This is an A level OCR A Gateway biology cheat sheet for Chapter 21 of Module 6. Specification reference - 6.1.3
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Minisatellites
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20-50 base pairs (bp) repeated 50-100 times. Also called VNTRs (Variable Number Tandem Repeats).
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Microsatellites
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2-4 bp repeated 5-15 times. Also called STRs (Short Tandem Repeats) or stutters
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Can repeat a varying amount of times on each homologous chromosome. The number of repeats is inherited from parents.
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1. Extract DNA
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Tissue sample is mixed with phenol solution. PCR can be carried out to multiply sample (more detail later).
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2. DNA fragmentation
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Restriction endonucleases - cut DNA at specific base sequence (restriction site).
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3. Gel electrophoresis
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Used to separate DNA fragments using charge and Mass of DNA fragments (more detail later).
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4. Denaturation
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Hello soaked with alkali to separate strands.
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5. Southern blotting
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Membrane that single strands of DNA are transferred on to.
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6. Hybridisation
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Complementary radioactive or fluorescent probes are added. Their base sequence is known and so they tag complementary regions so specific genes can be pinpointed.
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7. Disclosure
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X-rays or UV lights are used depending on what type of tag was used. The result will show lines where specific sequences were tagged and a DNA profile is created.
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PCRis used when only a small sample of DNA is available, for example at a crime scene. The DNA sample along with excess bases, primers and DNA polymerase are mixed and placed in the PCR machine
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1. Separating the strands (90-95C)
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30 seconds, this denatures the DNA - breaks hydrogen bonds between bases.
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2. Annealing the strands (55-60C)
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Primers bind to the ends of the DNA strands.
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3. DNA synthesis (72-75C)
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At least 1 minute, DNA polymerase (Taq polymerase) adds bases to the primer, complementary strand is made.
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The cycle is repeated as many times as necessary to produce enough DNA for the necessary usage.
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DNA mixed with primers, DNA polymerase, excess nucleotides and terminator bases (4 separate containers, one for each base).
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PCR performed to synthesise DNA.
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Terminator nucleotides cause transcription to stop. This therefore produces different lengths of DNA fragments.
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Process similar to gel electrophoresis started. Terminator nucleotides contain fluorescent markers, so base which ends sequence can be identified.
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Shortest fragment travels furthest so order of bases can be determined.
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Bioinformatics
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Stores and organises data.
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Computational biology
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Uses data to form theoretical models.
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Human genome
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10,000 Genomes Project UK10K.
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Genomes of pathogens
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Find source of infection.
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Identify antibiotic-resistant bacteria.
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Track progress of an outbreak.
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Identify target areas of pathogen genome.
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Identifying species (DNA barcoding)
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Identify sections of the genome that remain the same within species. Conserved regions in animals are in mtDNA and in plants chloroplast DNA.
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Evolutionary relationships
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Can calculate rate of mutations --> See how long ago two species had same DNA in common ancestor.
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Genomics is the study of genome.
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Proteomics is the study and amino sequencing of organisms' entire protein complement. More proteins exist than genes.
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Spliceosomes
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Enzyme complexes which cut out introns and some exons out of pre-mRNA. Exons can be rearranged differently, therefore one section of DNA can code for many proteins.
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Protein modification
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Proteins modified by other proteins. Can be lengthened or shortened.
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Design and construction of novel artificial pathways, organisms...
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Genetic engineering.
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Industrial contexts - fixed/immobilised enzymes and drug production.
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Synthesis of new genes e.g. treat cystic fibrosis.
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Synthesis of new organism. New nucleotides developed (other than ACTG) incorporated in DNA introduced in bacteria.
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Prokaryotes
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Easily genetically modified for hormones, antibiotics...
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Plants
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Agrobaterium tumefaciens which usually forms tumours. Desired gene inserted in plasmid, then in plant DNA. Forms a callus of GM plant cells
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Can also use electrofusion - Tiny electric shocks used to fuse the cells and nuclear membranes of two different cells together. Also used for producing monoclonal antibodies.
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Animals
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Cell membranes are harder to manipulate than plant cell membranes. Engineering used for medically important proteins and curing human genetic diseases.
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Pest resistance
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+ Less pesticide spraying
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- Non-pest insects are also affected
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Disease resistance
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+ Less crop loss
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- Superweeds (if genes spread).
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Herbicide resistance
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+ Less competition, higher yield
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- Lower biodiversity, superweeds
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Shelf-life extended
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+ Less food waste
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- Lower commercial value and demand
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Growing conditions
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+ Can grow in a wider range of conditions e.g. flood resistant
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- N/A
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Nutritional value
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+ Higher nut. val.
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- Allergies can develop due to new proteins
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Medical uses
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+ Medicines and vaccines
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- N/A
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Patenting
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+ N/A
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- Companies charge for seeds, can't harvest seeds, people who may need it the most cannot afford it
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GM pathogens used for research - modify virus to insert new genes in cells e.g. swine fever-resistant pigs, faster-growing salmon...
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Pharming
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Using animals to produce human medicines and research subjects.
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Medicine - From GM fertilised animals, human protein collected from milk...
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Research - Knock-out mice engineered to develop cancer for research.
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Issues
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- Human genes in animals
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- Reduce animals to commodities
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- Welfare compromised
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Germ line cell gene therapy
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Germ cells - Sex cells / embryo post-fertilisation.
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Insert healthy gene in germ cell.
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Illegal for human embryos - violation of human rights of unborn child, concerns of long term impacts...
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Somatic cell gene therapy
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Replace mutant allele with healthy one using viral vector.
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Higher rates of success, but still issues to fix e.g. mutant alleles passed on rather than healthy ones.
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