molecular biology week 2 (9/5/22)
S bacterial cells cause disease in mice, but R bacterial cells do not. Given that DNA is the transforming substance, which of the following would be expected to produce a transformation that would cause mice to become sick?
( rewatch lecture )
base composition varied between organism Lower orgaterm-18nisms varied G/C content (ex. clostridium= 0.27, e. coli = 0.5) Higher organisms rearranged between________ DNA can have variable composition
0.49-0.51 DNA
DNA as genetic material experiments
1) Griffith experiment demonstrated the transforming principle, converting non-virulent bacteria into virulent bacteria to kill mice. 2) Avery-McLeod-McCarty experiment demonstrated that DNA is the genetic material because degradation of DNA prevented bacterial transformation. 3) Hersy-chase experiment confirmed DNA is genetic material by only finding radioactive Phosphorous in bacteriophage DNA.
8 key features of the Watson-Crick Model for B-DNA
1. two polydeoxyribonucleotide strands twist about each other to form a double helix 2. phosphate and deoxyribose group from backbone on outside of the helix 3, Purines and pyrimidines base pair stacked inside the helix from planes perpendicular to helix axis 4. Helix diameter is 2.0 nm or 20 angstroms 5. Base pair are seperated by an average distances of 0.34 nm or 34 angstroms Structure repats itself after about 10 base pairs or every 3.4nm or 3.4 angstromes turn every 3.4 nm 6. Adenine always pairs to thymine and cytosine always pairs with guanine purine base pairing to a pyrimidine (A_T 2 H bonds, G-C 3H bonds) 7. Two strands are antiparallel 5' 3' /3' 5' 8. Presence of a major and minor group ( minor group is 1.2 nm 0r 12 angstroms, major groove 2.2 nm or 22 angstroms )
The 4th key feature of Watson and cricks model of B-DNA states Helix diameter is ____ nm or ___ angstroms
2.0nm or 20 angstroms
A -DNA was stable at ______% humidity
75
B-DNA was stable at ____% humidity
92
Chargaff's Rule
A=T and C=G
Central Dogma of Molecular Biology
DNA transcribed RNA translated protein
base composition
Expressed as fraction of base pairs G/C content =([G]+[C]/ all bases)
DNA as genetic material
Heat killed S cells purified so only transforming material remained
Who discovered DNA was the genetic material
Hershey and Chase
DNA transcribed into
RNA
Who discovered A DNA and B DNA
Rosalind Franklin
in 1928 what did Griffith study?
Streptococcus pneumoniae
Franklin and Wilkins
Used X ray diffraction to take pictures of DNA structure; discovered two forms of DNA
Angstroms
Used to measure dimensions of an atom 10^10
Rosalind Franklin
Woman who generated x-ray images of DNA, she provided Watson and Crick with key data about DNA
Virulance
ability of an organism to cause disease
chargaffs rule defined __________ __________
base pairing
Our Double helix is complementary in nature meaning?
by reading the sequence of one strand know the sequence of the other 5'ATGC3' 3'TAGC5' Each strand can serve as a template for synthesis
RNA reverse transcribe into?
cDNA (complementary DNA)
S bacteria
capusule, smooth edges, killed mice
Polysaccharides are
complex carbohydrates
Watson and Crick models based on X-ray diffraction patterns they focused their attention B-DNA diffraction patterns they found the diameter was ___ nm and helical turn ____ n
diameter was 2.0 nm and helical turn 0.64 n
The 1st key feature of Watson and cricks model of B-DNA states two polydeoxyribonucleotide strands twist about each other to form a _________ _________
double helix
S cells _____ the mice in Griffith study
killed
R bacteria
no capsule, rough edges, don't kill mice
Frankilin
obtained x ray diffraction patterns of extended DNA fibers observed that several characteristics appeared to change according to humidity
The 3rd key feature of Watson and cricks model of B-DNA states Purines and pyrimidines base pair stacked inside the helix from planes ____________ to helix axis
perpendicular
The 2nd key feature of Watson and cricks model of B-DNA states ______________ and ____________ groups from backbone on outside of the helix
phosphate and deoxyribose groups
streptococcus pneumonia virulence dependent on a __________ capuluse -protected the bacterium
polysaccharide
RNA translated into ?
protein (tRNA, rRNA)
What did they do in the Avery (1944) experiment
purified the transforming material from S cells and added it t live R cells , disruption of cells, centrifugation precipitation allowed the cells and mixture incubate and grow on agar 1 out of every 10000 were S type took newly formed S cells and grew on a second agar surface 2nd agar plate S colonies bred more S colonies (did get th last of it about 26 minutes in)
R cells
rough cell bacteria that is not surrounded by a capsule and does not kill the mouse; does not cause pneumonia
What did Chargaff do?
showed the molar content of bases ( base composition)
DNA replication
the process of making a copy of DNA
