Selfish DNA

Honors Genetics

DNA – Genes and the Rest Genic ( Gene containing portion of DNA) - Genes are viewed as “ORFS” – Open

Reading Frames – These are determined by a start

3’ TAC and a stop ATT5’Genes account for 25% of our DNA In a gene there are coding regionsExons Between the Exons there are intervening

sequences called Introns

What is the product of a Gene ? Proteins – All types such as

transmembrane proteins , transport proteins, immune proteins, messenger proteins, enzymes, channels, toxins, developmental proteins

( hox), transcription factors, and many more RNAs – m RNA ( intermediate in protein

synthesis), t RNA required for protein synthesis, r RNA( ribosomal RNA’s), RNAi, antisense RNAs, micro RNAs, snurps, spliceosome RNAs and many more

ORF

What is a Gene?

Gene Expression

Spliceosome – editing the primary transcript

Intron Borders

DNA to Protein Only 1% of DNA actually defines the

structure of genes and proteins Out of 46 chromosomes containing 30,00-

50,000 genes only 1% is actively engaged in keeping you alive

Making a Protein http://www.johnkyrk.com/DNAtranslation.h

tml

Genes are grouped in islands on chromosomes Genes are in clusters on chromosomes What is between – the space between the

genes contains DNA that has survived through evolution

It is believed to be the substance of mutations – contributing to change in the change for both the positive and negative

Genes were thought to be fixed in one location on a chromosome 17q31.2

Barbara McClintock discovered “ jumping genes” Jumping genes are referred to as mobile They have the ability to change their position and

jump from one chromosome to another Jumping genes are also called TRANSPOSONS

The Original Jumping Genes

Transposons 1) IS - insertion sequence. Inverted

repeats + transposase gene 2) Composite transposon. Two IS elements

+ antibiotic resistance gene(s) 3) Noncomposite transposon. Inverted

repeats + transposase gene + antibiotic resistance gene(s)

Transposon Action

Transposon structure

Transposable elements and the new meaning of mutation

Retrotransposons Retrotransposons move by a "copy and paste" mechanism

but in contrast to the transposons described above, the copy is made of RNA, not DNA.

The RNA copies are then transcribed back into DNA — using a reverse transcriptase — and these are inserted into new locations in the genome.

Many retrotransposons have long terminal repeats (LTRs) at their ends that may contain over 1000 base pairs in each.

Like DNA transposons, retrotransposons generate direct repeats at their new sites of insertion. In fact, it is the presence of these direct repeats that often is the clue that the intervening stretch of DNA arrived there by retrotransposition. About 40% of the entire human genome consists of retrotransposons.

Sines ( Short Interspersed elements) SINEs are short DNA sequences (100–400

base pairs) that represent reverse-transcribed RNA

Alus - Thousands of our Alu elements occur in the introns of structural genes.

Alu Action ALU elements have been accumulating in the human genome

throughout primate evolution, reaching a copy number of over a million per genome. However, most of these Alu copies are not identical and can be classified into several subfamilies (reviewed in DEININGER and BATZER 1993 ).

These different subfamilies of Alu elements were generated once mutations occurred within the "master" or "source" gene that actively retroposed at different rates and time periods of primate evolution (DEININGER et al. 1992 ).

Currently, the Alu retroposition rate is reduced by 100-fold from its peak early in primate evolution (SHEN et al. 1991 ). The vast majority of the Alu elements present in the human genome inserted before the radiation of extant humans and are therefore observed in all individuals in the human population.

Microsatellites Studies show that microsatellites, tandem repeat

sequences abundant in the genomes of higher eukaryotes, contain reiterating A-rich loci, which are involved in the higher-order organization of the chromatin

Other studies have shown satellites consisting of about 1 million copies of a 221-bp tandem repeat unit has been localized in the centromeres of 58 of the 64 horse chromosomes

Many hundreds of studies have implicated mutations in satellites, minisatellites, and microsatellites, in diseases which show genetic linkage, including studies on Crohn's disease

What is Selfish DNA? The theory that we creatures exist for the

preservation of genes and are nothing more than their throwaway survival machines.

Natural selection means the differential survival of the “ fittest”

Does natural selection “ choose” the most fit individuals or the most fit genes?

What are the characteristics of Selfish DNA? They have been called "junk" DNA and

"selfish" DNA. "selfish" because their only function seems

to make more copies of themselves and "junk" because there is no obvious benefit

to their host.

Some theories on Alus Some of these contain sequences that when

transcribed into the primary transcript are recognized by the spliceosome.

These can then be spliced into the mature mRNA creating a

new exon, which will be transcribed into a new protein product.

Alternative splicing can provide not only the new mRNA (and thus protein) but also the old.

In this way, nature can try out new proteins without the risk of abandoning the tried-and-true old one.

Alternative splicing http://www.exonhit.com/UserFiles/Image/

epissage.swf?PHPSESSID=otrsjha8drtbpuah7knuu4c394

http://www.exonhit.com/index.php?page=59

Alternative Splicing