What is DNA?


DNA, DeoxyriboNucleic Acid is a long polymer that carries the heriditary informantion of most of organisms, DNA is found in the nuclei of eukaryote cells and in the nucleiod of bacteria, we found also the DNA in some organells ( mitochondria and cell plastids (chloroplasts)) and in viruses.

Structure of DNA

The main structure of DNA is double helix which is composed of two antiparallel strands, these strands are made up of the sugar 2-deoxyribose, phosphate, and purine and pyrimidine bases.

 Each phosphate is linked to the 3′ position of the preceding deoxyribose and to the 5′ position of the following deoxyribose.

There are four bases found in the DNA:

Adenine (A)

Tthymine (T)

Guanine (G)

Cytosine (C)

Adenine, A, is always paired with thymine, T.

Cytosine, C, is always paired with guanine, G.

Each 2-deoxyribose is linked to one of four bases in the 1′ position via a covalent glycosidic bond.

we call a nucleoside a base linked to a sugar

we call a nucleotide a base linked to a sugar and a phosphate

Gen9 Genetics – DNA primer design


DNA play a great role in:

  • Cell living and growing
  • Maintain and propagation of genetic information from generation to generation
  • Synthesis the components of the cells

Replication of DNA

Each strand of the DNA contains all the information needed to form a new double stranded molecules.

after separtion of the double helix each strand is used as a template to form the new strand of DNA, this is carried out by enzymes called DNA polymerases, All DNA polymerases synthesize new DNA in a 5′ to 3′ direction.


Transcription is the processus of recopyin genetic information in DNA to form RNA (RiboNucleic Acid) by using RNA polymerases, the result RNA is used to make proteins by the cellular protein-synthesizing (translation) machinery.

After the synthesis of RNA, the DNA reverts to its double helix form.



What is Genetics

Genetic is the science that studies the behavior and nature of genes, a gene is a basic unit of heredity, so the genetics studies the variation and heredity in living organisms.

Short history of Genetics

  • Gregor Mendel is the father of Genetics, in 1865, After many experiences on hybridizing pea plants he reported that many series of traits passed down through generations.
  • In 1866, Mendel noted certain patterns of inheritance seemed to be transmitted independently of one another.
  • It wasn’t until 1900 that the scientific community recognize the observation of Mendel, and thus when three Europeans botanists reported the result of their breeding experiments and liked it to Mendel’s work.
  • The biologist at the university of Cambridge, William Bateson was exited to study the relation between Mendel’s observations and evolution, and he recruited for that a number of young scientist women. Later they noted that Mendel’s principles extended across the plant and animals.
  • In 2001, Willian Bateson named this discipline “Genetics”, and “Gene” the unit of this discipline is the factor that was inherited.


The Genetics studies the difference between the individuals. If there is a difference it is transmitted to the next generation by sexual reproduction, or other process. In brief genetics studies the descendance across diverse individuals through at least two successive generations.

The mechanism of heredity depends on probabilities, but only some statistical concepts are needed.

Molecular Genetics

The research of Morgan on the fly proved that the genes were on the chromosomes.

But it was still unknown what genes were made up of, what was their molecular structure, and biologists debates the genetic material was DNA or proteins.

In 1952, Alfred Hershey and Martha Chase at Cold Spring Harbor Laboratory ingeniously used viruses (proteins and DNA inside) and proved by a radioactive experience that the genetic material is the DNA.

After many research, James Watson and Francis Crick at the University of Cambridge determined that DNA was a double helix, and the structure is two strands wrapped around each other.

DNA (DeoxyriboNucleic Acid) is a very long polymer made up of four different nucleotides (Adenine (A), Guanine (G), Cytosine (C), and Thymine (T).). A always bind to T, and G always to C.

These long double helix strands make up chromosomes, chromosomes divided into thousand of unit to form genes.

Molecular biologists spent the 1950s and 1960s using the double helix structure of DNA elucidate the mechanism of genetic replication and function.

Gene Role in Organisms

  • DNA is made into RNA
  • RNA specifies the structure of a specific protein
  • DNA is transcribed into mRNA (RNA messenger) by the enzyme RNA polymerase (specific DNA sequences ensure that RNA polymerase transcribes certain genes only in the correct cell type at the proper time.)
  • The mRNA serves for the protein synthesis by using the ribosomes and tRNAs.

Role of Molecular Genetic

  • Learning what is the role of DNA in determining the regulation of gene expression.
  • DNA replication in cells.
  • Determination of the complete DNA Sequence of several organisms.
  • Determination of the sequence of proteins.
  • Trying to understand how the sequence of a proteins determines its function.
  • Study of mutations that results of the errors during the replication of DNA.