8 answers to end-of-chapter questions

8 Answers to end-of-chapter questions
Multiple choice questions
Structured questions
Cutting the gene / length of DNA for insulin from genome • From mRNA carrying information for making insulin • From the amino acid sequence for insulin b i Restriction / restriction endonucleases
• Sticky ends produced / the terminal portion has a stretch of
• the strands are not of the same length Biology Unit 1 for CAPE® Examinations Original material Cambridge University Press 2011 • DNA ligase
• Is used to link together the deoxyribose–phosphate backbones of the DNA molecule producing a closed circle of the double-stranded DNA • Adding of calcium ions to make the membrane more
permeable / by heat shock / adding calcium ions at 0 °C and raising it to 40 °C suddenly vii Cloning of the treated bacteria
Screening of the bacteria to determine which have the recombinant DNA • Multiplication / cloning of selected colony with insulin gene • Expression of gene / production of insulin Adding a gene that causes fluorescence under ultraviolet light • Adding a gene that produces a harmless product that can be plasmid rejoined, insulin gene joins insulin gene tetracycline-resistance with itself to form added to iii Exposed to ampicillin
• The 3 black and 3 grey colonies survive exposure to • The bacteria would have taken up the plasmid with the • These bacteria will include recombinant and non-recombinant • The circular foreign DNA which were taken up by some bacteria (white colonies) did not have the ampicillin-
Exposed to tetracycline
• Any colonies that are resistant to tetracycline would not have • These colonies would survive / the grey colonies • If the foreign DNA is added to the plasmid, the tetracycline • These colonies would die / the black colonies Biology Unit 1 for CAPE® Examinations Original material Cambridge University Press 2011 Essay questions

• Used to cut up viral DNA • To protect the bacteria from invading viruses / phages Obtain the required gene (cDNA) using mRNA carrying information for making insulin and reverse transcriptase • Make the single-stranded cDNA double stranded and with sticky • Use restriction enzyme to cut the vector plasmid / pBR322 • Vector has 2 antibiotic-resistance markers • The tetracycline-resistance gene would be cut by restriction enzyme • Mix the cut vector plasmid with the insulin DNA fragments and • Mix the plasmids / vector with the host cells / bacterial cells • Incubate in a calcium chloride solution to make bacterial cells more • Allow the bacteria to clone themselves • Screen the colonies to determine which ones have the insulin gene • Using replica plating, subject the colonies to ampicillin • The colonies that die do not have a vector / plasmid / antibiotic- • Subject the rest of the colonies to tetracycline • The colonies that die contain the insulin gene since tetracycline gene • These colonies are cloned and the insulin gene expressed • Disadvantage: could increase the risk of other, potentially pathogenic, bacteria taking up the genes and becoming resistant to antibiotics [2] • More efficient than collecting from animals • Identical to human insulin so better response / little immune reaction • Ethical / religious reasons for not collecting from animals DNA made by joining lengths of DNA from two different species • Organism which possesses DNA / genes from another species and which is incorporated in their genome and actually expressed. They are created to produce a new phenotype Biology Unit 1 for CAPE® Examinations Original material Cambridge University Press 2011 b Benefits
The social impact has to do with its potential and actual impact on human society and individuals • Higher crop yields so that people have more food • Enhance the nutritional content of crops (e.g. Golden Rice™) so that people are better fed / fewer deficiency diseases • Permit better targeted clean-up of wastes and pollutants • Lead to production of more effective and cheaper medicines
Potential hazards
• Produce super-weeds or otherwise interfere with ecosystems in unexpected ways, reducing crop yields so that people have less food • Increase costs of seed • Some seeds cannot be used for sowing the next year since they are modified to prevent germination thereby reducing crop production / increasing debt burdens • Cause antibiotics to become less useful Ethical impact is to do with issues of whether it is right or wrong, good or bad to conduct research and develop genetically modified organisms (GMOs) • It is good to conduct such research to develop GMOs that might improve nutrition, the environment and health • It is wrong to continue such research when the potential impact of the technology is unknown and many aspects of it remain to be understood • It is wrong to use the results of such research when it involves release of GMOs into the environment as once it is released it cannot be taken back / there are unknown risks The treatment of a disease by manipulating the genes in a person’s cells • Treatment of a genetic disorder by altering a patient’s genotype / Dominant allele can mask defective recessive allele when added to the genome • Recessive allele does not have to be removed / inactivated / switched • Dominant disease allele would have to be inactivated which is very Biology Unit 1 for CAPE® Examinations Original material Cambridge University Press 2011 Person suffering from CF has faulty CFTR protein • Results in thick mucus in respiratory passages • Faulty CFTR alleles are recessive single gene disorder • Somatic gene therapy employed • Normal allele is inserted into liposomes / vector • The vector / liposomes are introduced into patient by nasal sprays • The liposomes move through the plasma membrane carrying the • The allele must be incorporated into the affected cells / host’s • The dominant normal allele should be transcribed and then • Since it is somatic / cells die, treatment has to be repeated d Benefits
• Cures the patient / no longer suffers from the disease
• Relieves some symptoms

Hazards
• Allele may be inserted into another gene, altering the product / • Allele may be inserted into tissue other than target tissue with • Allele may be inserted into germ line and passed via gametes • Virus which carries allele may damage the tissue • Allele may be inserted into a promoter of a gene and may • Allele may be inserted in a position where it affects the genes that Biology Unit 1 for CAPE® Examinations Original material Cambridge University Press 2011

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