1.5.3 The Structure of DNA Flashcards
(26 cards)
The nucleic acid DNA is a
polynucleotide – it is made up of many nucleotides bonded together in a long chain
A DNA nucleotide
DNA molecules are made up of
two polynucleotide strands lying side by side, running in opposite directions
DNA molecules are made up of two polynucleotide strands lying side by side, running in opposite directions – the strands are said to be
antiparallel
Each DNA polynucleotide strand is made up of
alternating deoxyribose sugars and phosphate groups bonded together to form the sugar-phosphate backbone
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
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 3’ end and a 5’ end (these numbers relate to which carbon on the pentose sugar could be bonded with another nucleotide)
As the strands run in opposite directions (they are antiparallel), one is known as
the 5’ to 3’ strand
As the strands run in opposite directions (they are antiparallel), one is known as the 5’ to 3’ strand and the other is known as
the 3’ to 5’ strand
The nitrogenous bases of each nucleotide project out from the backbone towards
the interior of the double-stranded DNA molecule
A single DNA polynucleotide strand showing the positioning of the ester bonds
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
The purine adenine (A) always pairs with
the pyrimidine thymine (T) – two hydrogen bonds are formed between these bases
The purine guanine (G) always pairs with
the pyrimidine cytosine (C) – three hydrogen bonds are formed between these bases
This is known as
complementary base pairing
These pairs are known as
DNA base pairs
A section of DNA – two antiparallel DNA polynucleotide strands held together by hydrogen bonds
DNA is described as a
double helix (this refers to the three-dimensional shape that DNA molecules form)
DNA molecules form a three-dimensional structure known as a DNA double helix
name the different components of a DNA molecule
sugar-phosphate backbone, nucleotide, complementary base pairs, phosphodiester bonds, hydrogen bonds
phosphodiester bonds join
the nucleotides in the sugar-phosphate backbone
