3.5 Flashcards
(21 cards)
What is PCR? Potential applications?
Polymerase Chain Reaction:
- is a laboratory technique where small amounts of DNA are taken and amplified in order to have enough DNA to analyse
-forensic analysis (DNA found at crime scenes)
-DNA profiling (enough DNA to make a profile)
- preparing enough DNA for sequencing (pre natal screenings)
- DNA from bones, wildlife conservation, to detect viruses
Process of PCR
- a sample of double stranded DNA is taken and heated up to 95C which breaks the H-bonds to separate the two strands
- a primer is added and the temperature is dropped to 55C to allow the primer to anneal to the start of the section of interest
- the temperature is raised to 72C to allow Taq polymerase to add DNA nucleotides on from the primers to synthesis a copy of the section of interest
- cycle is repeated many times
Explain Gel electrophoresis
- DNA is extracted from a suitable source (blood, saliva, semen) and amplified using PCR
- restriction enzymes are then used to cut DNA into fragments
- these fragments are then loaded into wells in an agarose gel near a negative electrode
- when the current is switched on the DNA will move towards the positive electrode
- this separates DNA fragments according to their size, as smaller fragments travel further
DNA profiling
DNA profiling involves comparison of DNA
- non-coding sequences of DNA often contain repetitive sequences (satellite DNA)
- the number of repeats varies between individuals
- so when the DNA is cut into fragments, they vary in size according to the number of repeats b/w the cuts
Explain DNA profiling for forensic investigations
a 100% match is needed
- DNA profile from a material at a crime scene is compared with the DNA sample of a suspect or victim
- blood stains on a suspects clothing could be shown to come from a victim
- single hairs could be shown to come from a suspect
- semen from a sexual crime could be shown to come from a suspect
Explain how DNA profiling can be used in paternity investigations
- DNA profiles of the mother, the child, and the man need to be taken
- DNA profiles are compared and if any of the bands in the child’s profile do not occur in the mother or man, the man is not the father
- men sometime claim not be a father to avoid payment or raising a child
- women may wish to identify the biological father if they’ve had multiple partners
- a child may wish to prove their an heir to a deceased man
Genetic modification
genetic modification is carried out by gene transfer between species
- gene transfer involves removing a gene of interest from one organism and inserting it into the genome of another organism of a different species
—> to produce a particular protein
—> go give it a desired characteristic
NB: only possible due to universal genetic code
Restriction endonucleases
enzymes that cut DNA molecule into specific base sequences
DNA ligase
enzyme which joins together fragment of DNA by joining the sugar-phosphate backbones
Gene transfer to bacteria using plasmids
- a plasmid of a bacteria is isolated and then cut open using a restriction endonuclease
- the same redirection endonuclease is used to cut out a gene of interest from a cell
- the gene is then inserted into a plasmid and the sections joined together with DNA ligase
- a recombinant plasmid has been formed
- recombinant plasmids are replaced into bacterial cells by treating bacteria with calcium chloride, which increases their membrane permeability to take up the plasmids. or viruses can be used to inject the plasmids into bacteria
Why are plasmids useful as vectors?
- plasmids are small loops of DNA found in the cytoplasm of bacteria
- they’re easily removed & reinserted into bacterial cells
- are replicated & passed on when bacteria divide
- are easy to insert genes
What are sticky ends and why are they so useful in this process
- sticky ends are created when a restriction enzyme makes a staggered cut in a DNA molecule, leaving a few unpaired bases
- if 2 DNA molecule are cut with the same restriction enzyme their sticky needs are complementary and will reanneal with each other
genetic modification of plants and animals
assessment of potential risks and benefits associated with genetic modification of crops
What are clones
genetically identical organisms derived from a single origin parent cells by mitosis
Cloning animal embryos (embryo cloning)
- at an early stage of development all cells in an animal embryo are totiptent stem cells
—> meaning that they can divide and differentiate into every type of cell & therefore could each become a new individual - embryos are usually split at the 8 cell stage
- after this cells are no longer totipotent, therefore max. 8 cells can be produced this way
-can increase dairy her, sheep flock size
- little interest in method because embryo is produced by sexual reproduction so the desired characteristics cant be determined
cloning adult animals (somatic cell cloning)
methods have been developed for cloning adult animal cells using differentiated cells (cell specialised for a specific function
can be used for reproductive cloning (surrogacy) or therapeutic cloning (tissue or organ transplants)
reproductive cloning:
production of cloned embryos by somatic cell nuclear transfer
- a diploid cell is taken from an adult donor
- an egg cell is taken from another donor and it’s haploid nucleus is removed
- the diploid cell and enucleated egg cell are fused together using an electric shock
- the fused cell begins dividing by mitosis
- the embryo is placed into a uterus of a foster/surrogate mother
- the embryo develops normally into a lamb who is a clone of the donor of the diploid nucleus
therapeutic cloning
- produced embryos from adult somatic cells in the same way as reproductive cloning but the embryos are used as a source of stem cells
potential uses of therapeutic cloning
- creating replacement organs for transplant (still in development)
- replacing damaged tissue (eg. nerves, pancreas)
- burnt skin can be replaced
- cancerous bone marrow could be replaced
no risk of rejection as cells are from recipient
Ethical issues of somatic cell cloning
pros:
- curing disease
- replacing damaged organs
- increasing quality of life
- could be long term solution for health, which reduces financial costs
- reduces need for immunosuppressants
cons:
- unethical to clone a human and to destroy a potential life
- expensive
- time consuming
- not 100% reliable
