SINES

·         SINE’s, Short INterspersed Elements, are, as the name suggests, short DNA sequences. They are genetic elements with the ability to replicate themselves in the genome of a host cell. These elements are reverse-transcripted molecules of RNA who were transcripted from tRNA, a reaction that is catalyzed by RNA polymerase III. But these elements cannot produce the polymerase due to their short size and therefore are dependent of other elements of transpositions present in the host cell.

·         SINE’s are retrotransposions without LTR group (Non-long terminal repeat). LTR’s are used by virus to insert their genomic sequences in to the host genome and since these elements do not poses these terminal, they must associate with LINE’s.

·         Retrotransposons without LTR have 3 subtypes: LINE’s, SINE’s and Composite SINE Transposons. While LINE’s have the ability to perform all the functions required to retrotranposition, SINE’s do not have such capability and, therefore, link themselves with LINE’s. As for Composite SINE Transposons, two SINE’s connect to each other to flank and mobilize an intervening single copy DNA sequence.

Karyogram

A karyogram, also known as an ideogram, is a diagram or photograph representation of a karyotype (total number and appearance of chromosomes in the nucleus of an eukaryotic cell) arranged in pairs of homologous chromosomes of the same size, ordered by size and position of centromere.

Some zones of the chromosome, like the centromere and telomeres, are visible in the karyogram. Chromosome’s coloration shows dark zones intercalated with light zones, pending on GC and AT percentage.

Therefore, karyograms are very useful in cytogenetics due to the practical application for genetic studies such as hereditary anomalies (p.e. trisomy 21).

Figure 1. Karyogram of a human male karyotype using Giemsa as colorant.

Figure

Retrovirus

Retrovirus consists of two molecules of single-stranded RNA connected together. The double strand allows a higher rate of recombination gene.

 Virus are morphologically very similar to each other and are composed of proteins, RNA and membrane lipids.

The main feature of this virus is the reverse transcriptase enzyme that produces DNA from an RNA molecule.

The virus recognizes the cell surface and fuses with the plasma membrane. After penetration of the viral nucleocapsid, occurs the reverse transcription of virus RNA into viral DNA that migrates to the nucleus of the cell and integrates in the host cell DNA. Then starts the transcription of this DNA into viral RNA, consequently proteins are also produced and hundreds of new virus. One of the most familiar types of retrovirus is HIV, which infects humans blood T lymphocytes.

Endogenous Retrovirus

Endogenous Retroviruses are retroviral genomes inserted in vertebrate chromossomes, that might induce the synthesis of exogenous viruses. However, the majority does not have the capacity to form new viruses. So, these inactive sequences represent genome wide-repeats that can not proceed with any further proliferation.

 Fig.1- Human endogenous retrovirus (TEM)

Operon

It’s a group of genes from the gDNA (genomic deoxyribonucleic acid) in prokaryotes and some eukaryote organisms. The transcription of the operon simply takes to a polycistronic mRNA (messenger ribonucleic acid) molecule wich is composed by an operator, a promoter and other structural genes. The promoter associated to the operator controls the structural genes expression. The translation of the operon rises to several independent proteins with related metabolic functions.

DNA Transposons

DNA Transposons

  A small mobile genetic element (DNA) that moves around the genome or to other genomes within the same cell, usually by copying itself to a second site but sometimes by splicing itself out of its original site and inserting in a new location within the same or another chromosome, plasmid, or cell and thereby transferring genetic properties.

  Transposons have been used for transgenesis and insertional mutagenesis in different organisms, since these elements are not generally dependent on host factors to mediate their mobility. Consequently, DNA transposons are useful tools to analyze the regulatory genome, study embryonic development, identify genes and pathways implicated in disease or pathogenesis of pathogens, and even contribute to gene therapy.

Fig. 1: DNA transposon example

Cosmid

Cosmid

Figure 1 - A typical cosmid

                Cosmids are hybrid plasmid vectors that contain λ cos site. They were first described by Collins and Hohn in 1978. The λ cos site is the sequence needed so that the DNA molecule becomes recognized as part of the ‘λ genome’ by the proteins that package DNA into λ phage particles.

                Inside the cell, the cosmid DNA is incapable of directing the synthesis of new phage particles. As an alternative the cosmid DNA replicates as a plasmid.
The length of the cloned DNA can be as long as the available space within λ cos site. A cosmid can be 8 kb or less in size, so up to 44 kb of new DNA can be inserted before the packaging limit of the λ phage particle is reached. Recombinant DNA is obtained from colonies and can be used to build genomic libraries.