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BU5.4 DNA (Gene) Mutations
- 2. What are mutations? • Mutations are changes in the nucleotide sequence of DNA othey usually happen during DNA replication oin somatic (body) cells, mutations may affect the individual oin gametes (sex cells), mutations can be passed down and may affect an individual’s offspring • Mutations occur all the time!
- 3. What causes mutations? • Mutations occur all the time! • There are two ways in which DNA can become mutated: oMutations can be inherited from parent to child oMutations can be acquired via •random DNA replication errors •environmental damage
- 4. Are mutations helpful or harmful? • Many mutations are repaired by enzymes • Almost all mutations are neutral (have no effect) • Mutations can be bad, leading to cancer, aging, birth defects, and self-aborted embryos • Mutations can be good, leading to an increased chance of survival for the individual
- 5. Types of Mutations • Chromosomal Mutations oInvolve changes in the number or structure of chromosomes, therefore often affecting more than one gene. These mutations can change the location of genes on chromosomes and can even change the number of copies of some genes. WE WILL NOT DISCUSS THESE MUTATIONS IN CLASS AT THIS TIME. • Gene Mutations oInvolve mutations in base pairs of the DNA
- 6. Types of Mutations • Point Mutations oGene mutation that involves the change of one nitrogen base in DNA oCaused by substitution of one base pair for another in the sequence oCan be further classified as missense, nonsense, and silent based on how the “mutated” protein behaves
- 7. Missense Mutation Missense (substitution) mutation GGTCACCTCACGCCA ↓ CCAGUGGAGUGCGGU ↓ Pro-Val-Glu-Cys-Gly Often referred to as substitution. The base pair change results in a different amino acid; this may or may not affect the protein that results (ex. sickle cell) Normal gene GGTCTCCTCACGCCA ↓ CCAGAGGAGUGCGGU Codons ↓ Pro-Glu-Glu-Cys-Gly Amino acids
- 8. Nonsense Mutation Normal gene GGTCTCCTCACGCCA ↓ CCAGAGGAGUGCGGU Codons ↓ Pro-Glu-Glu-Cys-Gly Amino acids Nonsense mutation GGTCTCCTCACTCCA ↓ CCAGAAGAGUGAGGU ↓ Pro-Glu-Glu-STOP The base pair change results in a premature stop codon; protein is nonfunctional (ex. cystic fibrosis)
- 9. Silent Mutation Normal gene GGTCTCCTCACGCCA ↓ CCAGAGGAGUGCGGU Codons ↓ Pro-Glu-Glu-Cys-Gly Amino acids Silent mutation GGTCTTCTCACGCCA ↓ CCAGAAGAGUGCGGU ↓ Pro-Glu-Glu-Cys-Gly The base pair change results in the same amino acid; this results in no change in the protein.
- 10. Types of Mutations • Frameshift Mutations oResult from the addition or deletion of a nitrogen base. oThis type of mutation changes the “reading frame”. oBy shifting the reading frame”, frameshift mutations can change every amino acid that follows the point of the mutation. oThis mutation results in a completely different protein than intended. oThis mutation can alter a protein so much that it is unable to perform its normal functions.
- 11. Insertion (Addition) Normal gene GGTCTCCTCACGCCA ↓ CCAGAGGAGUGCGGU Codons ↓ Pro-Glu-Glu-Cys-Gly Amino acids Insertion mutation GGTGCTCCTCACGCCA ↓ CCACGAGGAGUGCGGU ↓ Pro-Arg-Gly-Val-Arg An extra base is added, causing a frameshift mutation (ex. Huntington’s disease)
- 12. Deletion Normal gene GGTCTCCTCACGCCA ↓ CCAGAGGAGUGCGGU Codons ↓ Pro-Glu-Glu-Cys-Gly Amino acids Deletion mutation GGTC/CCTCACGCCA ↓ CCAGGGAGUGCGGU ↓ Pro-Gly-Ser-Ala-Val A base is lost/deleted, causing a frameshift mutation (Ex. DiGeorge syndrome).
- 14. Is mutation a mechanism for evolution? • If no changes to genomes occur over time, there would be no evolution oToo much change in the DNA is harmful oToo little does nothing oA balance exists between the amount of new variation and the overall health (adaptiveness) of the new variant individual • Differences between closely related organisms show closely matched DNA sequences that diverged at some past time and that was adaptive for a given environment
Editor's Notes
- How did Cyclops from the X-Men get his superpowers? He was born with the mutation How did the Hulk and Spiderman get their superpowers? The Hulk was exposed to gamma radiation and Spiderman was bitten by a radioactive spider While the superpowers and abilities may be fictional, it is true that mutations can have significant impacts on people and evidence exists that radiation exposure can lead to an increased rate of mutations. First, let’s discuss the different types of mutations, then where or how they can occur. We will also talk about some environmental factors that can influence the rate of mutations, and finish by looking at some possible effects of mutations.
- Epidermodysplasia verruciformis – makes you grow warts that resemble trees.
- Changes in the third base of a codon often have no effect. With sickle cell disease, an inherited group of disorders, red blood cells contort into a sickle shape. The cells die early, leaving a shortage of healthy red blood cells (sickle cell anemia), and can block blood flow causing pain (sickle cell crisis). Infections, pain, and fatigue are symptoms of sickle cell disease. Treatments include medications, blood transfusions, and rarely a bone-marrow transplant.
- Cystic fibrosis affects the cells that produce mucus, sweat, and digestive juices. It causes these fluids to become thick and sticky. They then plug up tubes, ducts, and passageways. Symptoms vary and can include cough, repeated lung infections, inability to gain weight, and fatty stools. Treatments may ease symptoms and reduce complications. Newborn screening helps with early diagnosis.
- Huntington’s is an inherited condition in which nerve cells in the brain break down over time. It typically starts in a person's 30s or 40s. Usually, Huntington's disease results in progressive movement, thinking (cognitive), and psychiatric symptoms. No cure exists, but drugs, physical therapy, and talk therapy can help manage some symptoms.
- DiGeorge syndrome is a chromosomal disorder that results in poor development of several body systems. Its features vary widely, even among members of the same family. The syndrome can cause heart defects, poor immune system function, a cleft palate, and low levels of calcium in the blood. There's no cure, but treatments can usually address critical health concerns.