unit 6 (topic 1 & 2) Flashcards
which scientist performed X-ray chromatography in the 1950s?
Rosalind Franklin
what did Edwin Chargaff do?
analyzed DNA samples from different species. found that A=T (two H bonds) and C=G (three H bonds)
nucleotide structures
purines and pyrimidines
purines
-double ring shape
-A & G
pyrimidines
-single ring structure
-T, C, and U
how can h bonds aid in DNA replication?
they can break easily so this allows for DNA strands to be easily separated
watson and crick did what?
combined the findings of Franklin and Chargaff to create the first 3D, double helix model of DNA
key features of DNA
-double stranded helix
–>backbone: sugar-phosphate
–>center: nucleotide pairs
-antiparallel
–> 5’–>3’
–> 3’–>5’
–> 5’ end: phosphate group
–> 3’ end: hydroxyl group
key functions of DNA
-primary source of heritable info
–>genetic info is stored in and passed from one generation to the next through DNA
–>EXCEPT: RNA is the primary source of heritable info for some viruses
eukaryotic DNA
-Dna found in nucleus
-linear chromosomes
prokaryotic DNA
-dna is in nucleoid region
-chromosomes are circular
prokaryotes also contain
plasmids
plasmids
-small, circular DNA molecules that are seperate from the chromosomes
-they replicate independently from chromosomal DNA
-can be manipulated in labs
conservative model of dna replication
parental strands direct synthesis of an entirely new double stranded molecules
-parental strands are fully conserved
semi-conservative model
two parental strands each make a copy of themselves
-after one round of rep, the two daughter mole each have one parental and one new strand
-dna rep is an example of this
dispersive model
material in the two parental strands is dispersed randomly between the two daughter moles
-after one round of rep, daughter moles contain a random mix of parental and new dna
meselson and stahl model
preformed exp using bacteria
-bacteria was cultured with a heavy isotope, N15
-bacteria was transferred to a medium with N14, a light isotope
-dna was centrifuged and analyzed after each rep
steps in dna rep
- begins at origins of rep; various proteins attach to the origin and open the dna to form a rep fork
- helicase unzips dna strand at rep fork; ssbps bind to dna to keep it open; topoisomerase will help prevent strain ahead of the rep fork by relaxing supercoiling
- enzyme primase initiates rep by adding short segments of RNA (primers) to the parental dna strand
- antiparallel elongation; dna polymerase III attaches to each primer on the parental strand and moves in the 3’ to 5’ direction. adds nucleotides in 5’ to 3’ direction
- leading strand is synthesized in one segment, lagging is in clumps (Okazaki fragments)
- after dnap III forms an O fragment, DNAP I replaces rna nucleotides with dna nucleotides; dna ligase joins fragments forming a continuous dna strand
problems at the 5’ end
dnap III can only add nucleotides to a 3’ end, there is no way to finish on the 5’ end of a lagging strand, so dna would get shorter. but genes are protected from this bc of telemeres: repeating units of short nucleotide sequences that dont code for genes
