Unit II Study Guide Part A 1 Describe a duplicated or replicated chromosome A replicated chromosome 2 sister chromatids joined at a centromere joined by cohesion proteins Below two sister chromatids 2 To what does the cell cycle refer and what events stages steps etc are involved The cell cycle has two components 1 Cell growth 2 Cell division 2 general phases interphase and mitotic phase Interphase 3 stages G1 S G2 G1 new cell gows S chromosomes replicate G2 the cell prepares to divide Mitotic mitosis and cytokinesis M nucleus divides by mitosis Cytokinesis cytoplasm divides into 2 daughter cells each containing the original number of chromosomes 3 Why do cells organisms need to regulate or control the cell cycle The cell cycle is regulated at various checkpoints G1 G2 and M There are molecular signals in the cytoplasm that regulate the cell cycle Cancer results when there are errors in control of the cell cycle A cell wants to regulate what genes are passing through the cell cycle so that mutated genes aren t being replicated 4 How do cells organisms regulate or control the cell cycle Explain the role of checkpoints Explain the chemical control system that gets cells through the G2 checkpoint There are molecular signals in the cytoplasm that regulate the cell cycle Whether cell cycle STOPS or PROCEEDS through a checkpoint depends on what chemical signals are present 1st G1 restriction checkpoint cell cycle pauses i e cell hangs out just doing its job in G0 if directed to do so by signals or other signals can direct the cell to pass the checkpoint and enter S or even to undergo apoptosis 2nd G2 checkpoint if preparations for cell division are ok then signal molecules direct the cell to enter the M mitotic phase There are regulatory proteins that act as signal molecules that control the cell cycle Passage through through G2 checkpoint synthesis of a G2 cyclin fluctuates cyclically through the cell cycle When the amount of the G2 cyclin gets high it binds to is activated by a specific Cdk forms a Maturation Promoting Factor MPF signal to proceed through the G2 checkpoint Once past the checkpoint the cyclin part of MPF is degraded but the Cdk part becomes available again Cyclin protein fluctuates in concentration throughout cell cycle CDK cyclin dependent kinases bind to and activate cyclins to get through a checkpoint CDKs are always present MPF needed to go through G2 checkpoint Cyclin is gradualy synthesized during S and G2 When the cyclin level is high it binds to CDK which is always present and creates MPF This signal puts the cell through G2 checkpoint and initiates mitosis There is internal and external control of cell cycle 1 The first mechanism is the repeated internal synthesis and degradation of various cyclin clock molecules 2 The second mechanism uses feedback from other internal signals hormones external signals growth factors that adjust the activity of cyclins as needed 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 Mitosis division of the nucleus that preserves the parental chromosomes number in each daughter cell 1 Prophase centrosomes move to opposite poles spindle microtubules start to lengthen nuclear membrane starts to dissolve nucleolus disintegrates Diffused DNA that is replicated during S begins to condense into distinct chromosome 2 Prometaphase the nuclear membrane is gone and chromosomes are distinct The spindle apparatus is complete Kinetochores appear at each centromere Aster microtubules are at the cell edge a Kinetochore complex of proteins at the centromere that attach sister chromatids to spindle fibers Pole to kt b Non kinetochore pole to pole c Aster from centrosome to cell edge 3 Metaphase spindle microtubules move chromosomes Chromosomes line up in a single file at the midline or cell equator metaphase plate Sister chromatids of a replicated chromosome face opposite sides 4 Anaphase centromere splits Spindle microtubules pull apart sister chromatids toward opposite sides Each separated chromatid is now its own distinct chromosome 5 Telophase spindle disassembles nuclear membrane reforms and a nucleolus reappears Mitosis or nuclear division is now complete 6 Cytokinesis last stage cell membrane pinches in invaginates at cleavage furrow Cytoplasmic division is now complete 2 daughter cells are created each with identical DNA as parent and same chromosome number as parent Cytokinesis is a little different in plants a cellulose cell plate forms between plant daughter cells At the start of mitosis if you start with 46 chromosomes even after duplication of DNA the number is still 46 chromosomes This is because before DNA replication each chromosome consists of one chromatid After replication chromatids are duplicated and each chromosomes has 2 chromatids This is the result of a X shaped chromosome The chromatids will be separated in mitosis There can be 92 chromatids but it is still 46 chromosomes 6 What do cancer and the cell cycle have to do with one another What do cancer and gene regulation has to do with one another Cancer results when there are errors in the control of the cell cycle Cancer is caused when there is a mutation to genes Tumor suppressing genes TSG restrict cell division Proto oncogenes POGs stimulate cell division Cancer causing mutations involve TSGs POGs and other gene regulation issues in the cell cycle When there are mutations in POGs it can result in cell cycle overstimulation which can create to many cells and create a tumor On the other hand there can be a TSG mutation which fails to restrict the bad cells from dividing A combination of both will result in a tumor Cells need anchorage dependence and density dependent inhibition Cancer looses these growth factors which can create tumors 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 Somatic sex cells found in muscle and skin They are diploid come in pairs and are represented as 2n They contain 2 sets of chromosomes 1 maternal pair and 1 paternal pair Example human somatic cell is 2n 46 chromosomes 23 paternal and 23 maternal pair Germ cells gametes egg and sperm cells They are haploid represented as n 1 set Just one chromosome from each pair Example human gamete cell is n 23 chromosomes 8 Describe a karyotype
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