molecular biology2 Flashcards
what are the 3 different types of DNA replication?
- semiconservative model
- conservative model
- dispersive model
how long does it take to replicate the human genome
8 hrs
semiconservative model
how our DNA is made- this was found out in the meselson stahl experiment
a strand of DNA serves as a template to make a new one
conservative model
one molecule consist of both original strands and a new model consists of 2 new strands
dispersive model
2 molecules that are hybrids of parental and daughter dna- patch work of original and new DNA
how is speed achieved in DNA replication
because DNA replication happens at multiple places at one time with the replication fork moving in both directions
what direction is the growing strand synthesised in? why is this?
in a 5’ - 3’ direction
this is because dna polymerase only works in a 5’-3’ direction
in dna replication, what dictates what base comes next
the template strand
what Is the formation of the phosphodiesterase bond catalysed by?
it is catalysed by DNA polymerase
what does monomers called dNTP’S consist of
(deoxynucleotide triphosphate)
they consist of a deoxyribose sugar, 3 phosphates and a base.
what is the formation of the phosphodiesterase bond catalysed by?
DNA polymerase
how is DNA unwound in replication?
it is done by DNA helices
describe the leading and lagging strand replication in DNA
the leading strand is replicated continuously towards the replication fork
the lagging strand is replicated discontinuously away from the replication fork in OKAZAKI fragments
why is the replication fork asymmetrical
because the DNA replication is semi conservative, there is a leading and lagging strand that are moving in opposite directions.
what needs to be done to allow for enough room for Okazaki fragments to be made and how is it stabilised
in order to provide enough for Okazaki fragments to be generated, single strands have to be exposed which is done by DNA helices. it will be stabilised temporarily by DNA binding protein
how are new Okazaki fragments made?
they are made by DNA primate generating an RNA primer so a new Okazaki fragment can be made.
what are RNA primers
they are short templates that provide mark the starting point for the construction of the new DNA strand
what is required for DNA primase to produce another RNA primer to make a lagging strand
150 bases on the template strand
Werners syndrome
premature aging
what happens when there is not enough bases left on the template strand to produce a new RNA primer
usually in healthy people, telomerase will add information to the lagging strand in the form of TTAGGG repeated sequences, which allows an Okazaki fragment to be generated.
what happens when people don’t have the mechanism to add sequences to make an Okazaki fragment
the dna will become unstable and degrade leading to shortening of the chromosome which lead to Werners syndrome.
when DNA polymerase makes an error, how Is it fixed?
- errors can be removed during synthesis
- DNA polymerase has a site that adds bases and then an editing site which will proof read the base, the editing bade will remove the wrong base and add the right one
what is PCR used for
it is used to generate lots of copies of genetic material
how does PCR work
- the strands are heated to break hydrogen bonds
- RNA primers of known sequence can be added to mixture
- individual dna strands will bind to their matching RNA primers using hydrogen bonds
- DNA polymerase and monomers complementary to the DNA strand can be added to the picture, resulting in the synthesis of new dna
how is PCR used in the presence of infectious agents
- take sample/blood
- centrifuge to separate infected serum
- amplify the viral rna genome
- gel electrophoresis can then be used to determine if someone is infected using a normal blood control
how is per used to identify inheritance patterns
because repeated sequences on paternal and maternal chromosomes can be amplified and compared to their offspring (to see if they have inherited any particular conditions)
what can quantitative fluorescent PCR be used for
- detecting large chromosomal mutations
- screening for loos of heterozygosity
how does automated sequencing help in personalised medicine
because you use automated sequencing when you are looking at a particular chromosome, so it can be used to help confirm a diagnosis.
how is the lagging strand made?
it is made discontinuously due to the fact that it goes in a 3-5 direction.
therefore dna polymerase can only make this in a series of small chunks from 5-3 called Okazaki fragments.
what happens after the new DNA strands have been made on the leading and the lagging strand?
the enzyme exonuclease will remove the primers and DNA polymerase will fill the gaps with DNA.
function of DNA ligase?
this is the enzyme used in the final step, that will seal the strands together.
