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Home >> Genetics Dictionary >> Restriction site Reverse transcriptase

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Restriction Site
A DNA sequence recognized by a restriction endonuclease. Ribonuclease Any enzyme that hydrolyzes RNA.

Retina
The back wall of the eye onto which images are projected. From the retina, the information is sent to the brain via the optic nerve.

Retroviral Infection
The presence of retroviral vectors, such as some viruses, which use their recombinant DNA to insert their genetic material into the chromosomes of the host's cells. The virus is then propogated by the host cell.

Reverse Transcriptase
An enzyme used by retroviruses to form a complementary DNA sequence (cDNA) from their RNA. The resulting DNA is then inserted into the chromosome of the host cell.
2. An enzyme that synthesizes a single strand of DNA using RNA molecules as templates; occur in oncogenic RNA viruses

3. Any of the deoxyribonucleic acid (DNA) polymerases present in particles of retroviruses, that is, in virions of ribonucleic acid (RNA) tumor viruses and related viruses. These DNA polymerases are coded by the retroviruses and are able to carry out DNA synthesis using an RNA template. This reaction is called reverse transcription since it is the opposite of the usual transcription reaction, which involves RNA synthesis using a DNA template.

Thus, the viral DNA polymerases that carry out this reverse reaction have been called reverse transcriptases, and the viruses with this enzyme are called retroviruses because they reverse the usual flow of genetic information. Such viruses are much discussed now, since the etiologic agent of acquired immune deficiency syndrome (AIDS) is a retrovirus

Genetic information flow
DNA carries the genetic information of all living systems except RNA viruses. As shown in Figure the genetic information in DNA for proteins is first transferred to an RNA molecule, messenger RNA, by a process called transcription and then to the final product, protein, by a process called translation. The other process of information transfer in living systems except for RNA viruses is the multiplication of DNA by a process known as replication.

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In all living systems except some viruses, genetic information flows only from DNA to DNA and from DNA to RNA to protein.

Fig.l Modes of genetic information transfer found in all living systems except some viruses.

Modes of Genetic Information Transfer Found in all Living Systems Except Some Viruses

(a) DNA	(b) Transcription (RNA Polymerase)	(c) Replication (DNA Polymerase)	(d) RNA
(e) Translation	(f) DNA	(g) Protein

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Viruses are simple genetic systems that consist of genes coding for viral structural components and for proteins necessary for virus replication. VirusSes can replicate only in living cells. Viruses are grouped into three major classes according to the kind of nucleic acid contained in the extracellular and intracellular viral genomes.

There are viruses whose genome is only DNA (DNA viruses or deoxyviruses), viruses whose genome is only RNA (RNA viruses or riboviruses), and viruses whose genome is RNA in extracellular virus particles and DNA inside cells (retroviruses). There are also viruses whose genome is DNA in extracellular virus particles and RNA inside cells (pararetroviruses, that is, hepadnaviruses such as hepatitis B virus and caulimoviruses). Deoxyviruses use the same modes of information transfer as do cells. Riboviruses use information transfer from RNA to RNA in addition to information transfer from RNA to protein. Retroviruses use an additional mode of information transfer from RNA to DNA

Fig. 2 Modes of information transfer that characterize the replication of viruses in three major classes. (a) DNA viruses or deoxyviruses (example: smallpox virus); (b) RNA viruses or riboviruses (example: poliovirus); and (c) retroviruses (example: Rous sarcoma virus and human immunodeficiency virus).

DNA Viruses or Deoxyviruses

1. DNA
2. RNA
3. DNA
4. Protein

1. RNA
2. RNA
3. Protein
4. Protein

1. RNA
2. Virus DNA Polymerase
3. DNA
4. RNA
5. DNA
6. Protein
7. RNA

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Genetic Dictionary - Part 3 Reproductive Character Displacement - Restriction Enzyme Cutting Site Restriction Site - Reverse Transcriptase RFLP (Restriction Fragment Length Polymorphism) - RNA (Ribonucleic Acid) RNA Polymerase - Rule of Segragation Sagittal Crest - Scoliosis Secondary Cancer - Selfing Semi Conservative Replication - Sex Influenced Trait Sex Limited Trait - Sickle Cell Anemia Sigma Factor - Solenoid Structure Somatic Cell Genetic Mutation - Spina Bifida Splice Site - Stromatoporoid Structural Genomics - Synaptonemal Complex Syndactyly - Synteny Tandem Repeat - Telomere Telophase - Theropod Three Point Cross - Transduction tRNA (Transfer RNA) - Transition Transposable Element - Transposons Transversion - Trisomy 21 Tumor Suppressor Gene - Typology Unequal Crossing Over - Uracil Van Valen, Leigh - Virulence Virus - Vrijenhoek, Robert Wake, David - Wrangham, Richard X Chromosome - Xenograft Y Chromosome - Y Junction Zinc Finger - Zygonema / Zygotene