DNA Flashcards
Where is DNA found in eukaryotes and in prokaryotes and how is it stored?
Eukaryotes: stored in nucleus in linear strands
Prokaryotes: stored in cell (not membrane bound) in circles called plasmids
Describe Giffith’s experiment
The experiment was set out to prove that non-virulent strains become virulent once mixed with virulent heat-killed strains. A smooth variant was heat killed and produced a SMOOTH virulent strain that killed the mice.
What is meant by a smooth strain?
A smooth stain has a polysaccharide casing that blocks it from being recognised by the immune system. It is a virulent strain
What is meant by a rough strain?
A rough strain DOES NOT have a polysaccharide casing so it IS recognised by the immune system. It is non-virulent
What does the Hershey-Chase experiment prove?
It proves that DNA is hereditary and that bacteria replicates.
How did the Hershey-Chase experiment prove that DNA is hereditary?
Using bacteriophages, they inserted radioactive sulfur (for proteins) and radioactive phosphate (for DNA). They then mixed these bacteriophages with the bacteria to determine whether the radioactive signal was detected outside the bacteria or inside it.
they then centrifuged it to separate the bacteria from the bacteriophages - as they were bigger they would settle at the bottom.
After the bacteriophage had replicated and entered the bacteria, they found that almost no radioactive sulfur was detected, showing that protein is not hereditary.
They found all of the radioactive phosphate had been transferred inside the bacteria meaning the DNA was replicated and inherited.
In the Hershey-Chase experiment, the bacteriophage coat is labelled with?
Sulfur-35
Which bases are pyrimidines and which ones are purines?
pYrimidines: cYtosine & thYmine
puriNes: adeNiNe & guaNiNe
What is a nucleoside made from?
A base and sugar
What is a nucleotide made from?
A nucleoside and phosphate
What is Chargaff’s rule?
Adenine + Tymine = Cytosine + Guanine (number of Pyrimidines = number of purines
How do bases interact and form a structure?
Bases are hydrophobic and stack on top of each other and are seperated by van der Waals forces.
There is a distance of 0.34 nm between base pairs.
Are bases perpendicular or parallel to the helical axis?
Bases are perpendicular to the helical axis
What is A-DNA?
A-DNA is a right-handed dehydrated form of DNA. It has wider and tilted bases
What is B-DNA?
Right-handed DNA with major grooves and minor grooves that are joined by glycosidic bonds, which form the asymmetrical structure.
What is Z-DNA?
Z-DNA is a left-handed DNA that has a higher salt and C—G concentration
Where does max absorption occur for DNA melting?
260nm
How does DNA fragment size affect melting?
Longer fragments melt at higher temperatures and smaller fragments melt at lower temperatures
How does salt concentration affect melting?
A higher salt concentration leads to a higher melting temperature
How does hydrogen bonding affect melting?
More hydrogen bonds causes DNA to melt at a higher temperature. C/G bonds require more energy to break than A/T as they have 3 hydrogen bonds compared to the 2 hydrogen bonds
What is chromatin?
Chromatin is a complex that store the DNA (condensed)
What are the histones proteins that DNA wraps around?
The histones are H1, H2A, H2B, H3, H4
What histones make up the histone core?
H2A, H2B, H3, H4 make up the histone core. They are positively charges and attracted to the negatively charged DNA
Condensed regions of DNA are rich in what?
Rich in A-T regions. Called heterochromatin
The BCR-Abl fusion protein arises from a chromosomal translocation. True or False?
True, the BCR and ABL gene translocate to form the Philadelphia chromosome, which can cause leukemia.
Sickle-cell disease arises from a single nucleotide change in the alpha-globin gene. True or False?
False, sickle-cell disease is caused by a single point mutation in beta-globin.
In the Avery experiments, DNAase treatment of heat killed smooth strain material resulted in transformation of rough strain. True or False?
False, the heat killed smooth strain and DNAase resulted in no transformation of the rough strain as the dna had been destroyed. Proved that DNA is the transforming material.
In the Hershey-Chase experiment, centrifugation is used to pellet and purify the bacteriophage coats. True or False?
False, centrifugation is used to purify the E.coli form the bacteriophage.
What chemicals were used to label the DNA and proteins?
DNA was labelled with P-32 and proteins labelled with S-35.
The primary alcohol is on what carbon of deoxyribose?
Carbon 5
What carbon does the base attach to?
Carbon 1
