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Gene Regulation

Gene Regulation. Remember! All of your cells contain the exact same DNA. Your nerve cells do not look like or act like skin cells, so do they use the same genes? NO!. Gene Regulation. Genes are to be turned on/off based on whether they will be used or not!

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Gene Regulation

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  1. Gene Regulation • Remember! All of your cells contain the exact same DNA. • Your nerve cells do not look like or act like skin cells, so do they use the same genes? NO!

  2. Gene Regulation • Genes are to be turned on/off based on whether they will be used or not! • When a gene is on, it is said to be expressed.

  3. Gene Expression & Regulation

  4. Basic Structure of a Gene • When looking at a gene sequence, there are several important regions that enzymes & other proteins recognize.

  5. Basic Structure of a Gene • Promoter: region of gene where RNA Polymerase binds • Start: transcription begins • Stop: transcription ends • Regulatory Sites: near the promoter where regulatory proteins bind (turn genes on/off)

  6. Prokaryotic Gene Regulation • Remember! Prokaryotes have a single chromosome & are unicellular. • Small amount of DNA (simple) • Turn genes on/off to be efficient • Operon: group of genes that operate together for a function (turned on/off together) • Inducible • Repressible

  7. Prokaryotic Operon

  8. The Promoter Sequence • DNA sequence where RNA Polymerase binds • Remember! RNA Polymerase will make mRNA during transcription.

  9. The Operator Sequence • DNA sequence where a repressor protein binds

  10. Repressor Proteins • Bind to the operator sequence & block transcription • When the repressor is bound, NO GENES ARE EXPRESSED!

  11. 2 Types of Operons • Inducible Operon: normally “off” but can be switched “on” • In the presence of a substance, the substance causes the repressor to let go. • Repressible Operon: normally “on” but can be switched “off” • In the presence of a substance, the substance causes the repressor to bind to the operator.

  12. The lac Operon • E. coli uses lactose (sugar) as a food source. • The lactose needs to be metabolized (broken down). • There are 3 genes in the lac operon that work together to metabolize the lactose. • The presence or absence of lactose determines whether the genes are turned on/off. • Why would the bacteria express genes to break down lactose if there is no lactose?

  13. The lac operon will be turned on when: • Lactose is present • Lactose is absent When lactose is present! There would be no point in expressing genes to break down lactose if there is no lactose.

  14. When lactose is absent… • The repressor is bound & blocks transcription of the lac operon.

  15. Add lactose…

  16. The lac operon: • Normally “on” • Normally “off” Normally “off” (the repressor is bound)!

  17. The lac operon: • Inducible • Repressible Inducible! The operon is turned “on” when lactose is present!

  18. The lac Operon

  19. Eukaryotic Gene Regulation • No operons, genes are regulated individually • Similar process, but is much more complex than prokaryotic gene regulation

  20. Eukaryotic Gene Regulation • There is a promoter, several enhancers, & a “TATA Box” • TATA: helps position RNA Polymerase • Enhancers can act like operators & block transcription, & others can signal to unpack chromatin

  21. Eukaryotic Gene Regulation • Exons are EXPRESSED. • Introns are cut out of the mRNA copy & not expressed.

  22. Fun Fact! • Over 98% of the human genome is considered “junk” DNA! • This DNA is not expressed & the function is unknown.

  23. Cell Differentiation • After fertilization & mitosis occurs, cells specialize into their life-long functions. • Differentiation is controlled by hox genes. • Some genes get turned off permanently (your liver cells do not express genes that make proteins in the skin). • Manipulation of these genes can alter what parts grow where (a leg out of your head?!).

  24. Humans carry the gene for a tail, but it’s usually turned off!

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