Biology 1B - DNA/RNA and proteins Flashcards
what is the structure of DNA (Watson and crick model)
A polymer of nucleotides ( base, deoxyribose sugar, phosphate)
DNA strands run antiparallel with 10 base pairs per turn of double helix
Describe the charges in DNA
Made up of the sugar phosphate backbone which is highly charged and hydrophilic (polar)
and nitrogenous bases in the centre as they are hydrophobic (non polar)
why does DNA dissolve in water
due to the highly charged sugar phosphate backbone
describe purines
purines are a type of nitrogenous bases
Adenine and guanine are purines
purines contain two infused rings composed of carbon and nitrogen atoms
describe pyrimidines
pyrimidines are a type of nitrogenous bases
Cytosine and Thymine are pyrimidines
pyrimidines are a 1 ringed structures composed of carbon and nitrogen atoms
describe the 5’ and 3’ end of DNA
5’ - has phosphate attached meaning you cannot add a new nucleotide at this end
3’ - there is a H rather than a Hydroxyl on the deoxyribose sugar 2nd carbon meaning you can add new nucleotides
what did Rosalyn franklin do
played huge role in discovering the structure of DNA by helping Watson and crick
describe the role of hydrogen bonds in base pairing
specific base pairing is due to the number of hydrogen bonds
A&T - have two hydrogen bonds between them
G&C -have 3 hydrogen bonds between them
bases pair this way as purines and pyrimidines pair together
who discovered specific base pairing
Watson and crick with help from Rosalyn franklin
what provided evidence that DNA carries genetic information
studies of bacteriophages showing only the DNA and not the protein enters the bacterial cell
showing DNA and not protein carries genetic material
what is the semiconservative model of DNA replication proposed by Meselson-Stahl
Two strands of parental molecule separate and each functions as a template for synthesis of a new, complementary strand
describe the Meselson-Sthal experiment that demonstrated the semi conservative replication of DNA
1) DNA from E.coli cultured in medium containing 15N (isotope) and then transferred to medium containing 14N
2) Extracted DNA at time intervals (after first and second replication)
3) after 1 replication - DNA formed a single intermediate band, indicating each DNA molecule contained one old (heavy) and one new strand (light)
4) after two replications - two bands appeared, one intermediate and one completely light
5) proved semiconservative model where each inherits one strand from parent and synthesises a new complementary strand
what is helicase function in DNA replication for leading and lagging strand
unwinds parental double helix at replication forks
what is single-strand binding protein function in DNA replication for leading and lagging strand
binds to and stabilises single stranded DNA until it can be used as a template
what is topoisomerase function in DNA replication for leading and lagging strand
corrects overwinding ahead of replication forks breaking, swivelling and re-joining DNA strands
what is primase function in DNA replication for leading and lagging strand
leading - synthesises a single RNA primer at 5’ end of leading strand
lagging - synthesises an RNA primer at 5’ end of each Okazaki fragment
what is DNA polymerase III function in DNA replication for leading and lagging strand
leading - continuously synthesises leading strand from primer
lagging - elongates each Okazaki fragment leading onto the primer
what is DNA polymerase I function in DNA replication for leading and lagging strand
leading - removes primer from 5’ end of DNA, adding onto the adjacent 3’ end
lagging - the same for each fragment
what is DNA ligase function in DNA replication for leading and lagging strand
leading - joins the 3’ end of the DNA that replicates the primer to the rest of the leading strand
lagging - joins the Okazaki fragments
