9700 · 6.2
Protein synthesis — FAQ
Frequently asked questions for 9700 Protein synthesis. Direct answers first, then deeper explanation — then practise with marking.
What are the main stages of protein synthesis in Cambridge Biology 9700?
The main stages are transcription and translation. Transcription is the synthesis of a messenger RNA (mRNA) copy from a DNA gene template in the nucleus. Translation is the synthesis of a polypeptide chain from the mRNA code at a ribosome in the cytoplasm.
How do mRNA, tRNA, and ribosomes contribute to protein synthesis?
Messenger RNA (mRNA) carries the genetic code from DNA to the ribosome. Transfer RNA (tRNA) acts as an adaptor, bringing specific amino acids to the ribosome that match the mRNA codons. Ribosomes, composed of ribosomal RNA (rRNA) and proteins, are the sites of translation, facilitating the binding of mRNA and tRNA and catalysing the formation of peptide bonds.
What is the significance of the genetic code being degenerate and universal?
The genetic code is degenerate because most amino acids are specified by more than one codon, which can reduce the harmful effect of some point mutations. It is universal because the same codons specify the same amino acids in nearly all organisms. This universality provides strong evidence for a common evolutionary origin of life and allows for genetic engineering applications where genes can be transferred between species.
What is the difference between an intron and an exon?
In eukaryotic genes, an intron is a non-coding sequence that is transcribed into pre-mRNA but is removed during a process called splicing. An exon is a coding sequence that is retained in the mature mRNA and is expressed to form part of the final polypeptide. Prokaryotic genes do not contain introns.
Why is post-transcriptional modification necessary in eukaryotes?
It is necessary to convert the initial pre-mRNA into a stable, mature mRNA ready for translation. Splicing removes non-coding introns, creating a continuous coding sequence. The 5' cap helps the ribosome bind and protects the mRNA from degradation. The 3' poly-A tail increases mRNA stability and aids its export from the nucleus.