DNA is sometimescalled "the blueprint oflife" because it containsthe code, or instructionsfor building an organismand ensuring thatorganism functionscorrectly.Just like a builder usesa blueprint to build ahouse, DNA is used asthe blueprint, or plans,for the entire organism.
Scientists knew that the material that makes up genes must be able to do 2 things:1. Give instructions for building and maintaining cells2. Be able to be copied each time a cell divides and contain identical genes
It is the chemicalcomponent ofchromosomes, which arelocated in the nucleus ofevery cell.Stretches of DNA (orstretches ofchromosomes) code forgenes.Gene - a segment of DNAthat codes for a protein,which in turn codes for atrait (skin tone, eye color,etc), a gene is a stretch ofDNA.
DNA is made up of subunits callednucleotidesNucleotide = consists of a sugar, aphosphate, and a baseFour bases adenine, thymine, guanine,and cytosine (A, T, G, C)Each base has a different shape
Chargaff’s RuleIn 1950’s,biochemist namedErwin Chargafffound that theamount of adeninein DNA alwaysequals amount ofthymine
Also found thatamount of guaninealways equalsamount of cytosineChargaff’s Rulehelped scientistsunderstand thestructure of DNA
Franklin’s DiscoveryChemist RosalindFranklin was ableto make imagesof DNAmolecules
X ray diffraction =X rays are aimedat DNA moleculesand the raybounces offThe pattern madeby the bouncingrays is captured onfilm, suggestingthat DNA has aspiral shape
Watson and Crick’s ModelJames Watsonand Francis Crickused Franklin’s Xray images toconclude thatDNA must looklike a long,twisted ladder
DNA’s Double HelixDouble helix =shaped like a twistedladderTwo sides of theladder are made up ofalternating sugarparts and phosphateparts
Each rung of theladder is made of apair of basesThe rungs of theladder can occur inany order (as long asthe base-pair rule isfollowed)—A alwayswith T, G always withC
For instance, a stretch of DNA could beAATGACCAT (which would code for adifferent gene than a stretch that read:GGGCCATAG).All in all, there are billions of bases incells, which code for all the things anorganism needs to function.
Making Copies of DNAThe pairing of bases allows the cell to“replicate”, or make copies of, DNAPairs of bases are complementary—meaning they only pair with eachother, and both sides of the DNAladder pair together
How Copies areDuring replication(copying process), MadeDNA molecule splitsdown the middle,where the basesmeetThe bases on eachside of the moleculeare used as apattern for a newstrand
As the bases areexposed,complementarynucleotides areadded to eachside of the ladderTwo DNAmolecules areformed half ofeach DNA is oldand half is new
When Copies are MadeDNA is copiedevery time a celldividesThe job ofunwinding,copying, and re-winding the DNA isdone by proteinswithin the cell
DNA is usuallyfound with severalkinds of proteinsOther proteins helpwith the process ofcarrying out theinstructions writtenin the code of DNA
ScientiStS’ contributionSErwin Chargaff: discovered base-pairruleRosalind Franklin: used X-rays to findDNA’s spiral shapeWatson and Crick: built 3-D model ofDNA