DNA Replication Flashcards
gregor mendel
worked with peas to develop preliminary ideas about genetics and inheritance
genotype
what the genes say (Rr, rr, RR)
phenotype
what the genes show (blue eyes, tall, etc.)
erwin & chagoff
demonstrated that DNA had equal masses of A/T and C/G, helping watson and crick with their theory
purines
A/G, because they have two C rings
pyrimidines
C/U/T, one ring
structure of DNA
phosphate-sugar-base-base-sugar-phosphate
antiparallel
dna strands go in opposite directions, on is 3’-5’, the other is 5’-3’
polymerase
enzymes that replicate DNA, works only in the 5’-3’ direction
leading strand
5’-3’ strand, synthesized continuously
lagging strand
3’-5’ strand, synthesized in chunks
polymerase 1
reads bases and corrects mistakes
polymerase 3
adds bases
single-strand binding proteins (SSBP)
stabilizes the DNA when it has been forked
helicase
splits H-bonds and creates a DNA fork
RNA primase
starts the new strand by adding a chunk of RNA to the old strand
ligase
connects the Okazaki fragments
Okazaki fragments
parts of the DNA that have been copied in the opposite direction of the replication direction (3’-5’ strand copied) but not connected to form a longer DNA strand
Messelson & Stahl (M&S)
theorized the process of DNA replication through an experiment in which they used a radioactive marker to mark the original DNA strand. after several rounds of replication, they tested to see what the DNA looked like, finding that there was a small amount of marked DNA settled at the bottom of the test tube, showing that DNA is replicated in a semiconservative model.
conservative model
original strand is kept intact and essentially copy/pasted to create the new one. the two strands at the end are one new, one old. the tube in M&S would show such a small amount of the original DNA that it wouldn’t even be observable.
dispersive model
original strand replicated such that the two new strands have the old strand equally distributed throughout. the test tube in M&S would show the marker dispersed within it.
semiconservative model
original strand is split in two and the daughter strands have one old side and one new side. M&S tube shows a small amount of marked DNA at the bottom, enough to be observable. (this is what they saw)
deletion (chromosomal mutation)
section of chromosome is removed (ABCDE -> ADE)
duplication (chromosomal mutation)
section of a chromosome is repeated (ABCDE -> ABCBCDE)
inversion (chromosomal mutation)
reverses a sequence within a chromosome (ABCDE -> ADCBE)
reciprocal translation (chromosomal mutation)
two different chromosomes cross over and trade (not 13/13, but 13/10; creates chromosome sections that code for genes not addressed on that chromosome)
Rosalind Franklin
showed through an X-ray graph that DNA was a double helix
Hershey & Chase
marked viral DNA and viral proteins to see which conveyed genetic information. results showed that it was DNA
point mutation
a change made to a single base during DNA replication
silent mutation (point mutations)
change in a single base that has no effect on the protein that is coded for
nonsense mutation (point mutation)
change in a single base resulting in a strand that doesn’t code for anything
conservative missense mutation (point mutation)
change in a single base that codes for a new protein with similar properties to the original, resulting in little change to the trait
non-conservative missense mutation (point mutation)
change in a single base that codes for a new protein entirely, resulting in observable change to the trait
frameshift mutation
changes the codons through insertion or deletion of bases
deoxyribose (DNA) vs dideoxyribose (dDNA)
DNA has an OH group on the 3’ carbon, which means the sequence can continue. dDNA has simply an H on the 3’ carbon, so the sequence stops replicating.
sanger sequencing steps
- split the DNA into four tubes, adding dDNA bases for one base in each tube (one has A, one has T, once has C, and one has G)
- let the DNA replicate in the tubes, creating strands of different lengths
- run this through a gel and sequence the genes (longest on top, so the last base would be the top mark)
- [optional] if the DNa was color-dyed, you can use a computer to sequence the DNA
