• 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 bonds 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

• Within eukaryotic genes, there are both?coding?and?non-coding sequences?of DNA
  • The coding sequences are called?exons?and these are the sequences that will eventually be?translated?into the amino acids that will form the final polypeptide
  • The non-coding sequences are called?introns?and are?not translated?(they do not code for any amino acids)
• When transcription of a gene occurs, both the exons and introns are transcribed
• This means the RNA molecule formed (known as the?primary transcript) also?contains exons and introns
• As the?introns?are not to be translated, they must be?removed?from the RNA molecule
• The?exons?are then all?fused together?to form a continuous RNA molecule called mature?mRNA?that is ready to be translated
• This process is sometimes called ‘splicing’ and is part of the process of?post-transcriptional modification?(referring to the modification of the RNA molecule?after transcription?but before translation occurs)

The RNA molecule produced from transcription of a gene contains introns that must be removed before translation can occur