explain the effect of point and frameshift gene mutations on a cell?

Answer 1

Simply put, the genetic code shows us that amino acids are coded for by TRIPLET codes in DNA. This means that if a nucleotide sequence is disrupted by a deletion for example, the "frameshift" will be changed.

Take this sequence for example
ACT GGC GGT CTG CCA AAT ACA

-now a point mutation of this sequence would change only ONE amino acid codon, note the G-->A substitution in the 3rd codon. Usually, 1 amino acid is not enough to affect a protein, but sometimes it is (sickle cell anemia for example is caused by a SINGLE BASE POINT mutation)
ACT GGC GAT CTG CCA AAT ACA

A frameshift mutation involved usually an insertion or a deletion of a nucleotide, take the same sequence as above, but notice in the 3rd codon, the G is deleted, and it changes EVERY codon thereafter:
ACT GGC GTC TGC CAA ATA CA_

So when the DNA sequence is taken out of the right "triplet frame", that is a frameshift mutation.

Frameshift mutations usually result in nonsense mutations, which are a result of a premature stop codon, or disruption of splice sites. Transcripts of premature stop codons and disrupted splice sites are degraded, and not translated.

Answer 2

A point mutation changes ONLY one base and in so doing changes JUST that "point" where the transition or trasnsversion occurs (transition changes from a purine to purine or pyrimidine to pyrimidine (a-g or c-t for example) - transitions are usually MUCH safer and do less overall damage than do transversions which change from a purine to a pyrimidine or a pyrimidine to a purine (a-t or t-g for example)).

Basically, since only 1 base pair is affected then you may no longer be able to produce that particular protien but the rest of the strand is still intact and unaffected as you travel down the line.

SO an example of a point mutation would be in the first position:

Original - agtagtag
Mutated - ggtagtag

A frame shift is much more deleterious, generlaly speaking. Frame shifts are caused by insertions or deletions of bases. Since the actual NUMBER of bases changes in the case of frame shift mutations this changes the "reading frame" for every base down the line, thus affecting the production of EVERY protein instead of just the one for which the affected area codes to produce.

see below (using numbers to better illustrate):

Original - 123123123123
mutated- 1223123123123

By just adding the second 2 in the beginning you can see that, while the orignal reading frames would have progressed in an orderly fashion and each codon would have read as 123 123 123 123 the codons will now be read as 122 312 312 312 3. This is RADICALLY different and thus NONE of the proteins that should have been encoded by this strand of DNA will be produced.

So you can see how much worse it is and why such mutations are generally extremely BAD.