Lecture 6 - Transposons in Prokaryotes | Genetics (Zoology) by ILLL, DU - Biotechnology Engineering (BT) PDF Download

 Page 1


 
Institute of Lifelong Learning, University of Delhi 
 
 
 
 
 
 
NME-Zoology 
Genetics 
Lesson: Transposons in Prokaryotes 
Lesson Developer: Dr. Jaya Malhotra
1
 
                     Dr. Shailly Anand
2 
College/Dept: Hansraj College 
Deen Dyal Upadhyay College 
University of Delhi 
 
 
 
 
 
 
 
 
 
 
 
Page 2


 
Institute of Lifelong Learning, University of Delhi 
 
 
 
 
 
 
NME-Zoology 
Genetics 
Lesson: Transposons in Prokaryotes 
Lesson Developer: Dr. Jaya Malhotra
1
 
                     Dr. Shailly Anand
2 
College/Dept: Hansraj College 
Deen Dyal Upadhyay College 
University of Delhi 
 
 
 
 
 
 
 
 
 
 
 
TRANSPOSONS IN PROKARYOTES 
 
Institute of Lifelong Learning, University of Delhi  Page 2 
 
 
Table of Contents 
 
 
? Introduction  
? Genetic instability led to discovery of transposons 
 
? Transposons in prokaryotes 
? IS elements 
? Composite transposons 
? TN3 like elements 
? Summary  
? Exercise/ Practice 
? Glossary 
? References/ Bibliography/ Further Reading 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Page 3


 
Institute of Lifelong Learning, University of Delhi 
 
 
 
 
 
 
NME-Zoology 
Genetics 
Lesson: Transposons in Prokaryotes 
Lesson Developer: Dr. Jaya Malhotra
1
 
                     Dr. Shailly Anand
2 
College/Dept: Hansraj College 
Deen Dyal Upadhyay College 
University of Delhi 
 
 
 
 
 
 
 
 
 
 
 
TRANSPOSONS IN PROKARYOTES 
 
Institute of Lifelong Learning, University of Delhi  Page 2 
 
 
Table of Contents 
 
 
? Introduction  
? Genetic instability led to discovery of transposons 
 
? Transposons in prokaryotes 
? IS elements 
? Composite transposons 
? TN3 like elements 
? Summary  
? Exercise/ Practice 
? Glossary 
? References/ Bibliography/ Further Reading 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
TRANSPOSONS IN PROKARYOTES 
 
Institute of Lifelong Learning, University of Delhi  Page 2 
 
 
Introduction 
A major variation in nearly all genomes is caused by Transposable elements (TEs), also 
known as "jumping genes," which are DNA sequences that move from one location on the 
genome to another. The mark of a transposon is that it does not utilize an independent form 
of element like phage or plasmid but directly hops from one site to another. Often 
transposons carry additional sequences to new sites and thus result in genome restructuring 
leading to mutation. Transposons have been identified in almost all the living organisms 
that include bacteria, fungi, protists, plants and animals. Bacteriophages can also integrate 
themselves in bacteria and thus can be considered as transposons but because of its large 
size and huge number of genes other than those required for transposition it is not 
considered as transposons.  
Transposons that mobilize via DNA are widespread in both prokaryotes and eukaryotes. 
Each transposon carries genes that code foe enzyme activities required for its own 
transposition, although it may also require ancillary functions of the genome in which it 
resides like DNA polymerase or DNA gyrase. 
Transposable elements of all kinds can promote rearrangements of the genome directly or 
indirectly: 
a. Transposition event itself may cause deletions or inversions or lead to the movement 
of a host sequence to a new location. 
b. Transposons serve as substrates for cellular recombination systems by functioning as 
portable regions of homology: two copies of a transposon at different location may 
provide sites for reciprocal recombination. 
Watch the video and learn about transposon: 
https://www.youtube.com/watch?v=sHpg7puzfcQ  
 
 
 
Value Addition: Video 
Heading text: Simple transposition mechanism  
Body text: Click on the link below and learn about the mechanism of transposition 
https://www.youtube.com/watch?v=0d76-gbOYtg  
Source: You Tube 
Page 4


 
Institute of Lifelong Learning, University of Delhi 
 
 
 
 
 
 
NME-Zoology 
Genetics 
Lesson: Transposons in Prokaryotes 
Lesson Developer: Dr. Jaya Malhotra
1
 
                     Dr. Shailly Anand
2 
College/Dept: Hansraj College 
Deen Dyal Upadhyay College 
University of Delhi 
 
 
 
 
 
 
 
 
 
 
 
TRANSPOSONS IN PROKARYOTES 
 
Institute of Lifelong Learning, University of Delhi  Page 2 
 
 
Table of Contents 
 
 
? Introduction  
? Genetic instability led to discovery of transposons 
 
? Transposons in prokaryotes 
? IS elements 
? Composite transposons 
? TN3 like elements 
? Summary  
? Exercise/ Practice 
? Glossary 
? References/ Bibliography/ Further Reading 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
TRANSPOSONS IN PROKARYOTES 
 
Institute of Lifelong Learning, University of Delhi  Page 2 
 
 
Introduction 
A major variation in nearly all genomes is caused by Transposable elements (TEs), also 
known as "jumping genes," which are DNA sequences that move from one location on the 
genome to another. The mark of a transposon is that it does not utilize an independent form 
of element like phage or plasmid but directly hops from one site to another. Often 
transposons carry additional sequences to new sites and thus result in genome restructuring 
leading to mutation. Transposons have been identified in almost all the living organisms 
that include bacteria, fungi, protists, plants and animals. Bacteriophages can also integrate 
themselves in bacteria and thus can be considered as transposons but because of its large 
size and huge number of genes other than those required for transposition it is not 
considered as transposons.  
Transposons that mobilize via DNA are widespread in both prokaryotes and eukaryotes. 
Each transposon carries genes that code foe enzyme activities required for its own 
transposition, although it may also require ancillary functions of the genome in which it 
resides like DNA polymerase or DNA gyrase. 
Transposable elements of all kinds can promote rearrangements of the genome directly or 
indirectly: 
a. Transposition event itself may cause deletions or inversions or lead to the movement 
of a host sequence to a new location. 
b. Transposons serve as substrates for cellular recombination systems by functioning as 
portable regions of homology: two copies of a transposon at different location may 
provide sites for reciprocal recombination. 
Watch the video and learn about transposon: 
https://www.youtube.com/watch?v=sHpg7puzfcQ  
 
 
 
Value Addition: Video 
Heading text: Simple transposition mechanism  
Body text: Click on the link below and learn about the mechanism of transposition 
https://www.youtube.com/watch?v=0d76-gbOYtg  
Source: You Tube 
TRANSPOSONS IN PROKARYOTES 
 
Institute of Lifelong Learning, University of Delhi  Page 2 
 
 
Broadly the transposons can be classified into three categories according to the way they 
transpose (Fig 1). 
 
 
 
Fig 1. Types of transposons classified on the basis of their 
transposition. 
Source: Author 
1. Cut and paste transposons – Transposon is excised from the original position and 
inserted to another position in the genome. The target site is cleaved and ligated 
after the integration of the transposon. They are also called as excisive transposons. 
For example IS elements and composite transposons in bacteria. Cut and paste 
transposons are found in both prokaryotes and eukaryotes. This method of 
transposition is also known as conservative mechanism of transposition since the 
transposon cuts itself and move to another position, so no new copy of transposon is 
created unlike replicative transposons (Fig 2). 
 
 
 
Page 5


 
Institute of Lifelong Learning, University of Delhi 
 
 
 
 
 
 
NME-Zoology 
Genetics 
Lesson: Transposons in Prokaryotes 
Lesson Developer: Dr. Jaya Malhotra
1
 
                     Dr. Shailly Anand
2 
College/Dept: Hansraj College 
Deen Dyal Upadhyay College 
University of Delhi 
 
 
 
 
 
 
 
 
 
 
 
TRANSPOSONS IN PROKARYOTES 
 
Institute of Lifelong Learning, University of Delhi  Page 2 
 
 
Table of Contents 
 
 
? Introduction  
? Genetic instability led to discovery of transposons 
 
? Transposons in prokaryotes 
? IS elements 
? Composite transposons 
? TN3 like elements 
? Summary  
? Exercise/ Practice 
? Glossary 
? References/ Bibliography/ Further Reading 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
TRANSPOSONS IN PROKARYOTES 
 
Institute of Lifelong Learning, University of Delhi  Page 2 
 
 
Introduction 
A major variation in nearly all genomes is caused by Transposable elements (TEs), also 
known as "jumping genes," which are DNA sequences that move from one location on the 
genome to another. The mark of a transposon is that it does not utilize an independent form 
of element like phage or plasmid but directly hops from one site to another. Often 
transposons carry additional sequences to new sites and thus result in genome restructuring 
leading to mutation. Transposons have been identified in almost all the living organisms 
that include bacteria, fungi, protists, plants and animals. Bacteriophages can also integrate 
themselves in bacteria and thus can be considered as transposons but because of its large 
size and huge number of genes other than those required for transposition it is not 
considered as transposons.  
Transposons that mobilize via DNA are widespread in both prokaryotes and eukaryotes. 
Each transposon carries genes that code foe enzyme activities required for its own 
transposition, although it may also require ancillary functions of the genome in which it 
resides like DNA polymerase or DNA gyrase. 
Transposable elements of all kinds can promote rearrangements of the genome directly or 
indirectly: 
a. Transposition event itself may cause deletions or inversions or lead to the movement 
of a host sequence to a new location. 
b. Transposons serve as substrates for cellular recombination systems by functioning as 
portable regions of homology: two copies of a transposon at different location may 
provide sites for reciprocal recombination. 
Watch the video and learn about transposon: 
https://www.youtube.com/watch?v=sHpg7puzfcQ  
 
 
 
Value Addition: Video 
Heading text: Simple transposition mechanism  
Body text: Click on the link below and learn about the mechanism of transposition 
https://www.youtube.com/watch?v=0d76-gbOYtg  
Source: You Tube 
TRANSPOSONS IN PROKARYOTES 
 
Institute of Lifelong Learning, University of Delhi  Page 2 
 
 
Broadly the transposons can be classified into three categories according to the way they 
transpose (Fig 1). 
 
 
 
Fig 1. Types of transposons classified on the basis of their 
transposition. 
Source: Author 
1. Cut and paste transposons – Transposon is excised from the original position and 
inserted to another position in the genome. The target site is cleaved and ligated 
after the integration of the transposon. They are also called as excisive transposons. 
For example IS elements and composite transposons in bacteria. Cut and paste 
transposons are found in both prokaryotes and eukaryotes. This method of 
transposition is also known as conservative mechanism of transposition since the 
transposon cuts itself and move to another position, so no new copy of transposon is 
created unlike replicative transposons (Fig 2). 
 
 
 
TRANSPOSONS IN PROKARYOTES 
 
Institute of Lifelong Learning, University of Delhi  Page 2 
 
          Fig 2. Cut and paste mechanism of transposition. The 
transposon is cleaved and integrated to another position in the 
genome.  
Source: Author 
Learn more about cut and paste mechanism of transposons by clicking the link 
https://www.youtube.com/watch?v=XYZHMGUGq6o  
2. Replicative transposons – these types of transposons are replicated before 
transposition. An enzyme known as transposase helps in the insertion of one copy to 
a new site while another copy remains at the original site. This insertion is facilitated 
by another enzyme resolvase encoded by the DNA sequence on such transposons. It 
is only present in prokaryotes (Fig 3). Examples Tn3 and Mu phages 
 
 
Fig 3. Mechanism of transposition by replicative transposons. 
One copy move to new position and the other copy is present at 
the original site.  
Source: Author 
 
3. Retrotransposons – As the name suggests retro means going back so in such 
types, retrotransposons produces an RNA molecule which is reverse transcribed into 
DNA molecule with the help of the enzyme reverse transcriptase. This newly 
synthesized DNA is then inserted into a new position in the genome. It is only 
present in eukaryotes (Fig 4).