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Cell Cycle

Cell Cycle. G1. S. G2. M. Prophase : Chromosomes condense into visible structures. Nuclear envelope breaks down. Interphase microtubules disassemble. Spindle forms. Prometaphase: Chromosomes make attachments to each pole and align on the spindle equator (metaphase plate).

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Cell Cycle

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  1. Cell Cycle G1 S G2 M

  2. Prophase: • Chromosomes condense into visible structures. • Nuclear envelope breaks down. • Interphase microtubules disassemble. • Spindle forms. • Prometaphase: • Chromosomes make attachments to each pole and align on the spindle equator (metaphase plate).

  3. Opposing forces & polym slowly move chromosomes to equator

  4. Metaphase: • Chromosomes are aligned on equator. • Within a chromosome, sister chromatids are attached to opposite poles via attachment of kinetochores to microtubules.

  5. N

  6. Microtubules attach to chromatids at kinetochores

  7. Centrioles and centrosomes duplicate during S & G2

  8. Anaphase: • A- Sister chromatids separate. • Sister chromatids (now independent chromosomes) move along kinetochore microtubules to the pole to which they are attached. • B- The poles move apart.

  9. Microtubules Forces at anaphase are exerted at kinetochores and overlap zone Minus end directed motors + - Plus end directed motor

  10. Telophase: • Spindle disassembles. • Chromosomes decondense. • Nucleus reforms (nuclear envelope reassembles). • Interphase microtubule array reforms.

  11. Nuclear envelope breakdown occurs thru’ fragmentation Lamin phosphor- ylation at prophase Lamin dephosph at ana- telophase

  12. Thermodynamics determines whether a reaction CAN go • The change in free NRG (DG) for a reaction determines whether or not it is spontaneous. • The units for DG are cal/mol. • If DG is negative - the reaction is spontaneous and considered thermodynamically favorable. • If DG is positive - the reaction is NOT spontaneous and considered thermodynamically UNfavorable. • The sign AND magnitude of DG matters! • The standard free energy change (DG’) is the free energy change figured under a set of specified conditions, called standard conditions. • Standard conditions: 25C, 1 atm, 1 M concentration for all reactants (except H20 which is at 55.6 M), pH 7 (‘).

  13. Enzymes are proteins designed to fit a specific substrate(s) Enzyme Substrates Enzyme/Sub- strate Complex Enzyme & Products

  14. Induced fit model for enzymes

  15. (ES) S + E (EP) E + P Diffusion & Affinity Catalysis Product release

  16. Enzymes decrease the activation energy in reactions Transition state or hi NRG intermediate W/o enzyme Reactants + enzyme G free NRG Products Progress of rxn

  17. Analogies for NRG barriers

  18. Michaelis-Menten Kinetics Vmax Km

  19. Enzymes use common mechanisms to catalyze rxns Hold substrates correctly.  Reduces diffusion limits. Manipulate charges (electrons).  Increases reactivity of groups. + + - - Physically or chemically stress bonds

  20. Control of Enzyme Activity • Alter enzyme synthesis (expression) • Alter transcription • Alter translation • Regulate degradation rate • Zymogens • Chymotrypsinogen to chymotrypsin • Cofactors (calmodulin, Mg2+, Ca2+) • Phosphorylation • Inhibitors & Activators • Allosteric - not at active site • Competitive inhibition bind at active site Conformational changes

  21. O ¯O P O¯ O O ¯O P O¯ O Phosphorylation ACTIVATING ADP + kinase ATP + kinase INHIBITING ADP + kinase ATP + kinase

  22. Enzyme inhibitors • Important for cellular regulation of enzyme activity (turn off enzyme), useful for scientists (study transition state), important for pharmaceutical/biotech companies (drugs, antibiotics, pesticides). • Enzyme inhibitors fall into two broad classes: • Irreversible inhibitors - bind tightly, often covalently. • Reversible inhibitors - bind loosely and can be displaced. • Competitive - bind to enzyme’s active site. Can be overcome by high [S]. Raises Km; Vmax same. • Noncompetitive - bind to site on enzyme other than active site.Cannot be overcome by high [S]. Km same; lowers Vmax. • Uncompetitive - binds to and stabilizes ES complex. Lowers Km; lowers Vmax.

  23. Lineweaver-Burk plots of reversible enzyme inhibitors Uninh. Inh. Competitive Noncompetitive Uncompetitive

  24. Competitive Inhibition Can be overcome by increasing [S] substrates inhibitor E

  25. Binding of allosteric effectors& Conformational changes Allosteric binding site Active site

  26. Feedback Inhibition E-1 A E-2 E-3 C B D F final product Active Inactive

  27. Biological Oxidations • Removal of electrons and replacement of C-H or C-C bonds w/ C-O bonds • CH3 CH2OH CHO COOH • CO2

  28. Lactic Acid or Ethanol +CO2 2 NADH OR O2 NADH Krebs Cycle e¯ Transport ATP Synthase 32 ATP CO2 Glycolysis is required for both anaerobic and aerobic metabolism Glucose 2 ADP 2 NAD+ 2 ATP 2 NADH Pyruvate

  29. Glycolysis Summary 2ADP + 2NAD+ 2ATP + 2NADH

  30. Glycolysis

  31. How Can the Production of ATP Be Thermodynamically Favored? These compounds have a lower affinity for their phosphate group compared to ATP.

  32. Hexokinase Kinases phosphorylate

  33. Phosphofructokinase Enzyme names relate to substrate names ATP  AMP 

  34. Pyruvate kinase Or in glycolysis sometimes to product names

  35. Isomerases move atoms around Phosphoglucose isomerase

  36. Dehydrogenases remove H

  37. Krebs cycle

  38. Pyruvate enters the Krebs cycle via Coenzyme A

  39. Krebs or citric acid cycle 2C 6C 4C NADH + H+ NADH + H+ CO2 5C NADH + H+ 4C CO2 FADH2 GTP

  40. 3H+ 2H+ 4H+ 2H+ O2 2H+ 4H+ H2O ATP 2H+ ADP + Pi 2e- 3H+ Oxidative phosphorylation ATP synthase IV III I NADH -200 mV pH  8 Inner Membrane Electron transport system

  41. Viruses come in many flavors • All contain nucleic acid and some protein • DNA or RNA • single-stranded or double-stranded • RNA viruses are positive sense strand, negative sense strand, or retroviruses • reverse transcriptase • Protein Coat protects nucleic acid and mediates binding to host cell. • Viroids have no protein coat

  42. Bacteriophage inject DNA into host

  43. HIV is a retroviral provirus

  44. Virus life histories • Typically host-cell specific, only replicating in a host • Lytic viruses escape by lysing and killing host • Lysogenic viruses live in host for long periods of time, continually releasing more virus • Typically, take over host transcription & translation machinery. • Capsids assembled in cytoplasm or PM

  45. Prokaryotes • No nucleus or organelles • Circular DNA • complex biochemistry • Rods, cocci, spirochete.

  46. More prokaryotes • Typically reproduce by simple fission. • Quite rapid

  47. Prokaryotes can exchange genes thru conjugation Plasmid

  48. Fungi • Multicellular forms make mycelia and hyphae • Cell walls of chitin • Generally haploid throughout most of life cycle

  49. Fungal diversity • Ascomycota: yeasts and mildews • meiosis produces spores held in asci or sacs • Basidiomycota: Club fungi, mushrooms. • haploid hyphae conjugate to form dikaryons • Diploids form in basidia to produce haploid spores • Zygomycota: Molds • hyphae lack septa = multinucleate

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