DNA, Chromosomes and Genes

Key Questions

  • DNA is called the blueprint of life because it contains the instructions needed for an organism to grow, develop, survive and reproduce. DNA does this by controlling protein synthesis. Proteins do most of the work in cells, and are the basic unit of structure and function in the cells of organisms.

  • Genes are the basic units of heredity and are located on chromosomes.

    Genes are sections of DNA, whereas chromosomes are the structures that DNA folds into before cell division. Each human somatic cell contains 23 pairs of chromosomes. All of the genes that code for the creation, growth, and development of a human person are found in these chromosomes. In addition to DNA, these chromosomes contain histone proteins that help in the packaging of the DNA into chromosomes.

    In eukaryotic cells, chromosomes are found in the nucleus but in prokaryotic cells they are free to move about.

  • Answer:

    Deoxyribonucleic Acid is the meaning of it. It is a nucleic acid that is the carrier of genetic information.


    DNA are the letters of deoxyribonucleic acid.

    All life on earth uses this nucleic acid as the genetic code.

    A nucleic acid is a polynucleotide. A polynucleotide consists of three basic units: a phosphate group, a 5 carbon sugar (pentose), and a nitrogenous base. The five carbon sugar is deoxyribose. Since a polynucleotide chain, the phosphate and deoxyribose units are repetitive, the variation is provided by the nitrogenous bases.

    There are four bases: adenine, guanine, cytosine, and thymine.
    Both adenine and guanine are purines which have a double ring structure. Cytosine and thymine are pyramidines which consist of a single ring structure.

    The DNA molecule is double helix, a spiral shaped ladder. The upright or backbone of the ladder is made of alternating pentose and phosphate groups held together by covalent bonds. The rungs or steps of the ladder consist of the bases. These bases are joined to the pentose sugars with covalent bonds. Adenine pairs with thymine using two hydrogen bonds and cytosine pairs with guanine using three hydrogen.


    The genetic code is determined by the linear sequence of the bases.

    For example the sequence of adenine guanine thymine does not carry the same message as guanine thymine adenine.

    The code is arranged in triplet form which codes for RNA which in turn codes for amino acids which form the basis of proteins.