NAME: 17. (12 pts total) You have discovered yet another mutant strain of E. col
ID: 195315 • Letter: N
Question
NAME: 17. (12 pts total) You have discovered yet another mutant strain of E. coll. You hypothesize that the mutation makes a nonfunctional DNA Polymerase III. Page 4 genecration(a) (4 pts) You decide to conduct an experiment similar to the one Meselson and Stahl used to elucidate the details of DNA replication. You grow the bacteria in medium containing "N (heavy), and then switch it to medium containing N (light). Upon centrifuging in a cesium chloride gradient to separate the DNA of densty varying densities, draw what you would expect after 1 round of replication in the control situation (regular bacteria) and with the mutant. Explain your reasoning Use the drawing of what generation 0 would look ike (before replication) as a guide: (b) (4 pts) Below is a small segment of Rrin enonding normal DNA Pol Ill and the corresponding primary protein structure. Using the genetic code n-t on p. 5 as a guide, give an example of how a single base change could result in a nonfunctional pruin, d show how it would change the protein sequence Indicate what kind of mutation you made, snd sxplain. 5... GAU UAU UCU AUG AUU...-3 Asp Tyr Ser Met lle (c) (4 pts) If DNA ligase was nonfunctional instead of DNA Pol how would that affect the process of replication in these bacteria? Explain in detailExplanation / Answer
17. With regular bacteria
At 0 hours
15N ---------
15N ---------
After 1 cycle we molecules of hybrid DNA as follows
15N ---------
14N ---------
15N ---------
14N ---------
mutant bacteria
At 0 hours
15N ---------
15N ---------
After one cycle, the result would remain the same as the mutant DNA polymerase wont be able to replicate the DNA.
And the DNA at both 0 hours and after 1 generation in N-14 medium would remain the same as follows:
15N ---------
15N ---------
b) Stop codons arecoded by three codons UAA, UAG and UGA. A point mutation in the tyrosine codon (UAU) can lead to a stop codon (UAG). The protein will be truncated and thus will be non functional.
After mutation the RNA and protein will be as follows
GAU UAG UCU AUG AUU
Asp STOP CODON (after a stop codon has been read the ribosomes stop the translation of the mRNA)
c) In DNA replication, DNA ligase plays a major role in ligating (joining) the okazaki fragments of the lagging strand replication. If ligase is mutated and non functional then these fragment wont get ligated into a single strand and the replicated DNA will have single stranded breaks which leads to unstability and further damage to the genome.
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