4.2.3 Transcription Flashcards
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
- translation
During transcription
DNA is transcribed and an mRNA molecule is produced
During translation
mRNA (messenger RNA) is translated and an amino acid sequence is produced
Transcription: this stage of protein synthesis occurs in
the nucleus
Part of a DNA molecule
unwinds (the hydrogen bonds between the complementary base pairs break)
Part of a DNA molecule unwinds, catalysed by
helicase, like in DNA replication
Part of a DNA molecule unwinds, catalysed by helicase, this exposes
the gene to be transcribed (the gene from which a particular polypeptide will be produced)
A complementary 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
Free activated RNA nucleotides pair up (via hydrogen bonds) with
their complementary (now exposed) bases
Free activated RNA nucleotides pair up (via hydrogen bonds) with their complementary (now exposed) bases on one strand
the template strand
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
The sugar-phosphate groups of these RNA nucleotides are then bonded together by the enzyme
RNA polymerase
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
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
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
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 is the strand that is transcribed to form 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
DNA polymerase is the enzyme involved in
DNA replication
RNA polymerase is the enzyme involved in
transcription
The mRNA codons have the same base sequence as the non-transcribed strand, and the tRNA anticodons have the same base sequence as the transcribed strand except
RNA, which has the base Uracil, replacing Thymine
