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Unit 7

Unit 7 . Gene Expression and Mistakes. 1 Genetic Expression. Involves putting genetic information into action to make proteins for living cells Simply put: genes code for proteins

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Unit 7

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  1. Unit 7 Gene Expression and Mistakes

  2. 1 Genetic Expression • Involves putting genetic information into action to make proteins for living cells • Simply put: genes code for proteins • Proteins are tools specifically designed to build (structural) or operate (functional) components of living things • The central dogma is that information is passed from DNA to RNA to protein to trait, and all organisms do this (exception?)

  3. 2 Mutations • Heritable changes in genetic information • Will be passed on to every cell that develops from the original one • Most important in sex cells • Often caused by mistakes made during DNA replication - Occur roughly once in every 10 million bases • Can also be caused by mutagens

  4. 3 mutagens • chemical (pesticides, smoke) or physical (x-rays, UV radiation) agents in the environment • Can change DNA base sequence permanently • Can interfere with base-pairing during DNA replication • Can weaken the DNA strands, causing breaks and inversions

  5. 4 Point Mutations • Gene mutations that involve changes in one or a few nucleotides • Occur at a single point • Generally occur during DNA replication • There are three types: substitutions, insertions, and deletions (genetic information is lost)

  6. 5 Substitutions • One base is changed to a different base • Sometimes this has no effect (ex. CCC and CCA still code for proline) • Sometimes results in changing an amino acid (ex. CCA to ACC changes from proline to threonine)

  7. 6 Insertions and Deletions • Where one base is inserted or removed from the DNA sequence • Remember that DNA is read three bases at a time, so inserting or deleting will causing those groupings to shift in every codon after that mutation • Called frame shift mutations because they shift the reading frame of the genetic message • Usually change every amino acid after the mutation, altering a protein so much that it is not able to perform its normal functions

  8. 7 Chromosomal mutations • Sometimes the mutation is a whole region on the chromosome • Can have deletion, duplication, inversion (oriented in reverse direction), and translocation (involves 2 chromosomes)

  9. 8 Effects • MOST havelittle to no effect on the expression of genes • Some produce genetic variations, which could be good or bad • Some negatively disrupt gene function • The amount of change is what determines whether the effect will be good or bad • Mutations can also be a source of genetic variation, the base upon which organisms evolve

  10. 9 harmful • When the structure of the protein has changed dramatically • Can also make an organism less adapted to its environment • Some cancers • Sickle cell anemia – point mutation in one of the polypeptides, changes it shape so that it cannot carry oxygen

  11. 10 Beneficial • Often produce proteins with new or altered functions that can be useful to organisms in different or changing habitats • For example: mutations in insects that help them resist pesticides; mutations in bacteria to resist antibiotics • In humans, mutations that have increased bone density and strength and that increase resistance to HIV

  12. 11 Evolution • Genetic variety is essential to evolution • Mutations sometimes create better proteins that in some way allow the organism to be better adapted to its environment • This is how new traits are introduced into a population • Has to be a mutation in the sex cells in order for it to be passed on

  13. 12 Polyploidy • When chromosomes fail to separate in meiosis, resulting in gametes that are 3N or 4N (extra sets of chromosomes) • Common in plants (about 1/3 of flowering plants) • In plants, creates larger and often stronger plants • Ex. Bananas, limes

  14. 13 Polyploidy in Animals • 1-2% of human fetuses are polyploidy but never make it to birth. • Essentially never seen in animals • Does in occur in some insects • Trisomy disorders are more common for animals, where you get an extra copy of only one chromosome, not a whole set, but most of these do not make it to birth except for 13, 18 and 21.

  15. What might be the effect of a mutation in the promoter sequence of a gene? Polymerase would not be able to bind.

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