DNA double helix is
DNA double helix is
The correct option is D Complementary and antiparallel
Introduction to the structure of DNA
DNA is a double stranded helical molecule in which each strand is composed of repeating units of deoxyribonucleotides.
Each deoxyribonucleotide is composed of a deoxyribose sugar with a phosphate attached to its 5′ carbon and a nitrogenous base attached to its 1′ carbon.
The adjacent nucleotides are connected by phosphodiester bonds between the 3′-OH group of one nucleotide and the 5′ phosphate group of the next nucleotide.
The sugar and phosphodiester bonds form the backbone of each DNA strand and the nitrogenous bases are projected inwards.
Complementary
The nitrogenous bases of each strand form pairs with the complementary base on the opposite strand .
Adenine pairs with thymine using 2 hydrogen bonds and cytosine pairs with guanine using 3 hydrogen bonds.
The base pairs are stacked one upon the other like the rungs of a ladder.
Thus,the two strands of DNA double helix are said to be complementary to each other.
Antiparallel
One end of the polynucleotide chain has a sugar residue with a free 5′ carbon attached to a phosphate group that is not linked. This end is called the 5′ end.
The other end has a sugar residue with a free 3′ carbon attached to a -OH group that is not linked. This end is called the 3′ end.
The two DNA strands are said to be antiparallel as they run parallel but are oriented in opposite directions, i.e, the 3′ end of one polynucleotide chain lies opposite to the 5′ end of the other.
Without supercoils
The DNA double helix is a very long molecule which is packaged within the nucleus of the cell by forming a chromatin with nucleosomes ( DNA wrapped around a core of 8 histone molecules) and then it is further coiled and supercoiled to form higher order structures such as chromatin fibres and chromosomes. Thus, the DNA double helix is not without super coils.
Always circular
DNA is not always circular. Extrachromosomal DNA such as plasmids in prokaryotes, mitochondrial DNA, chloroplast DNA, etc are circular in nature but chromosomal DNA is linear.
Introduction to the structure of DNA
DNA is a double stranded helical molecule in which each strand is composed of repeating units of deoxyribonucleotides.
Each deoxyribonucleotide is composed of a deoxyribose sugar with a phosphate attached to its 5′ carbon and a nitrogenous base attached to its 1′ carbon.
The adjacent nucleotides are connected by phosphodiester bonds between the 3′-OH group of one nucleotide and the 5′ phosphate group of the next nucleotide.
The sugar and phosphodiester bonds form the backbone of each DNA strand and the nitrogenous bases are projected inwards.
Complementary
The nitrogenous bases of each strand form pairs with the complementary base on the opposite strand .
Adenine pairs with thymine using 2 hydrogen bonds and cytosine pairs with guanine using 3 hydrogen bonds.
The base pairs are stacked one upon the other like the rungs of a ladder.
Thus,the two strands of DNA double helix are said to be complementary to each other.
Antiparallel
One end of the polynucleotide chain has a sugar residue with a free 5′ carbon attached to a phosphate group that is not linked. This end is called the 5′ end.
The other end has a sugar residue with a free 3′ carbon attached to a -OH group that is not linked. This end is called the 3′ end.
The two DNA strands are said to be antiparallel as they run parallel but are oriented in opposite directions, i.e, the 3′ end of one polynucleotide chain lies opposite to the 5′ end of the other.
Without supercoils
The DNA double helix is a very long molecule which is packaged within the nucleus of the cell by forming a chromatin with nucleosomes ( DNA wrapped around a core of 8 histone molecules) and then it is further coiled and supercoiled to form higher order structures such as chromatin fibres and chromosomes. Thus, the DNA double helix is not without super coils.
Always circular
DNA is not always circular. Extrachromosomal DNA such as plasmids in prokaryotes, mitochondrial DNA, chloroplast DNA, etc are circular in nature but chromosomal DNA is linear.
