Chapter 12 Section 4 Gene Regulation and Mutations
- Slides: 20
Chapter 12 Section 4: Gene Regulation and Mutations MAIN IDEA: GENE EXPRESSION IS REGULATED BY THE CELL, AND MUTATIONS CAN AFFECT THIS EXPRESSION
Gene Regulation Cells have the ability to control which genes are transcribed and when they are transcribed Switching genes “on” and “off” Depending on cell, some genes are always off (skin cell vs. muscle cell)
Mutations Mutation – change in an organism’s DNA How? Naturally – mistakes in replication (RARE…why? ) DNA Damage – as a result of environmental factors
Sources of Mutations Spontaneous Physical – rare, naturally occurring – Radiation: UV, X-Ray, etc. Chemical – nicotine, asbestos, alkaloids, amines Biological – viruses (HPV, Epstein-Barr) Mutagen Effects death = substance which can cause mutations of mutations can range from no impact, to illness, to
Types of Mutations: Genes or Chromosomes? Gene Mutations Point Mutations Substitution Silent/Missense/Non sense Duplication Translocation Inversion Deletions/Insertions Cause Chromosomal Frameshifts Mutations
Point Mutations (Substitution) Substitute one nucleotide for another, resulting in a new codon 3 Outcomes: Silent Missense Nonsense
Point Mutation: Silent Two Results: Codon codes for the same amino acid Codon codes for an amino acid that does not affect the structure of the protein – NO CHANGE IN FUNCTION! We are unaware of these mutations Serine Point Mutation Serine • UCG • Changes G►A • UCA
Point Mutation: Missense Result: Base change causes a different codon, which codes for a different amino acid Change affects that area of protein and likely alters function Serine Point Mutation Threonine • UCG • Changes U►A • ACG
Sickle-Cell Anemia Missense Mutation Example A single nucleotide change causes a missense point mutation that results in abnormally folding proteins and deformed red blood cells.
Point Mutation: Nonsense Base change causes a stop codon, which terminates translation early This causes an incomplete protein to be produced; the resulting protein is non-functioning Serine Point Mutation STOP CODON • UCG • Changes C►A • UAG
Cystic Fibrosis Nonsense Mutation Example A single point mutation in the gene sequence causes a stop codon to be coded for in the middle of the m. RNA sequence. The effects of CF are catastrophic, including coughing, wheezing, excess mucus in lungs, risk of lung infection, and early death
Frameshift Mutations Disrupt normal codons by adding or removing bases, thus “shifting” the reading “frame” during translation Insertion – extra base added Deletion – removal of base These mutations cause all amino acids down the line to be incorrect or missing
Chromosomal Mutations Inversion – segments of chromosomes are inverted (flipped) Duplication Deletion – duplicated parts of chromosomes – missing parts of chromosomes Translocation parts – segments of chromosomes exchange
Body-Cell vs. Sex-Cell Mutations Body (somatic) cell mutations – occur in cells of body and are not passed on to children Skin, nerve, heart, kidney, etc. Sex (germ-line) cell mutations – occur in sex cells and may be passed down to children Sperm or egg
Polar Bears and Brown Bears Polar Bear Evolution
Teenage Mutant Ninja Turtles. . ? ?
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