L4 BIO 101 Cell Division Lecture Notes PDF

Introduction to Biology BIO 101 Cell Division Lecture 04  CELL CYCLE The cell cycle is an ordered series of events involving cell growth and cell division that produces two new daughter cells. CELL DIVISION Cell division is the process by which a parent cell divides into two...

Introduction to Biology BIO 101 Cell Division Lecture 04  CELL CYCLE The cell cycle is an ordered series of events involving cell growth and cell division that produces two new daughter cells. CELL DIVISION Cell division is the process by which a parent cell divides into two or more daughter cells. Cell division usually occurs as part of a larger cell cycle. 2 3 4 1. Usually longest part of the cycle G1 Interval or gap after cell division 2. Cell increases in mass 3. Number of cytoplasmic components S Time of DNA synthesis (replication) doubles 4. DNA is duplicated G2 Interval or gap after DNA replication 5 MITOSIS CELL DIVISION Period of nuclear division Usually followed by cytoplasmic division Four stages Prophase Metaphase Anaphase Telophase 6  PROPHASE 1. Duplicated chromosomes begin to condense 2. New microtubules are assembled 3. One centriole pair is moved toward opposite pole of spindle 4. Nuclear envelope starts to break up 5. Spindle forms 6. Spindle microtubules become attached to the two sister chromatids of each chromosome 7  METAPHASE 1. All chromosomes are lined up at the spindle equator 2. Chromosomes are maximally condensed 8  ANAPHASE 1. It starts by splitting each paired chromosome into two sister chromatids, now known as daughter chromosomes. 2. The daughter chromosomes are pulled towards the opposite end of the cell due to the contraction of the spindle fibers. 3. At the end of this phase, each pole contains a complete set of chromosomes. 9  TELOPHASE 1. Chromosomes de-condense 2. Two nuclear membranes form, one around each set of unduplicated chromosomes 10  CYTOKINESIS 1. Cytoplasmic Division 2. Usually occurs between late anaphase and end of telophase Two mechanisms 1. Cleavage (animals) 2. Cell plate formation (plants) 11  RESULTS OF MITOSIS 1. Two daughter nuclei 2. Each with same chromosome number as parent cell 3. Chromosomes in unduplicated form 12  SIGNIFICANCE OF MITOSIS 1.It is responsible for the growth and development of multi-cellular organisms. 2.Mitosis facilitates the development of a single-cell zygote into a full-grown adult. 3.It helps in maintaining the same number of chromosomes in daughter cells after division 4.It helps in repairing damaged or worn-out tissues. 5.The way in which the skin cells that cover a child's body grow and divide is an illustration of mitosis 13  HeLa CELLS Growing cells in culture allows researchers to investigate processes and test treatments without danger to patients Most cells cannot be grown in culture Line of human cancer cells that can be grown in culture Descendants of tumor cells from a woman named Henrietta Lacks Lacks died at 31, but her cells continue to live and divide in labs around the world. These cells have been invaluable for medical research. They’ve been used to create the polio vaccine They were the first human cells to go up in space to see the effect of zero gravity Vital in cloning In vitro fertilization Gene mapping 14  MEIOSIS CELL DIVISION 6/29/2024 15  HOMOLOGOUS CHROMOSOMES 6/29/2024 16  CROSSING OVER Each chromosome becomes zippered to its homologue All four chromatids are closely aligned Non-sister chromosomes exchange segments After crossing over, each chromosome contains both maternal and paternal segments 17  M PHASES IN HUMAN Germ cells (2n) undergo meiosis to produce gametes (n) Gametes are sex cells (sperm, eggs) & meet at fertilization 6/29/2024 18 MEIOSIS Two consecutive nuclear divisions Meiosis I Meiosis II DNA is NOT duplicated between divisions Four haploid nuclei are formed Meiosis I Meiosis II Prophase I Prophase II Metaphase I Metaphase II Anaphase I Anaphase II Telophase I Telophase II 19  MEIOSIS I PROPHASE I 1. Each duplicated, condensed chromosome pairs with its homologue 2. Homologues swap segments 3. Each chromosome becomes attached to microtubules of newly forming spindle 20  METAPHASE I 1. Chromosomes are pushed and pulled into the middle of cell 2. Sister chromatids of one homologue orient toward one pole, and those of other homologue toward opposite pole 3. The spindle is now fully formed 6/29/2024 21  ANAPHASE I TELOPHASE I 1. Homologous chromosomes segregate 1. The chromosomes arrive at opposite poles from each other 2. The cytoplasm divides 2. The sister chromatids of each 3. There are now two haploid cells chromosome remain attached 4. This completes Meiosis I 6/29/2024 22  MEIOSIS II PROPHASE II 1. A new spindle forms around the chromosome 2. Microtubules attach to the kinetochores of the duplicated chromosomes 23  METAPHASE II 1. Chromosomes are pushed and pulled into the middle of cell 2. All of the duplicated chromosomes are lined up at the spindle equator, midway between the poles 24  ANAPHASE II TELOPHASE II Sister chromatids separate to become 1. The chromosomes arrive at opposite ends of the cell independent chromosomes 2. A nuclear envelope forms around each set of chromosomes & the cytoplasm divides 3. There are now four haploid cells 25  RESULTS OF MEIOSIS Four haploid cells produced Differ from parent and one another 6/29/2024 26  SIGNIFICANCE OF MEIOSIS 1.Meiosis gives rise to four haploid cells from the parent cell. 2.Meiosis is responsible for the formation of sex cells or gametes which might be responsible for sexual reproduction. 3.Due to recombinations in parental characters, variations occur, which are necessary for the evolution process. 4.The number of chromosomes is halved during meiosis; this allows gametes to fuse to form a zygote containing a mixture of paternal and maternal chromosomes. 5.Depending on the species, meiosis can create spores or gametes. 27 6/29/2024 28 6/29/2024 29 SIGNIFICANCE 30  THANK YOU 6/29/2024 31