2) Outline what occurs during transcription. [10]

Transcription is the process where the DNA code of a gene is copied to make m-RNA (messenger RNA). DNA is too large to fit through the nuclear pores, and contains many codes that aren’t always needed at a given time.  So the m-RNA only carries that code needed to make specific proteins out of the nucleus to the ribosome.

Transcription takes place in the nucleus.

A gene is one small piece of DNA that contains the code needed to produce one polypeptide (protein) at the ribosome.

RNA polymerase is the enzyme that untwists and unzips DNA at the beginning of transcription and then reads the DNA strand to produce m-RNA.

RNA polymerase reads the antisense strand of DNA (the side containing the code to make a polypeptide). It reads the antisense DNA from 3’ to 5’.

The new m-RNA is made in the 5’ to 3’ direction.

The sense strand of DNA is the side of DNA that does not contain a code to make a polypeptide. It is not read by the RNA polymerase.

The promoter is the beginning code of DNA on the gene. It is where the RNA polymerase begins reading the DNA code, and is always the 3 letter triplet TAC.

Elongation is the process where the new m-RNA is lengthened in the 5’-3’ direction.

The terminator code is section of DNA that stops transcription. It’s code is complementary to the stop codons of m-RNA.

The newly created m-RNA of eukaryotic cells must first have any non-coding sections of m-RNA removed.  These non-coding sections are called introns since they remain in the nucleus.

The finished m-RNA that now contains the code needed to make the polypeptide is called an exon since it leaves the nucleus and then heads for the ribosome for translation.