mol. bio. chapter 35 =>Mutations.

Question 1

What causes mutations?

Answer 1

• May be due to a change in base sequence in DNA when replicated or mRNA transcribed.
• Wrong repair

Question 2

how frequent are these mutations occuring?

Answer 2

1 in every 10’6 cell divisions.

Question 3

What is a Point mutation?

Answer 3

occurs when there is a base change in the template/noncoding strand.
Single base change, may be:
-Transition: when a given pyramidine base is changed into another pyramidine or a purine into another purine.
-Transversion: When a Purine changes into TWO pyramidines or a pyramidine changes into either of the two purines.

Question 4

What is a silent mutation

Answer 4

It is the most common outcome of the mutation results when a change has occurred at the third nucleotide of the 3 letter codon sequence.
(When the mutaion still codes for the same)
=> Due to wobble effect since the codon is the least sensitive to changes, thus may code for the same AA as well and no change in translation will have occurred.

Question 5

What is a Missence mutation?

Answer 5

When the change of a single base causes the reading of the codon of a different amino acid than which was intended.
The wrong amino acid will have been incorporated into the amino acid and three possible outcomes of this exist:

• Acceptable missence mutation.
• Partially acceptable missence mutation.
• Unacceptable missence mutation.

Question 6

What is an acceptable missence mutaion:

Answer 6

When the wrong change in the base causes the reading of another AA but doesnt effect the function of the Protein.
Eg. Folding wasnt effected by it due to similar properties of the amino acids that were exchanged.

Question 7

What is a Partially acceptable missence mutaion?

Answer 7

When the change in base which caused the wrong amino acid to be incorporated results in an abnormal but somewhat functioning protein.

Question 8

What is an unacceptable missence mutation?

Answer 8

When the change of base which caused an exchange in AA incorporated effects the protein so that it wont be functional at all.

Question 9

Define Nonsence mutation.

Answer 9

When the change of a base results in the coding for a STOP codon (prematurely)
This ends the protein synthesis and the most likely outcome is a protein that doesn’t function at all.

Question 10

What is a frameshift mutation?

Answer 10

Not substitution, but insertion or deletion.
Deletion is when a base is missing
Insertion has occurred when a base has been added.

Since there isnt any punction in the reading of the codons in translation where will be no realization by the translation machinery about the missing/added nucleotide and all codons read after the mutation site will be coding for a different AA. (however some may code for the same bcs only letter per code will have been changed)

• Two outcomes:
• May result in an instant stop codon =>possibility of a protein that is still intact.
• May miss a stop codon and keep synthesizing untill next codon.may synthesize a protein that is much larger then intended and will fold completely differently.