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Can someone please simply outline the stages of protein synthesis? Also, if possible, could you separately describe the role of mRNA and tRNA in protein synthesis, as that always seems to come up and I'm still not great on it. Thanks :)
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First stage of protein synthesis: TRANSCRIPTION.
Making a single-stranded mRNA copy of the DNA coding strand.
- The DNA gene unwinds and unzips (by hydrogen bonds breaking)
- RNA nucleotides bind to the exposed bases by complementary base pairing (with Uracil instead of Thymine) - catalysed by RNA polymerase enzyme
- Sugar-phosphate backbone forms between RNA nucleotides
- An mRNA molecule is made
- The mRNA passes out of the nucleus, through a nuclear pore
The second stage: TRANSLATION.
The assembly of polypeptides (proteins) at ribosomes.
- The mRNA binds to a ribosome
- tRNA transports amino acids to the ribosomes for the assembly of the polypeptide
- The anticodon (3 base sequence) on the tRNA binds to its complementary codon on the mRNA
- A second tRNA molecule with the next complementary anticodon brings its amino acid to the ribosome
- A peptide bond forms between the adjacent amino acids
- The ribosome moves along the mRNA strand reading the next codon.
- The next tRNA brings another amino acid, and another peptide bond forms, whilst the first tRNA leaves
- The polypeptide chain grows until a stop codon is reached, and it is complete
- Made in the nucleus and passes into the cytoplasm
- Are folded lengths of RNA
- At one end are three exposed bases where an amino acid can bind
- At the other end are three unpaired nucleotide bases known as an anticodon
- Each anticodon can bind temporarily to its complementary codon on the mRNA strand
- Single- stranded copy of the genetic code on the DNA
- Shorter than DNA, so it can easily leave the nucleus
- The sequence of codons (triplets of nucleotide bases) dictates the order of amino acids assembled
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