Understanding Translation Processes - AP Biology

mRNA is the template used during translation. The mRNA strand is read and "translated" into a polypeptide by tRNA.

DNA would be the template for transcription, not for translation.

Transcription leads to the production of hnRNA (heterogeneous nuclear RNA), which primarily consists of pre-mRNA and must go through processing and modification to form mRNA and leave the nucleus.

The other three choices, mRNA (messenger RNA), tRNA (transfer RNA), and rRNA (ribosomal RNA), all play active roles in the process of translation. mRNA serves as the codon template. tRNA matches anticodons to mRNA and carries amino acids. rRNA forms a large part of the ribosome structure and plays a functional role as the site of translation.

Every codon is composed of three RNA nucleobases, and codes for a specific amino acid; however, there can be multiple codons that code for one amino acid. The start codon, AUG, signals the beginning of translation and codes for methionine.

While there is only one start codon (AUG), but there are three different stop codons (UGA, UAG, and UAA) that can each signal for the end of translation, or termination. During the translation process, tRNA is used to bring amino acids (corresponding to the codons in the mRNA sequence) to the ribosome, which become attached via peptide bonds to form a polypeptide.

The genetic code is degenerative, meaning that multiple codons can code for the same amino acid. It is also unambiguous: a particular codon will always code for one amino acid. That being said, it would be wrong to assume that an amino acid will only have one codon, as an amino acid can have multiple different codons that code for it.

In translation, the mRNA is positioned in the ribosome and read in the 5'-to-3' direction. Initiation of translation is triggered by a tRNA attached to a methionine entering the P site of the ribosome. The mRNA will then be read, and additional amino acids will be added to the chain, which grows in the P site. New tRNA enters the A site and old tRNA exits the E site, but the amino acid chain is always anchored to the tRNA in the P site.

Stop codons are a signal for the ribosome to recruit a release factor. Release factors are proteins that dissociate the translation complex and release the polypeptide chain.

There are no tRNAs that match stop codons and there is no "special" terminal amino acid. Chaperones are involved in folding proteins, but they are not involved in the termination of translation.

Elongation continues until a stop codon occupies the A-site of the ribosome. The stop codon is a three-base signal present within the mRNA. There are three stop codons: UAG, UAA, and UGA.

There are three principle steps to translation. Initiation occurs when the ribosomes encounters the start codon, AUG, and recruits a methionine tRNA. Elongation of the polypeptide occurs as the ribosomes continues to recruit tRNA molecules and build the peptide chain. Termination occurs when the ribosome encounters a stop codon and releases the completed polypeptide.

Translation, the process of synthesizing a polypeptide from an mRNA template, primarily occurs in the cytoplasm. Another possible answer would be the rough endoplasmic reticulum. Both the rough endoplasmic reticulum and cytoplasm contain ribosomes, which are essential for translation.

The mitochondria are essential for cellular respiration, and are the site of the citric acid cycle and electron transport chain. The nucleus houses DNA and synthesizes ribosomes (in the nucleolus). The Golgi apparatus modifies and packages proteins in vesicles after translation is complete.

After DNA is transcribed into RNA, the RNA goes through post-transcriptional modifications and is then sent out of the nucleus to the cytoplasm. From there, the mRNA is brought to the ribosomes, some located on the rough endoplasmic reticulum and some free-floating, in order to be translated into proteins. Proteins are then packaged and transported to their respective locations for usage.

The nucleolus is responsible for synthesizing and assembling ribosomal subunits. The nucleus houses DNA and is the site of transcription, but not translation. Mitochondria are essential for cellular respiration and ATP synthesis. Lysosomes digest cellular wastes and defective proteins.

Missense mutations are point mutations that cause a single amino acid in a protein to be changed. This may or may not affect the functionality of the protein. When one amino acid is replaced by another amino acid from the same class, such as replacing one polar amino acid with another, functionality is usually retained. When an amino acid from a different class is used, such as replacing an acidic amino acid with a basic amino acid, the protein folding may be affected and functionality may fail.

The other answers describe other types of mutations. Silent result in no change to the protein primary structure. Nonsense mutations cause early termination. Frameshift mutations shift the reading frame of the codon sequence, severely altering the protein composition.

Translation is the process of making a polypeptide chain from an mRNA template. No new molecules of RNA or DNA are synthesized during this process. tRNA is used to bring amino acids to the ribosome, binding an anticodon to the exposed codon of mRNA. The amino acid is then released from the tRNA and added to the growing chain of amino acids attached to the ribosome. When the ribosome reaches a stop codon, it releases the mRNA strand and amino acid sequence. The amino acid sequence is the final result of translation, and is known as a polypeptide.

Polypeptides can then undergo folding to become functional proteins. All enzymes are proteins, but not all proteins go on to become enzymes; some serve other functions.

The three steps for the elongation process of translation are codon recognition, peptide bond formation, and translocation. These steps essentially correspond to the different tRNA positions in the ribosome. tRNA enters and matches the codon of the mRNA strand. A peptide bond is then formed between the tRNA amino acid and the ribosomal amino acid chain. The empty tRNA and peptide strand then shift to make room for the next residue to enter to ribosome structure.

RNA spicing occurs in the nucleus as part of post-transcriptional modification. Introns are removed to generate a mature mRNA strand before translation can occur.

Translation is the process where ribosomes synthesize proteins from an mRNA strand. In eukaryotes, this process occurs in the cytosol with free ribosomes or across the membrane of the endoplasmic reticulum using membrane-bound ribosomes. In prokaryotes, translation occurs in the cytoplasm.

The start codon (AUG) codes for the amino acid methionine. The start codon is the nucleotide triplet on the mRNA strand that signals the start of the codons to be translated. Each codon triplet binds to a complementary anticodon triplet on a tRNA molecule that carries a corresponding amino acid.

In the initiation stage of translation, a 5’ cap forms at the 5’ end of the mRNA strand, which is composed of the small ribosomal subunit and initiation factors. Initiation factors are proteins that facilitate the start of translation during the initiation stage. Once this complex is assembled, it “scans” the mRNA strand for the start codon, AUG. The initiator tRNA molecule coding the anticodon UAC and carrying the corresponding amino acid methionine is recruited and binds to the start codon. This makes methionine the first amino acid in the polypeptide chain. The large ribosomal subunit then associates with the complex, placing the methionine tRNA in the P-site of the large subunit. There is an alternative model of initiation in which the mRNA scanning complex does not form at the 5’ end. This model is believed to occur under stress responses.

The mRNA strand is translated into a protein using triplets, or three nucleotides. Each triplet is called a codon. Messenger or mRNA codons bind to complementary anti-codons on tRNA molecules, which carry the corresponding amino acids.

The wobble position refers to the ability of the third position nucleotide of the codon and first position nucleotide of the anticodon tRNA sequence (when reading in a 5’ to 3’ direction) to exhibit non-standard base pairing. This allows fewer tRNA molecules to exist because a tRNA molecule is able to bind to more than one codon, which increases efficiency.

During the elongation stage of translation, GTP is used to provide the energy to translocate a tRNA molecule from the A-site to the P-site. GTP is also required to move the ribosome down the mRNA strand to the next codon.