The cell cycle lecture PDF

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lecture on the cell cycle and how it pertains to the human body...

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Lecture 12: The Cell Cycle Lecture Objectives: 1. Describe the typical cell cycle of prokaryotes. Include and define the terms binary fission and generation time 2. Define the following terms: a. Chromosome b. Chromatin c. Gene d. Genome e. Karyotype 3. Describe the human genome and karyotype in terms of: number of basepairs, number of genes, and number of chromosomes. 4. Draw a circle diagram of the eukaryotic cell cycle. Label all phases. 5. Discuss what goes on in each of the phases on the diagram. Note where checkpoints exist. Also, discuss G0, and discuss cell cycle regulation in general terms. 6. Describe what “PMAT” means. 7. Discuss what happens in each stage of mitosis. 8. Describe cytokinesis in both plant cells and animal cells, noting the differences. 9. Describe what is meant by the term “polar division” and why this process was (and still is) important in your development. Class Notes: ● Prokaryotic Cell Division ○ A prokaryotic cell divides by binary fission ○ The main circular DNA molecule of the cell is replicated ■ Replication begins at a replication origin and proceeds in both directions ○ Prokaryotic cells can have a generation time as short as 20 minutes ■ Generation time - general term for the period from the start of one cell division to the start of the next cell division ●

Organization of Eukaryotic DNA Molecules ○ Eukaryotic DNA molecules are organized in chromosomes A. ■ Each chromosome is made of chromatin ● Chromatin is packaged into dense chromosomes during cell division ○ Protects the DNA ■ Each chromosome contains hundreds to thousands of genes ● Genes are the functional units of heredity ● A gene contains the instructions to make a protein or RNA molecule ● The complete DNA sequence for an organism is the genome ■ Each species has a characteristic number of chromosomes ● The number varies between species

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The assortment of chromosomes for an individual is the karyotype Humans have 46 chromosomes

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Eukaryotic Cell Cycle ○ The cell cycle describes the status of cells in relationship to growth and division ■ When cells reach a certain size, growth either stops or the cell must divide ■ Most, but not all, eukaryotic cells are capable of dividing ■ The generation time for eukaryotic cells varies widely, but is usually 8-20 hours ○ Cell cycle has two main phases – interphase and cell division (mitosis + cytokinesis) ○ Interphase is divided into three parts, defined with respect to DNA replication ■ The DNA is completely replicated during the synthesis phase or S phase ■ The period before the S phase is a “gap” phase, G1 phase ● Most cellular growth occurs in this phase ● Cells that do not divide become arrested in this phase, then called ■ The period between the S phase and cell division is the G2 phase ● The G2 phase is usually short; cells in this phase are committed to and preparing for cell division ○ Cell division has two main parts – mitosis and cytokinesis ■ Mitosis - the process that distributes a complete copy of the duplicated genetic information to each daughter cell ■ Cytokinesis - the process of dividing the cytoplasm into two separate cells ■ Some cells can have mitosis without cytokinesis

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Mitosis ○ Mitosis is generally divided into 4 stages: prophase, metaphase, anaphase, and telophase ○ Mitosis is a continuous process

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Prophase ○ Prophase – chromatin condenses to form chromosomes 1. ■ Each chromosome (duplicated during S phase) forms a pair of sister chromatids ● Sister chromatids are joined at a centromere by protein tethers ● Centromeres contain a kinetochore where microtubules will bind ■ A system of microtubules organizes between the two poles of the cell ● In animals and some other eukaryotes, centrioles are found in the MTOC ■ By the end of prophase: the nuclear membrane has disappeared ● The sister chromatids are attached by their kinetochores to microtubules from opposite poles

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Some call the later part of prophase prometaphase, usually defined to include vascularization of the nuclear membrane and attachment of kinetochores to microtubules

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Metaphase ○ Metaphase – chromosomes line up along the midplane of the cell ■ Chromosomes are most condensed, most visible, and most distinguishable ■ The mitotic spindle has two types of microtubules: ● Kinetochore microtubules - extend from a pole to a kinetochore ● Polar microtubules - extend from a pole to the midplane area, often overlapping with polar microtubules from the other pole

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Anaphase ○ Anaphase – sister chromatids separate and are moved toward opposite poles ■ The protein tethers at the centromere ■ Each former sister chromatid can now be called a chromosome ■ Model for the mechanism that moves chromosomes to the poles ● Motor proteins move the chromosomes towards the poles ● Kinetochore microtubules shorten behind the moving chromosomes ● Polar microtubules lengthen the entire spindle

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Telophase ○ Telophase – the processes of prophase are reversed ■ The mitotic spindle is disintegrated ■ Nuclear membranes reform around the genetic material to form two nuclei ● Each with an identical copy of the genetic information ■ Nucleoli reappear, and interphase cellular functions resume

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Cytokinesis ○ Cytokinesis - process that divides the cell into two daughter cells ■ Cytokinesis usually begins in telophase and ends shortly thereafter ● In animals, a cleavage furrow develops – usually close to where the metaphase plate was ● In plants, a cell plate develops – usually close to where the metaphase plate was ■ Cytoplasm is usually distributed randomly but roughly equally between daughter cells...