7.What are the possible biological roles of the cap and poly-A tail of mRNA?
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The cap and poly-A tail of mRNA have multiple roles. First of all, they help to prevent degradation of the mRNA molecules. Second, they help the mRNA attach to the ribosome subunits during RNA translation.
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once the DNA has been transcribed, spliced and modified, the new mRNA is moved out of the nucleus of the cell and into the cytoplasm.  There, a ribosome attaches to it.  The mRNA serves as a template for translation.\n\nHere's how that works.  mRNA is read in groups of 3 nucleotieds.  Each group of 3 is called a codon.  When the ribosome is attached to the mRNA, new amino acids that correspond to the codon can get added to the chain.\n\nEssentially, the ribosome moves like a train down the mRNA, stopping at each codon.  Every time it stops, a tRNA can enter and drop off an amino acid.  The tRNA has to be specific to that codon otherwise, it can't enter the ribosome.  The tRNA that is specific to a certain codon, is also specific to the amino acid it carries.  So indirectly, each codon corresponds to an amino acid.\n\nThe role that DNA plays is that it encodes for the mRNA and the mRNA encodes for the protein.\n\nThere's a lot of nuance that I didn't get to, like anticodons, reading frames, P sites, A sites, E sites, etc...If you care about these specifics, post another question ;p
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the first one is RNA. You can tell by the U at the end of the sequence
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the functions are:\nmRNA: Carries information and goest to ribosomes\ntRNA: Goes to the cytoplassm and picks up the amino acids\nrRNA: Makes the ribosomes
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Just like the opposite of start codons, which initiate the translation process, these are the ones that terminate the process; i.e. the ones that tell the ribosomes to stop translation.\n\nAnd why they are that way depends on the type of protein being produced, and in which organism.
302803
inside of the cell there is an organel called Ribosome(protein syntesis factory),we have DNA(in the nucleus) mRNA and tRNA(in sytoplasem) as well(i hope u know the function of each of them! if not ask me to explain!) well...based on the codes on mRNA,tRNAs go and sit on ribosomes  and they carry spesific amino acids with themselves,ribosome does the syntesis and connect the amino acids together and make a chain,this chain we be the next protein chain(it was the shortest and easiest explanation!)
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I can tell you for a fact that, at least in bacterial translation systems, this phenomenon is possible, but it would require a sequence mutation to happen.\n\nIn bacteria there are ribosomal recognition sequences on the 5-prime end of the mRNA called leaders. Ribosomes use rRNA-mRNA complement sequence homology to recognize and bind, and initiate translation. If you were to mutate the upstream leader so that it was better recognized by the ribosome (in other words it would initiate translation more often) you could, in fact, decrease the amount of transcription and still get higher levels of the protein being produced.\n\nI'll admit, this is an area I haven't personally studied for about a decade, so I'm a bit out of date on the recent litterature, but as far as I remember the mechanisms for ribosomal-mRNA recognition in eukaryotes isn't as well understood as the bacterial system. I don't know if a comparable event would be possible in eukaryotic cells.
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Brian B is partially correct, but I think it goes a bit deeper than that.  The introns of a pre mRNA are spliced out as mentioned before, but to what is the cause and function of introns is more complex.  \n\nFor example bacteria have no introns for the most part.  Why would eukaryotes want to carry around the extra DNA and take the energy to replicate it?   The answers to this are still being worked out, but one thing that introns do is that they enable a gene to be transcribed in slightly variable forms.  This is called alternate splicing.  The gene may skip an exon giving the finished mRNA a different sequence and hence a slighty different protein.  This gives the cell more options in its regulation.\n\nIf you consider the human genome codes for only ~30,000 genes, which was far lower than anyone expected, alternate splicing allows for the complexity that one would expect for an organism as complex as a human being.  (throw in post translational modification of proteins and that really gives you the complexity)\n\nSo introns allow for gene complexity and are therefore evolutionarly advantageous.\n\nHope this helps\n\nStooleo
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I have no idea about the second part of your question, and I'm not entirely sure if it's true, but I'll tell you what RNA is.\n\nRNA is essentially a copy of DNA that can travel out of the nucleus and to other parts of the cell. RNA is used as instructions. DNA can't leave the cell or it'll be destroyed by enzymes looking for viruses.\n\nMessenger RNA (or mRNA) is the one that goes from the nucleus to the ribosomes (where proteins are made) with instructions for which specific protein is to be made. Transfer RNA (tRNA) brings the appropriate amino acids (pieces of protein) to the Ribosomes so that the desired proteins can be made.\n\nthere are many other types of RNA, such as ribosomal RNA, but I know much less about those.\nhope this helps!
902807
the mRNA and tRNA are actually not controlled. The only thing controlled is the formation of RNA. It is formed from a complementary strand of DNA. That mRNA which goes through nuclear pores to the Ribosome. When it reaches to ribosome it attaches with the ribosome. The mRNA has a specific in a group of three like: A-U-T. Each code refers to a unique tRNA which then brings an amino acid to form a polypeptide chain. At the end there is a code which is subscribed as a STOP Code by the nucleus. This codes are what coontroll the process of protien synthysis. But the formation of mRNA from a complementaery strand is controlled by nucleus And the movement of mRNA as well as tRNA. is also controlled by nucleus (to some extent)\nHope this Helps
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> *How are the codes for proteins carried from the nucleus to the ribosomes?\nmRNA, messenger RNA, is transcribed from the "template" strand of DNA for that particular gene.  The mRNA may leave the nucleus and enter the cytoplasm, where it will encounter a ribosome.\n\n> A single strand of DNA has the bases AGTAAC. Using letters, show a matching DNA strand from this pattern.\nTCATTG\n\n> *How is tRNA used when cells build proteins?\ntRNA is a sequence of three nucelotides bound to the corresponding amino acid.  The ribosomes "read" the mRNA, match it, in reading frame, with the corresponding tRNA, and add the amino acid to the growing polypeptide.\n\n> *You begin as one cell. Compare the DNA in one of your brain cells to the DNA in one of your heart cells\nGenerally speaking, the nuclear DNA in your heart cell will be the same as the nuclear DNA in your brain cell.
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no \nthe lack of it might be.\nit is related to the attachment of the poly-A tail to the mature m-RNA strand.
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During translation, mRNA previously transcribed from DNA is decoded by specialized cellular structures called ribosomes to make proteins. Protein biosynthesis is divided into initiation, elongation and termination phases.\n\nThe ribosome has sites, which allow another specialized RNA molecule, known as tRNA, to bind to the mRNA. Binding of the correct tRNA to the mRNA on the ribosome is accomplished by an "anticodon" that is part of the tRNA. Thus, the correct tRNA, chemically linked to a specific amino acid, is directed to the ribosome to be added to a growing (nascent) polypeptide. The chemical process of connecting two amino acids is shown in the picture below.\n \nThe chemical process of connecting two amino acids resulting in a dipeptide and a water molecule\nAs the ribosome travels down the mRNA one codon at a time, another tRNA is attached to the mRNA at one of the ribosome sites. The first tRNA is released, but the amino acid that is attached to the first tRNA is now moved to the second tRNA, and binds to its amino acid. This translocation continues on, and a long chain of amino acid (protein), is formed.\n\nWhen the entire unit reaches the stop codon on the mRNA, it falls apart and a newly formed protein is released. This is termination. It is important to know that during this process, many enzymes are used to either assist or facilitate the whole procedure.
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mRNA is a carrier  of a genetic message hence the name. It carries the message in the form that a machinary for protein synthesis will understand and translate in amino acid sequence. Ribosomes and tRNAs can not directly read the genetic information from DNA hence the need for the mediator to do the job.
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Although polypeptides are subunits of Proteins, the protein manufacturer does not have subunits that start with a word 'poly'.\n\nThe 2 main components of Ribosomes are protein molecules and ribonucleic acid (RNA).  \n\nIn order to achieve better detail, we need to find out what makes proteins and RNAs.  \n\n\n\n ~*~ RNA ~*~\n\nThe subunits of RNA are:\n\n1) Gene\n2) Nucleotides\n3) Nitrogen Bases - Guanine, Cytosine, Adenine and Uracil\n5) Phosphodiester bond\n6) Sugar\n7) Phosphate group\n\n\nArranged are the substances, from big to small\n\nA RNA is composed of segments of genes\n\nThese genes are known as nucleotides\n\nIt takes only 1 chain of nucleotides to form a RNA\n\nA chain of nucleotides are formed by sugar phosphate backbone (one strand) - phosphodiester bond\n\nOne nucleotide is made up of a nitrogen base (either Adenine, Uracil, Guanine or Cytosine), a sugar (ribose) and a phosphate group. \n\n\ntherefore a segment of RNA looks,\n\nas illustrated below:  \n\n AAUUGGCUAAGCC <--------- nitrogen bases\n----------------------------- <------- phosphodiester bond \n\n\n\n ~*~ Proteins ~*~\n\nStarting from the smallest:\n\nAmino group + Carbon group = amino acid \n\namino acid + amino acid = peptide\n\npeptide + peptide = small polypeptide\n\nsmall polypeptide + small polypeptide = peptones/ large polypeptide\n\npeptones + peptones = protein
241608
Messenger RNA (mRNA)\nMessenger RNA is RNA that carries information from DNA to the ribosome sites of protein synthesis in the cell. Once mRNA has been transcribed from DNA, it is exported from the nucleus into the cytoplasm (in eukaryotes mRNA is "processed" before being exported), where it is bound to ribosomes and translated into protein. After a certain amount of time the message degrades into its component nucleotides, usually with the assistance of RNases.\n\nTransfer RNA (tRNA)\nTransfer RNA is a small RNA chain of about 74-93 nucleotides that transfers a specific amino acid to a growing polypeptide chain at the ribosomal site of protein synthesis during translation. It has sites for amino-acid attachment and an anticodon region for codon recognition that binds to a specific sequence on the messenger RNA chain through hydrogen bonding. It is a type of non-coding RNA.\n\nRibosomal RNA (rRNA)\nRibosomal RNA (rRNA) is a component of the ribosomes, the protein synthetic factories in the cell. Eukaryotic ribosomes contain four different rRNA molecules: 18S, 5.8S, 28S, and 5S rRNA. Three of the rRNA molecules are synthesized in the nucleolus, and one is synthesized elsewhere. rRNA molecules are extremely abundant. They make up at least 80% of the RNA molecules found in a typical eukaryotic cell.
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The DNA has to be wrapped up very tightly to fit all of it into the nucleus.  This is a complex process involving chromatin (DNA and associated proteins).  For example, histones are groups of protein molecules that the DNA strand wraps around to help compact its shape.  For a gene to be expressed (transcribed) a section of the the DNA has to become 'unwrapped' and 'exposed' to the transcription machinery.  Methylation and Acetylation of histones play significant roles in this process.\n\nAny good, recent, biochemistry textbook will explain these issues.  If you go to pubmed, they have an online book section.  Click on any of the biochemistry books and enter into the search field "DNA, chromatin", or "DNA, histones", or "gene expression, chromatin" and you will find lots of info. and probably pictures too.\n\nBest wishes and good luck.