Biological Molecules Flashcards
What is the aim of genetic engineering?
To remove a gene (or genes) from one organism and transfer it into another so that the gene is expressed in its new host
What is recombinant DNA?
- It is DNA made by joining pieces from two or more different sources
- The DNA that has been altered by this process and which now contains lengths of nucleotides from two different organisms is called recombinant DNA (rDNA)
- The organism which now expresses the new gene or genes is known as transgenic organism or Genetically modified Organism
Why is genetic engineering useful?
- Overcomes barrier to gene transfer between species
- Unlike selective breeding, where whole sets of genes are involved, genetic engineering often results in the transfer of a single gene
What is the overview of gene transfer?
- For a GMO
1. The gene that is required is identified and it may be cut from a chromosome, made for mRNA by reverse transcription or synthesised from nucleotides
2. Multiple copies of the gene are made using PCR
3. The gene is inserted into a vector which delivers the gene to the cells of the organism. Examples of vectors are plasmids, virtues and liposomes
4. The vector takes the gene into the cells
5. The cells that have the new gene are identified and cloned
What are the necessary things for genetic engineering?
- Enzymes, such as restriction endonuclease, ligase and reverse transcriptase
- Vectors, including plasmids and viruses
- Genes coding for easily identifiable substances that can be used as markers
What is the class of restriction enzymes?
-Restriction endonuclease are a class of enzymes from bacteria which recognise and break down the DNA of invading viruses known as bacteriophages (phages for short)
What is the function of the restriction enzyme?
- They cut the sugar-phosphate backbone of DNA at specific places within the molecule
- This is why they are known as endonuclease (endo for within)
What is the role of restriction enzymes in bacteria?
To restrict a viral infection
How does a restriction enzyme work?
- Each restitution enzyme binds to a specific target site on DNA and cuts at that site
- These target sites, or restriction sites are specific sequences of bases
- E.G. the restrictions enzyme BamHI always cuts DNA where there is a GGATCC sequence on one strand and its complementary sequence, CCTAGG, on the other
How is bacterial DNA protected from the attack of a restitution enzyme?
Bacterial DNA is protected from such an attack either by chemical markers or by not having the target sites
How do restriction enzymes cut?
- Straight across the sugar phosphate backbone to give blunt ends
- Staggered fashion to give sticky ends
What are sticky ends?
- They are short lengths of unpaired bases
- They are known as sticky ends because they can easily form hydrogen bonds with complementary sequences of bases on other pieces of DNA cut with the same restriction enzyme
How do you find the wanted DNA?
- When long pieces of DNA are cut with a restitution enzyme, there will be a mixture of different lengths
- To find the specific piece of DNA required involved separating the lengths of DNA using gel electrophoresis and using gene probes
- Multiple copies of the required piece of DNA can be made used PCR
How do you insert a gene into a plasmid vector?
-In order to get a new gene into a recipient cell, a vector has to be used e.g. plasmid
What are plasmids?
- Short, circular pieces of double stranded DNA
- Plasmids occur naturally in bacteria and often contains genes for antibiotic resistance
- They can even be exchanged between bacteria (and even different species of bacteria)
- If the genetic engineer inserts a piece of DNA into a plasmid, then the plasmid can be sued to take the DNA into a bacterial cell
