Week 9 - Cell Division, Mitosis and Meiosis 2021 PDF

Cell Division, Mitosis and Meiosis Dr Fatemeh Moheimani (Pharm-D, MSc, PhD) Week 9 – Cell Biology SCI1023-N-GJ1-2021 21/03/2022 Learning Outcomes • Describe the processes of cell division: • mitosis and • meiosis • Consider how meiosis encourages genetic diversity. Overview Part I • Cell Divisio...

Cell Division, Mitosis and Meiosis Dr Fatemeh Moheimani (Pharm-D, MSc, PhD) Week 9 – Cell Biology SCI1023-N-GJ1-2021 21/03/2022 Learning Outcomes • Describe the processes of cell division: • mitosis and • meiosis • Consider how meiosis encourages genetic diversity. Overview Part I • Cell Division • Mitosis • Watching a video Part II • Meiosis • Watching a video Part III • Discussing an original research paper relevant to our topic. Part IV • Practice Q&A • Filling the Module Evaluation Part I Cell Division in prokaryotes • Most prokaryotic cells divide by the process of binary fission. • Cell grows and DNA loop replicates semiconservatively. • DNA loops are pulled to opposite sides of the dividing cell. • The new cells are called daughter cells. They are clones because they contain identical sets of DNA. Cell Division in eukaryotes • Mitosis • Meiosis https://askabiologist.asu.edu/cell-division Mitosis Cell Division Mitosis • Mitosis is how somatic or non-reproductive cells divide. Mother cell • A single cell divides into two cells that are replicas of each other and have the same number of chromosomes. • Mother and daughter cells are genetically identical. Daughter cells Mitosis Stage Diagram Description Prophase Prometaphase Metaphase Anaphase Telophase Cytokinesis The Cell Cycle (Eukaryotes) In eukaryotic cells the cell cycle is divided to: • Interphase: cells spend most of their life • Cells increase in size (Gap 1). • They replicate their DNA (S phase). • They continue to grow (Gap 2). • Mitotic phase: • They divide • Resting phase: • A phase where the cell has left the cycle and has stopped dividing (Gap 0). Late G2 phase • DNA has already been replicated (S phase). • DNA sits within the nucleus as two connected copies called sister chromatids. Centromere: the region of a chromosome to which the microtubules of the spindle attach, via the kinetochore, during cell division. Cohesins hold sister chromatids together after DNA replication until anaphase when removal of cohesin leads to separation of sister chromatids Late G2 Phase • The cell has copied its centrosome. • The centrosome is an organelle that serves as • the main microtubule organising centre of the cell, and • a regulator of cell-cycle progression. Prophase • Chromosomes begin to condense • The mitotic *spindle forms • The nucleolus disappears * Spindle = fibers made of microtubules that appear during mitosis which move and separate chromosomes. Prometaphase • Also known as late prophase • Chromosomes are condensed and compact. • The nuclear envelope breaks down releasing the chromosomes into the cell. • The mitotic spindle begins to organize the chromosomes. Metaphase • All chromosomes are attached to the spindle and line up along the metaphase plate. • The cell ensures that each kinetochore is attached to the spindle to allow an equal split between the new cells. Anaphase • Sister chromatids are separated into individual chromosomes and microtubules attached to kinetochores pull the pairs apart. • Microtubules not attached to kinetochores push the two ends of the cell in opposite directions. Telophase • • • • Nearly there! Spindle is broken down Nuclear membrane reforms Chromosomes decondense Cytokinesis • The cytoplasm is divided between the two new cells and the cell membranes form. • In animal cells a band of actin pinches the two cells apart. • In plant cells a cell plate forms to create a new cell wall. Mitosis https://youtu.be/C6hn3sA0ip0 Mitosis Stage Diagram Description Prophase Prometaphase Metaphase Anaphase Telophase Cytokinesis Summary of Mitosis End of Part I Part II Meiosis Cell Division 4 Haploids (n) each contain different genetic information from each other and the parent cell Meiosis • The production of gametes; • female egg cells, or • male sperm cells • Cell division happens twice. • After meiosis, the sperm and egg cells can join to create a new organism. Diploid (2n) Meiosis I - Prophase I • Chromosomes begin to condense but they also pair up, known as synapsis. • The two chromosomes are held together by proteins known as the synaptonemal complex. • Crossing over can occur at random between the pairs (homologues). Crossing Over • The reciprocal exchange of genetic material between nonsister chromatids during prophase I of meiosis. • The resultant chromosomes are neither entirely maternal nor entirely paternal, but contain genes from both parents. Metaphase I • The spindle begins to attach to the chromosomes and they line up at the metaphase plate. • However, in meiosis each homologue of a pair binds to the spindle of opposing sides of the cell. • Sister chromatids will not be separated but homologue pairs will be. Anaphase I and Telophase I • Just like in Mitosis chromosomes are pulled to opposing ends of the cell in Anaphase I and the spindle breaks down in Telophase I. • The chromosomes decondense and the nuclear envelope begins to reform. • However, in meiosis the resulting cells are now haploid. Meiosis II • Mitosis for haploid cells • The cells from meiosis I have chromosomes that consist of two sister chromatids. • Meiosis II separates the sister chromatids resulting in haploid cells with non-duplicated chromosomes. Meiosis https://www.youtube.com/watch?v=-8L_l4wgIQs Summary Mitosis and Meiosis 2n/2c: 2 homolog (diploid) unreplicated chromosome (2 chromatids) 1n/1c: 1 single chromosome (haploid) that is unreplicated 2n/4c: 2 homolog chromosomes (diploid) consisting each of 2 sister chromatids 1n/2c: 1 single chromosome in which DNA has been duplicated End of Part II Summary • Cell Division • Mitosis • Meiosis Questions 1) What are different stages of eukaryotic cell cycle? What happens at each stage? 2) What are different stages of mitosis? 3) What are different stages of meiosis? Questions 1) True or false? Mitosis encourages genetic diversity. 2) What statement is true? a. Crossing over occurs during prophase of mitosis. b. Sister chromatids will not be separated during Metaphase I of meiosis. c. The resulting cells of telophase I of meiosis are diploid. d. All of the above. Relevant research •Respir Res. 2015 Oct 29;16:132. doi: 10.1186/s12931-015-0293-4. Pharmacologically-induced mitotic synchrony in airway epithelial cells as a mechanism of action of anti-inflammatory drugs R J Freishtat , G Nino , Y Tsegaye, S E Alcala, A S Benton , A M Watson, E K M Reeves, S K Haider, J M Damsker •PMID: 26511361 •PMCID: PMC4625853 •DOI: 10.1186/s12931-015-0293-4 Free PMC article Take 5 min to fill the Module Feedback for Cell Biology how to access? - directly from your Blackboard Ultra - by following the link in the emails that you have received - via MyTU Student Portal Thank you