In protein synthesis, during transcription, mRNA complements the DNI template strand. During translation, the ribosome reands mRNA. Its codons specify the amino acids that must be added to the growing polypeptide by tRNA.
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Protein synthesis: This process occurs begins with transcription and continues with translation.
→ Transcription ⇒ mRNA syntheis
- The first step before protein synthesis begins is to synthesize messenger RNA, mRNA.
- This is the coping process of the DNA section for the desired protein, and it happens in the nucleus.
- RNA polymerase is in charge of reading the original DNI strand for mRNA synthesis.
→ Translation ⇒ Cytoplasm stage
- Translation takes place when the formed mRNA moves to the cytoplasm through the nucleus membrane pores.
- Once in the cytoplasm, mRNA meets a ribosome, which is the primary structure for protein synthesis.
- Ribosomes are organelles composed by the association of proteins with rRNA and tRNA. They can be found in the rough endoplasmic reticulum or floating in the cytosol.
- While the ribosome reads mRNA strain from its 5´ extreme to 3´, tRNA adds the correct amino acids to build the polypeptide.
A ribosome meets the mRNA molecule.
According to the codons that are being readen in mRNA, tRNA transfers the correct amino acids to build the polypeptide chain.
- Codons are short sequences of three nucleotides that carry the genetic information for the aminoacids´ assembly.
mRNA has start and end codons. Between them, there are codons that code for the amino acids to be added to the chain. The start is the signal of the synthesis initiation. When the ribosome reaches the end codon, protein synthesis is over.
There exists a total of 64 codons.
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One of them is the start codon → AUG → Metionine
- 61 codify amino acids, and
- the remaining three are stopping points → UAA, UAG, UGA.
Each tRNA molecule has two sites. One of them that couples with the codon of the mRNA molecule, named anticodon. The other site couples with an amino acid.
tRNA allows amino acids to align according to the nucleotidic sequence in the mRNA molecule.
The correct order of the steps is as follows.
5. ______ mRNA leaves the nucleus and enters the cytoplasm.
1. ______ A small ribosomal subunit binds to an mRNA and the first tRNA at the start codon.
3. ______ The large ribosomal subunit joins the small subunit, mRNA, and tRNA complex, and a fully functional ribosome is formed.
6. ______ The ribosome binds to a second tRNA with the proper anticodon.
8. ______ The amino acids associated with the first two tRNAs are joined.
7. ______ New tRNAs with the proper anticodon come into the ribosome and their amino acids are added to the growing protein; old tRNAs are ejected from the ribosome.
2. ______ A stop codon is encountered on the mRNA, which signals that protein synthesis is finished.
4. ______ The finished protein is released and the ribosomal subunits separate.
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