Bio lecture 20
If a mutation in the coding region of a gene changes a UGU codon to UGG, what type of mutation occurred? Explain what effect, if any, this mutation will have on the polypeptide produced by expression of the gene. What if the codon changed to AGU? To UGA?
. This would be a missense mutation because the resulting amino acid would be different than what it was supposed to be. This change would affect the polypeptide by giving it an amino acid that is different from what was originally supposed to be there. If the codon changed to AGU, it would also be a missense mutation and the same thing would happen. If it changed to UGA, this would be a nonsense mutation, which means that the codon is now a stop codon. The mRNA would stop being translated when the ribosome hit this codon, and the resulting amino acid would not function as it should.
Would an error or mistake in DNA replication, transcription, or translation have the biggest affect on the cell.
A mistake in DNA replication would have the biggest affect on the cell. DNA is a master code error. DNA is permanent information storage that everything goes back to to express genes.
At what location of the coding region would a nonsense mutation have the least effect? most?
A nonsense mutation would have the least effect at the end of a coding region. It would have the most effect at the beginning.
What accurately describes silent mutations?
A silent mutation changes the DNA sequence of a gene and the mRNA sequence produced by transcription of the gene, but does not alter the polypeptide sequence generated by translation. Mastering Bio Input: All mutations alter the DNA sequence of a gene, and any changes in the coding region of a gene will be copied into the mRNA when the gene is transcribed. Silent mutations specifically refer to mutations that alter a codon specifying an amino acid (and thus part of the coding region) to a different codon that corresponds to the same amino acid. Therefore, silent mutations do not change the amino acid sequence of the polypeptide generated by expression of the gene.
What is the relationship to amino acid, tRNA, and anticodons?
A specific type of tRNA can only be attached to one type of amino acid; the anticodon of a tRNA determines with which codon an mRNA it interacts; the enzymes that attach amino acids to tRNAs determine which codons correspond to which amino acids; a tRNA only has one anticodon
Do you think a mutation that altered the amino acid Glu to Asp would have as much of an effect as the missense mutation in hemoglobin to create sickle cell? (Both are hydrophilic)
Because both amino acids are hydrophilic there is a possibility that the protein might still be able to function normally (this is not definitive).
T/R: Different types of cells in multicellular organisms have different genes
False... all the cells in multicellular organism have the same genes
T/F: Most of the genes in a cell are expressed
False...not all genes in a cell are expressed or needed.
T/F: Most of the DNA sequence of a chromosome is part of a gene
False..Most of the DNA sequence is not part of the gene; only around 2,3,or 4 percent of the DNA sequence is part of a gene
Why does addition or deletion of one nucleotide in the coding region of a gene virtually always alter the structure and function of a protein?
Insertions and deletions can cause frameshift mutations. This alters how nucleotides are grouped into codons and can change all amino acids after the mutations. This typically alters the polypeptide length (# of amino acids) essentially: All codons after the insertion or deletion have the potential to be altered this includes the stop codon; Polypeptide produced could be longer or shorter depending how the codons are altered by the mutation
Explain why a mistake made during transcription that alters the sequence of an mRNA is not a mutation. Describe the effects this type of mistake would have in a cell.
Mutations are changes to the DNA only. A mistake made during transcription would not change the DNA. This mistake would affect a cell by creating an mRNA strand that might code for a different amino acid if the mistake took place within an exon, because the exons are the codons that get expressed.
A nucleotide is inserted in the middle of the coding region of a gene. What are the potential effects on the polypeptide produced by expression of the gene?
The insertion has the potential to alter only amino acids specified by codons after the inserted nucleotide, and could change the length of the polypeptide chain. Mastering Bio Input: An insertion of one nucleotide in the coding region of a gene has the potential to change all codons after the insertion, including the codon that now contains the insertion. Amino acids that are specified by codons before the insertion will not be altered. Changing how nucleotides are grouped into codons virtually always (if not always) changes the position of the stop codon, making the polypeptide chain either longer or shorter depending on where, if anywhere, a "new" stop codon is now present.
Explain why/how some mutations do NOT alter the amino acid sequence of the polypeptide generated by transcription and translation. Write out a valid mRNA sequence (i.e. one that could be translated properly in a cell) with five amino acids and use it to give an example of a mutation that would not alter the amino acid sequence of the polypeptide chain produced by expression of the gene.
Permanent change in the DNA sequence of an organisms genome is random and not necessarily harmful. Its a source of genetic diversity and mutations provide raw material for evolution to occur. Mutations do not always change the amino acid sequence of a polypeptide. The feature of the genetic code that allows this is redundancy; multiple codons can specify for the same amino acid. There are a few reasons why a mutation in the DNA might not alter the amino acid sequence of a polypeptide. One reason might be that the mutation occurred at a place that codes for an "intron" in a eukaryotic mRNA. This mutation would be removed during processing. Another reason might be that the mutation changes a pair of nucleotides into something that also codes for the same amino acid that it originally coded for (a silent mutation). Finally, if the mutation takes place in the terminator region of the gene, the mRNA would be weirdly long and would include the next gene, but there would still be a "stop" codon at the end of the first gene, so only the first polypeptide sequence would be coded for.
Imagine that a mutation causes ALL tRNAs in a cell with the anticodon CCC, which interacts with the codon GGG that normally specifies Gly, to be attached to the amino acid Ser instead. What part of the translation machinery would have to malfunction for this to occur in a cell? How would polypeptides in a cell be affected?
The enzymes are responsible for attaching the amino acids to the tRNAs. The anticodon of a tRNA determines with what codon it interacts. Only tRNAs attached to the anticodon CCC will have the wrong amino acid Ser attached to its enzyme. Ser rather than Gly will only be added to GGG codons. The other codons that correspond with Gly will still attach proper amino acid.
What determines the potential effects of a missense mutation on the structure and function of a protein? A nonsense mutation? Explain your answers.
The potential effects of a missense mutation are determined by the properties of the amino acid that was coded for. For example, does the new amino acid have a hydrophilic or hydrophobic R-group? Replacing a hydrophilic amino acid with a hydrophobic one (or vice versa) might change the structure or function of a protein. Another example is a regular hemoglobin versus sickle cell. Because one amino acid is different in regular hemoglobin takes on a total different shape. When the protein takes a different shape it doesn't work the same way. A nonsense mutation changes a codon that specifies an amino acid to a stop codon. The potential effects of a nonsense mutation are determined by the location of the nonsense mutation within the gene. The closer the nonsense mutation is to the beginning of the gene, the more the polypeptide will be affected because it will be missing more amino acids.
During transcription, RNA polymerase makes a mistake that results in a one nucleotide insertion right before the start codon of an mRNA. What effect, if any, will this have on the polypeptide produced by translation of the mRNA? What about if a nucleotide was deleted right after the stop codon?
This would change the group of codons and might even delay the start of of transcribing mRNA. The result of deleting a codon might elongate the mRNA strand.
T/F: The set of genes expressed in a particular cell is different under different conditions
True...A muscle cell when oxygen is present expresses genes for cellular respiration but when there is a lack of oxygen genes are expressed to allow fermentation to occur
T/F: An individual chromosome has many genes
True...An individual chromosome has many genes along it
T/F: some genes in a cell are never expressed
True..cells are generally really specialized and are only going to need a handful of genes to actually be expressed
A gene contains the information for a protein with 612 amino acids. Which of the following mutations in the coding region of the gene would be most likely to result in a dysfunctional protein when the gene is expressed?
a substitution mutation that changed the codon for the third amino acid to a stop codon Mastering Bio Input: Making the third codon a stop codon would result in a polypeptide with only two amino acids. A polypeptide that lacks most of the amino acids normally present will not be able to carry out its function. While two of the other mutations could inhibit/prevent a protein from functioning properly, it's also possible that there would be minimal or no effect. A single amino acid change might not alter the final 3D shape of the polypeptide if the "new" amino acid has similar properties to the "old" one (e.g. both had hydrophobic R-groups). Insertion of three nucleotides would add only one amino acid (and depending on where it's inserted potentially change one other amino acid). Removing a nucleotide just before the start codon cannot change the amino acid sequence produced by translation, so that change wouldn't have any effect.
What would happen in a cell if enzymes that normally attach the amino acid Cys to tRNAs with the anticodon ACA (which is complementary to the codon UGU that specifies Cys), attached Cys to tRNAs with the anticodon AAA (which is complementary to the codon UUU) instead?
tRNAs attached to AAA anticodons would have the wrong amino acid attached to the enzyme that would bind to the sequence.
