Lecture 11: DNA Structure Flashcards
What is the building block that makes up DNA?
Nucleotides
How are adjacent nucleotides bonded together? How does this form?
Via a phosphodiester bond called phosphodiester linkage. This forms under a condensation polymerisation reaction which releases H2O.
What are the purines?
Adenine and Guanine. The purines are made of a six-membered ring and a 5-membered ring of carbon. Making them two rings long.
What are the pyrimidines?
Thymine, Uracil and Cytosine. The pyrimidines are only made of a 6-membered ring of carbon. Making them one ring long.
Describe the structure of a nucleotide.
A nucleotide is composed of three parts. A nitrogenous base, ATCG. A five carbon sugar (a pentose) and one to three phosphate groups.
In DNA the sugar is called deoxyribose while in RNA its just ribose. The difference is that deoxyribose lacks an oxygen atom on the second carbon in the ring.
There are one - three phosphate groups on the 5 prime carbon (5’) and a hydroxyl group on the 3’ carbon (3’). We call these the 5’ phosphate group and the 3’ prime hydroxyl group, or the 5’ end and the 3’ end.
What are the two families of nitrogenous bases called?
Purines and Pyrimidines
Complementary base pairing in DNA vs RNA
DNA : Adenine - Thymine, Cytosine - Guanine.
RNA : Adenine - Uracil, Cytosine - Guanine
What is the diameter of DNA and why?
The diameter of DNA is three units wide. This is because a purine always bonds to a pyrimidine in complementary base pairing. A pyrimidine is one unit long while a purine is two units long, 1 + 2 = 3.
How does the beginning monomer used to form a polynucleotide differ from the end product?
The beginning nucleotide has 3 phosphate groups however 2 are lost in the polymerization reaction.
If the component of Adenine is 22% in DNA what is the % of the other three bases?
Thymine = 22% Guanine = 28% Cytosine = 28%
What is another name for the structure known as a polynucleotide?
Nucleic acid.
Why is DNA considered semi conservative?
DNA replication is referred to as a semi conservative process as the hydrogen bonds between neighbouring bases break releasing the strands. A new strand is synthesised corresponding to each parent strand. Because one original strand is reused in the creation of a new DNA molecule it is considered semi conservative.
How are bases from anti-parallel strands held together?
They are held together through hydrogen bonds. There are two hydrogen bonds between A - T and three hydrogen bonds between C - G.
What does the term ‘DNA strands are antiparallel,’ mean and why is it important?
It means that one strand runs in the 5’ - 3’ direction and the other runs in the 3’ - 5’ direction. This is important because if they both ran in the same direction complementary base pairing wouldn’t work.
How many strands are in a RNA molecule vs a DNA molecule?
2 in DNA 1 in RNA.
