What holds one strand of DNA together?
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Answer:
Normal Strand: alanine - methionine - histidine
Mutated Strand: glutamine - cysteine - no third amino acid.
Explanation:
Messenger ribonucleic acid (mRNA) is the RNA that is used in cells for protein synthesis. It has a single strand made by the transcription of DNA by RNA polymerase. It contains four nucleotides: Adenine (A), Guanine (G), Cytosine (C), and Uracil (U).
Before transcribing, we need to create the complementary strand of the DNA. We're going to write out the nucleotides of the complementary strand by matching the nucleotides in these pairs: (A & T) and (C & G).
Normal Strand: GCA ATG CAC
Complementary Strand: CGT TAC GTG
Next, we can transcribe this to find our mRNA. We're going to do the same thing to the complementary DNA strand, but with Uracils instead of Thymines. So our pairs are: (A & U) and (C & G)
Complementary DNA Strand: CGT TAC GTG
mRNA Strand: GCA AUG CAC
You'll notice that the mRNA strand is almost exactly like the new mRNA strand, but with Uracil instead of Thymine.
Each set of three nucleotides is known as a codon, which encodes the amino acids that ribosomes make into proteins. To read the codons, you need to have a chart like the one I attached. Start in the middle and work your way to the edge of the circle. Some amino acids have multiple codons. There are also "stop" and "start" codons that signify the beginning and ends of proteins.
mRNA Strand: GCA AUG CAC
Amino Acids: Ala Met His
Our sequence is alanine, methionine, and histidine.
A frameshift mutation occurs when a nucleotide is either added or removed from the DNA. It causes your reading frame to shift and will mess up every codon past where the mutation was. This is different than a point mutation, where a nucleotide is <em>swapped</em> because that will only mess up the one codon that it happened in. Frameshift mutations are usually more detrimental than point mutations because they cause wider spread damage.
Let's repeat what we did earlier on the mutated strand to see what changed.
Mutated Strand: CAA TGC AC
Complementary Strand: GTT ACG TG
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Complementary DNA Strand: GTT ACG TG
mRNA Strand: CAA UGC AC
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mRNA Strand: CAA UGC AC
Amino Acids: Glu Cys X
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Our amino acid sequence is glutamine, cysteine, and no third amino acid.
As you can see, removing the first nucleotide of the strand caused every codon to change. The last codon is now incomplete and won't be read at all. If this happened in a cell, the protein that was created from this mutated strand would be incorrect and may not function completely or at all.
