Protein Synthesis - Transcription Flashcards
(9 cards)
What is a polynucleotide?
Polymer made up of repeating mononucleotide sub-units
Describe structure of ribonucleic acid (RNA)
- polynucleotide
- contains the pentose sugar ribose
- RNA is generally single stranded
- Contains base uracil instead of thymine
- RNA uses information in DNA to make proteins
Describe the structure of messenger RNA (mRNA)
Long strand arranged in a single helix
Base sequence of mRNA is determined by the sequence of bases on a length of DNA in transcription
Describe the function of mRNA
mRNA leaves the nucleus via a nuclear pore and enters the cytoplasm
Where is associates with the ribosomes
It acts as a template for protein synthesis
How is mRNA suitable for its function?
Possesses information in the form of codons
Chemically unstable (sing-stranded) - so polypeptide synthesis will not continue indefinitely
What is transcription?
The relevant gene in the DNA in the nucleus is ‘copied’ into a molecule of RNA called mRNA or messenger RNA
How is pre-messenger RNA produced from DNA in the process of transcription?
1) DNA helicase enzymes causes a short section of DNA to unzip
- exposing the nucleotide bases in that region
2) nucleotide bases on the template strand pair with their complimentary nucleotides from the pool present in the nucleus
3) the enzyme RNA polymerase moves along the strand and joins the nucleotides together
- to form a pre-mRNA molecule
4) as RNA polymerase adds the nucleotides one at a time to build a strand of pre-mRNA
- the DNA strands rejoin behind the RNA polymerase
5) when RNA polymerase recognises a stop code it detaches and and the production of of pre-mRNA is complete
6) Pre-mRNA then undergoes splicing and then mRNA leaves the nucleus through a nuclear pore
Process of Transcription
1) transcription takes place in the nucleus where the DNA double helix unwinds by DNA helicase and the hydrogen bonds break
2) once the strands are separated, the sequence on the template strand is used to produce a mRNA molecule
3) mRNA is produced by free nucleotides in the nucleoplasm
4) RNA polymerase is involved in the synthesising of the mRNA with the same base sequence as the coding strand (sense strand)
5) complementary base pairing ensures that the order of bases on the DNA exactly determines the order on RNA
6) the completed mRNA exits the nucleus through a pore in the nuclear envelope into the cytoplasm
7) this is where the second stage takes place called translation
Describe what happens during splicing in transcription
Introns are removed by enzymes before the mRNA leaves the nucleus
This leaves just exons or coding regions of mRNA
