BSC2011 Summer 2013 Exam #2 Study Guide 1 1. Describe a duplicated (or “replicated”) chromosome. • Replicated Chromosome: 2 sister chromatids joined at a centromere o Joined by cohesin proteins 2. To what does the cell cycle refer and what “events” (stages, steps, etc.) are involved? • Cell Cycle: The series of events that take place in a cell leading to its division and duplication (replication) o The cell cycle creates new cells & allows cells to grow • Two parts: o Cell growth o Mitotic cell division 3. Why do cells/organisms need to regulate or control the cell cycle?BSC2011 Summer 2013 Exam #2 Study Guide 2 • Make sure that the cells are developing & functioning properly • Get rid of old, damaged, diseased, “malfunctioning” cells 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. • Cell cycle regulated by molecular signals in the cytoplasm & checkpoints • Three major checkpoints: G1, G2, and M checkpoints • The presence or absence of specific chemical signals determines whether a cell stops or proceeds through a checkpoint in the cell cycle • G1: Restriction Checkpoint o Signals determine whether the cell… A) Pauses & enters G0, where the cell “hangs out” and does the job it was intended to do B) Passes the G1 checkpoint and enters “S” (synthesis) C) Passes the G1 checkpoint and undergoes apoptosis (cell death) • G2 Checkpoint: o Cell assess if preparations are “ok” o If yes, signals direct the cell to enter “M” (mitotic phase) o Maturation Promoting Factor (MPF): A particular cyclin-Cdk complex needed to get through the G2 checkpoint Cyclin is gradually synthesized during S and G2 Cyclin concentration high enough binds to & is activated by a particular Cdk protein complex now called MPF MPF signal moves the cell through the G2 checkpoint & into mitosis MPF NOT at G1 checkpoint • M Checkpoint: o Cell assesses if mitosis proceeded successfully o If yes, signals direct the cell to enter cytokinesis (cell division)BSC2011 Summer 2013 Exam #2 Study Guide 3 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: Cell division that preserves the parental number of chromosomes in the two daughter cells o Asexual reproduction • General purpose of Mitosis: o Create new cells quickly (replication) o Growth & repair Replace worn-out or damaged cells Enable multicellular organisms to grow Mitosis diploid (2n) diploid (2n) • Interphase o G1 Cell grows in size and synthesizes mRNA proteins o Synthesis (S) Chromosomes (DNA) replicate Centrosomes replicate o G2 Rapid cell growth & protein synthesis • Prophase o Centrosomes move to opposite poles o Spindle microtubules start to lengthen o Nuclear membrane begins to dissolve o Nucleolus disintegrates o DNA begins to condense into distinct, replicated chromosomes • Prometaphase o Nuclear membrane is gone o Chromosomes are clearly distinct o A kinetochore (kt) appears at each centromere o Spindle is completeBSC2011 Summer 2013 Exam #2 Study Guide 4 o Aster forms • Metaphase o Spindle microtubules move the chromosomes o Chromosomes line up single file along the midline/equator/metaphase plate • Anaphase o Centromeres split o Spindle microtubules pull apart sister chromatids toward opposite poles • Telophase & Cytokinesis o Spindle disassembles o Nuclear membrane reforms o Nucleolus reappears • Result of Mitosis: o 2 diploid (2n) daughter cells o Same number of chromosomes as parent cell o Identical DNA sequences as parent cell “Clones” of parent cellBSC2011 Summer 2013 Exam #2 Study Guide 5 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? • Cancer: A genetic disease caused by mutations to genes • Cancer-causing mutations usually involve tumor suppressing genes (TSGs), proto-oncogenes (POGs), and other genes that regulate the cell cycle • Ex) Normal tumor-suppressing genes (TSGs) restrict cell division o TSG mutation uninhibited cell growth cancer • Ex) Normal proto-oncogenes (POGs) stimulate cell division o POG mutation overstimulated cell growth cancer 7. Compare/contrast somatic vs. germ cells (aka. sex cells or gametes) with respect to location in an organism, function, how they are formed, and chromosome number. Gametes/Sex Cells/Germ Cells Somatic/Body Cells Location in Organism Ovaries/testes Everywhere in the body except the ovaries/testes Function Fertilization/sexual reproduction Many different types withBSC2011 Summer 2013 Exam #2 Study Guide 6 many different functions Method of Formation Meiotic cell division Mitotic cell division Chromosome # ½ the # of chromosomes for a given species Humans - 23 (haploid) Full # of chromosomes for a given species Humans - 46 (diploid) 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 arranged in homologous pairs o Uses visible, condensed chromosomes from a cell undergoing mitosis • Karyotypes can be useful to detect: o Abnormal chromosome number o Abnormal chromosome size o Sex 9. What does it mean when we say that, in eukaryotes, “chromosomes exist in pairs?” What are the two chromosomes that make up a pair called? How are they similar to each other? How are they possibly different from each other? • In eukaryotes, chromosomes exist in pairs that are made up of one maternal and one paternal chromosome • The two chromosomes that make up a pair are called homologous chromosomes • Homologous chromosomes have the same: o Length o Centromere position o Staining pattern o Genes for the same characteristics at corresponding loci • Homologous chromosomes can have different: o Sequences of DNA within the chromosomeBSC2011 Summer 2013 Exam #2 Study Guide 7 10. Compare/contrast diploid chromosome number with haploid chromosome number. In what types of cells are these different numbers of chromosomes found? •
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