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    how does a change in the dna sequence affect the amino acid produced during translation?


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    Translation: DNA to mRNA to Protein

    Genes encode proteins, and the instructions for making proteins are decoded in two steps: first, a messenger RNA (mRNA) molecule is produced through the transcription of DNA, and next, the mRNA serves as a template for protein production through the process of translation. The mRNA specifies, in triplet code, the amino acid sequence of proteins; the code is then read by transfer RNA (tRNA) molecules in a cell structure called the ribosome. The genetic code is identical in prokaryotes and eukaryotes, and the process of translation is very similar, underscoring its vital importance to the life of the cell.

    Translation: DNA to mRNA to Protein

    By: Suzanne Clancy, Ph.D. & William Brown, Ph.D. (Write Science Right) © 2008 Nature Education

    Citation: Clancy, S. & Brown, W. (2008) Translation: DNA to mRNA to Protein. Nature Education 1(1):101

    How does the cell convert DNA into working proteins? The process of translation can be seen as the decoding of instructions for making proteins, involving mRNA in transcription as well as tRNA.

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    The genes in DNA encode protein molecules, which are the "workhorses" of the cell, carrying out all the functions necessary for life. For example, enzymes, including those that metabolize nutrients and synthesize new cellular constituents, as well as DNA polymerases and other enzymes that make copies of DNA during cell division, are all proteins.

    In the simplest sense, expressing a gene means manufacturing its corresponding protein, and this multilayered process has two major steps. In the first step, the information in DNA is transferred to a messenger RNA (mRNA) molecule by way of a process called transcription. During transcription, the DNA of a gene serves as a template for complementary base-pairing, and an enzyme called RNA polymerase II catalyzes the formation of a pre-mRNA molecule, which is then processed to form mature mRNA (Figure 1). The resulting mRNA is a single-stranded copy of the gene, which next must be translated into a protein molecule.

    Figure 1: A gene is expressed through the processes of transcription and translation.

    During transcription, the enzyme RNA polymerase (green) uses DNA as a template to produce a pre-mRNA transcript (pink). The pre-mRNA is processed to form a mature mRNA molecule that can be translated to build the protein molecule (polypeptide) encoded by the original gene.

    © 2013 Nature Education All rights reserved.

    Figure Detail

    During translation, which is the second major step in gene expression, the mRNA is "read" according to the genetic code, which relates the DNA sequence to the amino acid sequence in proteins (Figure 2). Each group of three bases in mRNA constitutes a codon, and each codon specifies a particular amino acid (hence, it is a triplet code). The mRNA sequence is thus used as a template to assemble—in order—the chain of amino acids that form a protein.

    Figure 2: The amino acids specified by each mRNA codon. Multiple codons can code for the same amino acid.

    The codons are written 5' to 3', as they appear in the mRNA. AUG is an initiation codon; UAA, UAG, and UGA are termination (stop) codons.

    © 2014 Nature Education All rights reserved.

    Figure Detail

    But where does translation take place within a cell? What individual substeps are a part of this process? And does translation differ between prokaryotes and eukaryotes? The answers to questions such as these reveal a great deal about the essential similarities between all species.

    Where Translation Occurs

    Within all cells, the translation machinery resides within a specialized organelle called the ribosome. In eukaryotes, mature mRNA molecules must leave the nucleus and travel to the cytoplasm, where the ribosomes are located. On the other hand, in prokaryotic organisms, ribosomes can attach to mRNA while it is still being transcribed. In this situation, translation begins at the 5' end of the mRNA while the 3' end is still attached to DNA.

    In all types of cells, the ribosome is composed of two subunits: the large (50S) subunit and the small (30S) subunit (S, for svedberg unit, is a measure of sedimentation velocity and, therefore, mass). Each subunit exists separately in the cytoplasm, but the two join together on the mRNA molecule. The ribosomal subunits contain proteins and specialized RNA molecules—specifically, ribosomal RNA (rRNA) and transfer RNA (tRNA). The tRNA molecules are adaptor molecules—they have one end that can read the triplet code in the mRNA through complementary base-pairing, and another end that attaches to a specific amino acid (Chapeville , 1962; Grunberger , 1969). The idea that tRNA was an adaptor molecule was first proposed by Francis Crick, co-discoverer of DNA structure, who did much of the key work in deciphering the genetic code (Crick, 1958).

    Within the ribosome, the mRNA and aminoacyl-tRNA complexes are held together closely, which facilitates base-pairing. The rRNA catalyzes the attachment of each new amino acid to the growing chain.

    The Beginning of mRNA Is Not Translated

    Interestingly, not all regions of an mRNA molecule correspond to particular amino acids. In particular, there is an area near the 5' end of the molecule that is known as the untranslated region (UTR) or leader sequence. This portion of mRNA is located between the first nucleotide that is transcribed and the start codon (AUG) of the coding region, and it does not affect the sequence of amino acids in a protein (Figure 3).

    So, what is the purpose of the UTR? It turns out that the leader sequence is important because it contains a ribosome-binding site. In bacteria, this site is known as the Shine-Dalgarno box (AGGAGG), after scientists John Shine and Lynn Dalgarno, who first characterized it. A similar site in vertebrates was characterized by Marilyn Kozak and is thus known as the Kozak box. In bacterial mRNA, the 5' UTR is normally short; in human mRNA, the median length of the 5' UTR is about 170 nucleotides. If the leader is long, it may contain regulatory sequences, including binding sites for proteins, that can affect the stability of the mRNA or the efficiency of its translation.

    Source : www.nature.com

    Impact of mutations on translation into amino acids (video)

    Using an amino acid translation table to understand the impact of point and frameshift mutations.

    Current time:0:00Total duration:8:52


    Impact of mutations on translation into amino acids

    Using an amino acid translation table to understand the impact of point and frameshift mutations.

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    An introduction to genetic mutations

    Mutagens and carcinogens

    The effects of mutations

    Impact of mutations on translation into amino acids

    This is the currently selected item.

    Mutation as a source of variation

    Aneuploidy & chromosomal rearrangements

    Genetic variation in prokaryotes

    Evolution of viruses

    Practice: Mutations Next lesson Biotechnology Sort by:

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    Log in Emma a year ago

    Posted a year ago. Direct link to Emma's post “what type of diseases can...”

    what type of diseases can you get from bad mutations?

    • Aiden Thatcher a year ago

    Posted a year ago. Direct link to Aiden Thatcher's post “Well, a good example of a...”

    Well, a good example of a disease that you could get from a bad mutation, is Sickle Cell Anima. Sickle Cell Anima is caused when 1 codon (DNA code unit) is inherited in its mutated version from both parents. That one single error in the many, many codons that code a red blood cell, causes a whole slew of errors in the creation of the body’s red blood cells. The codon in question causes the misplacement of a single atom in the hemoglobin protein, that causes it fold over during its production. This causes the new red blood cells to sickle shaped (Like a ( shape), thus the name, and causes numerous malfunctions within the cell. Sickle Cell Disease is just one example of the many bad things that one can get from a bad genetic mutation and it is very interesting that one tiny little error in the DNA code could have such a tremendous effect in a person. Other examples of genetic disorders include Muscular Dystrophy, Down’s Syndrome, and Cystic Fibrosis. I hope I answered your question. :)

    Jett Dormitorio 4 years ago

    Posted 4 years ago. Direct link to Jett Dormitorio's post “When does mutation normal...”

    When does mutation normally happen,in birth,during development or other things?

    • Kelsie O 4 years ago

    Posted 4 years ago. Direct link to Kelsie O's post “During development, as a ...”

    During development, as a fetus, when the body is replicating cells at a rapid rate. Although environmentally caused mutations (ie. cancer) are also common

    heidi.hatten 3 years ago

    Posted 3 years ago. Direct link to heidi.hatten's post “Is a mutation like a mist...”

    Is a mutation like a mistake in the DNA? In my bio class they said that mistakes in translating DNA were very rare like 1 in a billion, so is a mutation like this or is it different? Also how can an extra nucleotide get inserted or changed, how does this process specifically happen?

    • RowanH 2 years ago

    Posted 2 years ago. Direct link to RowanH's post “Yes a mutation is a mista...”

    Yes a mutation is a mistake in the DNA, compared to what it should be. It is rare for it to happen, but there is also a lot of DNA in your cells. In a diploid human cell, there are over 6000 million basepairs of DNA. And when that is copied for cell division, mistakes can happen. As you say, this may be only one in a billion, but with billions of bases, you get some mistakes. As well as copying into the wrong base, maybe the polymerase doing the copying will slip and skip a base or so. Another way that mutations can happen if the DNA gets damaged and isn't repaired properly. This damage could be from x-rays, UV radiation, or mutagenic chemicals. They tend to cause different types of damage, which is repaired in different ways. Sometimes DNA is damaged in a way that both strands break, and the cell will try to glue them back together. However, this is not always perfect and mistakes can be introduced. There may be bases missing, especially if the nucleotides at the DNA ends were damaged so they couldn't be stuck straight onto each other.

    edwardlessey612 a year ago

    Posted a year ago. Direct link to edwardlessey612's post “What is codons and mutati...”

    What is codons and mutations? I can't get to fully understand.

    • jas55555 a year ago

    Posted a year ago. Direct link to jas55555's post “Codons are a group of thr...”

    Codons are a group of three nucleotides, while mutations are mistakes in a cell's DNA where certain nucleotides are either swapped, inserted, deleted (I think there are other examples too but these are the main ones), which can either have small effects (example: changing one amino acid) or huge effects (example: changing the protein permanently). Hope this helped!

    Courtney Campbell a year ago

    Posted a year ago. Direct link to Courtney Campbell's post “When would you use U-A?”

    When would you use U-A?

    • jas55555 a year ago

    Posted a year ago. Direct link to jas55555's post “So do point mutations inc...”

    So do point mutations include frameshift mutations? Because I searched point mutations up and it is apparently a change in a single nucleotide of DNA (swap, insertion, deletion), and a frameshift seems to be an an insertion or deletion that changes the reading frame of the DNA.

    • x.asper

    Source : www.khanacademy.org

    Video of DNA: mutations

    Video of A single change in the DNA nucleotide sequence of a gene can cause the wrong amino acid to be produced. This deceptively simple change in turn can affect the structure or function of a protein. Though some mutations are harmful, most are not.

    DNA: mutations

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    DNA: mutations

    A single change in the DNA nucleotide sequence of a gene can cause the wrong amino...

    Encyclopædia Britannica, Inc.

    Article media libraries that feature this video: mutation


    An important source of genetic variation comes from mutations. A mutation is a change in the DNA sequence of a gene. Though some mutations are harmful, most are not. A mutation may change a trait in a way that may even be helpful, such as enabling an organism to better adapt to its environment.

    The simplest mutation is a point mutation. This occurs when one nucleotide base is substituted for another in a DNA sequence. The change can cause the wrong amino acid to be produced. In some cases, the change has little effect. In other cases, the incorrect amino acid can affect the structure or function of the protein being encoded.

    Here’s an example of how this works. This sentence composed of three-letter words is similar to a DNA sequence made up of three-base sequences called codons:

    Now, what happens if one letter is changed?

    The sentence now has a different meaning! Notice that the change affects just one word. If this was a DNA sequence, a change in one codon might not cause problems. But in some cases, it can have a severe effect. For example, here’s part of the DNA sequence for hemoglobin, a blood protein that carries oxygen to the tissues:

    Each DNA codon codes for a specific amino acid. For example, the codon GAG codes for the amino acid glutamic acid. The amino acids, in turn, are the building blocks for the hemoglobin protein.

    Now look at what happens when a point mutation occurs:

    This single mutation causes the amino acid valine to be encoded rather than glutamic acid. This one change has a critical effect on the structure of the hemoglobin molecule, causing the condition known as sickle cell anemia.

    Another type of mutation is a frameshift mutation. This occurs when a base is added to or deleted from a DNA sequence.

    Let’s look at our sentence again:

    Now let’s add a letter:

    This changes the message starting at the point where the letter was added. It affects that word as well as all of the words “downstream” – that is, the words that follow.

    The same thing can happen in a gene. Here’s a normal sequence:

    Now watch what happens when you add a base:

    The downstream message is completely different!

    A similar problem occurs when something is deleted:

    Frameshift mutations can cause drastic problems. As you can see, none of the downstream amino acids in either example make sense for the protein they are encoding. Because there are so many changes to the amino acid sequence, the resulting protein most likely will not be able to function.

    Source : www.britannica.com

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    James 11 month ago

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