DNA Flashcards
Where is DNA and how is it organised in a eukaryotic cell?
In the nucleus, associated with histone proteins in linear strands. It is arranged in 23 pairs of chromosomes.
Where is DNA and how is it organised in a prokaryotic cell?
Free in the cytoplasm, ‘naked’ DNA and circular.
How many strands is a DNA molecules comprised of?
2 polynucleotide strands.
What do the strands run in?
Opposite direction-ANTIPARALLEL
How is the sugar-phosphate backbone formed?
Alternating deoxyribose sugars and phosphate groups bonded together.
How are the two antiparallel DNA polynucleotide strands held together?
Hydrogen bonds between nitrogenous bases.
How many hydrogen bonds between Adenine and Thymine?
2
How many hydrogen bonds between Guanine and Cytosine?
3
What is the process called when bases bond together?
Complementary base pairing.
What is the form of DNA described as?
Double helix=the three-dimensional shape formed by the twisting of the DNA molecule.
Why do you use detergent and heat in DNA purification?
-Disrupts the phospholipid bilayer and nuclear membranes, releasing the DNA.
-Heat also denatures enzymes released from the cell that would otherwise begin to digest the DNA.
Why must you then cool down the mixture immediately, whilst stirring?
-Prevents the DNA itself from breaking down
-Stirring ensures the whole mixture is cooled
Why do you add protease enzyme?
-Protease denatures and removes the proteins, leaving just the DNA
What is the purpose of adding ice-cold ethanol?
-Nucleic acids are insoluble in ice-cold ethanol and so the DNA forms a precipitate (white layer) at the top of the test tube mixture
How is DNA copied?
Semi-conservative replication.
