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AQA A-Level Biology - Gene technology Exam Questions with Latest Update
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AQA A-Level Biology - Gene technology Exam Questions with Latest Update
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AQA A-Level Biology - Gene technologyExam Questions with Latest Update
How can target genes be isolated using restriction enzymes? - Answer--DNA contains
specific pallindromic sites called restriction sites
-Restriction enzymes can cut DNA at these restriction sites (active site complementary
to specific base sequence of DNA)
-If there is is a restriction site either side of the target gene
-Restriction enzymes can be used to cut the target gene out
-Restriction enzymes leave the DNA with sticky ends (unpaired bases)
How can target genes be isolated using reverse transcriptase? - Answer--As cells only
have two copies of each gene, it is hard to access these in the nucleus
-Reverse transcriptase can convert mRNA into its complementary DNA
-This DNA has no introns as splicing has taken place to form the mRNA
Ηow can target genes be isolated through artificially synthesizing the gene? - Answer--
Use a gene machine to make the DNA from scratch
-Join about 25 nucleotides together at once to form an oligonucleotide
-Join the oligonucleotides together to form a synthetic gene
-This method can be used to design your own genes/proteins
What do you need to add to the target gene so that it can be inserted? - Answer--
Promotor region - short sequence of DNA that RNA polymerase is complementary to
-Terminator region - indicates that the RNA polymerase can leave
-Sticky ends
-Marker gene
Vector - Answer--Something that's used to move DNA from one place to another
Give two examples of vectors - Answer--Virus - bacteriophage
-Plasmid - double stranded loop of DNA that transfers genes between bacteria
How can the gene be inserted into a vector? - Answer--Use the SAME restriction
enzyme to cut the plasmid at its own restriction site
-Ensures the sticky ends of the plasmid and target gene are complementary
-Use DNA ligase to reform the phosphodieseter bonds between DNA
-Forms recombinant DNA (DNA from more than one source/organism e.g. human target
gene and bacteria)
Transgenic organism - Answer--Contains recombinant DNA
How can the vector be inserted into the bacteria? - Answer--Use ice cold calcium
chloride
, -Heat shock
-Doing this increases the permeability of the bacteria cell wall
Marker genes - Answer--Genes that are paired with target genes to ensure the vector
has been inserted properly
Why are marker genes used? - Answer--To check which bacteria have taken up vectors
and hence become transgenic
-These transgenic bacteria are also called transformed bacteria as they contain
recombinant DNA (Target gene, marker gene and their own plasmid DNA)
-Because bacteria often don't take up vectors
Give two examples of marker genes - Answer--U.V. Fluoresence
-Antibiotic resistance
Why are marker genes easily identified? - Answer--Only bacteria that have accepted the
vector (transformed bacteria) will:
-Fluoresce under under U.V. Light
-Will be able to survive in an antibacterial culture
What does the use of maker genes ultimately enable? - Answer--Selection of
transformed bacteria
-Can culture these to harvest the target gene protein
What is the purpose of the polymerase chain reaction (PCR)? - Answer--Used to
amplify DNA (make millions of copies)
-Sometimes called in vitro DNA amplification
What do we need to carry out PCR? - Answer--DNA sample
-Excess of free DNA nucleotides to not limit the rate of reaction
-Primer - short sequence of DNA that is complementary to the start of the DNA sample -
this is used to select which part of the DNA is copied
-DNA polymerase
What is the method of PCR? - Answer--Heat to 95 degrees celcius to break the
hydrogen bonds between DNA making it single stranded
-Cool to 50 degrees celcius to allow the primers to anneal through complementary base
pairing. This makes DNA double stranded again so that DNA polymerase can bind
-Heat to 70 degrees so that DNA polymerase can join together the free DNA
nucleotides attached through complementary base pairing through condensation
polymerisation forming phosophodiester bonds
-Repeat the cycle to double the DNA (1 - 2 - 4 - 8 etc)
Gene therapy - Answer--Changing the faulty allele that causes the genetic disease
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