![]() The structure of RNA is similar to DNA with a few small exceptions. There are several different types of RNA, each having different functions in the cell. This intermediate messenger is messenger RNA (mRNA), a single-stranded nucleic acid that carries a copy of the genetic code for a single gene out of the nucleus and into the cytoplasm where it is used to produce proteins. The mechanism by which cells turn the DNA code into a protein product is a two-step process, with an RNA molecule as the intermediate.ĭNA is housed within the nucleus, and protein synthesis takes place in the cytoplasm, thus there must be some sort of intermediate messenger that leaves the nucleus and manages protein synthesis. Therefore, a gene, which is composed of multiple triplets in a unique sequence, provides the code to build an entire protein, with multiple amino acids in the proper sequence ( ). For example, the DNA triplet CAC (cytosine, adenine, and cytosine) specifies the amino acid valine. Similar to the way in which the three-letter code d-o-g signals the image of a dog, the three-letter DNA base code signals the use of a particular amino acid. A triplet is a section of three DNA bases in a row that codes for a specific amino acid. The sequence of bases in a gene (that is, its sequence of A, T, C, G nucleotides) translates to an amino acid sequence. Recall that proteins are polymers, or chains, of many amino acid building blocks. The interpretation of genes works in the following way. Gene expression, which transforms the information coded in a gene to a final gene product, ultimately dictates the structure and function of a cell by determining which proteins are made. Each particular gene provides the code necessary to construct a particular protein. A gene is a functional segment of DNA that provides the genetic information necessary to build a protein. Just as the cell’s genome describes its full complement of DNA, a cell’s proteome is its full complement of proteins. Whatever the cellular process may be, it is almost sure to involve proteins. Some of these critical biochemical reactions include building larger molecules from smaller components (such as occurs during DNA replication or synthesis of microtubules) and breaking down larger molecules into smaller components (such as when harvesting chemical energy from nutrient molecules). ![]() One of the most important classes of proteins is enzymes, which help speed up necessary biochemical reactions that take place inside the cell. Most structural components of the cell are made up, at least in part, by proteins and virtually all the functions that a cell carries out are completed with the help of proteins. This refers to the fact that DNA contains the information necessary for the cell to build one very important type of molecule: the protein. It was mentioned earlier that DNA provides a “blueprint” for the cell structure and physiology. ![]() Explain how the genetic code stored within DNA determines the protein that will form.coli bacteria, translation of the mRNA begins even before transcription is finished.By the end of this section, you will be able to: So, several proteins can be made from one mRNA. Several ribosomes can attach to a molecule of mRNA one after another and begin making proteins. The threonine-specific tRNA releases its threonine and leaves and the new protein floats away. Upon encountering the stop sequence, the ribosome detaches from the mRNA and splits into its two parts. The ribosome shifts down one codon so that the stop sequence is now in the A-site.The phenylalanine-specific tRNA leaves the P-site and goes off to find another phenylalanine.A peptide bond forms between the phenylalanine and the threonine.An amino acyl-tRNA (anti-codon) with an attached threonine comes into the A-site of the ribosome. ![]() The ribosome shifts so that the P-site now contains the UUU codon with the attached phenyl-alanine tRNA and the next codon (ACA) now occupies the A-site.The methionine-specific tRNA leaves the P-site and goes off to gather another methionine.A chemical bond forms between the methionine and phenylalanine (in a protein, this covalent bond is called a peptide bond).An amino acyl-tRNA (anti-codon = AAA) with an attached phenylalanine comes into the A-site of the ribosome.An amino acyl-tRNA (anti-codon = UAC) with an attached methionine comes into the P-site of the ribosome.A ribosome binds to mRNA with the AUG codon in the P-site and the UUU codon in the A-site.
0 Comments
Leave a Reply.AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |