Test 2, Deck 4 Flashcards
The aa-tRNA that carries the amino acid tyrosine (TYR) normally has the anticodon, AUA.
a. How would the process of translation be affected if a mutation caused the anticodon of tyr tRNA to be AUU?
The anticodon of tyr-tRNA would be recognized as the codon UAA in mRNA. This codon is usually a stop codon, but in the presence of the mutated tyr-tRNA, the amino acid tyrosine would be added to the polypeptide chain when UAA reaches the A-site of the ribosome and translation would continue. The resulting polypeptide would be longer than normal.
The aa-tRNA that carries the amino acid tyrosine (TYR) normally has the anticodon, AUA.
b. How might this mutation affect the cell?
Since there are 3 stop codons, if they are present in equal proportions, then 1/3 of the proteins will be affected, Since the only change to these proteins will be the extra amino acids added to the end of the polypeptide, the effect on the functionality of the proteins depend on how the additional amino acids affect the processing of these proteins. If their presence prevent or adversely effect processing, then the proteins may not function correctly and this would most likely be harmful to the cell. Cells with a significant number of non-functional proteins are likely to die.
A translocation occurred that changed the position of a promoter so that the non-template strand was transcribed.
a. How would this effect transcription of the gene? Explain.
a The gene would not be transcribed, though an RNA primary transcript may be produced.
A translocation occurred that changed the position of a promoter so that the non-template strand was transcribed.
b. Would the mRNA be translated? Justify your response.
b If an mRNA was produced, and if an acceptable start codon (AUG) is present near the 5’ end of the mRNA, translation may be initiated. If a stop codon is present in the reading frame, translation would continue until the stop codon is reached.
A translocation occurred that changed the position of a promoter so that the non-template strand was transcribed.
c. How would this effect the cell? Explain.
The proteins specified by the gene with the mutated promoter would not be present in the cell. If only one copy of this gene exist, and if the protein is crucially important for the cell, then the cell would die. If multiple copies of the gene exist, then the cell may still be able to function normally. If the gene specified a protein that was not crucial, then the cell may be still able to function normally.
The sequence of the protein, insulin (a hormone) is nearly identical for many animals. Some of the differences that been observed in one area of the protein are:
cattle: ala ser val sheep: ala gly val pig: thr ser ile horse: thr gly ile a. Would you expect this region of the insulin protein to be crucial for hormonal activity? Explain your response.
Since there is so much variation in this region of the insulin protein and since there is no indication that the insulin protein is non-functional in these animals, it appears that this region of the protein is not crucial to hormonal activity.
The sequence of the protein, insulin (a hormone) is nearly identical for many animals. Some of the differences that been observed in one area of the protein are:
cattle: ala ser val sheep: ala gly val pig: thr ser ile horse: thr gly ile b. Would single nucleotide substitutions account for the amino acid differences? Explain.
Yes, because a single nucleotide is the difference between Ala and Thr, Ser and Gly, and Ile and Val. But between some animals there would have to be more than one nucleotide change because there is more than one amino acid changing. The one that only have one amino acid changing is a single nucleotide change.
How do nucleotides link together to form a polynucleotide? (polynucleotides are chains of nucleotides)? What is meant by a 3’-5’ linkage?
the 3’ carbon of one nucleotide is connected to the 5’ carbon of another nucleotide with a phosphate group in between. this linkage creates a single-stranded DNA molecule; a polynucleotide
Which nucleotides are complementary? What does complementary mean in this case?
A with T, two bonds between them
C with G, three bonds between them
also nucleotides with 2 rings (adenine and guanine) bind with nucleotides with 1 ring (thymine and cytosine) which maintains an equal distance between the sides
DNA is composed of two polynucleotide chains called DNA strands. How do the two strands link together?
the strands are held together by hydrogen bonds between complementary bases.
The two strands of DNA are said to be antiparallel. What does antiparallel mean in this case?
the DNA strands are oriented in opposite directions. so, if one strand is oriented 5’ to 3’ the other strand will be 3’ to 5’.
Compare the effects of different types of mutation. Which would cause the most changes to the protein?
Silent mutations do not make any change to the amino acid sequence.
Insertions and deletions that cause frameshift mutations are likely to cause more changes than missense mutations. Insertions or deletions of triplets would not cause a frameshift, so would create fewer changes to the protein.
Although insertions and deletions that cause frameshift mutations can create the most amino acid changes in the protein, insertions and deletions that occur in the beginning of an exon would cause more changes than insertions or deletions near the end of an exon.
The extent of the changes resulting from a nonsense mutation depend on the the location of the mutation; mutations near the beginning of the gene would create a much shorter protein than nonsense mutations near the end of the gene.
How would a mutation in an intron affect the gene product?
Mutations that occur within an intron would be very unlikely to have any effect on the amino acid sequence of the protein since they are removed from the mRNA
What are genes made of ? Structure of genes
Genes are made of DNA, nucleotides (nitrogenous base, 5-carbon sugar and phosphate group)
Where are genes found? What identifies a piece of DNA as a gene?
Genes are found on a specific locus on a chromosomes. They are identified as gene because they have a specific sequences of nucleotides within the DNA (coding sequences) and they have promoter and terminator sequences.
