weber uiuc edu 28 November 2007 MCB150 Lecture 36 Lecture 36 28 November 2007 Announcements Friday 7 Dec is the last day of instruction o For the last pre post lecture questions Lecture 40 will have 8 pre lecture questions o Check the gradebook by the 5PM for errors Ask to see Alejandra if there are discrepancies Check exam scores homework weekly review attendance etc o Deadline for conflict final is also 5PM There will be one more weekly review assignment due Final Exam is 13 Dec 1 30PM Not 7PM No no no no no o Content and format will be just like the other three exams Mitosis Summary of the last lecture or so Be sure to review this summary and know the different phases of Mitosis The molecular details have been covered Anaphase A and Anaphase B is important o Understand it because it is going to be on the exam Ask him in office hours if necessary o They do not happen one after another They happen concurrently just have different functions o One is the kinetochore microtubules pulling of the sister chromatids the other is the movement of the poles into opposite directions pushing the boundaries of the cell farther apart o Remember that it is the motor proteins that are doing the movement o Both events happen during anaphase Cytokinesis As anaphase wraps up and telophase begins the cell also starts cytoplasmic division M phase ends when one parent cell becomes two daughter cells Have seen the contractile ring before o The myosin motor proteins pull the actin belt tighter until it pinches the cell into two This is part of M phase but NOT part of mitosis o M phase is comprised at mitosis and cyctokinesis Two different things o Cytokinesis doesn t happen when telophase ends the cell wants all of it to finish together o The ring of actin on the interior of the cell is formed while mitosis is occurring As the cell is putting the nucleus back together relaxing the chromatin and disassembling the mitotic microtubules the cell is also forming the actin ring tightening the belt and beginning the process of pinching off the cell Page 1 of 7 weber uiuc edu 28 November 2007 MCB150 Lecture 36 SEM IMAGE An example of a sea urchin embryo dividing from fertilized egg stage into the two cell stage The contractile ring of actin is on the INSIDE of the plasma membrane in the cell The belt is tightened from the inside The actin monomers when popped off end up inside the cell Summary We have now finished the big picture at the end of the continuous arc dealing with cell life and function We have talked about how a cell is built from macromolecules We have talked about how it gets the energy it needs We have talked about how the information is transferred from DNA to protein We have taken the tour of all the organelles in eukaryotes We have seen replication The rest of the semester contains a bunch of different topics that are related to what we ve learned along the way It will draw upon what we have learned o The rest of the topics will jump around o To understand the remaining material we should review the previous information Special Topic 1 Genetic Regulation What is the bill for protein synthesis How much energy does it cost to make one copy of one protein o Keep in mind that even the simplest cell can make thousands of different proteins and up to millions of copies of some of those proteins o Almost never make just one copy of the protein To answer the question we need to account for energy requirements in each step o Consider everything in terms of ATP usage considering the others CTP GTP TTP as being equivalent We will look at the lacZ gene in E coli because it is simpler o 3000 bp in the DNA for this gene To make an mRNA from that gene how many bases will be in the mRNA 3000 Every base gets transcribed from the gene No introns o If we assume each NTP is equivalent in energy which they are each NTP will be considered equivalent to an ATP Therefore there will be 3000 ATP units used to transcribe one of lacZ gene Remember during aerobic respiration we only make 36 ATP per glucose molecule o The steps of translation take up 3 more ATP equivalents Some are GTP review the steps of translation Need to charge the tRNA 1 ATP First step in elongation phase binding of next tRNA 1 ATP Translocation step 1 GTP 1 ATP equivalent Therefore for each amino acid will use up 3 ATP equivalents Page 2 of 7 weber uiuc edu 28 November 2007 MCB150 Lecture 36 o Roughly 1000 amino acids in the final protein slightly less because of the STOP codon so there will be 3000 ATP equivalents used 3000 ATP equivalents to do the translation o Total 6000 ATP equivalents used to make one copy of this protein o If the E coli does translation at about 20 amino acids second then about 50 seconds to make the protein 20 AA second is about the rate of the ribosome moving along the mRNA staying just behind the RNA polymerase during cotrasnscriptional translation That is equivalent to 120 ATP equivalents used second 6000 ATP 50 seconds o In the simplest case when the cell doesn t have to transcribe introns like the eukaryotes 120 ATP equivalents are used each second From this we see that it is very expensive to make proteins And there are very many proteins structural regulatory enzymes etc Looking at it another way it would be too expensive to make every protein all of the time Regulation Can a cell turn off genes it doesn t need Yes o This is the essence of regulation turn things on when you need them and off when you do not E coli can use different sugars for food sources o There is a special set of enzymes to for each sugar lactose arabinose maltose dextrose sucrose Different sets for each o There is no need to make the ones that break down lactose when lactose isn t present It makes no sense to make those enzymes it wastes energy o Keep those genes turned off until there is a need to digest the other sugars Many of the genes in any cell prokaryote and eukaryote are turned off and on as the needs of the cell change o More scientific the cell adjusts its metabolism to achieve maximum growth in a given environment o Easier turn it on turn it off Are all genes regulated No o Will have to make some regulatory products first To regulate others will have to make regulatory control proteins o E g If Gene X is always used all the time then it doesn t make sense to create proteins to regulate it The cell would never turn off that gene so a regulatory protein doesn t make sense o Genes that are turned on all …