Gene technology Flashcards
Gene definition
DNA base sequence which codes for either the amino acid sequence of a polypeptide or a functional RNA
Genome definition
All the DNA in a cell
Proteome definition
The range of proteins a cell can make
Intron definition
Non-coding DNA WITHIN a gene
Non-coding multiple repeats definition
Non-coding DNA BETWEEN genes
What kind of DNA is the DNA of chloroplasts and mitochondria the same as?
Prokaryotic
What do genome projects determine?
The DNA base sequence of an organism’s genome
How can genome projects be used to determine an organism’s proteome?
Allow the amino acid sequence of a protein to be determined
Why is it easier to determine the proteome of prokaryotic DNA?
No introns, shorter so faster
How can genome projects be used in medical research?
Can identify the antigens of microorganisms for use in vaccine production
What 2 features in eukaryotes makes it difficult to translate the genome into the proteome?
Non-coding DNA and regulatory genes
How is a DNA base sequence determined?
Chain termination sequencing
What 4 components are needed in chain termination sequencing?
- Sample of DNA
- 4 normal DNA nucleotides
- DNA polymerase
- Primer
What is added in chain termination sequencing that fluoresce a different colour?
Chain terminating nucleotides which can’t form a phosphodiester bond and so stop DNA replication
What are DNA fragments run on in chain termination sequencing?
Electrophoresis gel
Recombinant DNA definition
DNA made from 2 or more different species
What are the 3 methods of producing a DNA fragment in in vivo gene cloning?
- Reverse transcriptase
- Restriction enzymes
- Gene machine
What does reverse transcriptase do and how does this method produce a DNA fragment (3 steps)?
Forms DNA from mRNA
1. mRNA coding for (insulin) removed (from beta cells in human pancreas)
2. Reverse transcriptase makes cDNA from mRNA
3. DNA polymerase makes cDNA double-stranded
How do restriction enzymes produce a DNA fragment?
Hydrolyse phosphodiester bonds at recognition sites which forms sticky ends
Why is the gene machine more efficient in producing a DNA fragment than the other 2 methods?
- Very accurate
- Faster as no need to isolate DNA/RNA
- No introns so can be expressed by prokaryotes
- Any sequence of nucleotides can be made
What must be added to a DNA fragment before it is inserted?
Promoter and terminator
Vector definition
Carries the gene into the cell
How is a gene bound to a plasmid (3 steps)?
- Restriction enzymes cut open the plasmid
- Sticky ends of the plasmid are complementary to the sticky ends of the gene
- DNA ligase joins nucleotides of plasmid and inserted gene
How is a DNA fragment introduced to a host cell?
Heat shock makes the cell’s membrane more porous so the plasmid/gene can pass through more easily
What does a marker gene do?
Identifies which cells have taken up the plasmid/gene
How does an antibiotic resistance marker gene identify bacteria containing the plasmid?
Only cells containing the plasmid survive
Which process identifies which plasmids contain the recombinant DNA?
Replica plating (ampicillin, tetracycline, marker gene disruption etc.)
Why is PCR used?
Amplifies a particular DNA base sequence
What are the 3 differences between PCR and DNA replication?
- Heat is used to break hydrogen bonds instead of DNA helicase
- Taq polymerase is used instead of DNA polymerase
- Primers are used to replicate a section of DNA instead of whole molecule
Why is the tube containing ingredients kept on ice in PCR?
Reduces enzyme activity to prevent damage to DNA
What 4 ingredients are needed in PCR?
- DNA we want to copy
- DNA nucleotides
- Taq DNA polymerase
- Primers
Primer definition
Short, single-stranded DNA with a complementary base sequence to the start and end of the gene to be copied
Why are primers needed in PCR?
Mark where DNA replication should occur from, allow DNA polymerase to bind, keep the strands separated
Why are 2 different primers needed in PCR?
DNA has 2 strands which different complementary base sequences
- Why is the sample of DNA first heated to 95°C in PCR?
Breaks the hydrogen bonds to separate strands
- Why is the sample of DNA then heated to 55°C in PCR?
Allows primers to bind
- Why is the sample of DNA then reheated to 72°C in PCR?
Taq DNA polymerase binds and joins DNA nucleotides to create a new strand
How is the number of DNA molecules made in each cycle calculated in PCR?
2^x
Why does DNA replication eventually stop in PCR?
All of the primers or DNA nucleotides were used up
What is one use of PCR?
Used to make many copies of DNA found at a crime scene for genetic fingerprinting
What is gene therapy used for?
Used to cure a genetic disease caused by a mutated gene
How does gene therapy cure a genetic disease?
Functional gene is inserted into DNA of a cell which expresses the mutated gene so functional protein is produced
What are the 3 ways of inserting a gene into a cell in gene therapy?
- Using a virus
- Liposomes (phospholipid vesicles containing DNA) fuse with cell surface membrane
- Recombinant plasmid injected into cell
What is somatic gene therapy?
Gene is inserted into somatic cells (normal adult body cells) which express the mutated gene
Which type of somatic cells would be best to target in gene therapy and why?
Adult stem cells so all daughter cells contain the functional gene and less repeat treatments are needed
What is germ line gene therapy?
Gene inserted into sperm or egg cells
What are the advantages and disadvantages of GERM LINE gene therapy?
Advantages: functional gene passed on to offspring so genetic disease isn’t inherited
Disadvantages: illegal as could be used for cosmetic uses, can cause side effects
What are the 4 disadvantages of gene therapy?
- Multiple treatments required as cells die - short term
- Still some faulty cells present
- Viruses can cause immune responses/side effects
- DNA may insert into the middle of another gene, forming a non-functional protein
Why is gel electrophoresis used?
Separates out DNA fragments by length and charge
What makes DNA negatively charged?
Phosphate groups
How does gel electrophoresis separate DNA fragments?
DNA attracted to positive electrode, shorter DNA fragments travel the furthest
How are unknown lengths of DNA fragments determined using gel electrophoresis?
Compared to KNOWN lengths of DNA fragments on the gel
How can PROTEINS be separated by gel electrophoresis?
By mass and charge
What are DNA probes used for?
Identify the presence of a certain allele
DNA probe definition
Short, single-stranded piece of DNA with a complementary base sequence to the allele
How does a DNA probe identify a certain allele?
Binds the allele and have a radioactive/fluorescent label for detection
Name the 6 stages of genetic screening
- Extraction
- Digestion
- Separation
- Southern blotting
- Hybridisation
- Autoradiography
What happens in the extraction stage of genetic screening?
- DNA extracted from cell using homogenisation and centrifugation
- (PCR used to amplify DNA)
What happens in the digestion stage of genetic screening?
DNA cut with restriction enzymes at recognition sites
What happens in the separation stage of genetic screening?
DNA fragments separated by length and charge using electrophoresis
What happens in the southern blotting stage of genetic screening?
DNA transferred from gel to a nylon membrane and made single-stranded
What happens in the hybridisation stage of genetic screening?
- Complementary DNA probes added which bind to allele
- Membrane washed to remove any unbound probes and prevent false positives
What happens in the autoradiography stage of genetic screening?
Fluoresence/radioactivity identified using photographic/X-ray film
VNTR definition
Repeating DNA base sequences found BETWEEN genes
How is genetic fingerprinting different to genetic screening?
Uses restriction enzymes and DNA probes complementary to VNTRs
How are genetic fingerprints used in paternity tests?
All the bands in a child’s genetic fingerprint which don’t match the mother’s must match the father’s
How are genetic fingerprints used in forensic science?
Genetic fingerprint of DNA found at a crime scene compared with the genetic fingerprint of a suspect
How are genetic fingerprints used in animal and plant breeding?
Want to breed unrelated individuals to increase genetic diversity so check that there is variation between bands on genetic fingerprints
How are genetic fingerprints used in medical diagnosis?
Genetic fingerprints of known types of tumour compared to genetic fingerprints of a patient’s tumour to diagnose it