6.1

• Mutations are changes in the sequence of nucleotides in DNA molecules.
• Types of mutations include insertion/deletion mutations, point mutation/substitution, nonsense mutation, missense mutation, and silent mutation.
• Some people object to genetic engineering due to the potential effect it might have on the environment, or because of the idea that genetically modified seeds would not be as easily available to poorer farmers.
• Benefits of genetic engineering include insect resistance in crops such as soya and genetically used animals used to produce pharmaceuticals.
• Mutations can either have neutral effects where the mutation causes no change to the organism, for example in a case where the mutation occurs in a non-coding region of DNA or is a silent mutation, as described above.
• Some mutations are beneficial, for instance, humans developed trichromatic vision through a mutation.
• Harmful mutations include a mutation in the CFTR protein which causes cystic fibrosis.
• Whether a mutation proves to be beneficial or detrimental to an organism will depend on the environment of the organism.
• Gene expression can be controlled at the transcriptional, post-transcriptional and post-translational levels.
• An example of transcriptional control is the lac operon, which is a length of DNA composed of structural genes and control sites which controls the expression of beta-galactosidase responsible for hydrolysis of lactose in E.coli.
• The operon consists of a promoter region which is the binding site for RNA polymerase to initiate transcription, operator region where the inhibitor binds and structural genes which give rise to 3 products, beta galactosidase, lactose permease and another enzyme.
• The inhibitor protein is coded for by a regulator gene, located outside the operon.
• In a case where the concentration of glucose is high and the concentration of lactose is low, the transcription of the structural genes is inhibited due to binding of the repressor to the operator region.
• Bacteria which have successfully taken up a plasmid can be identified with the help of marker genes.
• DNA profiling can also be used to determine genetic relationships between organisms.
• Gel electrophoresis is a process used to separate the DNA fragments and proteins according to their size using an electric current.
• If a plasmid takes up the insert, base pairing takes place between the complementary ends which are then sealed with the use of DNA ligase which forms phosphodiester linkages.
• The fragments are incubated with the plasmids.
• Isolated DNA fragments can be placed in plasmids in a following way: Plasmid and gene are cut with the same restriction enzyme to create complementary ends.
• A recombinant DNA molecule is created.
• Restriction enzymes cut DNA at specific base sequences and so are extremely useful in genetic engineering whereby genes from one species can be added to a different species.
• Gene sequencing has allowed for the sequences of amino acids in polypeptides to be predicted and has allowed for the development of synthetic biology.
• If sticky ends are missing, they can be added.
• Somatic gene therapy is a short-term solution only and needs to be repeated, whereas germ-line therapy is a permanent solution which will be passed down to the offspring.
• Gene therapy is the insertion of a normal allele into target cells to replace a faulty allele, such as the allele which causes a cystic fibrosis.
• Comparing genomes of individuals enables differences to be identified which can then be used for development of personalised medicine tailored to a particular genome, as well as in studies of human diseases.
• DNA profiling is a forensic technique used to identify individuals by characteristics of their DNA.
• Main techniques used in DNA profiling are: Polymerase chain reaction known as PCR which is used to amplify the DNA by making millions of identical copies of a given DNA sample.
• Plasmids are the most common vectors but viruses are also used in genetic engineering.
• Electroporation facilitates the process by increasing the permeability of bacterial membranes thus increasing the chance of success.
• There are many ethical considerations regarding genetic engineering.
• There are two types of gene therapy: somatic gene therapy where the allele is introduced to the target cells only and germ line gene therapy where the allele is introduced to embryonic cells, thus meaning every cell contains the normal allele.
• Genetic engineering is used in the formation of transgenic microorganisms, where electroporation is used to stimulate bacterial cells to take up plasmids.
• In a case where the concentration of glucose is low and concentration of lactose is high, lactose binds to the repressor thus causing the shape of its DNA binding site to change, therefore making it ineffective.
• Gene expression can also be controlled by transcription factors which have the ability to switch genes on and off.
• Gene expression is controlled at the post-transcriptional level by editing of the primary mRNA transcript, during which the non-coding regions called introns are removed, thus creating a mature transcript consisting only of protein-producing regions known as exons.
• Gene expression can be controlled at the post-translational level.
• Homeobox genes are involved in controlling the development of body plan of organisms thus aiding the development of a zygote to a complete organism.
• DNA sequencing begins with the process of mapping where the existing information about the genome is used to identify the locus of a particular gene within the genome.
• Comparing genomes between species is significant as it allows evolutionary relationships between species to be determined, and it is also beneficial to medical research.