Learning Genetics (2)

Now, only a couple of years later, no scientist using genetic engineering would work without the “ gene scissors “ Genschere . The CRISPR-Cas9 has revolutionized the methods of genetics.

What does CRISPR-Cas9 mean? CRISPR means “Clustered Regularly Interspaced Short Palindromic Repeats” and they occur as short DNA repeats (length 23–47 bp) within of the genomes of Archaea and bacteria.

The CRISPR process comprises three parts: there are two RNA-molecules involved – the CRISPR RNA, the tracr RNA and also an endonuclease (an enzyme) which is called Cas9 (formerly called Csn1). Cas stands for “CRISPR associated”. Endonucleases are enzymes which cut up DNA or RNA. Cas9 is a pair of sharp molecular scissors, guided by an RNA molecule.

Remember: DNA and RNA are the polymeric molecules that carry the genetic information. DNA is the molecule that stores the genetic information in the chromosomes of eukaryotes. RNA is the genetic material of many viruses. In bacteria and eukaryotes the RNA is transcribed from DNA and carries the information for protein synthesis (translation) to the ribosomes.

What is the function of CRISPR-Cas9 in the bacterial cell and how does it work? The bacterial CRISPR-Cas9 system helps each bacteria to destroy viruses and immunize itself against virus DNA or RNA that infects the cell. The defense mechanism is basically divided into 3 stages.

First, the adaptation: the Cas9 endonuclease finds specific regions on the viral DNA or RNA and snips out short parts of the viral genome (spacers). These parts are then inserted into the CRISPR loci of the bacterial genome. Second, the expression: the inserted spacers are transcribed into CRISPR-RNA (crRNA). Together with the tacrRNA (trans-activating crRNA) the two RNA molecules form a complex that guides the Cas9 to its target sequence.

In the third stage, interference , the Cas9/crRNA destroys the infectious viral DNA or RNA. Thereby, CRISPR-Cas forms a kind of prokaryotic immune system by memorizing the invasive viral DNA or RNA and makes subsequent destruction of foreign DNA or RNA more efficient. If the same virus reappears, the bacteria is able to identify the viral genome and cut it up to render it harmless .

What does Genome Editing mean? Genome Editing (also called genome engineering) is a method of inserting specific genes into the target genome, to alter certain genes or to delete specific genes from the genome. Scientists have modified the CRISPR-Cas9 system so that it is now also possible to use it in eukaryotic cells from multicellular organisms, e.g., plants, animals or even humans. The CRISPR-Cas9 is a highly reliable , easy-to-use and versatile method for genome editing in the laboratory. The site-specific Cas9 endonuclease is guided to its target DNA by the CRISPR-RNA and the tracrRNA in bacteria. For genome editing specific guide-RNA (gRNA) is designed to specifically target a certain nucleotide sequence. Thus, scientists can use CRISPR-Cas9 to cut out specific genes or silence genes (by cutting out functional parts of the gene) in the organism they wish to investigate. They may insert activator sequences into certain genes to induce gene expression or they may insert new genes into the genome or replace specific sequences within genes.

What are the benefits of using CRISPR-Cas9 for Genome Editing? Emmanuelle Charpentier and her colleagues discovered a way to simplify Genome Editing. They combined the two RNA-molecules to create one single molecule. When the two molecules are unified , the investigators only have to program one RNA-molecule after the gene sequence. This manipulated molecule will direct Cas9 to cut this specific gene sequence off the viral genotype and incorporate it into the CRISPR-sector of the bacteria (or eukaryotic cells). The cell will then have the new character traits that the geneticists wanted it to have or will lose old character traits. The system is simple, requiring just a Cas endonuclease and a gRNA against the target sequence.

What does the future hold for CRISPR-Cas9? We can see how the CRISPR-research developed rapidly over the last five years. In 2012 there were 127 publications that concerned CRISPR-Cas9. Only one year later the number rose to 277 publications. In 2015, two years later, the amount mounted up to almost 500. We can expect current developments of up to 1,100 papers about CRISPR-Cas9 this year. More and more scientists are interested in CRISPR-Cas9 and want to discover ways to develop it.

Bibliography 1. http://dict.leo.org 2. www.cdc.gov 3. www.dict.cc 4. www.mpg.de 5. www.nature.com 6. www.webster-dictionary.org

EXERCISE: 1. What is CRISPR? a) an auto immune response b) a virus infection c) an adaptive immune system of prokaryotes

2. What are the benefits of CRISPR? a) is able to cut any genes in a precise location by either adding or removing nucleotides b) inexpensive c) easy

3. Where does CRISPR come from? a) a French molecular biologist developed CRISPR b) an American molecular biologist developed CRISPR c) it was developed by a German molecular biologist

You’ll find the answers on: http://tinyurl.com/weiterbildung-englisch

Die Autorin: Carmen Lobitz mail@lobitz-seminare.de www.lobitz-seminare.de Carmen Lobitz ist freie Trainerin, Lehrerin und MTA. Sie gründete 1998 in Berlin lobitz seminare, die u.a. Englischseminare für Health Professionals anbieten.

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Lösung für Exercise:

Answer: 1. a), b) Answer: 2. b) Answer: 3. b)

Learning Genetics (2)

What does CRISPR-Cas9 mean?

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Learning Genetics (2)

What does CRISPR-Cas9 mean?

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