Question

Describe the process of how your cells make a protein from a gene. Just a hint, you should only describe two of the following three processes: replication, transcription, translation.

Answer 1

Information that originally was in the genome, enshrined in DNA, then gets transcribed into messenger RNA. And then that information is translated from the messenger RNA to a protein. these two are the main process through which cells make a protein from a gene.

Transcription

Transcription is the process by which the information in a strand of DNA is copied into a new molecule of messenger RNA (mRNA). DNA safely and stably stores genetic material in the nuclei of cells as a reference, or template. Meanwhile, mRNA is comparable to a copy from a reference book because it carries the same information as DNA but is not used for long-term storage and can freely exit the nucleus. Although the mRNA contains the same information, it is not an identical copy of the DNA segment, because its sequence is complementary to the DNA template.

Transcription is carried out by an enzyme called RNA polymerase and a number of accessory proteins called transcription factors. Transcription factors can bind to specific DNA sequences called enhancer and promoter sequences in order to recruit RNA polymerase to an appropriate transcription site. Together, the transcription factors and RNA polymerase form a complex called the transcription initiation complex. This complex initiates transcription, and the RNA polymerase begins mRNA synthesis by matching complementary bases to the original DNA strand. The mRNA molecule is elongated and, once the strand is completely synthesized, transcription is terminated. The newly formed mRNA copies of the gene then serve as blueprints for protein synthesis during the process of translation.

3 5 0.00 3' DNA helix 5 Promoter RNA polymerase Initiation Sigma factor 31 5 DOK 100 5 Terminator RNA Elongation 5' DO000 5 3 Termination RNA Polymerase RNA Rho factor

Translation

Translation is a process by which the genetic code contained within a messenger RNA (mRNA) molecule is decoded to produce a specific sequence of amino acids in a polypeptide chain.The key components required for translation are mRNA, ribosomes, and transfer RNA (tRNA).During translation, mRNA nucleotide bases are read as codons of three bases. Each ‘codon’ codes for a particular amino acid. Every tRNA molecule possesses an anticodon that is complementary to the mRNA codon, and at the opposite end lies the attached amino acid. tRNA molecules are therefore responsible for bringing amino acids to the ribosome in the correct order ready for polypeptide assembly.it is important to know that a single amino acid may be coded for by more than one codon. There are also specific codons that signal the start and the end of translation.Aminoacyl-tRNA synthetases are enzymes that link amino acids to their corresponding tRNA molecules. The resulting complex is charged and is referred to as an aminoacyl-tRNA.

For translation to begin, the start codon 5’AUG must be recognised. This is a codon specific to the amino acid methionine, which is nearly always the first amino acid in a polypeptide chain.At the 5’ cap of mRNA, the small 40s subunit of the ribosome binds. Subsequently, the larger 60s subunit binds to complete the initiation complex. The next step (elongation) can now commence.

The ribosome has two tRNA binding sites; the P site which holds the peptide chain and the A site which accepts the tRNA.While Methionine-tRNA occupies the P site, the aminoacyl-tRNA that is complementary to the next codon binds to the A site, using energy yielded from the hydrolysis of GTP.Methionine moves from the P site to the A site to bond to new amino acid there, and so the growth of the peptide has begun. The tRNA molecule in the P site no longer has an attached amino acid, and so leaves the ribosome.The ribosome then translocates along the mRNA molecule to the next codon, again using energy yielded from the hydrolysis of GTP. Now, the growing peptide lies at the P site and the A site is open for the binding of the next aminoacyl-tRNA, and the cycle continues. The polypeptide chain is built up in the direction from the N terminal (methionine) to the C terminal (the final amino acid).

One of the three stop codons enters the A site. No tRNA molecules bind to these codons so the peptide and tRNA in the P site become hydrolysed releasing the polypeptide into the cytoplasm.The small and large subunits of the ribosome dissociate ready for the next round of translation.

Lysin tRNA e obch U AC A A GU U U Lી A U G U U UU CA A A Translation direction mRN A Ribosome