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Importance of Cell Division in Life Processes

This article explores the reasons why cell division is crucial for the continuity of life, including reproduction, growth and development, and tissue renewal. It also discusses the organization and structure of chromosomes and the different types of cells in the human body.

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Importance of Cell Division in Life Processes

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  1. http://www.johnkyrk.com/chromostructure.swf

  2. Chapter 12 Chromosomes PART 1 AP BIOLOGY

  3. Why Divide? • The continuity of life • In order to survive, individuals must replace damaged cells • In order to grow, cell production must be greater than cell death

  4. 100 µm (a) Reproduction. An amoeba, a single-celled eukaryote, is dividing into two cells. Each new cell will be an individual organism (LM). Figure 12.2 A Why is Cell Division Important? • Unicellular organisms • Reproduce by cell division  increasing the population.

  5. 200 µm 20 µm (b) Growth and development. This micrograph shows a sand dollar embryo shortly after the fertilized egg divided, forming two cells (LM). (c) Tissue renewal. These dividing bone marrow cells (arrow) will give rise to new blood cells (LM). Why Do Multicellular Organisms Depend on Cell Division? • 1. Development & Growth • 2. Repair (ex: tissue renewal) • 3. Maintenance

  6. Cell Division (aka Mitosis) • Makes 2 genetically identicaldaughter cells from 1 parent cell • Before cells divide • They duplicate their genetic material  ensures that each daughter cell receives an exact copyof the genetic material, DNA

  7. Organization of the Genetic Material • All of a cell’s DNA (genetic information) is called its genome • In prokaryotes • Genome= single, long DNA molecule in a circle • In eukaryotes • Genome = several DNA molecules grouped in clumps (called chromosomes)

  8. DNA Molecules • DNA (in nucleus of eukaryotes) can be in 2 forms • Chromatin: DNA is nottightlypacked together (loosely coiled) • Occurs during interphase • Chromosomes: tightly packed together (TIGHTLY coiled) • Occurs during mitosis (cell division)

  9. Tightly coiled? Not tightly coiled?

  10. Chromatids = Two exact copies of DNA that make up a duplicated chromosome. Each chromosome is referred to as a sister chromatid. Sister chromatids attach to each other at the centromere

  11. How Does DNA Fit into a Small Cell? • Prokaryotic organisms • No nucleus; instead have a nucleiod region • DNA = 1, circular chromosome Binary fission – ‘division in half’ asexual reproduction

  12. How Does DNA Fit into a Small Cell? • Eukaryotic organisms split their DNA into several pieces (called chromosomes-many linear chromosomes) • stored within the cell's nucleus • DNA is coiled around proteins known as histones • Uses nucleosomesto form a “supercoil”

  13. DNA + histones form nucleosomes (help to “super coil DNA)

  14. Making Chromosomes **Occurs right before cell division (mitosis) Steps: • DNA copies itself through DNA Replication • The DNA coils (wraps) around proteins called histoneproteins. • Chromosomes are made.

  15. 50 µm The DNA molecules in a cellAre packaged into chromosomes

  16. Chromosome Structure • Two shapes of chromosomes • Single chromosome(1 copy of DNA); “V” shaped • Double Chromosome(2 copies of DNA); “X” shaped; a.k.a-duplicated chromosome Occurs right before cell division (mitosis)

  17. Chromosomes and Cell Division • In preparation for cell division (mitosis) • DNA is replicated (single  double chromosome) • V shape  X shape

  18. 0.5 µm A eukaryotic cell has multiple chromosomes, one of which is represented here. Before duplication, each chromosome has a single DNA molecule. Chromosomeduplication(including DNA synthesis) Once duplicated, a chromosome consists of two sister chromatids connected at the centromere. Each chromatid contains a copy of the DNA molecule. Centromere Sisterchromatids Separation of sister chromatids Mechanical processes separate the sister chromatids into twochromosomes and distribute them to two daughter cells. Sister chromatids Centromeres Figure 12.4 Each duplicated chromosomehas two sister chromatids, which separate during cell division

  19. Double Chromosome Structure Kinetochore attaches to spindle fibers Sister

  20. Another view…

  21. Chromosomes • Every eukaryotic species has a characteristic, unique# of chromosomes in EACH cell nucleus • Ex: Humans have 46 chromosomes • # of chromosomes does NOT necessarily equal complexity

  22. Different Types of Cells • There are 2 types of cells in the human body • Somatic cells: all body cells 2. Gametes: reproductive cells (sperm and egg)

  23. Different cell types  different cell divisions • Eukaryotic cell division consists of: 1. Mitosis, division of the nucleus 2. Cytokinesis, division of cytoplasm • Occurs in somatic (body)cells • In meiosis • Gamete cells are produced after a reduction in chromosome number

  24. Chromosome Number • Gametes (sperm/egg) have 1 copy of each chromosome and are called haploid. • Somatic (body) human cells have 2 copies of each chromosomes and are called diploid. • Human somatic cells have 23 PAIRSof chromosomes (total 46 chromosomes). • All pairs of chromosomes differ in size, shapes, and set of genes.

  25. Haploid vs. Diploid • Haploid= when a cell has 1 copy of each chromosome. • Expressed as n = 23 • Diploid= when a cell has 2 copy of each chromosome. (a.k.a TOTAL # of C’s in organisms) • Expressed as 2n = 46 Haploid sperm cell n Haploid egg cell n Fertilization 2n Diploid Zygote cell

  26. Practice…How many chromosomes are present in…?

  27. Practice…How many chromosomes are present in…?

  28. Set of Chromosomes • Each chromosome set contain 2 “homologues.” • Chromosomes have a “twin” or matching pair. • Homologous Chromosomes= chromosomes that are similar in shape, size, and genes. • Each homologue in a pair comes from eachparent!

  29. Chromosome Structure Homologous chromosomes are chromosomes that are similar in size, shape and their genetic content. These chromosomes separateduring cell division. There are 46 chromosomes in the human body. 23of them are from your mother and23chromosomes are from your father.

  30. Homologous Chromosomes • Homologous Chromosomes = chromosomes that are similar in size, shape, and genetic content. • The human body has 23 pairs of chromosomes. Each pair = 2 chromosomes, therefore human cells have 46 individual chromosomes. Half (23) come from your mom and half (23) come from your dad.

  31. The Cell Cycle PART 2 AP BIOLOGY

  32. The Cell Cycle • The mitotic phase alternates with interphase in the cell cycle • Interphasemitosisinterphasemitosis

  33. INTERPHASE S(DNA synthesis) G1 CytokinesisMitosis G2 MITOTIC(M) PHASE Figure 12.5 Phases of the Cell Cycle • 1. Interphase (90% of the cell’s life) • 2. The mitotic (M) phase

  34. Interphase can be divided into sub phases • 1. G1phase (GAP 1 phase) • cell grows in size • varies most in length from cell to cell • 2. S phase (synthesis phase) • DNA is copied (DNA replication) • Single  Double • Other organelles are copied (ex: centrosomes in animal cells) • 3. G2phase (GAP 2 phase) • More growth and preparation (make proteins) for mitosis http://www.cellsalive.com/cell_cycle.htm

  35. Another G phase of Interphase • Called G0 phase called the resting phase • The cell exits the “cycle” and (usually) does NOT reproduce again • Ex: muscle cells, nerve cells, red blood cells (fixed number) • RBC production in bone marrow but the life of RBC is 120 days, can’t reproduce

  36. Interphase“Intermission” or “Inbetween” • not part of mitosis • Includes stages G1, S, and G2 of the cell cycle • DNA is in chromatin form • Nucleus & nucleolus present • Longest phase of cell cycle

  37. cell cycle animation Checkpoints animation

  38. The Mitotic (M) phase • Is made up of 2 parts 1. Mitosis division of the nucleus (called Karyokinesis) 2. Cytokinesis  division of the cytoplasm

  39. Mitosis • Process of cell division in somatic cells where the cell’s nucleus divides into two nuclei • Each nuclei has the exact same number and kind of chromosomes (genetic info) as the parent cell • Used for cell growthand repair

  40. Mitosis • Continuous pathway (Early, Mid, & Late) • Consists of 4 phases and cytokinesis 1. Prophase 2. Metaphase 3. Anaphase 4. Telophase • Cytokinesis

  41. Remember:Interphase must occur before mitosis can occurInterphase is NOT MITOSIS Interphase before mitosis

  42. Prophase (X’s)“Pack Together” • Chromatin  Chromosomes condense • DNA “packs” together • Mitotic spindle fibers form from centrosomes • Centrioles are in centrosomes in animals • appear as asters in animals • Microtubule Organizing Centers (MTOC’s) (in plants) • Centrosomes & Spindle fibers move towards “poles” • Late:Nucleus and nucleolus disappear • kinetochore fibersattach to each kinetochore on each chromosome  they begin to migrate toward the cell center (paired chromatids)

  43. Mitotic Spindle Fibers On centromere of chromosome • Two types of spindle fibers • Kinetochore fibers- • Polar fibers Extend from across the poles from centriole to centriole

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