The Structure of DNA Flashcards
The nucleic acid DNA is a
polynucleotide – it is made up of many nucleotides bonded together in a long chain
DNA molecules are made up of …… polynucleotide strands lying side by side, running in …….. directions – the strands are said to be?
2
opposite
antiparallel
Each DNA polynucleotide strand is made up of
alternating deoxyribose sugars and phosphate groups bonded together to form the sugar-phosphate backbone.
These bonds are covalent bonds known as phosphodiester bonds
The phosphodiester bonds link the
5-carbon of one deoxyribose sugar molecule to the phosphate group from the same nucleotide, which is itself linked by another phosphodiester bond to the 3-carbon of the deoxyribose sugar molecule of the next nucleotide in the strand
Each DNA polynucleotide strand is said to have a …’ end and a ..’ end (these numbers relate to which carbon ……
3’ end 5’ end
on the pentose sugar could be bonded with another nucleotide)
As the strands run in opposite directions (they are……..), one is known as the .’ to .’ strand and the other is known as the .’ to .’ strand
antiparallel
5’ 3’
3’ 5’
The nitrogenous bases of each nucleotide project out ………….towards the interior of the ………….
from the backbone
double-stranded DNA molecule
The two antiparallel DNA polynucleotide strands that make up the DNA molecule are held together by
hydrogen bonds between the nitrogenous bases
These hydrogen bonds always occur between the same pairs of bases:
Which base pair has 2 hydrogen bonds
The purine adenine (A) always pairs with the pyrimidine thymine (T) – two hydrogen bonds are formed between these bases
These hydrogen bonds always occur between the same pairs of bases:
Which base pair has 3 hydrogen bonds
These hydrogen bonds always occur between the same pairs of bases:
Which base pair has 2 hydrogen bonds
This is known as complementary base pairing
These pairs are known as DNA base pairs
DNA is described as a double helix
This refers to the
spiral shape, where two complementary strands of nucleotides run in opposite directions and are held together by hydrogen bonds.
Make sure you can name the different components of a DNA molecule (sugar-phosphate backbone, nucleotide, complementary base pairs, phosphodiester bonds, hydrogen bonds) and make sure you are able to locate these on a diagram. Remember that phosphodiester bonds join the nucleotides in the sugar-phosphate backbone, and hydrogen bonds join the bases of the two complementary strands together. Remember that the bases are complementary, so the number of A = T and C = G. You could be asked to determine how many bases are present in a DNA molecule if given the number of just one of the bases. Note that knowledge of purines and pyrimidines is not required