BIOLOGY

DNA

DNA or deoxyribonucleic acid is the genetic material that we get in all living things, from bacteria to mammals .

DNA is found in the nucleus of eukaryotic organisms and in chloroplasts and mitochondria. In prokaryotes, the DNA is free floating in the cell.

DNA components

DNA is composed of monomers called nucleotides . The nucleotides combine with each other to form a polynucleotide, in this case, the DNA. Each nucleotide contains three main elements:

Nitrogenous bases

They are organic molecules that contain carbon, nitrogen, oxygen and hydrogen. They are called bases because they have an amino group that can bind extra hydrogen. In DNA you can distinguish four nitrogenous bases. These are adenine (A), guanine (G), cytosine (C) and thymine (T).

Pentose

It is a sugar of five carbons that in the case of DNA is known as deoxyribose . The carbon atoms of the pentoses are listed 1 ‘, 2’, 3 ‘, 4’ and 5 ‘(1’ is read as a prime).

Phosphate groups

The phosphate of the DNA establishes unions or “bridges” between the pentoses.

DNA structure

The DNA has a double helix structure that resembles a spiral staircase. On the outside of the helix, deoxyribose and phosphate groups form the DNA column, while inside are the nitrogenous bases, like the rungs of a ladder.

The DNA strands run in opposite directions. This is known as antiparallel orientation. The nitrogenous bases of a chain are linked to the bases of the opposite chain forming base pairs . The base pairs are only established between adenine and thymine or guanine and cytosine. This is known as the rule of complementarity of the bases. For example, if a DNA strand has the sequence AATTGGCC, the sequencing of the complementary strand will be GGCCAATT because it has the opposite sense.

DNA in the genes and genome

The DNA provides the code for all the activities of the cell. The gene is the part of the DNA in which this code is “written”. The genetic content of a cell is known as a genome. The study of the genome is genomics, which consists of determining the sequence of nitrogenous bases of DNA. The genome size of one of the simplest organisms, the bacterium Escherichia coli, is 4.6 million base pairs.

Key points to remember

  • The structure of DNA is a double chain in helix.
  • Phosphate and deoxyribose form the external columns of DNA and nitrogenous bases form the inner rungs of DNA.
  • The nitrogenous bases bind in specific pairs: adenine with thymine, cytosine with guanine.
  • DNA contains the genetic information of the cell.

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