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BF - MM3
Human Mutation and Their Functional Effects
| Question | Answer |
|---|---|
| Is the dystrophin gene large/ small? | Largest gene known |
| What % of the gene is comprised of introns? | 99% |
| What are two diseases that result from mutations in the dystrophin gene? | 1. Duchenne Muscular Dystrophy (DMD) 2. Becker Muscular Dystrophy (BMD) |
| What is the nature of the vast majority of mutations in DMD and BMD? | Deletions of one or more whole exons |
| If whole exon deletion occurs in both DMD and BMD, what happens to cause differences in severity? | 1. DMD = frameshift (deletion of non-multiple of 3 bases exon) 2. BMD = non-frameshift (Deletion of exon with multiple of 3 bases). |
| What happens to dystrophin protien in DMD in a) 85% of cases? b)15% of cases? | a) Protein unrecognizable as dystrophin b) No protein due to premature stop codon |
| What happens to dystrophin protein in BMD? | Truncated (shorter) dystrophin but semi-functional |
| For the requirements of translation. The stop codon must be: 1. On last... 2. Upstream of last... 3. Within... | 1. On last exon 2. Upstream of last EJC 3. Within 50-55 nucleotide bases from last EJC |
| What is dystrophin? | Cytoplasmic protein in muscle |
| What is the function of dystrophin? | Anchors muscle cytoskeleton to extracellular matrix |
| Binding: ? <--> dystrophin <--> ? | Glycoprotein, F-actin cytoskeleton |
| How are deletions in the dystrophin gene screened for? | Analysis of PCR products in gel electrophoresis (look for missing exons) |
| What does osteogenesis imperfecta lead to (changes to bones)? (2) | Increased none fragility and decreased bone mass |
| OI - Which two types are most common? | Type I and IV |
| OI - What kind of inheritance pattern in seen in OI? | Autosomal dominant |
| OI - What can be said about the origins of types II and III? | Can also be sporadic |
| OI - What gene are point mutations in 90% of all cases seen in? | ColA1/2 |
| OI - What type of collagen does ColA1/2 code for? | Type 1 collegen |
| OI - How can the structure of collagen be briefly described? | Triple helix |
| OI - In type I collagen, what does the ColA1 gene code for? | The two alpha-1 chains |
| OI - In type I collagen, what does the ColA2 gene code for? | The one alpha-2 chain |
| OI - In type I collagen, what is found every 3rd residue that is needed fro correct intertwining of triple helix? | Glycine |
| OI - In type I collagen, what is one of the most common point mutations? | Glycine being substituted (often for valine) |
| OI - Cells with a glycine -> valine substitution in type 1 collagen produce...? | A mixture of normal/ abnormal collagen |
| OI - What 3 things does the severity of OI depend on? | Haplo-insufficiency of ColA1 gene, nature of point mutation, where mutation occurs in triple helix |
| OI - What could the two outcomes be of a point mutation in type 1 collagen? | Substituting an amino acid (e.g. glycine) or premature stop codon |
| MILD OI - Major/ minor mutation? | Major (premature stop codon) |
| MILD OI - What gene is damaged, if any? | One ColA1 gene is damaged/ mutated |
| MILD OI - What chains are produced as a result of the damaged ColA1 gene? | ONE alpha-1 chain and one alpha-2 chain |
| MILD OI - What is the % of normal/ damaged collagen? | 50% normal, 50% damaged |
| MODERATE OI - What type of mutation | Missense mutation |
| MODERATE OI - Result of mutation on alpha-1 and alpha-2 chains? | alpha-1 is mutated and alpha-2 is produced normally |
| MODERATE OI - What is the % of normal/ damaged collagen? | 25% normal, 75% damaged |
| MODERATE OI - The mutation is at the N-terminus of helix so...? | Only minimal disturbances in packing |
| SEVERE OI - What type of mutation | Missense mutation |
| SEVERE OI - Result of mutation on alpha-1 and alpha-2 chains? | alpha-1 is mutated and alpha-2 is produced normally |
| SEVERE OI - What is the % of normal/ damaged collagen? | 25% normal, 75% damaged |
| SEVERE OI - The mutation is at the C-terminus of helix so...? | Major disturbances in packaging |
| Trinucleotide repeats - What are they? | Simple sequence repeats that occur throughout the human genome and are normal and stable |
| Trinucleotide repeats - Give 3 examples of non-pathological TRs? | Micro-satellites, telomers, centromers |
| Trinucleotide repeats - When can a mutation be pathogenic? | When the mutation causes the number of repeats to lengthen to an unstable repeat number (e.g. trinucleotide repeat expansion diseases) |
| Trinucleotide repeats - Of the following repeats, which are non-coding disorders and which are coding disorder? a)CGG b)CAG c)GCC d)GAA e)CTG | a)N-C b)C c)N-C d)N-C e)N-C |
| Trinucleotide repeats - Usually coding expandable repeats are CAG (glutamine). What pathology is caused? (3) | Neuromuscular, neurodegenerative, mental retardation |
| Trinucleotide repeats - What gene is implicated in myotonic dystrophy | DMPK |
| Trinucleotide repeats - What kind of gene is DMPK? | Protein kinase gene |
| Trinucleotide repeats - What is myotonia? | Failure of muscle to relax after contraction |
| Trinucleotide repeats - What is dystrophy? | Muscle weakness |
| Trinucleotide repeats - In fragile x, how is the FMR gene silenced? | By methylation |
| Trinucleotide repeats - What happens in Kennedy disease? | Polyglutamate tracts accumulate in androgen receptor protien |
| Trinucleotide repeats - In Kennedy disease, what does loss of androgen receptors cause? (2) | Neurodegeneration and androgen insensitivity -> testicular feminisation |
| Trinucleotide repeats - What happens in huntingtons disease? | Polyglutamate tracts accumulate in Huntington protein |
| Trinucleotide repeats - Unlike normal Huntington protein, the mutated type aggregates where? | In the nucleus |
| Trinucleotide repeats - The mutation confers a gain of function as the mutated Huntington aggregates are what? | Cytotoxic |
| Trinucleotide repeats - 'Anticipation' The expansion grows through... leading to...? | Successive generations...increasingly severe presentation |
| Trinucleotide repeats - Do spontaneous triplet expansions happen? | Yes - but rare |
Created by:
benfenner1
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