In molecular biology and genetics, translation (Protein Synthesis) is the process by which ribosomes in the cytoplasm or endoplasmic reticulum create proteins following the process of transcription of DNA to RNA in the cell's nucleus. Translation takes place in the cytoplasm of prokaryotes (bacteria and archaea), where the big and small ribosomal subunits bind to the mRNA. In eukaryotes, a phenomenon known as co-translational translocation causes translation to take place in the cytoplasm or across the endoplasmic reticulum membrane.
The general transfers (Central Dogma) define the typical flow of biological information: DNA may be transferred to DNA (DNA replication), DNA information can be translated into mRNA (transcription), and proteins can be produced using the information in mRNA as a template (translation).
Molecular Machinery Required
1. Ribosome
Ribosomes are macromolecular machinery present in all organisms that synthesise biological proteins (mRNA translation). Ribosomes join amino acids in the order indicated by messenger RNA (mRNA) codons to produce polypeptide chains.
Ribosomes are macromolecular machinery present in all organisms that synthesise biological proteins (mRNA translation). Ribosomes join amino acids in the order indicated by messenger RNA (mRNA) codons to produce polypeptide chains.
- Ribosomes are made up of two primary parts: small and big ribosomal subunits. Each subunit is made up of one or more ribosomal RNA (rRNA) molecules as well as several ribosomal proteins (RPs or r-proteins).
- Ribosomes and their accompanying components are sometimes referred to as translational machinery.
- The sequence of DNA that encodes the amino acid sequence of a protein is translated into a messenger RNA chain.
- Ribosomes attach to messenger RNAs and utilise their sequences to determine the right amino acid sequence to produce a specific protein.
- Transfer RNA (tRNA) molecules choose and transport amino acids to the ribosome, where they attach to the messenger RNA chain through an anti-codon stem-loop.
- There is a unique transfer RNA for each coding triplet (codon) in the messenger RNA that must have the appropriate anti-codon match and carry the right amino acid for incorporation into a developing polypeptide chain.
- A ribosome is a ribonucleoprotein complex composed of RNA and proteins.
- (30S) primarily functions as a decoder and is also attached to mRNA.
- (50S) is primarily a catalytic enzyme that is also linked to aminoacylated tRNAs.
2. RNA
In the cell, numerous kinds of RNA are employed for diverse functions. Messenger RNA (mRNA) and transfer RNA (tRNA) are the two primary forms of RNA utilized in translation (transfer RNA). As the intermediary between DNA and proteins, mRNA uses a specific combination of four amino acids, CGAU, in each mRNA (Cytosine, Guanine, Adenine, Uracil).
Ribosomal RNA (rRNA)
Ribonucleic acid is the RNA contained in ribosomes, the molecules responsible for catalysing protein synthesis (rRNA). A ribosome's three-dimensional structure is influenced by the three-dimensional structure of an rRNA core.
- The peculiar three-dimensional structure of rRNA, which comprises internal helices and loops, results in the creation of the A, P, and E sites inside the ribosome.
- Additionally, following careful examination of the RNA and protein, it has been determined that various ribosomal proteins may bind to rRNA at particular residues.
- Tetracycline and streptomycin have binding sites on bacterial rRNA, which have recently been discovered.
- This discovery gives rRNA's function a new facet.
Transfer RNA (tRNA)
The transfer RNA is regarded as responsible for selecting the proper protein or amino acids necessary by the organism, therefore assisting the ribosomes. It is found at the ends of each amino acid. This is also known as soluble RNA, and it serves as a bridge between the messenger RNA and the amino acid.
- Transfer RNAs are typically small molecules with a length of 70–90 nucleotides (5 nm) and are encoded by a variety of genes
- The D-arm and T-arm, among other components of a tRNA's structure, help to explain its high level of specificity and effectiveness.
Given the chemical similarity of many amino acids, it is amazing that just 1 in 10,000 amino acids is improperly connected to a tRNA. - Like all other biological nucleic acids, transfer RNAs have a sugar-phosphate backbone. The directionality of the molecule is determined by the orientation of the ribose sugar.
Messenger RNA (mRNA)
This particular type of RNA works by transferring genetic material into ribosomes and transmitting instructions about the kinds of proteins that the body cells need. These RNA types are known as messenger RNAs based on their functions. As a result, the mRNA is essential for the transcription process as well as for protein synthesis.
- The main job of mRNA is to act as a bridge between DNA's genetic code and the proteins' amino acid composition.
- Multiple regulatory regions found in mRNA can affect the time and pace of translation.
Additionally, because it has locations for the docking of ribosomes, tRNA, and numerous auxiliary proteins, it makes sure that translation happens in an orderly manner. - Cells create proteins, which can function as structural molecules, enzymes, or equipment for moving different cellular parts.
3. Amino Acid Activation
The process of attaching an amino acid to its corresponding transfer RNA is known as amino acid activation, also known as aminoacylation or tRNA charging (tRNA). The AMP-amino acid is then bound to a tRNA molecule by aminoacyl tRNA synthetase, which releases AMP and attaches the amino acid to the tRNA. The aminoacyl-tRNA that results is considered to be charged.
- To create a 5' aminoacyl adenylate intermediate, the amino acid's carboxyl group must first covalently bond to the -phosphate of the ATP molecule. This process releases inorganic pyrophosphate (PPi) (aa-AMP).
aa + ATP ⟶ aa-AMP + PPi
- An aminoacyl group is attached to the 3'-OH of the tRNA by a nucleophilic assault on the intermediate aminoacyl adenylate, which releases an AMP molecule.
aa-AMP + tRNA ⟶ aa-tRNA + AMP
- Class I and class II aminoacyl t-RNA synthetases are separated into two categories. By means of a transesterification process, the aminoacyl group is first transferred by Class I enzymes to the 2'-OH of the tRNA molecule and subsequently to the 3'-OH of the tRNA. The transfer of the aminoacyl group from the 3'-OH of the tRNA to the aminoacyl group is catalysed by Class II enzymes in a single step.
aa + ATP + tRNA ⟶ aa-tRNA + AMP + PPi
4. Enzymes and Factors
Initiation factor
- Proteins called initiation factors attach to the tiny subunit of the ribosome when translation, a step in protein creation, starts.
- Repressors and initiation variables might collaborate to impede or delay translation.
- To assist them in beginning or speeding up translation, they can engage with activators.
- They are simply referred to as IFs in bacteria (i.e., IF1, IF2, and IF3) and eIFs in eukaryotes (i.e, eIF1, eIF2, and eIF3).
- Sometimes, translation initiation is referred to as a three-step procedure that initiation factors assist in carrying out.
- The tiny ribosome is the first place the tRNA containing the methionine amino acid interacts, followed by the mRNA and then the giant ribosome.
Elongation factor
- A group of proteins called elongation factors works at the ribosome during the synthesis of proteins to speed up translational elongation from the production of the first to the final peptide bond in a developing polypeptide.
- Prokaryotes' most prevalent elongation factors are EF-Tu, EF-Ts, and EF-G.
- Elongation factors used by bacteria and eukaryotes are essentially similar but have different structures and research nomenclatures.
- The fastest stage of translation is elongation.
- It occurs at a rate of 15 to 20 amino acids added per second in bacteria (about 45-60 nucleotides per second).
- The rate in eukaryotes is around two amino acids per second (about 6 nucleotides read per second).
Termination factor
- A termination factor is a protein in molecular biology that mediates the end of RNA transcription by identifying a transcription terminator and inducing the release of freshly synthesised mRNA.
- This is part of the mechanism that controls RNA transcription to maintain gene expression integrity, which is seen in both eukaryotes and prokaryotes, but the process in bacteria is well known.
- Rho (ρ) is the most well-researched and documented transcriptional termination factor.
5. Amino acid
The initiation of the amino acid, the tRNA, and the mRNA all congregate inside the ribosome during commencement. The mRNA strand is still intact, but the start codon, AUG, represents the actual beginning site. Keep in mind that the start codon is the group of three nucleotides that starts the gene's codified sequence. The start codon specifies the amino acid methionine, so keep that in mind as well. Therefore, the amino acid that enters the ribosome first is called methionine.
Steps of Translation
Translation or protein synthesis involves 3 steps, i.e., Initiation, Elongation, and Termination.
1. Initiation
- We need a few essential components before translation can begin. These consist of: Ribosomes (which come in two pieces, large and small) and an "initiator" tRNA, which contains the first amino acid in the protein, which is often methionine - An mRNA holding instructions for the protein we'll make (Met).
- These components have to fit together perfectly during initiation. They come together to create the initiation complex, the molecular framework required to begin the production of a new protein.
- Translation initiation occurs inside your cells and the cells of other eukaryotes as follows: initially, the tRNA containing methionine binds to the small ribosomal subunit.
- Together, they recognise the 5' GTP cap on the mRNA's 5' end and attach it to it (added during processing in the nucleus).
- When they reach the start codon, they terminate their "walk" along the mRNA in the 3' direction (often, but not always, the first AUG).
- The situation in bacteria is a little different. In this instance, the small ribosomal subunit does not move from the 5' to the 3' end of the mRNA. Instead, it binds directly to certain mRNA sequences.
- These Shine-Dalgarno sequences "point out" start codons to the ribosome by coming just before them.
2. Elongation
- Before any amino acids have been connected to create a chain, but after the initiation complex has formed.
- The P site, in the centre of the ribosome, is the first location of our first tRNA, which carries methionine.
- A new codon is exposed in a different position, known as the A site, right next to it.
- The following tRNA, whose anticodon is a perfect (complementary) match for the exposed codon, will "land" at the A site. It is now time for the action, which is the production of the peptide bond that joins one amino acid to another after the matching tRNA has arrived at the A site.
- In this phase, the amino acid of the second tRNA's A site is joined to the methionine from the first tRNA.
3. Termination
- The termination process is how translation comes to an end.
- Once a stop codon (UAA, UAG, or UGA) in the mRNA enters the A site, the process is terminated.
- Release factors, which aren't tRNAs but neatly fit into the P site, are proteins that identify stop codons.
- By causing it to add a water molecule to the last amino acid in the chain, release factors tamper with the enzyme that usually builds peptide bonds.
- With the release of the newly created protein, this process separates the chain from the tRNA.
Importance of RNA Translation
- Translational control is essential for cancer growth and survival.
- Cancer cells must often control the translation phase of gene expression, although it is unclear why translation is prioritised over transcription.
- While cancer cells frequently contain genetically changed translation factors, cancer cells are considerably more likely to adjust the amounts of existing translation factors.
- Cancer cells also regulate translation to adapt to cellular stress.
- During stress, the cell translates mRNAs that can help the cell cope and survive.
- To counteract the downstream effects of cancer, future cancer therapies may involve disrupting the cell's translation machinery.