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❶The transfer RNAs are also called the translational adaptor molecules.

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Protein biosynthesis


Transcription and translation are the two main processes that are involved in protein synthesis. Transcription is the first step that takes place in three phases; initiation, elongation and termination. In order to ensure that gene transcription is done correctly, each of the three stages is controlled by co-activators and transcription factors.

This process takes place in the cell nucleus. Translation is the process through which proteins are synthesized from RNA. It takes place in the cytoplasm, the location for ribosomes. Translation is carried out in four phases; activation, initiation, elongation and termination.

At this stage of protein synthesis, amino acids are fixed with tRNA molecules. Biosynthesis is mainly followed by two events; post-translational modification and folding of proteins. In the process of synthesis and after it, polypeptide chains are often folded into structural units.

It is this process that is referred to as protein folding. The task of protein synthesis in the cells begins at the N-terminal end of a polypeptide chain. Before the formation of an active protein, modifications have to be made to the polypeptide.

By simply placing an order with us, you are guaranteed original papers that are creatively designed to earn you the greatest points. Protein biosynthesis Protein biosynthesis can be simply defined as the process through which cells are able to build proteins for use by the body.

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A current, generalized picture of protein synthesis would require the following participants: A pool of subcellular ribonucleoprotein particles called ribosomes. This requirement is satisfied not only by the intact ribosomes but also by stoichiometric amounts of small and large subunits. Two or more enzymatic components transfer factors and elongation factors involved in polypeptide chain elongation. Certain cofactors required for chain initiation and termination, as well as for the release of completed chains from their sites of synthesis.

Siekevitz then working in P. Most of the key experiments have subsequently been performed with just two systems: All the experimental results with the in vitro systems indicate that protein synthesis consists of four broad sequential steps as follows: Ribosomes are the organelles of protein synthesis consisting of large and small subunits.

A ribosome is a highly specialized and complex structure. The 30S subunit contains 21 proteins and a 16S RNA molecule of about nucleotides of which 11 are specifically methylated. The 50S subunit contains 34 proteins and a large RNA molecule of 23S comprised of about nucleotides, 22 of which are methylated; as well as a smaller one of 5S species with nucleotides, none of which are methylated.

Protein components of both the subunits are also distinct. The large subunit contains about 34 polypeptides in more or less equimolar amounts. The small subunit contains 21 such polypeptides. All the proteins are different. Only two proteins are common in both the subunits. Some of these proteins remain attached to the specific regions of RNA providing attachment to other proteins.

These proteins are called primary binding proteins. The two subunits can be further dissociated by treatment with 4. The subunits contain about 55 per cent RNA and 45 per cent protein. The ribosomal proteins are insoluble in water at pH 7. Ribosomes can be reassembled from their component RNAs and proteins.

So far as the active centres of ribosome are concerned, it has got various sites for protein functioning— mRNA binding site, peptidyl P site, aminoacyl A site, peptidyl transferase site, TU site and EFG site Fig. It is close to the P site. IF3 binds to this site. P site is mostly located on the 30S subunit and is able to bind initiator tRNA. A site is close to the P site. Most of the functions found with the A site are on the 50S subunit.

Peptidyl transferase site lies somewhere in the region connecting the A and P sites, close to the terminus of tRNA. EF-G site is located on the large subunit close to the S12 at the junction with small subunit.

A different mechanism of protein synthesis is found certain strains of Baccilus brevis, a spore- forming bacterium. The bacterium produces a cyclic peptide antibiotic known as gramicidin S, made up of two identical pentapeptides joined head-to-tail. The biosynthesis of this antibiotic does not depend on the presence of ribosomes or mRNA.

The amino acids are activated by the formation of enzyme bound thioesters. The activated carbonyl group of the proline residue in the dipeptide reacts with the amino group of the valine residue on the same enzyme to yield a tripeptide. The process is repeated again with ornithine and then with leucine to give a pentapeptide bound to the E 1 enzyme. The growing peptide is transferred one by one to different sulphydryl groups with the formation of a peptide bond each time.

Finally, the activated pentapeptides attached to two different E I molecules react with each other to form cyclic gramicidin S. This mode of protein synthesis is uneconomical compared with the ribosomal mechanism. A peptide containing more than about fifteen residues is not synthesized by this mechanism. Lipmann suggests that this polypeptide synthesis may be a surviving relic of a primitive mechanism of protein synthesis used early in evolution.

Ribosomal protein synthesis may have evolved from fatty acid synthesis. The transfer RNAs are also called the translational adaptor molecules. They occupy an important position in protein synthesis because they provide the link between the nucleotide and the amino acid codes.

For this reason the tRNA have received considerable attention since their discovery in He also created techniques for the sequencing of nucleic acids in general. Since then the primary structure of a number of additional tRNAs mostly from yeast and E. The length of different species appears to vary from 76 to 85 nucleotide residues.

Their molecular weight is about These modifications take place on one of the four bases only after it has been incorporated into the polyribonucleotide chain. From a wide variety of sources the sequences of more than tRNAs have been determined. The single-stranded RNA chain forms a clover leaf structure Fig. A standard orientation and terminology for the generalized representation of a tRNA in the clover leaf form are illustrated in the figure.

There are four loops and four major arms. The arms are named for their structure or function. The other arms consist of paired stems and unpaired loops. The D arm is named for the presence of di-hydrouracil D base.


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Protein synthesis is the process whereby DNA encodes for the production of amino acids and proteins. It is a very complex and precise process and as proteins make up over half of the dry mass of a cell, it is a vital process to the .

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Essays Related to Protein Synthesis 1. Types of Protein Molecules. 2. Protein Synthesis - Translation and Transcription. 3. Transcription And Protein Synthesis. 4. Research Proposal - Proteins. 7. RNA vs DNA/5(3).

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In this essay we will discuss about Protein Synthesis. After reading this essay you will learn about: 1. Mechanism of Protein Synthesis 2. Ribosomes in Protein Synthesis 3. Non-Ribosomal Polypeptide Synthesis 4. Transfer RNA (tRNA) 5. Free Essay: Protein Synthesis Protein synthesis is one of the most fundamental biological processes. To start off, a protein is made in a ribosome. There are.

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- Protein Synthesis Protein Synthesis is the process whereby DNA (deoxyribonucleic acid) codes for the production of essential proteins, such as enzymes and hormones. Proteins are long chains of molecules called amino acids. Essay on Protein Synthesis Protein synthesis is the process whereby proteins are produced, or synthesized, in living things according to "directions" given by DNA (deoxyribonucleic acid) and carried out by RNA (ribonucleic acid) and other proteins.