The steps involved in the biosynthesis of proteins including the roles of RNA
Protein biosynthesis is the process in which the DNA codes specifically to produce many amino acid monomers and proteins. It Is a necessary process for the development, growth and maintenance of a cell. Proteins are needed in the cell for many reasons, and they have a number of dissimilar roles. For example, some of them are vital for the function, structure and regulation of your bodies tissues and organs, whereas other proteins act as enzymes which control metabolism in the body.
How is RNA different from DNA structurally?
? In RNA, the pentose sugar found is ribose, compared to deoxyribose in DNA.
? The long polynucleotide chain is single stranded alternative to DNA which is double stranded
? The unique nitrogenous base found in RNA is Uracil, rather than Thymine which is found in DNA.
Transcription is the first of two steps in protein synthesis where pre-mRNA can be made using a small part of DNA as a template. During this stage, enzymes located in the cell’s nucleus begin to unwind the needed section of DNA to synthesise the protein so that RNA can be made. The enzyme Helicase disrupts the different hydrogen bonds between two strands and makes it possible for the RNA to form as a duplicate copy of one side of the DNA strand. As an immediate result of this, the four bases of DNA on the nucleotides are exposed. The free RNA nucleotides are lined up and then adjoined to their complementary DNA bases (Adenine joins with Thymine, the Uracil base strand pairs up with Adenine, Guanine base joins with Cytosine and the cytosine base attaches to guanine. It Is sent to different areas of the cell to help bring together various amino acids that form proteins. Another enzyme called RNA polymerase moves along this same strand and starts to join all the nucleotides together. It binds to the single strand consisting of the coding gene and then starts to read the information coded by the DNA strand from the 3′ end to the 5′ end. This is how a pre-mRNA molecule is formed. As the enzyme RNA polymerase joins the nucleotides to produce a pre-mRNA strand, DNA strands start to re-join behind it. This causes approximately 12 base pairs on the DNA molecule to be exposed at a time. When the RNA polymerase comes to a certain sequence of bases that is recognised as being a ‘stop’ codon it detaches and frees itself to complete the production of pre-mRNA.
The specific genetic code is known for being a hurdle of instructions explaining how particular information can be encoded with DNA or RNA for the translation of proteins. This code identifies how codons can interpret and identify which specific amino acid must be added to a position or place within the polypeptide chain. Both DNA and RNA normally use four different building blocks, which encrypts the genetic information. For the coding of one out of the 20 different amino acids, the information within the nucleotide sequence must be encoded by an arrangement of at least three nucleotides (codon or triple). Using the codon sequences, the cell is able to interpret 64 different codes for 20 individually different amino acids. This means that for each individual amino acid, there will be over one responsible codon. A genetic code could be referred to as being ‘degenerate’ as a single amino acid could be coded for by one or more than one codon.
In prokaryotic cells, mRNA is directly produced from DNA as a result of transcription. However, in eukaryotic cells, pre-mRNA Is produced instead, to get mRNA the pre-mRNA has to be spliced. In eukaryotic cells, the DNA of a single gene is made up of exons which code for particular proteins and introns which don’t. Therefore, the intervening introns would prevent the synthesis of a polypeptide chain. In the pre-mRNA of eukaryotic cells, the base sequences that are corresponding to the introns are removed and in contrast, the exons join together during the process of splicing. The majority of prokaryotic cells do not have introns, so the splicing of the DNA would not be relevant.
mRNA molecules are rather large, so it would be difficult for them to leave via the nucleus. One they have been spliced, they leave through tiny nuclear pores. Surrounding the nucleus, the mRNA starts to attach to the ribosome in preparation for translation.
The second stage of protein synthesis is translation. Before this stage of protein synthesis happens, some specific amino acids are attached to their complimentary tRNA molecules, and each of these particular reactions are catalysed by an enzyme named aminoacyl synthetase. This process occurs in the cytoplasm, where mRNA binds to the ribosomes. Firstly, the start codon located at the end of the mRNA molecule attaches to the ribosome. tRNA is responsible for carrying a specific amino acid, methionine. The tRNA molecule with the complementary sequence of anticodons starts to move towards the ribosome and joins with the specific codon on the mRNA. Another tRNA molecule that consists of a complementary anticodon (UCG) pairs with the upcoming codon in the mRNA (ACG). This time the transfer RNA molecule carries a different amino acid, threonine. The ribosome then moves along the mRNA strand ultimately bringing together two tRNA molecules at any time. Each of these two tRNA molecules pair up with the codons on the mRNA strand. The two amino acids that are carried by tRNA molecules, methionine and threonine are joined together with a peptide bond using ATP which is required for energy and an enzyme. The ribosome then moves onto the third codon while linking the amino acids on the last two tRNA molecules. Subsequently, the first tRNA molecule is released from methionine (its amino acid) and is then encouraged to collect another amino from the selection in the amino acid pool within the cell. This continues until a long polypeptide chain is built up. This synthesis of the polypeptide chain continues until the ribosome reaches a ‘stop’ codon. This causes the mRNA, the last tRNA molecule and the ribosome to separate indicating the completion of the polypeptide chain.
RNA is a molecule that consists of a single strand, with ribose as its distinct sugar unit. There are three distinct types of RNA, messenger RNA, ribosomal RNA and transfer RNA. Messenger RNA is synthesised directly from a small DNA segment and is then transported to the cytoplasm. This is where protein synthesis occurs. This process involves transfer RNA and ribosomal RNA. Ribosomal RNA combines with proteins in the cytoplasm to form ribosomes. This ribosome holds all the enzymes needed. It attaches to mRNA and keeps it stabilised while proteins are synthesised from the encrypted genetic code in the mRNA. Transfer RNA (tRNA) interprets the genetic code on the mRNA in the cytoplasm and translates it into three amino acids. These amino acids exit the ribosome, and then exit the cell to produce proteins.