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The Processes of Cell Division --- Mitosis and Meiosis
Reproduction of Cells The Processes of Cell Division --- Mitosis and Meiosis
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Cell Size Review… What are some of the difficulties a cell faces as it increases in size?
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Cell Size Review… The larger a cell becomes, the more demands the cell places on its DNA. In addition, a larger cell is less efficient in moving nutrients and waste materials across its cell membrane.
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Cell Size and Limits Living cells store critical information in DNA.
As a cell grows, that information is used to build the molecules needed for cell growth.
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Cell Division In order for cells to survive, they must constantly exchange ions, gases, nutrients, and wastes with their environment. These exchanges take place at the cell’s surface. To perform this function efficiently, there must be an adequate ratio between the cell’s volume and its surface area. As a cell’s volume increases, its surface area increases, but at a decreased rate. If you continued to increase the cell’s volume, it would soon be unable to efficiently exchange materials and the cell would die.
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Compensation For Cell Size Limitations
Before a cell grows too large, it divides into two new “daughter” cells in a process called cell division. Before cell division, the cell copies all of its DNA.
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Reproduction of Cells Section 1 Chromosomes
Section 2 Cell Division & Mitosis Section 3 Meiosis Online interactive tutorial for additional materials:
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By the Time We Finish This Segment …
Describe the structure of a chromosome. Identify the differences in structure between prokaryotic chromosomes and eukaryotic chromosomes. Describe the events of cell division in prokaryotes. Compare the numbers of chromosomes in different species. Explain the differences between sex chromosomes and autosomes. Distinguish between diploid and haploid cells.
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Chromosomes - Made of DNA + Protein
Eukaryotes DNA wrapped around proteins called histones. Chromosomes are linear strands Prokaryotes Simpler in structure than eukaryotes. Chromosomes are circular
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Structure of a Chromosome
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Basic Terms Chromosomes - the double helix (double strand of 2 sugar-phosphate backbones) and are tightly coiled up. Chromatid - Pairing with another chromosome to form two sister chromatids. Centromere – “button” that holds chromosomes together. Chromatin (DNA+histones) - is the loose form of chromosomes seen during interphase.
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Anatomy of a Chromosome
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Chromatin - Interphase
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Rate of Cell Division – Which takes less time??
Prokaryotes Binary Fission - the process of cell division in prokaryotes. Eukaryotes Mitosis - nuclear division producing two identical daughter cells
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What is the difference between binary fission and mitosis?
Is NOT a form of asexual reproduction IS a form of cellular reproduction that produces new cells for growth, repair, and the general replacement of older cells Binary fission … Is a form of asexual reproduction of an organism (single-celled)
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Chromosome Numbers Each species has a characteristic number of chromosomes in each cell.
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Chromosome Numbers, continued
Autosomes and Sex Chromosomes Chromosomes in an organism that are responsible for making body cells = autosomes. (2n) = diploid Skin, Muscle, Hair, Kidney, Blood, etc. Sex chromosomes are chromosomes that determine the sex of an organism. (1n) = haploid Humans have 23 PAIRS chromosomes, but 46 total chromosomes
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Chromosome Numbers, continued
Diploid and Haploid Cells Cells having two sets of chromosomes are diploid (2n). (Also known as somatic cells) Most all cells in our body Haploid cells (1n) have only one set of chromosomes. (Also known as gametes) Sex cells 1 comes from mom and 1 comes from dad
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Karyotype Karyotype – an organized profile of one’s chromosomes.
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Mitosis (Cell division in eukaryotes)
Cellular division that produces 2 identical cells Somatic cells
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By the Time We Finish This Segment …
Name the two parts of the cell that are equally divided during cell division in eukaryotes. Summarize the events of interphase. Describe the stages of mitosis. Compare cytokinesis in animal cells with cytokinesis in plant cells. Explain how cell division is controlled.
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Cell Division in Eukaryotes
Cell Cycle The cell cycle is the repeating set of events in the life of a cell. The cell cycle includes cell division and interphase. Cell division in eukaryotes includes nuclear division, called mitosis, and the division of cytoplasm, called cytokinesis. THESE ARE ALL KINDS OF CELLS (somatic, diploid) EXCEPT…Sex CELLS!!!
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Reminder …. Types Of Cells and How They Divide
Somatic cells = All cells EXCEPT sex cells Hair, Skin, Liver, Blood, etc. Go through the process of MITOSIS Sex cells (gametes) = Go through the process of MEIOSIS!
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Cell Division – Trick to help remember…
I Pray More At The Church Interphase – loooonnnngggg Intermission = longest stage of (NOT CONSIDERED PART OF MITOSIS!!!!) G1 (growth), S (synthesis), G2 (prep for ÷) G0 – can occur after G1, exiting the cell cycle; as is
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Cell Division in Eukaryotes, continued
Interphase Interphase consists of growth (G1), DNA replication (S), and preparation for mitosis (G2)
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Mitosis: Nuclear division occurs (P, M, A, T)
Somatic cell Division Somatic cells (body cells) divide for the purpose of growth, replacement, and repair of damage cells or tissues. Interphase: Preparation = DNA replicates, chemicals and organelle synthesis occurs. Mitosis: Nuclear division occurs (P, M, A, T) Cytokinesis: Division of the cytoplasm occurs, forming 2 genetically similar diploid cells
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Cell Division - Steps of Mitosis
Back to: (I) Pray More At The Church Prophase – the beginning of the PROduction as DNA forms into rod-shaped chromosomes Sidebar notes: the 2 copies of the chromatids have occurred (S phase), and remain connected to each other by the centromere As the centromeres separate, spindle fibers (microtubules – cell organelles chapter) radiate from the centromeres) … What macromolecule makes microtubules????
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Cell Division – Steps of Mitosis
Continuing…. I Pray More At The Church Metaphase – chromosomes line up in the Middle Anaphase – pull Away from and go to either side of the cell Telophase – chromosomes return to a less Tightly coiled chromatin state with nuclear envelops and a nucleolus around each of the new cells AT THIS POINT, the nucleus has split into 2, BUT NOT the cell itself…. Yet.
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Stages of Mitosis Notice that when the chromosomes separate = single chromosomes
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Cell Division – Cytokinesis
Continuing…. I Pray More At The Church - Cytokinesis – Cell Splits in the Center, resulting in 2 – 2n (diploid – non-sex) cells
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Cell Division - Cytokinesis
During cytokinesis in animal cells, a cleavage furrow pinches in and eventually separates the dividing cell into two cells. In plant cells, a cell plate separates the dividing cell into two cells.
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Control of Cell Division
Cell division in eukaryotes is controlled by many proteins. Control occurs at three main checkpoints. G1 (growth), S (synthesis), G2 (prep for ÷)
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Control of Cell Division, continued
When Control is Lost: Cancer Proteins that regulate cell growth are controlled by genes If mutations occur with the genes, protein function is affected, resulting in disruption of cell growth and division This disruption = uncontrolled growth of cells = Cancer
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Control of Cell Division, continued
When Control is Lost: Cancer An individual’s propensity for developing cancer depends on many factors Family genetics Exposure of carcinogens = cancer-causing agents Genetic mutations (mutagens) that can occur from exposure to carcinogens
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MEIOSIS (Cell division of sex cells) Gametes
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By the Time We Finish This Segment …
Compare the end products of meiosis with those of mitosis. Summarize the events of meiosis I. Explain crossing-over and how it contributes to the production of unique individuals. Summarize the events of meiosis II. Compare spermatogenesis and oogenesis. Define sexual reproduction
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Formation of Haploid Cells (Sex cells)
Meiosis - a process of nuclear division that reduces the number of chromosomes in new cells to half the number in the original cell. Meiosis leads to four haploid cells (gametes) rather than two diploid cells as in mitosis. Meiosis occurs ONLY with sex cells ---- All other cells are called somatic cells
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Formation of Haploid Cells (Sex cells)
In order to finish cell division of haploid cells with the correct number of chromosomes… (steps of mitosis x 2) Meiosis I and Meiosis II must occur Meiosis I includes prophase I, metaphase I, anaphase I, and telophase I. Results in DOUBLE the number of chromosomes needed for haploid cells to successfully exist and function in cell division. Therefore, Meiosis II must occur to complete the process resulting in 4 HAPLOID cells
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Stages of Meiosis – Notice split = TETRADS (2 Pair of Chromosomes)
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Stages of Meiosis – Notice split = TETRADS (2 Pair of Chromosomes), continued
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Formation of Haploid Cells (Sex cells)
During Prophase I of Meiosis: Crossing-over = when portions of homologous chromosomes (single strand of a pair of chromosomes) exchange genetic material, occurs during prophase I and results in genetic recombination. A reshuffling of genes occurs making individuals unique!! Genetically DIFFERENT cell results AND the forming tetrads of chromosomes
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Formation of Haploid Cells (Sex cells)
During Anaphase I of Meiosis Independent assortment the random separation of homologous chromosomes. Results in genetic variation or mixing of genetic traits. This is what allows you to have your dad’s color hair and your mother’s texture of hair!!
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Formation of Haploid Cells (Sex cells)
Meiosis II Is very similar to Meiosis I, EXCEPT Meiosis II does NOT go through interphase again…. Instead, Meiosis II begins in prophase II and continues through “Pray More At The Church” Meiosis II includes: prophase II, metaphase II, anaphase II, and telophase II. Four new haploid cells result.
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Meiotic Cell Division
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Development of Gametes
Spermatogenesis is the process by which sperm cells are produced. Oogenesis is the process that produces mature egg cells.
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Meiosis in Male and Female Animals
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Sexual Reproduction Sexual reproduction is the formation of offspring through meiosis and the union of a sperm and an egg. Offspring produced by sexual reproduction are genetically different from the parents.
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