Molecular Level Of Genetics: MDNA, Replication, RNA and Protein Synthesis?

Question

In DNA replication there are many opportunities for mistakes to occur. The DNA polymerase enzyme acts to duplicate genetic information and to insure correct genetic information is passed.

During duplication the polymerase enzyme acts to "proofread" the replication. Suppose a nucleotide molecule was added during the replication of a gene. The error would affect the polypeptide coded for by that gene.

a) how would the error in replication affect polypeptide?
b) What might be an agent or source of the error?
c) Should the mistake in replication occur what prevents the mistake from achieving duplication in the final genetic informtion when the cell divides?
d) If the mistake is not prevented in DNA replica the error results in mutation of the genetic information. Darwin would explain the mutation in terms of natural selection. What are 2 statements Darwin would make to explain the mutation.

Any input anyone has on this question would help me. Thanks!

Answer 1

a) An insertion mutation (adding a single nucleotide into the sequence) will likely have devastating effects on the protein. Proteins are made using three nucleotide base triplets, called codons, as signals for which amino acid to add to the chain next. So an mRNA sequence that reads like AAGUCGCAU is really AAG UCG CAU, coding for three specific amino acids. If you add in a new nucleotide (N) it will throw all subsequent triplets off, which means the genome will be read in an entirely different way-- The previous code now becomes AAN GUC GCA AU_ with the N being the new nucleotide. Insertions and deletions are particularly bad because they change every amino acid after the mutation in the protein, which usually causes the protein to be completely wrong and not work correctly.

b) A mutation can and does occur randomly by chance or by a mutagen. Mutagens are things that cause mutations in DNA -- Like Ultraviolet light (how people can get skin cancer from being in the sun too much), certain chemicals and even pathogens like viruses.

c) Cells have other mechanisms besides the proofreading capability of DNA polymerase. Certain proteins can recognize mutations and repair them, one example is the p53 protein which is called the guardian angel of the human genome because of its ability to repair mutations.

d) Well, if the mutation created a protein that did not help the cell or the organism (gave it an early onset, lethal disease) natural selection would put "pressure" on the cell to create fewer progeny either by dying earlier than other healthy cells or growing and dividing slower. If the mutation gave the cell or organism an advantage then natural selection would also put selective "pressure" on it to allow for the creation of more daughter cells than normal, or wild type, cells. By creating more daughter cells or children a cell or organism will increase the amount of that gene in a population (and vise versa for a harmful mutation) and thats how you get evolution. In this cause of an insertion, the protein would probably not function at all (although it may function, but will probably be toxic to the cell anyway), and depending on how vital the protein was to the cell or organism may cause it to die early.

Answer 2

Interesting question... I don't remember all of this, but here's what I do know.

a) Frame shift: the codons will all be "read" incorrectly, as the triplet of nucleotides will all be off by one, and the polypeptide will probably have differnet aminos.

b) Carcinogens is one possibility.

c) I have no idea, share if you do find out!

d) Keep in mind that darwin didn't know about genes, so he could only talk about the mutation if it were expressed. I'm not exactly sure how darwin would explain mutation, but he might talk about whether the mutation were neutral or if it caused a selective pressure.

Answer 3

Do your own homework.