weber uiuc edu 26 November 2007 MCB150 Lecture 35 Lecture 35 26 November 2007 Announcements Exam III Data Mean 102 Median 105 High 147 4 Low 30 Probably no adjustment to the grades Weekly Review due Friday ICES forms online Exam III questions that were missed by more than 50 of the class o What roles can actin binding proteins take Take a look at the table in the book that we should look at See previous notes o The genes in the nucleus mitochondria and what they stand for 2 rRNA all mitochondrial rRNAs are made from mitochondrial DNA roman numerals are ETC complex proteins only ETC proteins are made in the mitochondria but not all of the proteins in complex I are made in the mitochondria Kreb s enzymes are all nuclear origin ETC omplex I some in mitochondria some from nuclear mitochondrial ribosomal proteins all made by nucleus See the diagram o GPI anchored protein remember that signal presequence is cut off and some of the amino acids are left in the membrane 20 25 amino acids cut off from amino signal 20 25 are left in the membrane when some are cut off to make the anchor 50 amino acids in the protein are lost Visit during office hours to ask about the remaining questions Mitosis and M phase Discussing the events of M phase Mitosis and Cytokinesis Mitosis is the process of nuclear division Mitosis is a cycle that has no beginning or ending o We will jump in at an arbitrary point The Cell Cycle Broken Down We will start in interphase right at the beginning This is a brand new daughter cell that has just entered G1 lower left in the diagram o We cannot look at it and know that it is G1 o We know it is interphase because of interphase chromatin it is forming its interphase microtubule array and one centrosome adjacent to the nucleus What happens during interphase o The cell starts growing getting bigger creating its interphase microtubule array At some point the cell begins to enter S phase o Could not tell just by looking at it that it is in S phase o We cannot see the amount DNA Eventually it gets to G2 o Now the centrosome has been replicated This is visible o There are now two pairs of centrioles and there is approximately double the amoung of pericentriolar material o While in interphase the centrioles are adjacent to each other Page 1 of 9 weber uiuc edu 26 November 2007 MCB150 Lecture 35 o This is one way to tell when we are in G2 Enter M phase at Prophase Lots of interesting things happen in prophase o Break down depolymerize all the interphase microtubules the microtubule array and form mitotic tubules called the mitotic spindle apparatus o Condense the DNA into mitotic chromosomes Prior to this a mix of hetero and euchromatin Not any more o Replicated centerosome will migrate to the opposite side of the nucleus The centrosomes have separated themselves and are at opposite poles of the cell They start to configure mitotic spindle o At the end of prophase for the purposes of MCB150 the nuclear envelope disappears Our text uses late prophase for the disintegration of the nuclear envelope This is a matter of opinion but we will go with the author of our text o At this point the cell has opened up access to the fully condensed chromosomes Now need to get the microtubules to attach to the chromosomes Prometaphase o Begins with the attachment of the microtubule to a chromosome o Cannot happen until the nuclear envelope is gone This is why he teaches that the nuclear envelope disappears at the end of prophase The microtubules cannot get to the chromosomes until the envelope has disappeared o EXAM If asked a question on the exam the nuclear envelope disappears during prophase o This is the ballet of the chromosomes the pairs of sister chromatids bounce back and forth between the poles until they come to rest in the middle of the cell o They will eventually line up along an imaginary line called the metaphase plate The metaphase plate does not actually exist Metaphase o The chromosomes are now lined up Once the chromosomes are lined up on the metaphase plate then metaphase has begun o And then its over The cell is ready to separate the chromatids Anaphase o The separation of sister chromosomes pulled by their centromeres to opposite poles of the cells o The cell is starting to push its boundaries away from each other at the poles o Each piece of chromatin moves to opposite ends of the cell Telophase o Everything undone in the previous steps are redone here o Decondense the chromosomes relax them o Broke down the envelope in prophase create new ones here o Depolymerize mitotic tubules because it is almost time to go back to interphase where the mitotic array is needed o Essentially undo everything done during the previous steps Page 2 of 9 weber uiuc edu 26 November 2007 MCB150 Lecture 35 o Cytokensis begins during telophase The cytoplasmic membrane is starting to constrict Cytoplasmic division happens as early as late anaphase certainly by telophase This doesn t have to wait just as long as the DNA is out of the way Cytokinesis o Doesn t wait until mitosis is complete before the membrane starts to pinch off o Starts as early as late anaphase if not by then absolutely by telophase o At the finish of cytokinesis have two daughter cells back at G1 o These are the events broken down Fluorescent Microscopy Images General information about the images green is tubules tubulin blue is chromatin Interphase o Can see the nucleus but cannot yet see any chromosomes Early Prophase o The nuclear membrane is still intact o Begin to see chromosomes condensation squiggly lines o Also see two brightly glowing centrosomes that have replicated during interphase but not yet moved to opposite sides of the nucleus o A lot of the interphase microtubule array has been disassembled depolymerized o Making the M phase microtubule array begins Late Prophase o Close to prometaphase border o Chromosomes condensed o No nuclear envelope no nucleus o Only cytoplasm o Depolymerized all microtubule arrays starting to build the spindle apparatus o The centrosomes have migrated to opposite sides where the nucleus used to be o Microtubules begin to grab chromosomes pulled towards the metaphase plate Prometaphase o Some chromosomes have already been moved along the metaphase plate o Others have not yet been moved o Or some are being pulled back to the middle o It is a ballet back and forth Metaphase o Imaginary metaphase plate extends from upper right to lower left o All chromosomes are held in place by particular