Transposons final for zoology final year.pptx

transposons

1. UTTAM MEMORIAL COLLEGE SUBJECT-Molecular cell biology TOPIC-Transposons Presented by: Suthirtha Roy M.sc. Zoology (2 nd sem ) Guided by: Babli maam

2. SYNOPSIS Introduction Discovery of transposable element Characteristics of Transposable element Types of Transposons Cut and paste transposons Replicative transposons Retro elements Impact & application of Transposons Conclusion References

3. INTRODUCTION Transposons are DNA segments found in genomes of living organism. A transposable element (TE) is a DNA sequence that can change its relative position (self- transpose) within the genome of a single cell. These segments of DNA, found virtually all cells, move, or "jump," from one place on a chromosome (the donor site) to another on the same or a different chromosome (the target site).

4. Discovery of transposable element Barbara McClintock was a geneticist who  first discovered transposons, also known as "jumping genes", in corn (maize) in 1948. McClintock proposed the existence of "controlling elements" that could change position within the genome and affect gene expression. Later, in 1960s becteria were shown to posses transposable element. H er discovery is now a fundamental concept in genetics Her groundbreaking research earned her the Nobel Prize in Physiology or Medicine in 1983.

5. Characteristics of Transposable element They are DNA sequence that code for enzymes which bring about the insertion of an identical copy of themselves into a new DNA site. Transposition events involve both recombination and replication processes which frequently generate two daughter copies of the original transposable elements. one copy remains at the parent site while others appears at the target site. The insertion of transposable elements invariably disrupts the integrity of their target genes. Transposable elements carry signals for the initiation of RNA synthesis, they sometimes activate previously dormant genes. No homology exists between the transposons and the target site for its insertion.

6. Types of Transposons On the basis of their transposition mechanism, Transposons maybe categorized into following category:

7. Cut and paste transposons They transpose by cutting of the transposable sequence from one position in the genome and its insertion to another position within the genome. The cut and paste transposition involves two transposase sub units. Each transposase sub units binds to the specific sequences at the two ends of transposons. These subunit of transposons protein then come together and lead to the excision of transposon. The excised 'transposon-transposase complex' then gets integrated to the target recipient site. In this manner, the transposons is cut from one site by a mechanism mediated by transposase protein. Examples of cut and paste type of transposons are IS-elements, P-elements, in maize, hobo- elements in drosophila etc.

8. Fig.- Cut and paste transposons

9. Replicative transposons They transpose by a mechanism which involves replication of transposable sequence and this copy of DNA, so formed, is inserted into the target site while the donor site remains unchanged. In this type of transposition, there is a gain of one copy of transposon and both the donor and the recipient DNA molecule are having one-one transposable sequence each, after transposition. Example- Tn3-elements. Fig.- Replicative transposons

10. Retro elements Their transposition is accomplished through a process which involves the synthesis of DNA by reverse transcription by using elements RNA as the template. This type of transposition involves an RNA intermediate; the transposable DNA is transcribed to produce an RNA molecule. This RNA is then used as a template for producing a complementary DNA by the activity of enzyme reverse transcriptase. The single stranded DNA copy so formed, is then made double stranded and then inserted into the target DNA site. The transposable elements which requires reverse transcriptase for their movement are called retro transposons. The retro elements may be viral or non-viral.

11. Impact & application of Transposons Transposons have played a significant role in shaping the evolution of genomes. Their mobility can create mutations, alter gene expression, and contribute to genetic variation, which is vital for evolution. . Transposons have also been co-opted by organisms to serve beneficial roles, such as forming regulatory elements or contributing to the evolution of new genes. Scientists utilize transposons to study gene function, create transgenic models, and develop treatments for genetic diseases. However, unchecked transposition can lead to genetic disorders, cancers, and genome instability. Understanding their impact is crucial for grasping both the risks and evolutionary advantages they offer.

12. Conclusion Transposons, or "jumping genes," are dynamic DNA elements capable of moving within genomes. Discovered by Barbara McClintock, they revolutionized our understanding of genetic variability and regulation. They can move via different mechanisms: cut-and-paste, replicative, and retro transposition. Transposons can disrupt or activate genes, contributing to mutations, evolution, and genome complexity. They play critical roles in gene regulation, genome restructuring, and disease development. Understanding transposons provides insights into evolution, genetic diversity, and disease mechanisms.

13. References 1. Molecular cell biology : J.H Darnell, H. Lodish and D. Baltimore Scientific American book Inc USA 2. Molecular biology of the cell : B.Alberts , D. Bray, J. Lewis, M. Raff, K. Roberts, and J. D. Watson, Garland Publishing Inc NY 3. Molecular cell biology : P. K Gupta 4. Molecular cell biology : D Robertis

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