genome projects & genome technology Flashcards
Describe how DNA is replicated in a cell.
• DNA strands separate / hydrogen bonds broken;
• Parent strand acts as a template / copied / semi-conservative replication;
• Nucleotides line up by complementary base pairing; (Adenine & Thymine etc)
• Role of DNA polymerase: joins adjacent nucleotides on the developing strand via condensation and formation of phosphodiester bond;
• 5’ to 3’ direction
• Each new DNA molecule has 1 template and 1 new strand
• Formed by semi-conservative replication.
Why is the DNA heat to 95°C during PCR?
• Produce single stranded DNA
• Breaks WEAK hydrogen bonds between strands
Why do you add primers during PCR?
• Attaches to / complementary to start of the gene / end of fragment;
• Replication of base sequence from here;
• Prevents strands annealing
Explain why ‘base-pairs’ is a suitable unit for measuring the length of a piece of DNA.
• DNA = 2 chains / joined by linking of 2 bases / A with T and G with C/ purine pairs with pyrimidine;
• Bases are a constant distance apart / nucleotides occupy constant distance/
• each base-pair is same length / sugar-phosphate is a constant distance;
Name one mutagenic agent.
• high energy radiation /ionising particles e.g. named particles/α, β, γ & X-rays;
• benzene;
• x rays/cosmic rays;
• uv (light);
• carcinogen / named carcinogen;
• mustard gas / phenols / tar (qualified);
A deletion mutation occurs in gene 1.
Describe how a deletion mutation alters the structure of a gene.
• removal of one or more bases/nucleotide;
• frameshift/(from point of mutation) base sequence change;
Describe the main stages in the copying, cutting and separation of the DNA.
• heat DNA to 95°C / 90°C;
• strands separate;
• cool so that primers bind to DNA;
• add DNA polymerase/nucleotides;
• use of restriction enzymes to cut DNA at specific base sequence/ breaks phosphodiester bonds
• use of electric current and agar/gel;
• shorter fragments move further;
Describe the polymerase chain reaction.
• Heat DNA;
• Breaks hydrogen bonds/separates strands;
• Add primers;
• Add nucleotides;
• Cool;
• (to allow) binding of nucleotides/primers;
• DNA polymerase;
• Role of (DNA) polymerase;
• Repeat cycle many times;
Describe a plasmid.
• circular DNA;
• separate from main bacterial DNA;
• contains only a few genes;
Suggest one reason why DNA replication stops in the polymerase chain reaction.
• Limited number of primers/nucleotides; /
Primers / nucleotides ‘used up’.
• DNA polymerase (eventually)denatures
Suggest why the restriction enzyme has cut the human DNA in many places but has cut the plasmid DNA only once.
• enzymes only cut DNA at specific base sequence/recognition site/specific point;
• sequence of bases/recognition site/specific point (on which enzyme acts)
• occurs once in plasmid and many times in human DNA;
• (max 1 if no reference to base sequence or recognition site)
Describe how the bacteria containing the insulin gene are used to obtain sufficient insulin for commercial use.
• use of fermenters;
• provides nutrients plus suitable conditions for optimum growth/named
• environmental factor;
• reproduction of bacteria;
• insulin accumulates and is extracted;
Explain what is meant by a vector.
• Carrier;
• DNA/gene; (context of foreign DNA)
• Into cell/other organism/host;
Explain how modified plasmids are made by genetic engineering and how the use of markers enable bacteria containing these plasmids to be detected.
• isolate TARGET gene/DNA from another organism/mRNA from
• cell/organism;
• using restriction endonuclease/restriction enzyme/reverse transcriptase to
• get DNA;
• produce sticky ends;
• use DNA ligase to join TARGET gene to plasmid;
• also include marker gene;
• example of marker e.g. antibiotic resistance;
• add plasmid to bacteria to grow (colonies);
• (replica) plate onto medium where the marker gene is expressed;
• bacteria/colonies not killed have antibiotic resistance gene and (probably) the TARGET gene;
• bacteria/colonies expressing the marker gene have the TARGET gene as well;
mRNA may be described as a polymer. Explain why
• Made up of many (similar) molecules/monomers/nucleotides/units;
