discovery of DNA and DNA replication Flashcards
what is the mode of Dna replication
semi-conservative
who discovered the mode of dna replication
meselson and stahl
how does the semi-conservative mode of dna replication work?
each dna strand serves as a template and forms two “half” new strands
what kind of base pairing does the new strand follow
complementary base pairing rules
what are the other proposed models of dna replication
conservative and dispersive replication
what is the conservative replication model?
two strands of the original molecule serve as template then rewind into old molecule and new molecule
what is the dispersive replication model?
both chains of replicated molecules contain old and new segments
how did melson and stahl discover that dna is semi-conservative
grew bacterial cells in heavy nitrogen, then switched to lighter nitrogen and extracted DNA at various time intervals and observed their densities
is nitrogen 15 heavier or lighter than nitrogen 14
heavier
during melson and stahl’s experiment, what time intervals did they check the DNA density and how many rounds had it gone through?
0 min- 0 rounds
20 min- 1 round
40 min- 2 rounds
what round(s) did the dispersive DNA match the results
O and 1 rounds
what round(s) did the conservative DNA match the results
0 round
what do DNA polymerases assemble?
complementary polynucleotide chains from individual deoxyribonucleotides
what are the four different polymerases used (deoxyribonucleotide triphosphates)
dATP, dGTP, dCTP, and dTTP (one for each base)
DNA polymerase adds a nucleotide to which end of the nucleotide chain
3’ end (exposed hydroxyl group)
the oldest end of DNA has an exposed what
5’ triphosphate
the newest end of DNA strand has a what
3’-OH group
DNA polymerase assemble nucleotide chains in what directions
5’-3’ direction
which way to DNA strands run in comparison to other
antiparallel
what are the 3 things dna replication requires?
something to copy (parental DNA molecule)
someting to do the copying (enzymes)
building blocks to make copy (nucleotide triphosphates)
what was the hammerling experiment?
green alga cells were cut into pieces and observed to see which were able to express hereditary info
what did hammerling’s reciprocal graft experiment discover?
discovered hereditary info is stored in the cell’s nucleus
who discovered smooth and rough strain?
frederick griffith
was smooth strain or rough strain highly infective/pathogenic?
smooth strain
where the s cells still alive even if the mouse died in griffith’s experiment? were the r cells?
yes to s cells, no to r cells
if mice are infected with heat-killed s cells, what is expected to happen?
the mouse will live
what if the mice are infected with heat-killed s cells and live r cells? why does this happen?
the mouse dies
the transforming principle: live r cells can be converted to live s cells because of some factor present in and derived from dead s cells
what did oswald avery discover?
the chemical nature of griffith’s transforming principle=DNA
oswald avery destroyed RNA, proteins, and DNA at different points to see which had the transforming principle
true
what did hershey and chase do in their experiment?
labeled DNA and protein with radioactive isotope tracer (32P for DNA, 35S for protein)
what is a bacteriophage?
virus that can infect bacteria
how does infection by a virus occur?
when the virus injects DNA into the bacterial cell
what do bacteriaphages cause to bacteria?
lysis
how does lysis happen in bacteria?
when the virus DNA is inserted into the bacterial cell, it begins to replicate. once replication is complete, virions form (viral DNA and proteins assemble). the formation of the virions and the sheer number of them causes lysis
what was the hershey-chase experiment conclusion?
only DNA entered the cell and appeared in progeny phages
what percentage of radioactive proteins were found in the progeny phages?
less than 1%. most of it in the supernatant
what percentage of radioactive DNA was found in the progeny phages?
greater than 30%. most of it in the pellet
who discovered that DNA has a helical shape, using x-ray diffraction?
rosalind franklin
rosalind franklin discovered that DNA has a helical shape and that the molecule has a diameter of 3.4 nm and makes a complete turn of helix every 2 nm.
false. the diameter is 2 nm, and it turns every 3.4 nm
what did watson and crick do?
created a DNA model structure and explained how genetic information is stored and replicated
what evidence did watson and crick use to deduce the structure of DNA?
Chargaff, Franklin, and Wilkens
what is the difference between purines and pyrimidines?
purines have 2 rings, pyrimidines have one
which nitrogenous bases are purines? which are pyrimidines?
purines: adenine, guanine
pyrimidines: cytosine, thymine, uracil
what is the difference between adenine and guanine?
adenine has an amine while guanine has an oxygen
what is the difference between cytosine, thymine, and uracil?
cytosine has an amine
thymine has a methyl and oxygen
uracil has an oxygen
how many H bonds are between A and T/U versus G and C?
A=T (2)
G=-C (3)
what are chargaff’s rules?
amount of adenine=amount of thymine
amount of cytosine=amount of guanine
always an equal proportion of purines and pyrimidines
A=T, G=C, A+G=C+T
