Earth Science: Genetics Human – Feature Characteristics: Translation
The genetic code is shared by all organisms and is made up of codons. Combinations of these instruct the formation of the amino acids that are used in protein biosynthesis.
The structure of DNA consists of nucleic acids with four different nitrogen bases. Of these, a unit of three successive bases determines an amino acid. These base triplets of DNA that code specific amino acids are called codons. Their totality forms the genetic code, and each of these codons corresponds to one codon of mRNA.
All organisms use the same code; it is thus universal, although minor deviations are known to occur. Reading the codes takes place without overlapping; each nucleotide participates only on a single triplet and coding does not require an interval signal for the differentiation of triplets.
The combination of four bases into sets of three theoretically offers 64 possibilities to code different amino acids. This is more than needed to represent the 20 amino acids that are required for protein synthesis. Therefore, there are several codon combinations for each amino acid.
Character expression: translation
During translation, the genetic information—now present in encoded form following transcription in to the mRNA sequence—is converted from amino acids for the formation of polypeptides (proteins). This takes place on ribosomes, tiny corpuscles located in the interior of all cells. The amino acids required for protein biosynthesis are initially bonded inside the interior of a cell to a specific tRNA molecule, by using the nucleotides adenosintriphosphate (ATP) and with the aid of specific enzymes (aminoacyl-synthetase).
Due to base pairing, these tRNA molecules have a cloverleaf-like appearance. A specific base triplet (anti- codon) is located in one of the loops, which can bond to the complementary codon of the mRNA. When tRNA molecules are loaded with the equivalent amino acids, they transport them to the mRNA located at the ribosomes. Base pairing occurs between the codon of the mRNA and anticodons of the tRNA molecule, and the amino acids are linked to each other through peptide bonds.
After the mRNA has been completely read, the newly formed protein detaches from the ribosome. Frequently, several ribosomes read the same mRNA (polysomes) and the information obtained is used repeatedly in this manner, before RNA-dismantling enzymes (ribonuclease) break them up. The first codon is always for the amino acid methionine (starting codon). The end of the sequence is reached at one of the three stop-codons (UAG, UAA, and UGA), for which there is no loaded tRNA available.
RIBOSOMES
Living beings with cell nucleus (eu-karyotes) and those without (prokaryotes), have cell structures in which protein biosynthesis takes place These so-called ribosomes are roundish par tides consisting of two subunits, with a diameter of about 15 nm, made up of ribosomal RNA (rRNA) and proteins.
The small subunit is responsible for recognizing mRNA, while free amino acids are linked to form a long chain with the aid of the large subunit. At the start of protein biosynthesis both parts of the ribosome come together and then they detach again after the protein has been completed.
BASICS
ENZYMES are important catalysts in bio- chemical reactions, since they can lower the activation energy of these reactions.
Most enzymes act very specifically, i.e., only in conjunction with certain substrates. Most enzymes are proteins, but there are also ribonucleic acids, so-called ribozymes, that have a catalytic effect.