3.8 : Nucleic Acids Flashcards
Describe the structure of nucleotides
Contains :
A pentose monosaccharide
A phosphate group, an inorganic molecule that is acidic and negatively charged
A nitrogenous base - a complex organic molecule containing one or two carbon rings in its attached as well as nitrogen
How are polynucleotides ( nucleic acids ) formed ?
Nucleotides are linked together by condensation reactions to form a polynucleotide.
The phosphate group at the fifth carbon of the pentose sugar (5’) of one nucleotide forms a covalent bond with the hydroxyl group at the third carbon (3’) of the pentose sugar of an adjacent nucleotide.
These bonds are called phosphodiester bonds.
This forms a long, strong sugar - phosphate ‘backbone’ with a base attached to each sugar.
How are phosphodiester bonds broken?
By hydrolysis, which releases the individual nucleotides.
What does DNA stand for? What is it’s sugar?
Deoxyribonucelic acid.
Sugar : deoxyribose
Compare and contrast pyrimidines and purines
Pyrimidines - the smaller bases, which contain single carbon ring structures - thymine and cytosine
Purines - the larger bases, which contain double carbon ring structures - adenine and guanine
Describe the structure of DNA
Two strands of polynucleotides coiled into a double helix.
Held together by hydrogen bonds between the bases.
Each strand has a phosphate group (5’) at one end and a hydroxyl group (3’) at the other end.
The two parallel strands are arranged so that they run in opposite directions ( antiparallel ).
Describe the base paring rules
Adenine and thymine form two hydrogen bonds with each other.
Cytosine and guanine form three hydrogen bonds with each other.
This means that a small pyrimidine base always binds to a larger purine base. This maintains a constant distance between the DNA backbones, resulting in parallel polynucleotides chains.
How does genetic information leave the nucleus?
DNA is a very large molecule and so can’t fit through the nuclear pores so mRNA does it.
An individual strand of mRNA is only a section of the whole chromosome of DNA, and can therefore leave and travel to the ribosomes.
What is the length of 10 base pairs?
3.4nm
What are the differences between DNA and RNA?
DNA = deoxyribose ; RNA = ribose
DNA = thymine ; RNA = uracil
Like thymine, uracil is also a pyrimidine that forms two hydrogen bonds with adenine, so base pairing rules still apply.
What are the similarities between DNA and RNA?
They both form polymers by the formation of phosphodiester bonds in condensation reactions.
The bonds are hydrolysed to break the down.
How can DNA be extracted?
Grind sample in a mortar and pestle to break down cell walls.
Mix with detergent to break down cell membrane and release cell contents into solution.
Add salt to break the hydrogen bonds between the DNA and water molecules.
Add protease to break down the proteins associated with the DNA in the nuclei.
Add a layer of alcohol ( ethanol ) on top of the sample which causes the DNA to precipitate out of solution.
The DNA will be seen as white strands forming between the layer of sample and layer of alcohol. DNA can be picked up by ‘spooling’ it onto a glass rod.
