Unit 4:  The genetic revolution                                                       1   2   3   4  

2. CONCEPTS OF MOLECULAR GENETICS

2.1. Nucleic acids

a) Nucleotides

Nucleic acids are macromolecules formed by atoms of carbon (C), hydrogen (H), oxygen (O), nitrogen (N) and phosphor (P). These atoms are combined to form little molecules called nucleotides. Nucleic acids, DNA and RNA, are long chains of nucleotides.

b) Deoxyribonuclec acid (DNA)

The DNA molecule is made up of a double chain of nucleotides with structure of double-helix. This chains (or strands) are:

- Dextrorotatory (the two strands are twisted around each other in a shape of a double helix turning to the right)

- Antiparallel (one strand goes in a direction and its complementary strand in the opposite one)

- Complementary (The two strands of nucleotides are connected because the complementary nitrogenous bases are linked together by hydrogen bonds. The bases on each chain join together according to the following pattern: adenine-thymine and guanine-cytosine) 

The DNA is located inside the nucleus of the eukaryote cell and in the cytoplasm of prokaryote cells.

Its function is to store the genetic information.

Animation: DNA structure (McGraw Hill)

c) Ribonuclec acid (RNA)

RNA is formed by a single chain of nucleotides and much shorter than DNA. The nucleotides are similar in composition, but they contain ribose, instead of deoxyribose, and uracil instead of thymine.

It is located in both the cytoplasm as the nucleus of the cell, depending on the type. Each type perform a determine function in the transformation of the information stored in the DNA to proteins.

- Messenger RNA (mRNA). This is a copy of a fragment of DNA (one gene) that is formed inside the nucleus and then goes into the cytoplasm to be translated into a protein by the ribosomes.

- Transfer RNA (tRNA).  This transports the amino acids from the cytoplasm to the ribosomes.

- Ribosomal RNA (rRNA). This forms part of the ribosomes. These organelles translate the mRNA into proteins.

2.1. How could we distinguish in the laboratory if a fragment of nucleic acid

       is RNA or DNA?