BCHM 307 Spring 2018 March 9 Remembering the genetic code... 1. Cells have a mec
ID: 215235 • Letter: B
Question
BCHM 307 Spring 2018 March 9 Remembering the genetic code... 1. Cells have a mechanism for tagging and destroying proteins containing a C-terminal poly(Lys) sequence. What is the source of these proteins and why is destroying them helpful for the cell? 2. Cystic fibrosis is caused by a mutation in the 250,000-bp CFTR gene. The mature CFTR mRNA is only 6129 nucleotides. Why is the mature mRNA so much shorter than the gene from which it was transcribed? What is the minimum number of nucleotides required to encode the 1480- residue CFTR protein? a. b. 3. The CFTR gene (remember this from a previous clinical connection?) contains the sequence ATCATCTTTGGTGTT., which codes for residues 506-510 of the protein. a. Identify the residues in this segment of the protein. b. In the most common mutated form of the gene, this same segment of DNA has the sequence ATCATTGGTGTT.. What type of mutation has occurred and how does it affect the sequence of the encoded protein? c. How many reading frames are possible? Specify the amino acid sequences for all the possible reading frames. Which frames represent open reading frames? 4. A portion of DNA from a phage genome is shown a. b. 5-CGATGAGCCTTTCAGCACCGCTTAGTGAGGTTGCGCGCCACG-3 3-GCTACTCGGAAAGTCGTGGCGAATCACTCCAACGCGCGGTGC-5 Explain why a redundant genetic code helps protect an organism from the effects of mutations. 5. 6. Name the amino acids that are attached to the 3 end of the E.colitRNA molecules with the anticodon sequences a. GUG, b. GUU, or c. CGUExplanation / Answer
Answer-1:
Poly lysine residues are natural source obtained from the fermentation of various strains of bacteria Streptomyces. Poly Lys residues serve as a molecular marker which is important for the identification in order to degrade the protein molecule having Poly Lys residues present at the C-Terminal.
Protein molecules tagged with Poly lys residues are targetted for the degradation for the following reasons:
1. Peptides having poly lys residues often affects the activity of protein kinases, phosphatidyl-inositol kinases and adenylyl cyclase. So, since their activity is getting affected, the cell signalling pathways wold be affected too, because these molecules are majorly involved in cell signalling.
2. Poly lys residues causes the phosphorylation of the proteins associated with the membranes. Phosphorylation makes the molecule bulky, so if a phosphorylated protein belong to the membrane proteins then it may compromise the membrane permiability.
3. Due to presence of poly lys residues, distortion of cell membrane occurs due to the presence of polycations on the mebrane.
thus, in order to prevent the cell from such abnormal activities, proteins are therefore tagged which contains poly lys residues, so that a cell can continue its normal activity.
Answer-2:
(A) The mature mRNA is happen to be shorter than the original CFTR gene because of the nature of the mutation. In cystic fibrosis, there is a deletion (type of a muration) of phenylalanine 508. Since, most mutations occurs at the DNA level and the effects of mutations always occurs subsequently at mRNA and Protein levels. So, when the deletion occured in the gene, therefore, there will be automatically a shortening of the mRNA to be produced by transcription and so forth a defective protein will be produced.
(B) Total noumber of protein residues= 1480
1 codon = 3 nucleotides = 1 amino acid
Therefore, 1480 X 3 = 4440 nucleotides.
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