• The genome contains all the genes present in the nucleus of a cell. Gene varies in size from ...a few hundred DNA/RNA bases to more than few thousand bases.
  
  
• The haploid set of chromosome contains the total genome of the organism.
  
  
• The bacterium Mycoplasma genitalium has a small genome size of 0.58Mb and the plant ...Triticum aestivim has a large genome size of 16000Mb. The genome size in human is ...3200Mb.

Fig 1-1.3: Illustration of genome, from genome to a chromosome, from a chromosome to gene

 

1-1.3.1 Role of genes within cells:

• Genes contain the instructions for each cell to make proteins and RNAs. Genes are made up of DNA fragments.
  
  
• Within the cell the DNA performs two tasks:
  • Act as information repository including instructions in making the component molecules of the cells.
  • Pass on the information to the next generation.
    
• The mere presence of DNA does not implicate a cell to be alive and functional. Mammalian red blood cells (RBCs) discard nucleus during developmental process and thus lacks DNA in mature state.
  
  
• Genes are transcribed to RNA which are processed to various forms like mRNA, tRNA, rRNA etc. mRNA are translated to proteins depending on the regulatory signals. tRNA and rRNA serve as the components of translational machinery.
  
  
• New functions of RNA are also being discovered like regulatory (miRNA, siRNA etc) and catalytic (ribozymes) functions.
  
  
•  Proteins are structural components of cells, enzymes, hormones, various signalling molecules, receptors and other factors which are involved in performing the chemistry of life and are essential for the normal body function, for example, sugar conversion to energy and metabolite (small molecules) production in cell.