Protein Synthesis Flashcards
What is transcription?
It is when one strand of DNA acts as a template for the production of mRNA, a complimentary section of part of the DNA sequence. This occurs in the nucleus.
What is translation?
It is when the mRNA acts as a template to which complementary tRNA molecules attach and the amino acids they carry link together forming a polypeptide. This occurs on the ribosomes in the cytoplasm.
What happens in transcription?
DNA helicase breaks the hydrogen bonds between the bases of a specific region in the helix. This unwinds and separates the strands exposing the unpaired bases on the template strand. The enzyme RNA polymerase binds the template strand at the beginning of the sequence to be copied. Free RNA nucleotides align opposite the template strand based on the complementary bases. RNA polymerase moves along the strand forming bonds, these are added one at time, growing the strand. Behind the RNA polymerase the DNA strands rewind back into its double helix shape. RNA polymerase separates from the template when it reaches to stop codon. The production of the transcript is complete and the newly formed are in a detaches from the DNA.
Where does translation take place?
It takes place on the ribosome and involves tRNA.
What happens at the smallest subunit of the ribosome?
It is where the stop codon of the mRNA molecule attaches.
What happens at the largest subunit of the ribosome?
It has two sites for attachment of tRNA molecules which means two tRNA molecule which can occupy the ribosome at one time.
How does the ribosome act as a framework?
It moves along the mRNA holding the codon – anti codon complex together until the two amino acids attached to the adjacent tRNA molecules bind. The ribosome moves along the mRNA adding an amino acid one at a time until the polypeptide has formed. The order of bases in the DNA has determined the order of amino acids in the polypeptide chain.
What happens in the initiation stage of translation?
A ribosome binds the start codon on the mRNA. The first tRNA was an anticodon complimentary to the first code on the mRNA attaches at the first attachment site on the large subunit of the ribosome. The three bases in the codon on the mRNA bond to the three complementary bases of the anticodon with hydrogen bonds. The second tRNA with an anti codon complementary to the second codon on the mRNA binds the second attachment site on the ribosome through codon – anti codon interactions.
What happens in the elongation stage of translation?
The ribosomal enzyme catalyse is a peptide bond when the two amino acid’s are sufficiently close. The first tRNA leaves arrive so leaving the site vacant and returned the cytoplasm to bind to another copy of its specific amino acid. The ribosome progresses one code on along the mRNA in the ATP consuming step. The next tRNA binds.
What happens in the final stage of translation?
The cycle of chain elongation continues until the stop codon is reached. The ribosome – mRNA – polypeptide separates, the polypeptide can be further modified and a protein could consist of more than one polypeptide.
Why is several ribosomes used at one time?
As each ribosome produces a polypeptide several can be made at once.
What is tRNA and amino acid activation?
Once the tRNA is released from the ribosome it is free to collect another amino acid from the amino acid pool in the cytoplasm. Energy from ATP is needed to attach the amino acid to the tRNA which is known as amino acid activation.
