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AP Biology

AP Biology. We’ll go over tests from before break Go through study guide (get some hints) Begin chapter 18. Purpose of this chapter…. Cells are efficient because they conserve energy for processes that MUST be done.

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AP Biology

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  1. AP Biology We’ll go over tests from before break Go through study guide (get some hints) Begin chapter 18

  2. Purpose of this chapter… Cells are efficient because they conserve energy for processes that MUST be done. Cells have the ability to turn on or off genes depending on the proteins that are present or absent within the cell. We will learn how cells turn on or off genes to maintain cellular efficiency.

  3. Chapter 18- Gene Regulation • Bacteria respond to environmental change by regulating transcription. • Most of what we know about gene regulation is from bacteria. • We will be looking at E. coli bacteria • E. coli lives in the human intestinal tract

  4. Regulation of gene expression Vocabulary Tryptophan- amino acid needed for survival (bacteria) Feedback- allows cell to adjust the amount of tryptophan made based on availability of the amino acid Operon- the mechanism that controls gene expression

  5. Regulation of Gene Expression Vocabulary Continued: 4. Regulatory Gene- on DNA that regulates a gene further away 5. Promoter- A specific nucleotide sequence in DNA that binds to RNA polymerase- positioning it so it may begin transcribing mRNA 6. Operator- the on and off switch of DNA 7. Repressor- the mechanics of how the operon may be turned off (blocks attachment of RNA polymerase to promoter)

  6. Types of Gene Regulation • Negative Gene Regulation (shut off by an active repressor) • Repressible Operon • Inducible Operon • Positive Gene Regulation (turned on by an active repressor)

  7. Trp Operon

  8. Trp Operon

  9. Trp Operon

  10. Trp Operon • Trp operon is a repressible operon • Its transcription can be inhibited (repressed) when tryptophan is available • Trp binds allosterically to a regulatory protein

  11. Lac Operon • Lac operon is an inducible operon • It is usually shut off • But it can be stimulated (induced) when lactose (lac) is present

  12. Lac Operon

  13. Lac Operon

  14. Positive Gene Control Example is the lac operon (lac operon can be both positive and negative) Here’s why… E. coli prefers glucose to lactose so it will preferentially breakdown glucose rather than lactose (turning lac off) inducible However if glucose is NOT available there must be a gene that transcribes lac enzymes The absence of glucose increases the amount of cAMP in the cell (positive)

  15. Positive- Lac operon

  16. Positive- Lac operon

  17. AP Biology Review try and lac operons Finish chapter 18, begin chapter 19 today Test is February 1st

  18. Eukaryotic Regulation All organisms must regulate genes. Unicellular and multicellular organisms must continually turn genes on and off in response to external and internal cues. Human cells generally express 20% of its genes at a time Different cell types are different not in DNA but because of differential gene expression

  19. Signal NUCLEUS Chromatin Chromatin modification:DNA unpacking involvinghistone acetylation andDNA demethylation Stages in gene expression that can be regulated in eukaryotic cells DNA Gene availablefor transcription Figure 18.6 Gene Transcription Exon RNA Primary transcript Intron RNA processing Tail mRNA in nucleus Cap Transport to cytoplasm CYTOPLASM mRNA in cytoplasm Translation Degradationof mRNA Polypeptide Protein processing, suchas cleavage and chemical modification Active protein Degradationof protein Transport to cellulardestination Cellular function (suchas enzymatic activity,structural support)

  20. Regulation of Eukaryotic cells Regulation of chromatin structure Regulation of transcription initiation Mechanisms of post-transcriptional regulation

  21. Chromatin structure Histone Modifications- when structures around chromatin are changed a decrease in Transcription of gene occurs DNA methylation- long stretches of inactivated DNA

  22. Transcription Factors • Enhancers- Segment of DNA containing multiple control elements, located far from where the promoter is • These allow DNA to bend which brings the enhancers closer to transcription factors • DNA folds over top of itself

  23. Promoter Activators Gene DNA Distal controlelement TATA box Enhancer Figure 18.10-1

  24. Promoter Activators Gene DNA Distal controlelement TATA box Enhancer Generaltranscriptionfactors Figure 18.10-2 DNA-bendingprotein Group of mediator proteins

  25. Promoter Activators Gene DNA Distal controlelement TATA box Enhancer Generaltranscriptionfactors Figure 18.10-3 DNA-bendingprotein Group of mediator proteins RNApolymerase II RNApolymerase II Transcriptioninitiation complex RNA synthesis

  26. Post Transcriptional Regulation Alternative RNA splicing- some segments of the mRNA strand are treated as introns . (Regulatory strands control which genes are read as introns or exons) As a result alternative mRNA is actually synthesized. mRNA degradation- doesn’t last long weeks at most Initiation of translation- Some are prevented from attaching to a ribosome for translation

  27. Signal NUCLEUS Chromatin Chromatin modification:DNA unpacking involvinghistone acetylation andDNA demethylation Stages in gene expression that can be regulated in eukaryotic cells DNA Gene availablefor transcription Figure 18.6 Gene Transcription Exon RNA Primary transcript Intron RNA processing Tail mRNA in nucleus Cap Transport to cytoplasm CYTOPLASM mRNA in cytoplasm Translation Degradationof mRNA Polypeptide Protein processing, suchas cleavage and chemical modification Active protein Degradationof protein Transport to cellulardestination Cellular function (suchas enzymatic activity,structural support)

  28. AP Biology YAY the projector is working!  Finish chapter 19 today

  29. Chapter 19- Viruses • Virus- very simple, very small. • Lack metabolic machinery • An infectious particle consisting of a few genes packaged in a protein coat Are viruses living or non-living? Discussion-

  30. Discovery of Viruses Tobacco disease stunts growth of tobacco plants and gives leaves a mosaic coloration

  31. Viral Structure Membrane envelope Infect respiratory tract Rod shaped

  32. Viral Genomes • Many viruses differ in the type of genetic material they carry • Double-stranded DNA • Single-stranded DNA • Double-stranded RNA • Single-stranded RNA

  33. Capsids and Envelopes • Capsid- protein shell enclosing the viral genome • Depending on virus can be rod, polyhedral, or more complex • Viral envelope- membranes of host cell studded with glycoprotein spikes • Influenza have this membrane envelope which encloses the capsid

  34. Viral Replication • Lytic cycle- • Attachment of virus to host cell • Virus drops off genetic material • Genetic material goes into nucleus • Genetic material is replicated • Transcription occurs • Translation makes proteins • Lyse= break= as protein leave it lyses the cell (programmed cell death)

  35. Virulent phage- a virus that only replicates by a lytic cycle • Why is there still bacteria? • Natural selection favors bacterial mutants with receptor sites that are no longer recognized by the phage type • Bacteria produce restriction enzymes that recognize and cut up foreign DNA including phage DNA. This prevents phage to infect the cell

  36. Lysogenic cycle Lysogenic cycle- allows replication of the phage genome without destroying the host Temperate phage- use both lytic and lysogenic cycles Prophage- when DNA from phage is integrated into the host. Host lives silently within the bacterium

  37. Lysogenic Cycle Lysogenic cycle- the phage replicates without destroying the host cell Temperate phage- use both lytic and lysogenic cycles

  38. Lysogenic Cycle The λ phage is temperate λ binds to the surface of the cell and injects it with DNA Next step depends on lytic or lysogenic cycle Lysogenic= the λ DNA is incorporated into a specific site on the bacteria (E. coli) virus replicates without killing the host Lytic = viral genes turn the host cell into a λ producing factory lysing the host cell and infecting more cells.

  39. Animal virus diversity • Important variations - • The type of nucleic acid that serves as virus’ genetic material • Viruses equipped with an outer envelope use it to enter host cell • Viral envelope is derived from the host’s plasma membrane, although viral genes specify some of the molecules in the membrane

  40. Retroviruses • Retrovirus- have the most complicated cycles • Reverse transcriptase – enzyme that transcribes DNA from an RNA template provides RNA---- DNA flow • Human immunodeficiency virus- HIV – the virus that causes AIDS (acquired immunodeficiency syndrome) • Contain 2 single RNA strands, 2 reverse transcriptase • After HIV enters the host cell transcriptase is released in cytoplasm and it catalyzes the synthesis of DNA • The new DNA inserts itself into the DNA as a provirus (permanent)

  41. Evolution of Virus • Viruses have been found to infect every life form (bacteria, animals, plants, fungi, algae and protists) • Because virus depends on cells for their own propagation it is likely that they evolved after the first cell appeared. • Candidates- • Plasmids – circular DNA that are separate from chromosomes, independent from rest of the cell (can be transferred from 1 cell to another) • Transposons- DNA segments that can move from 1 location to another in a cells genome

  42. Vaccine- harmless variants or derivatives of pathogenic microbes, that stimulate the immune system to mount defenses against the actual pathogen.

  43. AP Biology REVIEW of chapter 18, 19 today- group work. Begin chapter 20 Monday we’ll review essay writing a bit, look at great essays vs not great essays. Essay next Wednesday

  44. AP Biology New seats??? Change to schedule!!! Chapter 18-20 test January 24!!! This Thursday!!! All labs will take place Jan 28-Feb 1

  45. Biotechnology Recombinant DNA- DNA segments from 2 different sources Biotechnology- the direct manipulation of organisms and their components to make useful products Genetic engineering- the direct manipulation of organisms and their genes for practical purposes

  46. Plasmids Plasmid- small circular DNA molecules with a small number of genes that replicated independently of a chromosome Basic cloning technique begins with insertion of a foreign gene into a bacterial plasmid to produce a recombinant DNA molecule Resulting cell is a recombinant bacterium Gene cloning- the production of multiple copies of a single gene

  47. Restriction enzymes • Restriction enzymes- enzymes that cut DNA molecules at specific locations • In nature bacteria use restriction enzymes to cut DNA molecules for protection • Restriction site- a specific site where DNA will be cut • Restriction fragments- small cuts of DNA • Sticky ends- the end of the cut plasmid • DNA ligase- glues and fuses DNA back together

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