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Chapter 12 notes

by: Cheryl bruce

Chapter 12 notes BIOL 112

Marketplace > Indiana University > Biology > BIOL 112 > Chapter 12 notes
Cheryl bruce
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These are chapter 12 notes including clicker questions and answers
Biology of the cell
Megan Dunn
Class Notes




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This 7 page Class Notes was uploaded by Cheryl bruce on Monday April 4, 2016. The Class Notes belongs to BIOL 112 at Indiana University taught by Megan Dunn in Spring 2016. Since its upload, it has received 10 views. For similar materials see Biology of the cell in Biology at Indiana University.


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Date Created: 04/04/16
Chapter 12: The cell Cycle Key Role of Cell Division • Reproduction: An amoeba dividing into two cells, each cell is an individual organism • Growth and development: Sand dollar zygote divides into two cells shortly after fertilization • Tissue renewal: Dividing bone marrow cells give rise to new blood cells Key points: • The cell division process is an integral part of the cell cycle • Each daughter cell has the identical genetic material as the original parent cell Cellular Organization of Genetic Material • Genome: a cell’s DNA or genetic information • Prokaryotes (bacteria, Archaea): single long circular DNA molecule • Eukaryotes: number of DNA molecules organized into chromosomes Cell division involves: • Replication of DNA in a parent cell (2 copies) • Distribution of DNA so that each daughter cell ends up with a complete genome • chapter 12 discusses cell division in somatic cells and chapter 13 discusses cell division in gametes • What is a somatic cell? Any cell in an organism besides the gametes aka body cells • Example: Human bone marrow cell • How many chromosomes does this cell have? 46 (2n) made up of 2 sets of 23 chromosomes One set inherited from each parent What are gametes? Egg and sperm How many chromosomes are found in a mature human sperm? 23 (n): one set of 23 chromosomes Number of chromosomes in somatic cell of various species Cabbage 18 Elephants 56 Hedgehogs 90 Alga (one particular species) 14 8 Size doesn’t matter • Chromosomes are made of chromatin, a complex of DNA and associated protein molecules • In eukaryotes, the DNA is a single linear molecule containing several hundred to a few thousand genes • The associated proteins function to maintain the structure of chromosomes and to help control gene activity Chromosome duplication and distribution during eukaryotic cell division: • Chromosomes are usually long and thin and are only in a condensed form when dividing • Centromere: region where two sister chromatids are tightly attached • Sister chromatids are attached by cohesins, a complex of adhesive proteins • Note: sister chromatids are considered “one” chromosome when attached • Each cell had an individual chromosome that is identical to the one in the parent cell Mitosis: occurs in somatic cells (2n to 2n) • Produces two daughter cell that are genetically identical Meiosis: occurs in germ cells (2n to 1n) • Produces four daughter cell that are genetically identical (generates gametes) • Division of nucleus Cytokinesis: division of the cytoplasm Mitosis and development: makes 200 trillion somatic cells Phases of the cell cycle: Interphase 90% of the cell cycle • 1. G1= “first gap” • 1. S- “synthesis” • 3. G2- “second gap” M Phase= Mitosis and cytokinesis (~10%) • Broken into five stages • Prophase • Prometaphase • Metaphase • Anaphase • Telophase • What is the difference between mitosis and cytokinesis? Mitosis is the division of the nucleus and cytokinesis is division of the cytoplasm • True or false: duplication is part of mitosis. False Mitotic Spindle • Aster: radical array of short microtubules that attached to the plasma membrane • Centrosome: microtubule organizing center in animals contains 2 centrioles • Kinetochores: a protein structure found at the centromere region of each sister chromatid • Nonkineochores Microtubules: function in elongating the whole cell during anaphase • Kinetochores microtubules: attach to kinetochores moves a chromosome towards the pole from which the microtubules extend Mitotic spindle is composed of: • Centromsomes • Spindle microtubules (kinetochore and nonkinetichores mircrotubuled) • Asters • Centromsomes: duplicated during interphase in animal cells and move apart during mitosis • Spindle microtubules: elongate by adding subunitsd of tubulin and shorten by losing subunitd of G2 of intertphase • In animal cells, each centrosome contains two centrioles • Chromosomes and centrosomes are duplicated in S phase Prophase • Chromatin fibers condense • Mitotic spindle begins to form • Centrosomes begin to move away from each other Prometaphase • Nuclear envelope fragments • Microtubules invade the nuclear area • A kinetochore microtubule attaches to each sister chromatid • Nonkinetochore microtubules interact with those of the opposite spindle Metaphase: • Longest phase in mitosis- last 20 minutes • Chromosomes convene on the metaphase plate • Kinetochore microtubules are attached to the kinetochore on each sister chromatid Anaphase: • Shortest phase in mitosis- last just a few minutes • Cohesion proteins are cleaved by the enzyme, sdeparase, and the sister chromatids spate as kinetochore microtubules shorten • Once separated, each chromatid becomes a full-fledged chromosome • Cell elongate as the nonkinetochore microtubules lengthen Telophase: • Nuclear envelope forms • Mitosis- division of one nucleus into to nuclei is complete Cytokinesis: • Division of cytoplasm is usually underway by late telophase • Daughter cells appear shortly after the end of mitosis Cleavage of an animal cell • Actin microfilaments interact with myosin molecules causing the ring to contract • Cleavage furrow deepens until the parent cell is pinched in two • Generates two completely separate cells (daughter cells) • Each daughter cell has its own nucleus and a share of cytosol, organelles, and other subcellular structures Binary Fission: Asexual reproduction • Amoeba and bacteria reproduce this way • In bacteria most genes are on a single chromosome that consists of circular DNA and associated proteins • Chromosome replication begins • Origin of replication • One copy of the origin moves towards • Replication continues • • When replication is finished, the plasma membrane grows inward and a new cell wall is deposited • Two daughter cells result Eukaryotic Cell Cycle: Timing and rate of cell division in plants and animals is crucial to normal growth, development, and maintenance In Mature Humans: • Skin cells divide • Human liver cells can divide but will do so only when need arises • Muscle and nerve cells • Cancer cells divide What controls the cell cycle? Cell Cycle Control System: Cyclically operating set of molecules in the cell that triggers and coordinates events in the cell cycle • Each rectangle represents a • Control system proceeds on its own- driven by a • System is subject to various internal and external regulations at various checkpoints • : A cell cycle control point where “stop” and “go” signals can regulate the cycle • Animals usually have built-in signals that halt cell cycle at check points until they are overridden by a signal Key questions are asked at each checkpoint G1 checkpoint: stop signal: Is DNA G2 Checkpoint: Stop signal: Is all DNA M checkpoint: Stop signal: Are all chromosomes The G1 Checkpoint: in mammalian cells • Most important checkpoint in mammalian cells • If a cell receives signal, it will enter G1,S,G2,M, and • If cell does not receive the signal, it will exit the cell cycle and switch to a • Most cells in the human body are in the • Liver cells can be “called back” from G0 phase to the cell cycle by external cues (e.g. growth factors released during a wound unjury) M checkpoint: • Anaphase will not begin until all the chromosomes are properly attached to the spindle at the • The regulatory protein complex is only activated when the chromosomes are properly attached to • The activated complex triggers a chain of events that activate , the enzyme that cleaves cohesions and allows the sister chromatids to separate Why is this checkpoint important? It make sure the cells: The Cell Cycle Clock: two types of regulator molecules control the pace of the cycle • Protein kinases: enzymes that activate or inactivate other protein molecules by phorsphorylating them • Specific proteins kinases give “go-ahead” signals to G1 and G2 checkpoints • Most of the time these molecules are present in the cell but in an inactive form • Referred to as Cycliin-dependent kinases (Cdks)- must be activated by Cyclins • Cyclins : proteins that activate cyclin-dependent kinases • Name comes from the fact that the concentration of these proteins fluctuating during the cell cycle • During anaphase, the MPF initiates a process that degrades cyclin • M phase promoting factor (MPF): Cyclin-Cdk complex activity MPF function to: • Trigger cells past the G2 checkpoint and into M phase • Promote mitosis by phosphorylating a wide variety of proteins, including other kinases Example: proteins involved in the breakdown of the nucleus or proteins involved in the formation of the mitotic spindle • Cdk concerntration does not fluctuate during the cell cycle. the cyclin fluctuates • the concentration of cuclin is the lowen G1 Phase: • The cell favors the degradation of cyclin and Cdk molecules is recycled S Phase- G2 phase: • Synthesis of cyclin begins and continues through G2 • Cyclin is protected against degradation End of G2 Phase: • Cdk and cyclin combine forming MPF • When cells have produced enough MPF molecules, they pass through the G2 checkpoint and begin mitosis Anaphase of mitosis: • Cyclin Is degraded, releasing Cdk • M phase is complete and cell enters G1 phase • Cdk activity fluctuated during the cell cycle


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