Polypeptide Synthesis Flashcards
What is the basic process of polypeptide synthesis?
- DNA provides instructions in the form of a long sequence of bases.
- Complimentary part of this sequence is made in the form of pre-mRNA (transcription)
- The pre-mRNA I spliced to form mRNA
- mRNA is used as a template for complimentary tRNA molecules to attach and amino acids they carry are linked to form a polypeptide (translation)
What is transcription?
The process of making pre-mRNA using part of the DNA as a template.
How and why are the two strands of DNA separated in the first stage of Transcription?
An enzyme acts on a region of the DNA to separate strands and exposes the nucleotide bases in that region.
What is the template strand and what is it’s role in the second stage of Transcription?
Nucleotide bases on one of the DNA strands (template strand) pair with the complimentary nucleotides from the nucleus.
What does RNA Polymerase do in the second stage of Transcription?
Moves along the complimentary nucleotide strand to join the nucleotides together to form a pre-mRNA molecule.
What happens as RNA Polymerase joins the nucleotide bases in the third stage of Transcription?
As RNA Polymerase adds the nucleotides to form pre-mRNA strand, the DNA strands re-join behind it so only a few base pairs of DNA are exposed at one time.
What happens when the RNA Polymerase reaches a STOP codon?
When it reaches a particular sequence of bases on the DNA that it recognises as a STOP triplet code, it detaches and the production of mRNA is complete.
Why does pre-mRNA need to be spliced in Eukaryotic cells?
The DNA of a gene is made up of sections of exons that code for proteins, and introns that do not. Intervening introns prevent the synthesis of a polypeptide.
What happens to the base sequence in splicing?
Base sequences corresponding to introns are removed and the functional exons are joined together.
What happens to the mRNA after it has been spliced?
mRNA is too large to diffuse out of the nucleus and so they leave via a nuclear pore. The mRNA is then attracted to the ribosomes and attach.
What is translation?
After transcription, the codons on the mRNA molecule are translated to amino acids that make up a polypeptide.
How does tRNA attach to amino acids?
A particular tRNA has a specific anticodon and attaches to a specific amino acid. Each amino acid therefore has one or more tRNA molecule, with its own anticodon of bases.
What is the role of the ribosome in the first stage of translation?
A ribosome becomes attached to the starting codon (AUG) at one end of the mRNA molecule.
What does the tRNA molecule do after the starting codon is displayed at the ribosome in the second stage of translation?
tRNA with the complimentary anticodon sequence (UAC) moves to the ribosomes and pairs up with the codon on the mRNA. This tRNA carries a specific amino acid.
What happens after another tRNA molecule is paired on the mRNA strand?
The ribosome moves along the mRNA, bringing together two tRNA molecules. The amino acids on the tRNA molecules are joined by a peptide bond using an enzyme and ATP which is hydrolysed to provide the required energy.
