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GENE EXPRESSION

GENE EXPRESSION. HOW DOES DNA KNOW WHEN TO MAKE A PROTEIN?. DNA and Individuality. Are all genes turned on in all cells?. The answer is NO!. Every body cell contains all DNA Cells “use” only genes specific for function EX. Red blood cells use only genes that make it carry oxygen

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GENE EXPRESSION

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  1. GENE EXPRESSION HOW DOES DNA KNOW WHEN TO MAKE A PROTEIN?

  2. DNA and Individuality Are all genes turned on in all cells?

  3. The answer is NO! • Every body cell contains all DNA • Cells “use” only genes specific for function • EX.Red blood cells use only genes that make it carry oxygen • Can you list more examples? • Skin cells only need proteins for structure and such • Nerve cells only need proteins that enable them to transmit impulses **THEREFORE, NOT ALL DNA IS EXPRESSED (MADE INTO PROTEIN) IN EVERY CELL!**

  4. MUTATIONS When DNA goes bad 

  5. IMPORTANT FACT! MUTATIONS MUST OCCUR IN SEX CELLS IN ORDER FOR THEM TO BE PASSED ON TO NEXT GENERATION!!!!!!!!!!

  6. I REPEAT……………… ONLY MUTATIONS THAT OCCUR IN EGG OR SPERM CELLS CAN BE PASSED ON TO OFFSPRING!! (Have you ever heard of a sperm fertilizing a skin cell to make a baby?? That is silly!)

  7. Chromosomal Mutations • Change in # of chromosomes or structure • EX: • NORMAL HUMAN BODY CELL = 46Let’s see this! • DOWN’S SYNDROME CELL = 47 Let’s see this!

  8. Gene Mutations • Change in actual DNA sequence • **Review** What does DNA ultimately code for? Proteins • Is construction of protein based on original DNA strand? Yes! (b/c it is what codes for mRNA)

  9. Gene Mutations con’t… • What would happen to protein made if DNA sequence was changed? • Wrong protein made • Wrong shape of protein • This would make protein unusable!

  10. Gene Mutations: Point Mutations • POINT MUTATION: • Base could be switched from one to another • EX: TCA on DNA makes mRNA AGU codes for Serine • If T changed to G, would be CGU which codes for • Arginine • Wrong AMINO ACID is coded for which means, wrong SHAPE or PROTEIN is made

  11. Gene Mutations: Frame-Shift 2. FRAME-SHIFT: • A base could be deleted or added • EX:TCATTT on DNA; • mRNA = AGUAAA codes for Serine +Lysine • If the T is deleted in the DNA, now is GUAAA • Ribosome will read GUA first which is for Valine • Similar if a base is added • WrongAMINO ACID is coded for = wrong PROTEIN made OR Translation will abruptly STOP

  12. Summary of Mutations • Must occur in sex cells to be passed on • Not all mutations are bad (depends on environment) • Ultimate source of variation within a species!!!!!! • Take humans for instance….do we all look the same????????? • Caused by: • Exposure to radiation (ex. UV Rays) • Exposure to certain chemicals (in cigarettes, emitted from factories)

  13. The Human Genome Human Chromosomes (46 in a normal human cell!) • Two types: • Normal chromosomes: 44 in each BODY CELL; 22 in each GAMETE (sex cell) • Sex chromosomes: 2 in each BODY CELL; 1 in each GAMETE (sex cell) • MALE: X and Y • FEMALE: X and X • Chances for having a boy or a girl?

  14. Chances for having a boy or girl? 50% OF COURSE…LET’S SEE! XY X X XX XY XY XX

  15. Environmental Expression Some genes are “turned on” under certain environmental conditions • EX. Himalayan Rabbit: Fur changes color due to TEMPERATURE change • WARM = White fur (no pigment produced) • COLD = Black fur Why does this make sense? • Because black absorbs the heat, helping little bunny rabbit to stay warm

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