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AP Bio Chpt. 17 Cheat Sheet by

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
 

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
 
half of parent strand is conserved in each daughter strand
- Meselson and Stahl

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 -
 

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

- reference drawings -

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
- reference drawings -

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