2.12 Mutations

Question 1

What are mutations?

Answer 1

changes to the base sequence of DNA

Question 2

What are the types of errors that happen during DNA replication that cause mutations?

Answer 2

• substitution: a base is substituted with another (e.g. ATGCCT becomes ATTCCT)
• deletion: a base is deleted (e.g. ATGCCT becomes ATCCT)
• insertion: an extra base is added (e.g. ATGCCT becomes ATGACCT)
• duplication: one or more bases are repeated (e.g. ATGCCT becomes ATGGCCT)
• inversion: a sequence of bases is reversed (e.g. ATGCCT becomes ATGTCC)

Question 3

What could go wrong with protein synthesis?

Answer 3

• mistakes in transcription can produce mistakes in the mRNA. this means the sequence of amino acids in the polypeptide chain produced will be wrong. however this will only affect the protein produced on this one occasion
• mutations that occur in DNA are responsible for genetic conditions, as the wrong sequence of amino acids in the polypeptide chain will always be produced. this can be inherited

Question 4

How do mutations in DNA affect protein synthesis?

Answer 4

• the order of DNA bases determines the order of amino acids in a particular protein
• if a mutation occurs, the order of DNA bases changes, causing a change in the sequence of amino acids in the polypeptide chain
• this means that the primary structure of the protein is altered
• because the primary structure determines what types of bonds form and where bonds form, the final 3D structure of the protein could change if the primary structure is altered
• this may impair the function of the protein

Question 5

When can mutations happen?

Answer 5

• during DNA replication for mitosis
• during DNA replication for meiosis - this will change the DNA in the eggs/sperm and so will be passed on to future generations

Question 6

Do all mutations have an effect?

Answer 6

• no, large amounts of DNA have no role in protein synthesis
• no, sometimes the sequence of DNA bases changes, but the same amino acid is produced, because there can be more than one base triplet that codes for one amino acid

Question 7

How can mutations affect cell function?

Answer 7

1. there is a change in the base sequence of DNA
2. there is a change in base sequence in mRNA
3. changed/different tRNA binds to mRNA during translation
4. so a different amino acid is brought and added to the polypeptide chain
5. this changes the type and position of bonds between R groups, as the primary structure of the protein has chained
6. this will change the 3D shape of the protein
7. so the protein’s function is altered, which may alter cellular function

Question 8

What is cystic fibrosis? What causes CF?

Answer 8

• a genetic disorder where mucus is abnormally thick and sticky
• caused by a mutation in the CFTR (cystic fibrosis transmembrane regulator) gene on chromosome 7

Question 9

Can genetic disorders be caused by numerous different mutations? Give an example:

Answer 9

• yes
• e.g. over 1000 possible mutations are known to cause CF

Question 10

What the most common mutation that causes cystic fibrosis?

Answer 10

• DF508 - the deletion of three nucleotides
• this causes the loss of the amino acid phenylalanine (the 508th AA) which causes misfolding of the CFTR protein