7.3 Transcription

Topic 7 Nucleic Acids & Proteins

Transcription 7.3.1 State that transcription is carried out in a 5’→ 3’

direction. (The 5’ end of the free RNA nucleotide is added to the 3’ end of the RNA molecule that is already synthesized).

7.3.2 Distinguish between the sense and antisense strands of DNA.

The sense strand (coding strand) has the same base sequence as mRNA with uracil instead of thymine. The antisense (template) strand is transcribed.

Transcription 7.3.3 Explain the process of transcription in prokaryotes,

including the role of the promoter region, RNA polymerase, nucleoside triphosphates and the terminator.

The following details are not required: there is more than one type of RNA polymerase; features of the promoter region; the need for transcription protein factors for RNA polymerase binding; TATA boxes (and other repetitive sequences); and the exact sequence of the bases that act as terminators.

Transcription

7.3.4 State that eukaryotic RNA needs the removal of introns to form mature mRNA.

Further details of the process of post-transcriptional modification of RNA are not required.

Transcription Transcription is the formation of a molecule of messenger

RNA (mRNA) from a DNA template in the nucleus. Transcription is carried out in a 5’ 3’ direction. DNA acts as a template but only one side of the DNA

double helix is a gene. This is called the antisense strand. The antisense strand is transcribed into mRNA by RNA

polymerase. The other side is complementary to the antisense strand and

is called the sense strand. The sense strand has the same sequence of bases as the

mRNA except with T not U.

Transcription

Ref: Biology for the IB Diploma, Allott

Transcription

Ref: IB Biology, Oxford Study Courses

Transcription The Promoter Region

A specific sequence of DNA bases at the start of the gene to which RNA polymerase binds.

It is found on the sense strand.

RNA Polymerase The enzyme adds nucleoside triphosphates (NTPs) using base

pairing to the DNA antisense strand.

Terminator Region A specific sequence of DNA bases marking the end of the

transcription process. RNA polymerase breaks free and the mRNA strand is released. It is found on the sense strand.

Role of the Promoter and Terminator in Transcription

Ref: Biology for the IB Diploma, Allott

Introns and Exons Many genes in Eukaryotes contain Introns. These are non-coding sequences that are transcribed but

not translated. The are found in newly transcribed mRNA but removed

to form mature mRNA. The sequences that are not removed are called Exons. Prokaryotes do not usually have introns. The removal of introns is called post-transcriptional

modification of RNA.

Introns and Exons

Ref: IB Biology, Oxford Study Courses

Transcription 7.3.1 State that transcription is carried out in a 5’→ 3’

direction. (The 5’ end of the free RNA nucleotide is added to the 3’ end of the RNA molecule that is already synthesized).

7.3.2 Distinguish between the sense and antisense strands of DNA.

The sense strand (coding strand) has the same base sequence as mRNA with uracil instead of thymine. The antisense (template) strand is transcribed.

Transcription 7.3.3 Explain the process of transcription in prokaryotes,

including the role of the promoter region, RNA polymerase, nucleoside triphosphates and the terminator.

The following details are not required: there is more than one type of RNA polymerase; features of the promoter region; the need for transcription protein factors for RNA polymerase binding; TATA boxes (and other repetitive sequences); and the exact sequence of the bases that act as terminators.

Transcription

7.3.4 State that eukaryotic RNA needs the removal of introns to form mature mRNA.

Further details of the process of post-transcriptional modification of RNA are not required.