plasmids.
Employed as carriers for transferring genes into host cells.
Share similar features with naturally occurring plasmids, including self-replication, ORI, and unique genes (e.g., drug resistance genes).

Cloning

Involves inserting a gene into a host cell using a vector.
Plasmids are ideal cloning vectors due to their small size, efficient ORI, and cloning capacity of 100-10,000 base pairs.
Some plasmids have multiple cloning sites for DNA insertion.
Cloning often involves using the ORI, selectable markers, the gene of interest, and multiple cloning sites.

Protein Production

Plasmid vectors facilitate large-scale, cost-effective protein production.
For example, the human insulin gene can be inserted into a plasmid vector and introduced into bacteria.
The bacteria multiply, producing insulin in large quantities.

Gene Therapy

A medical advancement utilizing plasmid cloning vectors to deliver healthy genes into human cells.
Aims to cure or eliminate diseases by replacing or repressing defective genes.
Vectors are administered through direct injection or intravenously.
Used to treat diseases like cystic fibrosis, thalassemia, and hemophilia.

Disease Models

Plasmids play a role in creating disease models.
Used to create rat genetic models by modifying embryonic stem cells.
Used to manipulate adeno-associated viruses to create human disease models.

Recombinant Plasmids

Created by inserting a gene of interest into a cloning vector, such as a plasmid.
Act as carriers for the gene of interest into host cells.
Enable expression of the gene of interest in the host cells.

Selectable Markers

Ensure host cells contain the desired plasmid.
Typically antibiotic resistance genes.
Allow selection of cells harboring the plasmid by exposing them to selective conditions.
Enable elimination of unmodified bacteria.
Used for various applications, including genetic manipulation in fruit flies.

Plasmid Example: Virulence Plasmids

Found in bacteria, making them pathogenic.
Enable bacteria to spread and replicate easily.
Examples include Escherichia coli (causing diarrhea and vomiting) and Salmonella enterica.

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Description

This quiz explores the characteristics and history of plasmids, small DNA molecules that replicate independently within host cells. It covers their discovery, construction, and the role they play in genetic engineering, including antibiotic resistance. Test your knowledge of plasmids and their significance in molecular biology.