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DNA transforms Bacteria
Frederick Griffith studied two strains of pneumonia |
pathogenic and nonpathogenic |
heat-killed pathogenic + nonpathogenic bacteria |
= pathogenic bacteria (live disease-causing) |
transformation |
change in genotype and phenotype due to assimilation of external DNA by a cell |
scientists studied to find the genetic material of chromosomes - protein vs. DNA
DNA transforms Bacteria (cont.)
Oswald Avery also proved that DNA was the molecule that transformed bacteria |
Viruses
DNA or RNA in a protein coat |
infect by taking over a cell's metabolic machinery |
Bacteriophages |
viruses that infect bacteria |
Henry and Chase showed that DNA was the genetic material that infected the bacteria |
Used radioactive isotope markers to label DNA and proteins of phages. Phage DNA entered the bacteria cell, but protein did not.
Chargaff's Rule
concentration of … [A] = [T] [C] = [G] |
Rosalind Franklin
x-ray crystallography |
image of DNA produced by x-rays diffracting when passing through DNA fibers |
DNA is a double helix, with two anti-parallel sugar-phosphate backbones, and nitrogenous bases in the molecule's interior |
anti-parallel - subunits run in opposite directions
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DNA is a polymer of nucleotides
components: nitrogenous base, deoxyribose sugar, phosphate group
bases: adenine, guanine, thymine, cytosine
Structure of DNA
DNA is a polymer of nucleotides connected by covalent bonds |
4 nitrogenous bases: |
Purines (double ring) [A] [G] |
Pyrimidines (single ring) - [C] [T] |
DNA base pairing |
PURINE always pairs with PYRIMIDINE |
2 of the same would be too wide/narrow |
3 hydrogen bonds between C and G |
2 hydrogen bonds between A and T |
DNA Replication
S phase of Interphase |
DNA made from existing DNA strand |
semiconservative model |
one parent strand serves as a template to a complementary strand |
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half of parent strand is conserved in each daughter strand |
DNA Replication (cont.)
origins of replication |
where replication of DNA molecule begins |
bacterial chromosome |
circular, single origin |
eukaryotic chromosome |
linear, thousands of origins |
replication fork |
Y-shaped region formed by unwinding of parent strands |
- reference drawings to understanding rest of replication -
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Proofreading DNA
DNA polymerase |
proofreads each nucleotide as it's covalently bonded |
mismatch repair |
other enzymes remove and repair incorrect nucleotides |
nucleotide excision repair |
mutated strand is cut out by enzyme nuclease, and the gap is filled with DNA polymerase and ligase |
- seen in skin cells when correcting thymine dimmers cause by UV rays
Evolution Significance of DNA Nucleotides
Mutations occur when uncorrected mismatched nucleotides are replicated and passed onto a daughter cell. Usually harmful and permanent genetic changes that support natural selection. |
Replication at Molecule Ends
Inside a Chromosome
eukaryotic cell |
one long DNA double helix with large amnt. of protein = |
chromatin |
the long DNA fits in the nucleus through packing |
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