NON – CODING DNA CHAITRALI .V. JADHAV

ROLL NO:- 07PAPER - 4

Noncoding DNA in Eukaryotes : Introduction

Each cell in our bodies has about 6 feet of DNA stuffed into it.

-However, less than one inch is devoted to genes! Non-coding DNA describes components of an organism’s DNA

sequences that do not encode for protein sequences. In many eukaryotes, a large % of an organism’s total genome size

is non-coding DNA. Amount of non-coding DNA & the proportion of coding versus non-

coding DNA varies greatly between species. Much of this DNA has no known biological function & was referred

to as “Junk DNA”.

Utricularia Gibba has 3% of non-coding DNA, which is low for flowering plants.

Types of non- coding DNA sequences

Non- coding functional RNA

Cis- and Trans- regulatory elements

Introns

Pseudogenes

Repeat sequences, transposons and viral elements

Telomeres

1.Non- coding Functional RNA

The RNA molecules which are not translated into proteins.

For eg:- Ribosomal RNA, Transfer RNA &

Micro RNA

2.Cis- and Trans- Regulatory Elements

Those are sequences that control the transcription of a nearby gene.

Located within 5’ or 3’ untranslated regions or within introns.

trans-regulatory element control the

transcription of a distant gene.

3. Introns

They are non-coding sections of a gene.

Transcribed in the precursor m-RNA sequence

but is ultimately removed by RNA splicing.

Most of the introns appear to be mobile

genetic elements.

4. Pseudogenes

They are related to known genes, that have lost their

protein-coding ability or are otherwise no longer

expressed in the cell.

Arise from retrotransposition or genomic duplication of

functional genes.

Therefore become “Genomic Fossils” : non-functional.

5.Repeat Sequences, Transposons & Viral Elements

Transposons & Retrotransposons are mobile genetic element.

Retrotransposons : LINEs, SINEs – account for large proportion of the

genomic sequences in many species.

Over 8% of the human genome is made up of endogenous retrovirus

sequences as a part of over 42% fraction that is recognizably derived

of retrotransposons.

Remaining 3% can be identified to be the remains of DNA

transposons.

6. Telomeres

Telomeres are regions of repetitive DNA.

Located at the end of a chromosome.

They provide protection from chromosomal

deterioration during DNA replication.

FUNCTIONS OF NON-CODING DNA

They have strong biological functions : some regions that are highly conserved are under evolutionary pressure & positive selection. Some specific sequences of non-coding DNA are essential for chromosome

structure, centromere function & homolog recognition in meiosis. From study over 300 prokaryotic & 30 eukaryotic genomes, eukaryotes

appear to require less amount of non-coding DNA. Apart from this : 1. protection of the genome 6. Enhancers

2. Genetic switches 7. Silencers

3. Regulation of gene expression 8. Promoters

4. Transcription factor sites 9. Insulators

5. Operators

USES OF NON-CODING GENE

Non-coding DNA evolution

Long range Correlations

Foreinsic anthropology

REFERENCES

www.Wikipedia.org www.google.com www.Princeton.edu T. A. Brown