Genetics Chapter 9: Molecular Structure of DNA and RNA
molecular genetics - study of DNA structure and function at a molecular level
4 crieteria for
... [Show More] DNA to fulfill it's role as genetic material - information, transmission, replication, variation
Frederick Griffith - studied streptococcus pneumoniae in mice to suggest that DNA is the genetic material
Avery, McCarty, and MacLeod - used Griffith's observations to prove that DNA is the transforming principal. They created purified type S DNA extract and mixed it with the type R cells
Hershey and Chase - provided evidence that DNA is the genetic material of the T2 phage. They labeled protein with S35 and DNA with P32, and mixed in a blender and centrifuged to separate the 2. There was a much higher percentage of protein outside the cell
Gierer and Schramm - isolated RNA from the tobacco mosaic virus and found that purified RNA still caused infection
4 levels of complexity of DNA and RNA - Nucleotides, strand, double helix, three-demesional structure
components of a nucleotide - at least one phosphate group, a pentose sugar (ribose or deoxyribose), and a nitrogenous base (A,T,C,G, or U)
purines - Guanine and Adenine: contain 2 rings
pyrimidines - Thymine, Uracil, and Cytosine: contain 1 ring
the base of a nucleotide is always attached to which carbon? - 1 prime
bonds within DNA - phosphodiester linkages between nucleotides, hydrogen bonds between bases
nucleic acid backbone - Sugar and phosphates
phosphodiester linkage - a phosphate attachment to the 5' carbon in one nucleotide and a 3' carbon in the other
directionality - each strand has directionality based on the orientation of it's sugar molecule
Linus Pauling - proposed that regions of proteins can fold into a secondary structure known as an a-helix. he used ball and stick models.
Rosalind Franklin and Maurice Wilkins - used x-ray defraction to figue out that: DNA is helical, it is too wide to only be a single helix, and a helix contains about 10 base pairs per full turn
Chargaff - A=T, G=C
Watson and Crick - deduced the double helical structure of DNA with a ball and stick model, using Pauling's and Franklin's experiments as a foundation
key features of DNA double helix - right-handed, the bases in opposite strands hydrogen bond according to Chargaff's rule, the two strands are antiparallel with regard to their 5'-3' directionality, and there are about 10 bps in a complete turn.
A DNA - formed in virto, right handed, 11bp per 360 turn, tilted from center axis, occurs under low humidity
B DNA - predominate form of DNA in living cells, right handed, 10bp per 360 turn
Z DNA - formed in vitro, left handed, zig-zag helical backbone, 12bp per 360 turn, tilted from center axis, high salt concentrations-formation is favored by a sequence of bases that alternate between purines and pyrimidines, at low salt concentration-formation is favored by methylation of cytosine bases, favored by negative supercoiling
methylation - a cellular enzyme attaches to a methyl group (-CH3) to the cytosine base
Triplex DNA - tripple helical, formed in vitro by mixing natural double stranded DNA with a synthetic third strand. third strand binds to major groove. has potential to specifically inhibit certain genes, as in cancer cells
possible structures of RNA molecules - bulge loop, internal loop, multibranched junction, stem-loop [Show Less]