DNA Test Part Four: Concepts Flashcards
Hershey and chase experiment
In their first experiment, Hershey and Chase used a bacteriophage with radioactive Phosphorus-32 marked DNA. They then allowed the phage to infect E. coli. The radioactive phosphorus was then found in the bacteria.
In a second experiment, they marked the phages proteins with radioactive Sulfur-35. This time, after the bacteria had been infected, the radio active element was not passed down.
Hershey and Chase concluded that when bacteriophages infect bacteria, their DNA enters the bacteria. This experiment proved that DNA contains hereditary information, rather than proteins.
How to extract DNA
The first step is to lyse or break open the cell. This can be done by hand or in a blender.
After the cells have broken open, a salt solution such as NaCl and a detergent solution is added. These solutions break down and emulsify the fat & proteins that make up a cell membrane.
Finally, ethanol is added because DNA is soluble in water. The alcohol causes DNA to precipitate, or settle out of the solution, leaving behind all the cellular components that aren’t soluble in alcohol.
The DNA can be spooled (wound) on a stirring rod and pulled from the solution at this point.
Dna can be extracted by dissolving the subject’s cells, and filtering out the liquids.
Watson and Crick
Watson and Crick used the images made by Franklin and Wilkins to create a model of DNA
Franklin and Wilkins
Franklin and Wilkins contributed to the discovery of the structure of DNA by using x-ray crystallography to get images of DNA
DNA replication steps
Helicase unzips DNA, gyrase unwinds it
DNA polymerase binds to the 3’ to 5’ strand and moves along 3’ to 5’, creating leading strand in the 5’ to 3’ direction
Since DNAP can only go one way, the lagging strand is made in fragments, which are linked by DNA ligase 1
DNAP goes back and corrects mistakes
Protein synthesis steps
RNA polymerase binds to the promoter, a base sequence signalling the start of the gene
DNA is synthesized in the 5’ to 3’ direction, creating only one strand. T is replaced by U
This pre-mRNA is spliced to remove the introns then travels to the ribosome
rRNA ribosome binds to mRNA
tRNA begins translating, matching the mRNA codons to its anticodons. Each anticodon is attached to an amino acid, which is then added to the polypeptide chain.
Once tRNA reaches the top codon, the process is finished and the chain detaches
Translation
The ribosome binds to mRNA at a specific area.
The ribosome starts matching tRNA anticodon sequences to the mRNA codon sequence.
Each time a new tRNA comes into the ribosome, the amino acid that it was carrying gets added to the elongating polypeptide chain.
The ribosome continues until it hits a stop sequence, then it releases the polypeptide and the mRNA.
The polypeptide forms into its native shape and starts acting as a functional protein in the cell.
Transcription
Initiation occurs when the enzyme RNA polymerase binds to a region of a gene called the promoter.
This signals the DNA to unwind so the enzyme can ‘‘read’’ the bases in one of the DNA strands.
For elongation RNA polymerase reads the unwound DNA strand and builds the mRNA molecule, using complementary base pairs.
Termination occurs when RNA polymerase crosses a stop sequence in the gene
