Chapter 19 Genetic Technology Essay QS

Question 1

Describe the use of recombinant DNA technology in the synthesis of human insulin by bacteria. [9]

Answer 1

• mRNA coding for insulin/isolate gene for human insulin
• from beta cells of islets of Langerhans/pancreas
• reference to reverse transcriptase
• to cDNA
• reference PCR / DNA polymerase / double strand
• reference sticky ends
• use of vector/virus/plasmid
• reference endonuclease / restriction enzymes
• to cut plasmid
• reference DNA ligase to join DNA
• inserted into suitable host cell / E. coli / bacteria
• reference method of insertion
• identification of modified bacteria
• reference growth / culture of engineered bacteria in fermenters

Question 2

Explain the roles of restriction endonucleases, ligases & reverse transcriptase in genetic engineering. [8]

Answer 2

Restriction endonucleases
- cut DNA
- at, restriction site / specific (base) sequences / target sequence
- ref. to palindrome
- give, sticky / blunt, ends

Ligases:
- join gene to, plasmid / (named) vector
- seal (sugar-phosphate) backbone
- make, phospho(di)ester / covalent, bonds
- make recombinant, DNA / plasmid / vector

Reverse transcriptase:
- makes cDNA
- from mRNA
- ref. to DNA single-stranded initially
- AVP

Question 3

Describe & explain the properties of plasmids that allow them to be used in gene cloning. [7]

Answer 3

• double stranded DNA
• have, restriction site / target sequence for restriction enzyme
• allows gene (for cloning) to be inserted
• small
• plasmid can, enter / transform / be taken up, by (host) cell / bacterium
• circular
• stable
• contain, (named) marker genes / (named) genes for antibiotic resistance
• used to identify, GM / transformed / recombinant, (bacterial) cells
• replicate, fast / independently (of host cell replication)
• get many copies of cloned gene
• AVP: may carry promoter / act as a vector / easy to extract from bacteria / high copy number

Question 4

Explain the use of genes for fluorescent or easily stained substances as markers in gene technology. [6]

Answer 4

• emits bright light
• when exposed to UV light
• visible colour change
• add marker gene to the, vector / plasmid
• easy to identify transformed bacteria
• gene of interest inserted, into / close to, marker gene
• easy to identify recombinant, DNA / plasmid
• easy to identify transgenic organisms
• examples; e.g. GFP / β galactosidase / GUS
• idea of no known risk

Question 5

Describe the principle of the polymerase chain reaction (PCR). [9]

Answer 5

• production of a large number of copies of a length of DNA / amplification of DNA
• rapid
• only small sample of DNA needed
• DNA, denatured / separated into two strands, by heat / at 95°C
• primer (DNA) added
• reference to annealing at, 60 - 65°C
• reference to complementary base pairing
• DNA / Taq, polymerase
• replicates (template) strand at, 70 - 75°C
• heated again to separate strands / process repeated
• Taq polymerase, is heat stable / has high optimum temperature
• does not need replacing each cycle
• efficient process

Question 6

Describe how the polymerase chain reaction is used to clone & amplify DNA. [8]

Answer 6

• DNA denatured / ssDNA produced
• by heating to, 94 / 95°C
• add primer (DNA)
• complementary base pairing (with sample DNA)
• at 55 - 65°C
• ref. to annealing
• DNA polymerase builds new strands / AW
• by adding free nucleotides
• at 70 - 75°C
• ref. to Taq polymerase thermostable
• does not need replacing
• new strand denatured & process repeated
• process is automated

Question 7

Explain how a microarray can be used to analyse gene expression in a tissue sample. [9]

Answer 7

• Microarray - a tool used to detect the expression of thousands of genes at the same time & to identify the genes present in an organism’s genome.
• Probes are, single-stranded DNA which are synthesised to be complementary for a specific base sequence.
• probes correspond to thousands of different genes

Procedure:
- extract mRNA
- mRNA used (as a template) to make cDNA
- by reverse transcription / using reverse transcriptase
- (c)DNA, linked to / labelled using, fluorescent dye
- (c)DNA added to microarray
- (c)DNA, binds to / hybridises, to probes
- by complementary base pairing
- excess (c)DNA washed off
- exposed to, UV light / laser
- fluorescence shows the expressed genes
- intensity of fluorescence shows level of gene expression

Question 8

Explain what is meant by bioinformatics & outline the role of bioinformatics following the sequencing of genomes of humans & parasites. [6]

Answer 8

• analysis of biological data using computer software
• databases of, gene / DNA / protein / amino acid, sequences
• ref. to large databases
• fast / accurate / efficient
• ref. to allows data to be, shared / pooled
• can predict, amino acid sequences / protein structure (from DNA sequence data)
• ref. to analytical tool; e.g. BLAST
• ref. to comparisons
• used to find methods to control parasites
• named example of control; e.g. vaccine
• AVP: personalised medicine, identify new diseases
• ref. to common ancestor
• phylogenetic analysis
• biodiversity / new species

Question 9

Explain the advantages of treating diabetics with human insulin produced by genetic engineering. [6]

Answer 9

• constant / reliable supply all year round / unlimited supply
• less risk of contamination / infection
• identical to insulin produced in the body
• less / no risk of allergic reaction
• does not stimulate the immune system
• fewer side effects
• can be produced without the killing of animals / ethical reason
• cheaper / easier to extract & purify
• more available / large amount
• more rapid response

Question 10

Explain the advantages of using recombinant DNA techniques to produce human proteins, such as factor VIII or adenosine deaminase. [7]

Answer 10

• can produce large(r) quantities
• use bacterial host / hamster cell host / insect larva cell
• product exactly the same as human protein
• (as) product has same amino acid sequence
• no immune response
• no side effects
• no risk of transfer of disease
• easier to obtain purified product

Question 11

Discuss the advantages of screening for genetic conditions. [8]

Answer 11

• information about the increased risk of person having genetic conditions
• ref. breast cancer / named example
• allows people to prepare for late onset genetic conditions
• ref. Huntington’s disease / Alzheimer’s disease / named example
• identify whether fetuses are going to develop a genetic condition
• so can give early treatment when born
• allows parents to prepare for the birth of a child who will need treatment for a considerable time or even throughout life
• identifies carriers of genetic conditions
• helps to provide early diagnosis
• allows couples who are both carriers of a genetic condition to make decisions about starting a family / having more children / seeking IVF

Question 12

Discuss the advantages & disadvantages of genetic screening for HD. [6]

Answer 12

Advantages:
- know of the allele before having children
- take steps not to pass on allele / gene / condition
- test embryo & terminate if positive / test IVF embryo & do not implant if positive
- appropriate, AI / donor oocyte / donor embryo
- activity / physiotherapy to delay onset

Disadvantages:
- know will suffer from incurable disease in time
- positive test on offspring means untested parent knows must have allele
- positive test on parent means any offspring has 1 in 2 chance of having allele

Question 13

Discuss the potential advantages of growing genetically modified crops, using examples to help your answer. [7]

Answer 13

• increase, food production / crop yields
• improve food, quality / taste / keeping properties
• add nutrients to crop (to improve human health)
• crops may be more tolerant to climate change
• crops, can be grown in poor quality land / do not need as much fertiliser
• pest / insect / fungal disease, resistance (increases crop growth)
• less pesticide used
• benefit to farmer; e.g. cost effective / health benefit
• benefit to environment; e.g. less effect on food chains, pollinators
• herbicide resistance reduces competition from weeds
• could engineer nitrogen-fixing ability in non-leguminous crops
• specific examples (crop variety & enhancement described) (e.g. Golden Rice for extra vitamin A)
• Bt maize / Bt cotton, kill (named) leaf-eating insects
• Flavr Savr tomato, stores better / can ripen on vine

Question 14

Outline the principles of genetic engineering. (4)

Answer 14

• add DNA to give a new (named), characteristic / protein
• restriction, enzyme to obtain, gene / section of DNA / to cut plasmid
• combine gene with, vector / plasmid
• introduce, (recombinant) vector / plasmid, to, bacterium / (named host) cell
• clone / multiply, (named, recombinant / GM) organism