Lesson 8 Mitosis Biology PDF

Lesson 8: The (Cellular) Circle of Life BIOL 1345 Biology I for Nursing Students  Learning Objectives (Study Guide) By the end of this lesson, students will 9. Describe what occurs during each phase of...

Lesson 8: The (Cellular) Circle of Life BIOL 1345 Biology I for Nursing Students  Learning Objectives (Study Guide) By the end of this lesson, students will 9. Describe what occurs during each phase of mitosis. be able to: 10. Identify each phase of mitosis in images. 1. List the structures of the prokaryotic & eukaryotic genomes. 11. Explain what occurs during cytokinesis. 2. Explain what is meant by homologous 12. Explain why it is important to regulate the cell chromosomes. cycle. 3. Distinguish genes and alleles. 13. Describe the importance of checkpoints in general and specifically the M checkpoint. 4. Explain how diploid & haploid cells are different from one another and give examples of each. 14. Explain how factors internal and external factors (e.g., cell density, & anchorage dependence) can 5. Differentiate between chromosomes, sister impact cell division. chromatids, and chromatin. 15. Explain how the growth of cancer cells is 6. Describe the function of centromeres. different from the growth of normal cells. 7. List the parts of the cell cycle in order. 8. Describe what occurs during each stage of the cell cycle. Type 2 Diabetes and Cell Division Type 2 diabetes can result when β cells do not undergo sufficient division. What determines when and if cells divide? Without enough β cells, insulin secretion decreases and cells cannot take up glucose. Swisa et al. Frontiers in Genetics 2017  Why Do Cells Divide? Cell division is used to generate new cells that are identical to the parental cell Single-celled organisms (like bacteria & protozoans), use cell division for reproduction In multicellular organisms, cell division is critical to many other functions Growth (e.g., zygote to adult) Repair damaged tissues Replace old or worn-out cells  Cells & Their DNA Cells are the smallest living things Genetic information is stored in the form of DNA Ribosomes use mRNA copies of DNA to build the proteins that are necessary for life The genome is its complete set of genetic information In prokaryotic cells, the genome includes a large chromosome & smaller plasmids In eukaryotic cells, the genome includes pairs of chromosomes found in the cell’s nucleus, and a circular chromosome in both the mitochondria and chloroplasts Background on Chromosomes The centromere appears as a constricted region of a chromosome and plays a key role in helping the cell divide up its DNA during division (mitosis and meiosis). The main functions include the attachment of sister chromatids, and it is the site for the attachment of spindle fiber  Eukaryotic Genomes Different species have different numbers of chromosomes in the nuclei of their cells Example: human (46 chromosomes) vs. chimpanzees (48 chromosomes) Members of the same species have the same number of chromosomes Most eukaryotic cells have two copies of each chromosome These “matching” pairs of chromosomes are called homologous chromosomes One copy of each homologous chromosome came from each parent Homologous chromosomes contain the same genes at the same position (locus)  Alleles Alleles are different versions of the same gene Different alleles lead to the synthesis of slightly different proteins Example: the TAS2R38 gene on chromosome 7 codes for receptors for bitter compounds, such as PTC ◦ Some alleles encode a protein that increases the detection of bitter taste ◦ Other alleles of encode proteins that decreases detection of bitter  Somatic cells are diploid (2n) Chromosome Number and Cells Diploid (2n) cells have 2 of each chromosome, one from each parent Somatic cells are diploid cells Somatic cells are all the cells in the body EXCEPT gametes Haploid (n or 1n) cells have 1 of each chromosome Gametes are haploid (n) Gametes are haploid These are the cells used in sexual reproduction Eggs and sperm  Visualizing the Genome A karyotype is a picture of a cell’s genome Haploid (n) Cell Diploid (2n) Cell The karyotype of a haploid cell contains one of each chromosome. Homologous chromosomes are arranged in pairs in the karyotype of a diploid cell.  Stop & Think it Through! Determine whether each statement describes a human somatic cell or gamete. How are homologous A cell with 23 chromosomes. chromosomes SIMILAR? A cell that is diploid. How are homologous A cell with 23 pairs of chromosomes. chromosomes DIFFERENT? A cell that is haploid.  The (Cellular) Circle of Life The lifecycle of a cell includes interphase & the mitotic phase Cells spend about 90% of their life in interphase This is when a cell grows, builds proteins, and duplicates its organelles This is also when the cell copies its DNA Interphase consists of the G1, S, and G2 phases The mitotic phase is the short period of time when the cell divides First, it divides its genetic information (using mitosis) Then, it divides its cytosol & organelles (using cytokinesis)  Organelles are The cell divides. duplicated. Cell “birth” The cell builds proteins & ATP is produced in ATP to prepare for the preparation for process of DNA replication. mitosis & cytokinesis. (everything but M) This is the resting stage that DNA is duplicated, most human cells are in. generating X-shaped chromosomes made Normal cellular functions of two identical sister happen here. chromatids.  Prophase Prophase is the first phase of mitosis In prophase, the cell’s chromatin condenses into compact sister chromatids The nuclear envelope around these chromatids starts breaking down The nucleolus (inside the nucleus) disappears The cell’s organelles migrate toward the edges of the cell, including its centrosomes Centrosomes are the organelles that build special microtubule proteins known as the mitotic spindle  Prometaphase By the time a cell reaches prometaphase, its nuclear envelope is completely broken down X-shaped duplicated chromosomes (made of two identical sister chromatids) are visible in this phase The sister chromatids are attached to one another in the chromosome’s centromere region Cohesin proteins (in the centromere region) “glue” the sister chromatids together tightly Kinetochore proteins (found at the end of the mitotic spindle) also attach here  Metaphase In metaphase, the cell’s chromosomes line up at the center of the dividing cell This central line of chromosomes is called the metaphase plate  Anaphase Sister chromatids are separated from one another during anaphase Enzymatic digestion & the pressure of the mitotic spindle’s “Tug of War” cause the centromere’s cohesin proteins to break Without these proteins, the sister chromatids are pulled to opposite edges of Metaphase Anaphase the cell As the chromatids are pulled apart, the dividing cell elongates Cohesin proteins  Telophase By telophase, the dividing cell’s chromosomes have completely separated New nuclear envelopes form around each set of chromosomes The chromosomes begin to de-condense back into chromatin The proteins of the mitotic spindle also dissolve Their amino acid monomers will be used to form the cytoskeleton in each of the daughter cells  Cytokinesis Cytokinesis overlaps with the end of mitosis. It is the process of dividing the cytoplasm of the cell and results in two identical cells. In animal cells, the plasma membrane of the parent cell pinches together in the middle This forms a deep cleavage furrow, which ultimately separates the two new cells In plant cells, a cell plate forms between the two new cells This plate will become the plant cell wall  Cell Cycle: A Review Cell division occurs during the mitotic phase of the cell cycle Part 1: Mitosis Function: dividing the genetic material of the cell Part 2: Cytokinesis Function: dividing the cytoplasm (organelles & internal fluid) of the cell  What Happens? What does it look like? (Draw a small picture!) Interphase (NOT part of mitosis!) Prophase Prometaphase Anaphase Telophase Cytokinesis (NOT part of mitosis!)  Identification Practice Stage: Stage: Stage: Stage: Stage: Stage: Stage:  Regulating the Cell Cycle The process of cell division is strictly regulated Cells monitor internal conditions to determine if they should divide Have a DNA mutation? No division! Have too many (or too few) chromosomes? No division! Cells also monitor external conditions to determine if they should divide Environment crowded with too many other cells? No division! Missing growth factors (chemical Cells have multiple checkpoints throughout messages)? No division! their life cycle to regulate the process of mitosis.  Checkpoints Three checkpoints ensure the cell cycle proceeds correctly. The final cell cycle checkpoint occurs during mitosis The cell checks that sister chromatids are attached to the mitotic spindle This attachment is required for the DNA to be equally divided Nondisjunction occurs when chromatids fail to separate from one another Daughter cells have incorrect numbers of chromosomes Down Syndrome is the result of a nondisjunction of a gamete External Conditions Influence Cell Division The anchorage dependence & density dependence of normal mammalian cells typically prevents mitosis from occurring when it is not needed Anchorage dependence means that cells will not divide if they are not attached to a growth surface (or to another cell) Density dependence means that cells will not divide if they are “squeezed together” with too many other cells  Cancer Cancer refers to a group of cells that are exhibiting uncontrolled growth They divide even without external growth signals They divide even with mutations or issues with chromosome duplication or spindle attachment Cancer typically starts with a mutation in a gene for a cell-cycle regulating protein Without the regulatory function of this protein, mutated cells reproduce constantly Ultimately, mutated cancerous cells will outnumber normal cells, leading to the formation of a tumor Type 2 Diabetes and Cell Division β cells become “tired” due to overstimulation from high fat and high sugar diet. They cannot divide enough to keep up with demand. What determines when and if cells Without enough β cells, insulin secretion decreases and cells divide? cannot take up glucose. Individuals must take supplemental insulin and eat a low sugar and fat diet. Swisa et al. Frontiers in Genetics 2017  To Prepare for Next Class…  Review your class notes Use the eTextbook & Other Helpful Resources to supplement your lecture notes  Complete the homework assignment Review what you didn’t understand and make another attempt. You can complete the homework as many times as you want!  Print the slides for Lesson #9  Eat some healthy foods and take a walk!