Polypeptide synthesis Flashcards
What does protein synthesis involve?
The production of a chain of amino acids that forms the primary structure of a protein
What are the stages of protein synthesis?
- Transcription of the gene in the nucleus
- Processing the mRNA
- Translation of the mRNA into a polypeptide chain
- Modification of the protein
What is the first step of transcription?
Hydrogen bonds holding DNA together are broken by DNA helicase. This unwinds the double helix and exposes the unpaired bases on the DNA strand
What is the next step in transcription after the hydrogen bonds are broken?
Free RNA nucleotides are present in the nucleus and the bind to the complementary DNA nucleotide of ONE strand of DNA, the template strand
What happens in transcription after free nucleotides have bound to the template strand?
RNA polymerase joins the new RNA nucleotides to make a pre-mRNA molecule. The DNA strand rejoins together behind it
How long does the RNA polymerase continue for?
Until a stop codon is reached
What is the difference in transcription between prokaryote and eukaryote cells?
Prokaryote transcription directly produces mRNA
Eukaryote transcription produces pre-mRNA which contains introns which, if left in, wouldn’t produce functional proteins
What type of bond forms between the sugar and phosphate molecules of adjoining nucleotides?
Phosphodiester bonds
What is translation
Conversion of mRNA to proteins
What do ribosomes do in the process of translation?
They read the mRNA bases and assemble the individual amino acids together
What is the first step of translation?
The ribosome attaches to the mRNA at the start codon methionine (AUG)
What is the next step in translation after the ribosome attaches to the methionine?
A tRNA molecule with the complementary anticodon to methionine (UAC) moves to the ribosome and binds to the codon
What is the next step in translation after the complementary anticodon to methionine binds to the methionine?
A tRNA with a complementary anticodon pairs with the next codon. This continues to happen
What happens between the amino acids that are bound to the mRNA?
Joined by peptide bonds using an enzyme and an ATP molecule in a condensation reaction
What is the next step in translation after the first two amino acids form a peptide bond between them?
The ribosome moves down the mRNA molecule so the second and third amino acids are joined
What happens to the tRNA molecule after the ribosome passes it?
It is free to pick up another amino acid
How long does the process of translation go on for?
Until a stop codon is reached
What does the sequence of DNA triplets determine?
It determines the codons on the mRNA
Which determines the order of tRNA molecules
Which determines the amino acid sequence and function of the protein
What can happen after the polypeptide chain has been translated? (3 things)
- Removal of methionine
- Addition of functional groups
- Structural changes such as the addition of disulfide bridges
What does the modification of the primary structure do to the protein?
It gives the protein its specific secondary structure that allows it to perform its function
