Gene Structure

16/11/2010 § 1 Comment

Although it was a small part of the textbook, we learned in class about which parts of genes are expressed and which sections actually intervene the genes that will later be used to code for proteins. Sections of a gene that do get expressed are exons and sections of a gene that do not get expressed are introns. Exons will get spliced together while introns simply get removed, kicked out of the sequence and will be reabsorbed as new nucleotides. After splicing, the length of genes obviously gets shorter and only the exons are existent in the RNA (this all happens during protein synthesis—transcription or translation) that will be used for translation.

Since introns don’t even get used at all, it seems that they are absolutely unnecessary for genetics in an organism, but sometimes they can be very useful in the reshuffling of exons and introns that happen in the Research & Development section of our genes. The sections of genes that are introns help shuffle exons around and make new sequences in the genes. Usually this doesn’t always work out because of natural selection. Nature doesn’t just agree with what will be a new set of genes. Sometimes though—even if it rarely happens—a new shuffle of genes just happens to work and it provides such a great leap on an organism’s road of evolution.

We also learned a bit about mutations in class. Although they are also quite rare—only one in a billion+ nucleotides have a mutation—the changes can either have a large effect or have no effect at all. Substitution mutations replace one nucleotide with a different one. Sometimes this may have no effect because certain amino acids are coded by more than one codon. (So changing UCU to UGC for cysteine makes no difference. It will still be cysteine.) Some substitutions also change the amino acid itself, depending on what codon is changed. This can lead to a protein deficiency, not having enough of a protein, but does not always make too much of a difference.

Other mutations can make all the difference in the organism’s cells. Either insertion or deletion can make a huge change in a cell’s genes. Insertion adds another nucleotide somewhere in the sequence of nucleotides and sometimes changes all of the amino acids that follow it. Deletion does the same but through another way. During deletion, a nucleotide is removed and the nucleotides that follow it are also changed because one nucleotide has been removed and all the other bases shift up, changing the coding sequence for amino acids. Basically, mutations change the meaning of DNA and provide a new meaning—sometimes not one the organism would understand.

Also, in order for scientists to identify treatable genetic disorders and in order to treat them, they had to map out the entire DNA sequence of a typical human. In the Human Genome Project (where billions of dollars were used), scientists researched human genes, found which gene was on which chromosome and what it was used for. Later they also compared human genes to that of laboratory mice or rats or other non-human organisms. The reason for doing all this—which was stated above—was to totally map out the human DNA sequence so that when a person has a treatable genetic disorder that isn’t helping them and actually slows them down in life, the disorder can be found in their genetic sequence and can be fixed.

The essay question was: How does information produce meaning? Mutations provide an example of how meaning is changed and shuffling introns also support how meaning is changed. For me, I easily understand the essay question if I use protein synthesis (transcription & translation) with RNAs and DNA molecules to explain how information, nucleotides, becomes meaning, proteins.

§ One Response to Gene Structure

  • Dave Ferguson says:

    Kari,

    Great post summarizing a lot of information. Also, I’m glad to see you’re confident about the essay question.

    Mr. F.

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