Questions and Answers
What is the consequence of a mutation that alters one of the splice site signals?
The intron is not removed and remains as part of the final mRNA molecule.
What type of mutation can cause a 'frameshift' in the translation of a gene?
Insertion or deletion of one or two base pairs
What is the effect of a deletion mutation involving one or more nucleotides from a DNA sequence?
It causes a 'frameshift' and produces a non-functional protein.
What is the result of an insertion of three nucleotides or multiples of three into a DNA sequence?
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What is the characteristics of the Fragile-X Syndrome?
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What is the consequence of a mutation that alters the splice site signal at the 5' end of an intron?
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What type of mutation can cause a 'frameshift' and produce a non-functional protein?
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What is the result of an insertion of many copies of the same triplet of nucleotides into a DNA sequence?
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What is the effect of a deletion mutation involving one nucleotide from a DNA sequence?
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What is the consequence of a mutation that alters the splice site signal at the 3' end of an intron?
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Study Notes
Types of Mutations
- Point mutations (single-base substitutions) occur when a single base is replaced by another
- Transitions occur when a purine (A or G) or pyrimidine (C or T) is replaced by the other
- Transversions occur when a purine is replaced by a pyrimidine or vice-versa
Missense Mutations
- New nucleotide changes the codon, producing an altered amino acid in the protein product
- Example: Sickle-cell disease, caused by a mutation at the 17th nucleotide of the beta hemoglobin gene, replacing A with T, changing the codon GAG to GTG, and altering the 6th amino acid in the protein chain from glutamic acid to valine
Nonsense Mutations
- New nucleotide changes a codon that encodes one of the STOP codons (TAA, TAG, or TGA), resulting in premature translation termination and production of a truncated defective protein
- Example: Cystic fibrosis, caused by a mutation converting a glutamine codon (CAG) to a STOP codon (TAG), resulting in a truncated protein with only 493 amino acids instead of the normal 1480
Splice-Site Mutations
- Occur during pre-mRNA processing, affecting the removal of intron sequences, and can lead to altered protein production
- If a mutation alters one of the splice site signals, the intron is not removed, and the final mRNA molecule contains an altered protein product
Large Scale Changes
- Insertions and deletions involve adding or removing base pairs from a DNA sequence, which can cause frameshift and produce non-functional proteins
- Examples: Deletion of one or more nucleotides from a DNA sequence, which can cause frameshift, producing a non-functional protein
- Insertions and deletions of three nucleotides or multiples of three may be less serious, preserving the reading frame, but can still cause inherited human disorders
Environmental Factors
- Induced mutations caused by environmental factors such as:
- Ultraviolet radiation from the sun
- Ionizing radiation, including x-rays
- Thermal disruption, hydrolysis
- Toxins, such as aflatoxin
- Cancer chemotherapy and radiotherapy
- Viruses
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