nucleic acid part 4 Flashcards
(30 cards)
what was the aim of the human genome project ?
to determine the human genome sequence , this would be beneficial as it would allow us to create personalised medicine
the whole genome is too large to sequence so it is cleaved into fragments , what are these called and how are they produced ?
restrictive fragments , enzymes called restrictive endonucleases
how do you sequence the DNA form the restrictive fragments ?
Cutting the original DNA with other restriction enzymes with different sequence selectivity will give new fragments whose sequences partly overlap the fragments from the first restriction enzymes. Sequencing the restriction fragments and identifying the regions that overlap the fragments from different restriction enzyme cleavage allows the complete DNA sequence to be determined.
what method does the sequencing machines use to determine the human genome ?
the sanger method
whats needed for the sanger method ?
template single strand of DNA , primer , DNA polymerase , the 4 deoxynucleotidetriphosphates ( dATP ,dCTP,dTTP,dGTP and also modified di - deoxynucleotidetriphosphates called ddNTP’s
what are the modified di -deoxynucleotide triphosphates ddNTP’s needed for ?
these terminate the strand elongation as they don’t have the OH group present on the C3’ so no phophsodiester bond can form
what is the gel electrophoresis used for ?
to determine where the ddNTP is for each fragment as this allows the base sequence to be determined for the restrictive fragment
how can the sanger method be accelerated ?
by using fluorescent labelling , the terminal base of each fragment is identified by its characteristic fluorescence . A different colour will be used ofr each ddNTP’s
what does UV light generate from water ?
hydroxy radicals
when dioxygen is present what does UV light cause ?
peroxy radicals to form
what can the free radicals produced cause ?
they can react with the negatively charged backbone of DNA which could cause the chain to cleave. If this happens on one strand then it is easily repaired, but breaks on adjacent strands in close proximity lead to separation and eventual cell death. Also the radicals can react with the nucleotide bases and cause them to be oxidised ( lose electrons).
how can the use of transcription factors lead to cancer ?
they bind between the amino acid and DNA bases of DNA which prevents protein binding as the bases have been modified
what is a photochemical reaction and what can this cause ?
this is when UV light causes 2 opposite pyrimidines bases to join or dimerise this causes errors during DNA replication as mutations occur
can the results of photochemical reactions be reversed and how ?
yes by the use of enzymes
how can the bases be altered ?
by UV light
what is an alkylating agent ?
this is a chemical that transfers an alkyl group ( CH3) to a nucleophile such as a nucleotide base of DNA.
give an example of an alkylating agent
dimethyl sulphate ( strong electrophile) that reacts with the N-7 of purines as it is not involved in hydrogen bonding so it has lone pair of electrons that are easily alkylated.
what do the nitrogen and sulphur mustards have attached to them and what does this occur ?
chlorine and nitrogen which are both highly electronegative and so they both become positively charged so there’s 2 electrophilic positions. This means that it can react twice with 2 separate DNA strands.
how are mustards a treatment against cancer ?
covalent crosslinks can occur between DNA strands so replication cannot occur
are some chemicals always alkylating agents ?
no some become active or are modified during excretion for example vinyl chloride
describe N -nitrosoureas
these are a selective anticancer agent which is biologically inactive until activation. they are selective as they target only cancer cells. They are activated as a solid tumour doesn’t receive enough oxygen so the environment becomes acidic which activates the anticancer agent.
what is a chain terminator ?
this is a modified nucleotide that prevents the nucleic acid chain from growing during replication
What is acyclovir ( zovirac) used for?
used to treat infectious diseases caused by a DNA virus such as herpes.
how is the acyclovir activated in vivio ?
the hydroxyl group is converted to a triphosphate
