• A?gene?is a?sequence of nucleotide bases?in a DNA molecule that?codes for the production of a specific sequence of amino acids, that in turn make up a?specific polypeptide?(protein)
• This process of protein synthesis occurs in?two stages:
  • Transcription?–?DNA?is transcribed and an?mRNA?molecule is produced
  • Translation?–?mRNA?(messenger RNA) is translated and an?amino acid sequence?is produced

   

Transcription

• This stage of protein synthesis occurs?in the nucleus?of the cell
• Part of a DNA molecule?unwinds?(the?hydrogen bonds?between the complementary base pairs?break)
• This exposes the?gene?to be transcribed (the gene from which a particular polypeptide will be produced)
• A complimentary copy of the code from the gene is made by building a?single-stranded nucleic acid molecule known as mRNA?(messenger RNA)
• Free activated RNA nucleotides?pair up (via hydrogen bonds) with their complementary (now exposed) bases on one strand (the template strand) of the ‘unzipped’ DNA molecule
• The sugar-phosphate groups of these RNA nucleotides are then?bonded?together by the enzyme?RNA polymerase?to form the sugar-phosphate backbone of the mRNA molecule
• When the gene has been transcribed (when the mRNA molecule is complete), the hydrogen bonds between the mRNA and DNA strands break and the?double-stranded DNA molecule re-forms
• The mRNA molecule then?leaves the nucleus?via a pore in the nuclear envelope

The transcription stage of protein synthesis – DNA is transcribed and an mRNA molecule is produced

Template and non-template strands

• In the?transcription?stage of protein synthesis, the section of the DNA molecule where the gene is located (the gene coding for a particular polypeptide)?unwinds?– the hydrogen bonds between the complementary base pairs break, causing the two DNA strands to ‘unzip’
• Free activated RNA nucleotides then pair up with the exposed bases on the DNA molecule but?only with those bases on one strand of the DNA molecule
• This strand of the DNA molecule is called the?template strand?or the?transcribed strand
• This is the strand that is transcribed to form the mRNA molecule (RNA polymerase binds the RNA nucleotides together to create the sugar-phosphate backbone of the mRNA molecule)
  • This mRNA molecule will then be translated into an amino acid chain

   

• The strand of the DNA molecule that is not transcribed is called the?non-template strand?or the?non-transcribed strand

The template strand of the DNA molecule is the one that is transcribed