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How many times is a single strand of mRNA translated into a protein?

How many times is a single strand of mRNA translated into a protein?



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In other words, is the mRNA damaged or somehow "marked completed" in the translation process? Or does it pop out the other side of a ribosome ready to be translated again? If the latter, how many copies of a protein result from a single strand of mRNA?

Thank you in advance!


I'm answering my own question for the benefit of anyone else who might be wondering about this. (Please note that I'm just a programmer, not a biologist, but thanks to David's comment, I was able to come to what I think are some correct conclusions.)

A single mRNA strand can be translated more than once, even more than once at the same time. Thepolysomethat David references is a group of two or more ribosomes all attached to the same mRNA strand, all working on translating it simultaneously.

I believe that it may be possible for a single mRNA strand to be translated hundreds or even thousands of times. My reasoning for this is that a virus injects one copy of its RNA into a cell, and from this one copy, new viruses are replicated until the cell bursts. This "burst size" varies by host cell and virus, but it can range from hundreds to tens of thousands or more. While there are still a lot of things I don't understand about the specific steps the RNA goes through (are there intermediary copies made from which multiple mRNA strands are produced?, etc.), it still seems to suggest that a single strand of mRNA can be translated a lot.


RNA-induced silencing complex

The RNA-induced silencing complex, or RISC, is a multiprotein complex, specifically a ribonucleoprotein, which functions in gene silencing via a variety of pathways at the transcriptional and translational levels. [1] Using single-stranded RNA (ssRNA) fragments, such as microRNA (miRNA), or double-stranded small interfering RNA (siRNA), the complex functions as a key tool in gene regulation. [2] The single strand of RNA acts as a template for RISC to recognize complementary messenger RNA (mRNA) transcript. Once found, one of the proteins in RISC, Argonaute, activates and cleaves the mRNA. This process is called RNA interference (RNAi) and it is found in many eukaryotes it is a key process in defense against viral infections, as it is triggered by the presence of double-stranded RNA (dsRNA). [3] [4] [1]


Contents

The brief existence of an mRNA molecule begins with transcription, and ultimately ends in degradation. During its life, an mRNA molecule may also be processed, edited, and transported prior to translation. Eukaryotic mRNA molecules often require extensive processing and transport, while prokaryotic mRNA molecules do not. A molecule of eukaryotic mRNA and the proteins surrounding it are together called a messenger RNP.

Transcription Edit

Transcription is when RNA is copied from DNA. During transcription, RNA polymerase makes a copy of a gene from the DNA to mRNA as needed. This process differs slightly in eukaryotes and prokaryotes. One notable difference is that prokaryotic RNA polymerase associates with DNA-processing enzymes during transcription so that processing can proceed during transcription. Therefore, this causes the new mRNA strand to become double stranded by producing a complementary strand known as the tRNA strand, which when combined are unable to form structures from base-pairing. Moreover, the template for mRNA is the complementary strand of tRNA, which is identical in sequence to the anticodon sequence that the DNA binds to. The short-lived, unprocessed or partially processed product is termed precursor mRNA, or pre-mRNA once completely processed, it is termed mature mRNA.

Eukaryotic pre-mRNA processing Edit

Processing of mRNA differs greatly among eukaryotes, bacteria, and archaea. Non-eukaryotic mRNA is, in essence, mature upon transcription and requires no processing, except in rare cases. [2] Eukaryotic pre-mRNA, however, requires several processing steps before its transport to the cytoplasm and its translation by the ribosome.

Splicing Edit

The extensive processing of eukaryotic pre-mRNA that leads to the mature mRNA is the RNA splicing, a mechanism by which introns or outrons (non-coding regions) are removed and exons (coding regions) are joined together.

5' cap addition Edit

A 5' cap (also termed an RNA cap, an RNA 7-methylguanosine cap, or an RNA m 7 G cap) is a modified guanine nucleotide that has been added to the "front" or 5' end of a eukaryotic messenger RNA shortly after the start of transcription. The 5' cap consists of a terminal 7-methylguanosine residue that is linked through a 5'-5'-triphosphate bond to the first transcribed nucleotide. Its presence is critical for recognition by the ribosome and protection from RNases.

Cap addition is coupled to transcription, and occurs co-transcriptionally, such that each influences the other. Shortly after the start of transcription, the 5' end of the mRNA being synthesized is bound by a cap-synthesizing complex associated with RNA polymerase. This enzymatic complex catalyzes the chemical reactions that are required for mRNA capping. Synthesis proceeds as a multi-step biochemical reaction.

Editing Edit

In some instances, an mRNA will be edited, changing the nucleotide composition of that mRNA. An example in humans is the apolipoprotein B mRNA, which is edited in some tissues, but not others. The editing creates an early stop codon, which, upon translation, produces a shorter protein.

Polyadenylation Edit

Polyadenylation is the covalent linkage of a polyadenylyl moiety to a messenger RNA molecule. In eukaryotic organisms most messenger RNA (mRNA) molecules are polyadenylated at the 3' end, but recent studies have shown that short stretches of uridine (oligouridylation) are also common. [3] The poly(A) tail and the protein bound to it aid in protecting mRNA from degradation by exonucleases. Polyadenylation is also important for transcription termination, export of the mRNA from the nucleus, and translation. mRNA can also be polyadenylated in prokaryotic organisms, where poly(A) tails act to facilitate, rather than impede, exonucleolytic degradation.

Polyadenylation occurs during and/or immediately after transcription of DNA into RNA. After transcription has been terminated, the mRNA chain is cleaved through the action of an endonuclease complex associated with RNA polymerase. After the mRNA has been cleaved, around 250 adenosine residues are added to the free 3' end at the cleavage site. This reaction is catalyzed by polyadenylate polymerase. Just as in alternative splicing, there can be more than one polyadenylation variant of an mRNA.

Polyadenylation site mutations also occur. The primary RNA transcript of a gene is cleaved at the poly-A addition site, and 100–200 A's are added to the 3’ end of the RNA. If this site is altered, an abnormally long and unstable mRNA construct will be formed.

Transport Edit

Another difference between eukaryotes and prokaryotes is mRNA transport. Because eukaryotic transcription and translation is compartmentally separated, eukaryotic mRNAs must be exported from the nucleus to the cytoplasm—a process that may be regulated by different signaling pathways. [4] Mature mRNAs are recognized by their processed modifications and then exported through the nuclear pore by binding to the cap-binding proteins CBP20 and CBP80, [5] as well as the transcription/export complex (TREX). [6] [7] Multiple mRNA export pathways have been identified in eukaryotes. [8]

In spatially complex cells, some mRNAs are transported to particular subcellular destinations. In mature neurons, certain mRNA are transported from the soma to dendrites. One site of mRNA translation is at polyribosomes selectively localized beneath synapses. [9] The mRNA for Arc/Arg3.1 is induced by synaptic activity and localizes selectively near active synapses based on signals generated by NMDA receptors. [10] Other mRNAs also move into dendrites in response to external stimuli, such as β-actin mRNA. [11] Upon export from the nucleus, actin mRNA associates with ZBP1 and the 40S subunit. The complex is bound by a motor protein and is transported to the target location (neurite extension) along the cytoskeleton. Eventually ZBP1 is phosphorylated by Src in order for translation to be initiated. [12] In developing neurons, mRNAs are also transported into growing axons and especially growth cones. Many mRNAs are marked with so-called "zip codes," which target their transport to a specific location. [13]

Translation Edit

Because prokaryotic mRNA does not need to be processed or transported, translation by the ribosome can begin immediately after the end of transcription. Therefore, it can be said that prokaryotic translation is coupled to transcription and occurs co-transcriptionally.


Can a single mRNA molecule make more than one protein?

I don't mean more than one kind of protein, but I want to know the number of proteins (of the same kind) that can be made from one mrna molecule. I saw somewhere that many proteins can be made from a single mrna molecule so I'm a bit confused as to what it means.

Yes, mRNA is often translated multiple times by ribosomes. In some cases they even form "assembly line" structures where multiple ribosomes are loaded onto the mRNA at the same time.

Absolutely. The mRNA is not consumed by the protein synthesis process, and can be used many times. The main limitation is the lifetime of the mRNA itself. RNA is not a super stable molecule in general, and the cell deliberately produces enzymes that break it down faster to retain control on its protein synthesis. You can imagine that if a single mRNA could stick around being translated into protein forever, the cell would never stop making that protein, even if it was no longer needed. Because of this, mRNAs in a human body are destroyed within a few hours, or a few days at the absolute most, depending on the sequence and structure of the mRNA. This is enough to make dozens or hundreds of copies of the protein, but it certainly doesn't go on forever.


Illumina library preparation

When starting an RNA-seq experiment, for every sample the RNA needs to be isolated and turned into a cDNA library for sequencing. The general workflow for library preparation is detailed in the step-by-step images below.

Briefly, the RNA is isolated from the sample and contaminating DNA is removed with DNase.

The RNA sample then undergoes either selection of the mRNA (polyA selection) or depletion of the rRNA. The resulting RNA is fragmented.

Generally, ribosomal RNA represents the majority of the RNAs present in a cell, while messenger RNAs represent a small percentage of total RNA,

2% in humans. Therefore, if we want to study the protein-coding genes, we need to enrich for mRNA or deplete the rRNA. For differential gene expression analysis, it is best to enrich for Poly(A)+, unless you are aiming to obtain information about long non-coding RNAs, then do a ribosomal RNA depletion.

The size of the target fragments in the final library is a key parameter for library construction. DNA fragmentation is typically done by physical methods (i.e., acoustic shearing and sonication) or enzymatic methods (i.e., non-specific endonuclease cocktails and transposase tagmentation reactions.

The RNA is then reverse transcribed into double-stranded cDNA and sequence adapters are then added to the ends of the fragments.

  • Forward (secondstrand) – reads resemble the gene sequence or the secondstrand cDNA sequence
  • Reverse (firststrand) – reads resemble the complement of the gene sequence or firststrand cDNA sequence (TruSeq)
  • Unstranded

Finally, the fragments are PCR amplified if needed, and the fragments are size selected (usually

300-500bp) to finish the library.


Protein Synthesis Contributors

To make the copied stretch of code (transcription) we need enzymes called RNA polymerases. These enzymes gather free-floating messenger RNA (mRNA) molecules inside the nucleus and assemble them to form the letters of the code. Each letter of DNA code has its own key and each new letter formed by mRNA carries a lock that suits this key, a little like tRNA.

Notice that we are talking about letters. This is important. Inside the nucleus, the DNA code is not understood, simply copied down – transcribed. Understanding the code by spelling out the words formed by these letters – translating – happens at a later stage.

RNA polymerase must find and bring over the appropriate mRNA molecule for each nitrogenous base on the template strand. Selected mRNA molecules link together to form a chain of letters. Eventually, these letters will spell out the equivalent of a phrase. Each phrase represents a specific (polypeptide) product. If the recipe is not exactly followed, the final product might be completely different or not work as well as it should.

Messenger RNA has now become the code. It travels to the next group of important contributors that work as manufacturing plants. Ribosomes are found outside the cell nucleus, either in the cell cytoplasm or attached to the rough endoplasmic reticulum it is ribosomes that make the endoplasmic reticulum ‘rough’.

A ribosome is split into two parts and the strand of mRNA runs through it like ribbon through an old-fashioned typewriter. The ribosome recognizes and connects to a special code at the start of the translated phrase – the start codon. Transfer RNA molecules enter the ribosome, bringing with them individual ingredients. As with all of these processes, enzymes are required to make the connections.

If each mRNA codon has a lock, tRNA possesses the keys. The tRNA key for an mRNA codon is called an anticodon. When a tRNA molecule holds the key that matches a three-nucleobase code it can open the door, drop off its load (an amino acid), and leave the ribosome factory to collect another amino acid load. This will always be the same type of amino acid as the anticodon.

Messenger RNA shifts along the ribosome as if on a conveyor belt. At the next codon another tRNA molecule (with the right key) brings the next amino acid. This amino acid bonds to the previous one. A chain of bonded amino acids begins to form– a polypeptide chain. When completed, this polypeptide chain is an accurate final product manufactured according to the instructions in the DNA recipe book. Not a pie or a cake but a polypeptide chain.

The end of the mRNA code translation process is signaled by a stop codon. Start and stop codons do not code for amino acids but tell the tRNA and ribosome where a polypeptide chain should begin and end.

The finished product – the newly synthesized polypeptide – is released into the cytoplasm. From there it can travel to wherever it is needed.


Benefits

Benefits of mRNA vaccines over conventional approaches are 1 :

  • Safety: RNA vaccines are not made with pathogen particles or inactivated pathogen, so are non-infectious. RNA does not integrate itself into the host genome and the RNA strand in the vaccine is degraded once the protein is made.
  • Efficacy: early clinical trial results indicate that these vaccines generate a reliable immune response and are well-tolerated by healthy individuals, with few side effects.
  • Production: vaccines can be produced more rapidly in the laboratory in a process that can be standardised, which improves responsiveness to emerging outbreaks.

Developmental Biology. 6th edition.

The regulation of gene expression is not confined to the differential transcription of DNA. Even if a particular RNA transcript is synthesized, there is no guarantee that it will create a functional protein in the cell. To become an active protein, the RNA must be (1) processed into a messenger RNA by the removal of introns, (2) translocated from the nucleus to the cytoplasm, and (3) translated by the protein-synthesizing apparatus. In some cases, the synthesized protein is not in its mature form and (4) must be posttranslationally modified to become active. Regulation can occur at any of these steps during development.

The essence of differentiation is the production of different sets of proteins in different types of cells. In bacteria, differential gene expression can be effected at the levels of transcription, translation, and protein modification. In eukaryotes, however, another possible level of regulation exists—namely, control at the level of RNA processing and transport. There are two major ways in which differential RNA processing can regulate development. The first involves the �nsoring” of which nuclear transcripts are processed into cytoplasmic messages. Here, different cells can select different nuclear transcripts to be processed and sent to the cytoplasm as messenger RNA. The same pool of nuclear transcripts can thereby give rise to different populations of cytoplasmic mRNAs in different cell types (Figure 5.26A). The second mode of differential RNA processing is the splicing of the mRNA precursors into messages for different proteins by using different combinations of potential exons. If an mRNA precursor had five potential exons, one cell might use exons 1, 2, 4, and 5 a different cell might utilize exons 1, 2, and 3 and yet another cell type might use yet another combination (Figure 5.26B). Thus, one gene can create a family of related proteins.

Figure 5.26

Roles of differential RNA processing during development. (A) RNA selection, whereby the same nuclear RNAs are made in two cell types, but the set that becomes cytoplasmic messenger RNAs is different. (B) Differential splicing, whereby the same nuclear (more. )


Gene Expression Steps

Gene expression steps, as already mentioned, can be found in more detail on the protein synthesis page. Any gene that codes for an amino acid sequence that produces a polypeptide chain or a protein is called a structural gene.

The below image shows a codon wheel. Messenger RNA codons are comprised of a combination of three of the following nucleobases:

A broad set of combinations give codes for one or more amino acids, as well as for start and stop signals implemented during the translation process. For example, AAA – starting from the center of the codon wheel and moving outward – codes for the amino acid lysine (Lys).

Structural genes have various components:

  • Start site: the first part of a gene that tells messenger RNA when and where to begin the transcription process.
  • Promoter: not part of the mRNA transcript but a part that assists in its formation.
  • Enhancers: catalysts that speed up the transcription rate.
  • Silencers: decelerators of the transcription rate. Some proteins are produced at certain times such as during puberty or fetal development silencer sequences stop these proteins from being produced when they are not required.
  • Exons: the part of the gene that codes for amino acid sequences.
  • Introns: non-coding parts of the gene that are not transcribed by messenger RNA but spliced out before mRNA leaves the nucleus. An intron is a regulatory and protective part of a structural gene.

Gene expression is specific to the transcription and translation of DNA gene sequences in eukaryotes and prokaryotes. While eukaryotic gene expression happens inside and outside of the cell nucleus in two distinct stages, prokaryotic gene expression occurs nearly simultaneously in free-floating DNA within the cell cytoplasm.

The following four transcription steps describe eukaryotic processes.

  • Initiation: a double strand of DNA splits so that an enzyme (RNA polymerase) can recognize the start site and attach to the promoter.
  • Elongation: RNA polymerase moves along the open strand of DNA to produce a growing strand of pre-mRNA.
  • Termination: the finished strand of pre-mRNA detaches from the DNA.
  • Processing: introns are spliced (by spliceosomes) and the exons joined to produce mature mRNA that codes for a single protein.

Translation is the follow-on step from transcription it is also composed of four similarly-named gene expression steps:

  • Initiation: the mRNA strand leaves the cell nucleus and binds to a ribosome. Ribosomes can be compared to assembly-line machines in a factory that produce the final product – proteins or polypeptide chains. A first transfer RNA molecule attaches to the ribosome in the form of a start codon. Each transfer RNA (tRNA) carries a single amino acid that fits according to each mRNA codon. A start codon carries the amino acid methionine .
  • Elongation: more tRNA molecules bring specific amino acids to the appropriate section of mRNA. This mRNA runs through the ribosome a little like a ribbon through an old typewriter. Amino acids are bound to each other by an enzyme called peptidyl transferase.
  • Termination: after reaching a stop signal called the stop codon, the translation phase ends.
  • Post-translation processing: the finished protein or polypeptide is used either inside the cell or sent outside of the cell to carry out its required function.


Messenger RNA- Explained


Messenger RNA is the type of RNA that is needed for protein synthesis.

In this article, we will describe how the cells in your body make proteins from start to finish, so that you can know the process of protein synthesis you the individual and vital role of messenger RNA (mRNA) plays in this process.

So How Does Your Body Produce Protein?

How does the body produce protein? We'll go over this now.

The body produces protein at a cellular level. Each cell in the body is equipped with all the organelles which are needed to synthesis protein. The end organelle that makes protein are the ribosomes. But before it gets to the ribosomes, which makes the complete end product of protein, the process begins in the nucleus of the cell.

The Nucleus Contains the Genes Needed to Make Protein

The process begins in the nucleus of the cell, because the nucleus contains the genes, which contains the information needed to make functional proteins.

The process of going from gene to protein consists of two major steps, which are transcription and translation. The flow of information from DNA to RNA to proteins is so important to biology that it is referred to many times as the central dogma of molecular biology.

Transcription

Transcription is the process by which information from the gene's DNA in the nucleus is transferred to a similar molecule called RNA. The type of RNA that contains information for protein synthesis is called messenger RNA. You can think of it as a messenger, because it carries the information, from the DNA in the nucleus to the ribosomes in the cytoplasm. Again, transcription is the process by which the messenger RNA is created, which will travel to the ribosomes, and deliver the vital message from the genes needed to make protein.

Translation

The next step after transcription is translation. This is the step where the mRNA comes into contact with the ribsomes, which reads the sequence of mRNA bases. A section of the mRNA consisting of a sequence of 3 bases is called a codon, which normally codes for a single amino acid. Proteins are long strings of amino acids put together. A type of RNA, then, called transfer RNA (abbreviated tRNA), assembles the protein, one amino acid at a time (or 3 bases at a time). It does this until it encounters a "stop" codon. This tells it to stop putting chains of amino acids together. The building of the protein is now complete. Thus, it will stop.

Below is an illustration of a messenger RNA being synthesized into a protein.


Watch the video: DNA, Hot Pockets, u0026 The Longest Word Ever: Crash Course Biology #11 (August 2022).