BSC 2011 UNIT II STUDY GUIDE Part A FALL 2008 PLEASE NOTE please also refer to and be able to work problems on the separately posted Study Guide Part B and C entitled Practice Mitosis Meiosis Problems and Practice Mendelian Inheritance Problems respectively The purpose of this study guide is to encourage you to review your notes text material and outside sources and to integrate numerous facts and terms into broad but meaningful concepts Please try and work on your own at first but don t hesitate to ask for assistance from either me or your TAs We will randomly select a question or part thereof to use on your Unit II exam Dr Spears UNIT II Patterns of Inheritance Mendelian genetics also cell division and cell cycle 1 Describe a duplicated or replicated chromosome A replicated chromosome consists of 2 sister chromatids that are joined by cohesion proteins at a centromere 2 sister chromatids however is still just one chromosome 2 To what does the cell cycle refer and what events stages steps etc are involved The cell cycle refers to two parts cell growth and cell division The two parts are referred to as interphase G1 S G2 and the mitotic M phase mitosis and cytokinesis The first stage of the cell cycle is two new daughter cells are created The second stage is a new cell grows in G1 The third stage is chromosomes DNA replicate in S The fourth stage is the cell prepares to divide in G2 The fifth stage is the M phase in which the nucleus divides mitosis and the cytoplasm divides cytokinesis creating 2 daughter cells with the same number of chromosomes as the parent cell During G2 of interphase after DNA that replicated in S the cell apotheosizes proteins and structures to prepare for cell division the centrosome replicates and centrioles synthesize microtubules needed to make the spindle Centrioles are absent in plant cells 3 Why do cells organisms need to regulate or control the cell cycle When cell division is unregulated errors occur which results in many diseases including cancer Tumor suppressing genes TSGs restrict cell division proto oncogenes stimulate cell division Several mutations in these genes cause cancer A POG mutation results in over stimulated cell growth example POG Ras mutation causes it to stimulate cell division when it shouldn t Mutation in TSGs results in uncontrolled uninhibited cell growth example TSG p53 if missing or defective causes a gene to not be activated to make protein needed to stop cell division P53 regulates the G1 checkpoint on chromosome pair 17 4 How do cells organisms regulate or control the cell cycle Molecular signals in the cytoplasm regulate the cell cycle Checkpoints at G1 G2 and M also regulate the cell cycle There is also internal and external control of the cell cycle Cyclins are clock molecules that regulate an internal ticking clock by changing its specific amounts The presence or absence of external signals called growth factors initiate passage through the G1 checkpoint example of external PDGF needed to stimulate mitosis when an injury occurs if there s no PDGF then cells remain at G0 if it is present cell s signaled to proceed into S Cells show anchorage dependence in which cell membrane proteins inhibit cell division when they lose contact with the dish to avoid piling up creating a tumor Cells also show density dependent inhibition in which cell membrane CAMS inhibit cell division so long as cells are in contact to avoid piling up Signaling pathways mutations cause cancerous cells to lose both anchorage dependence and density dependent inhibition Explain the role of checkpoints The presence or absence of specific chemical signals determines whether a cell stops or proceeds through a checkpoint in the cell cycle For example the G1 restriction checkpoint signals determine whether the cell pauses and enters G0 or whether the cell passes the G1 checkpoint and enters the S phase OR if it undergoes apoptosis Explain the chemical control system that gets cells through the G2 checkpoint Cell assesses if preparations are ok in G2 if yes then the signals direct the cell to enter the M phase MPF maturation promoting factor is a cyclin cdk complex needed to get through the G2 checkpoint A cyclin is gradually synthesized during interphase When the cyclin concentration is high enough it binds to and is activated by a particular Cdk and the protein complex is now called MPF MPF signal moves the cell through the G2 checkpoint into mitosis The specific cyclin needed for MPF begins late in S and peaks in G2 In G2 the cyclin binds to and is activated by Cdk making MPF After MPF is made and you get through the G2 checkpoint into mitosis cyclin gets degraded and Cdk gets recycled 5 What is the general purpose of mitotic cell division Describe the step wise process of mitotic cell division Compare the number of chromosomes before the start of mitosis at each step and at the end 6 What do cancer and the cell cycle have to do with one another What do cancer and gene regulation have to do with one another An unregulated cell cycle causes cancer see questions 3 4 In the multistep cancer model several mutations are needed to achieve a fully cancerous state thus an individual may inherit a predisposition for a type of cancer by inheriting 1 or 2 genes needed for cancer Cancer cells have telomerase activity and can synthesize and replenish telomere DNA telomeres usually act as a buffer and protect genes near the ends of chromosomes from getting lost during DNA replication and cell division 7 Compare contrast somatic vs germ cells a k a sex cells or gametes with respect to location in an organism function how they are formed and chromosome number Diploid all over the body somatic cells formed by mitosis 46 chromosomes purpose is to preserve the original parental number of chromosomes in the daughter cells Haploid reproductive organs gametes formed by meiosis 23 chromosomes purpose is to reduce diploid chromosome number in half 8 Describe a karyotype What does a karyotype reveal Why are karyotypes useful Karyotype an orderly display showing the number and types of chromosomes in a diploid cell and arranged in homologous pairs uses visible condensed chromosomes from a cell undergoing mitosis Karyotypes reveal abnormal chromosome number and abnormal chromosome size and also gender Karyotypes are useful because they can check for the abnormal chromosome number which causes many harmful diseases disorders such as Down s syndrome 9 What does it mean when we say
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