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CHAPTER 3

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  1. CHAPTER 3 Cells as Units of Life

  2. Cell Concept • Robert Hooke (1663) • English scientist and inventor • Viewed slices of cork and leaves using a primitive compound microscope • Called the box-like cavities that he observed “cells”

  3. Cell Concept • Anton van Leeuwenhoek • Dutch microscopist • Made extensive observations • High quality lenses improved cellular study during the19th century • Matthias Scheiden (1838) • German botanist • Announced that all plant tissue was composed of cells

  4. Cell Concept • Theodor Schwann (1839) • Described animal cells as being similar to plant cells • Rudolf Virchow (1858) recognized all cells come from preexisting cells

  5. Cell Concept • Cell Theory • All living organisms are composed of cells . • All cells come from preexisting cells.

  6. Organization of Cells • Prokaryotic Cells • Prokaryotic Cells(before + nucleus) • Lack a nucleus • Bacteria and cyanobacteria • 1st cell type to evolve • Genetic material located in region called nucleoid • 2 main parts: membrane and cytoplasm

  7. Organization of Cells • Eukaryotic Cells (true + nucleus) • DNA bound by a nuclear membrane • 3 main parts: membrane, nucleus, cytoplasm • Contain membranous organelles • Animals, Plants, Fungi, Protists

  8. Organization of Cells • Components of Eukaryotic Cells and Their Functions • Plasma Membrane • Fluid‑Mosaic Model • Current model of membrane structure • Composition • Phospholipidbilayer • Glycoproteins partially or wholly embedded. • Proteins function as receptors, recognition sites, and transport vehicles

  9. Organization of Cells • Plasma Membrane is a fluid structure • Increase cholesterol content, decrease membrane fluidity • Selectively regulates flow of molecules into and out of the cell • Provides many of the unique functional properties of specialized cells

  10. Organization of Cells • Nucleus • Storage and processing of genetic information • Chromosomes • Chromatin • DNA and DNA-binding proteins • Chromosomal DNA carries the genetic information encoding cellular RNA and protein molecules

  11. Organization of Cells • Nuclear Membrane • Separates nuclear contents from cytoplasm • Equipped with pores which allow movement of molecules between the nucleus and cytoplasm • Nucleoli • Synthesis of ribosomal RNA

  12. Organization of Cells • Endoplasmic Reticulum (ER) • Network of membranous channels extending through cytoplasm • Rough Endoplasmic Reticulum • Membranes studded with ribosomes • Functions in protein synthesis • Smooth Endoplasmic Reticulum • No ribosomes • Functions in lipid synthesis

  13. Organization of Cells • Ribosomes • Protein synthesis • Some attached to ER others free in Cytoplasm • Golgi Body • Stacks of flattened membranes • Functions in modification, packaging, and storage of ER products.

  14. Organization of Cells • Vesicle • Membranous sac • Transport and storage of materials • Lysosomes • Specialized vesicle • Contains hydrolytic enzymes • Functions in digestion of damaged organelles or pathogens

  15. Organization of Cells • Mitochondria • Double membrane organelle • Inner membrane folded into plate-like or finger-like projections called cristae • Site of ATP synthesis • Self-replicating • Have tiny, circular genome containing DNA that specifies some proteins of a mitochondrion.

  16. Organization of Cells • Cytoskeleton • Support and maintain cell shape • Movements within cell • Composed of • Microfilaments • Microtubules • Intermediate filaments

  17. Organization of Cells Centrioles • 9 triplets of microtubules arranged as a cylinder • Organization of the spindle apparatus during animal cell division • Located in centrosome • Replicate prior to cell division

  18. Organization of Cells • Surfaces of Cells and Their Specializations • Free Surface of Epithelial Cells • Cilia and Flagella • Motile extension of cell surface • 9 pairs of microtubules surrounding a central pair • Basal body found at base • Sweep materials past cell • Propel entire organism in single-celled and some small multicellular organisms

  19. Organization of Cells • Pseudopodia • Cytoplasmic streaming extends a lobe (pseudopodium) outward from the cell surface • Movement of cells • Microvilli • Small projections of cell surface produced by evaginations of the plasma membrane • Increase absorptive and digestive surface area of cells

  20. Organization of Cells • Specialized Junctional Complexes • Epithelial Cells • Tight Junctions • Act as seals to prevent passage of molecules between cells • Encircle cells • Adhesion Junctions • Link adjacent cells together • Encircle cell • Lie below tight junctions • Ex: Desmosome, Hemidesmosome • Communicating Junctions • Form tiny canals allowing passage of small molecules and ions between cells • Ex: Gap Junction

  21. Organization of Cells Movements Across Membranes • Membrane Function • Plasma membranes maintain cellular integrity • 3 methods of movement: diffusion/osmosis, transport, endocytosis • Most cell membranes are selectively permeable • Permeable to water • Variably permeable or impermeable to solutes

  22. Diffusion/Osmosis • Diffusion • Movement of particles from an area of higher concentration to an area of lower concentration of particles or molecules • Gases, urea, lipid-soluble solutes, alcohol easily diffuse across membranes

  23. Diffusion/Osmosis • Osmosis • Movement of water molecules across a selectively permeable membrane from an area of higher water concentration to an area of lower water concentration • Hypoosmotic • Isosmotic • Hyperosmotic

  24. Transport • Carrier-Mediated Transport • Facilitated Diffusion • Requires special trans-membrane proteins transporters • Enable solute molecules to cross the phospholipid bilayer • Ex: Glucose • Transport is from higher to lower concentrations • No metabolic energy required

  25. Transport • Active Transport • Requires transporters • Materials are transported against a concentration gradient • Ex: Na+, K+ • Requires an expenditure of energy • As much as 10% to 40% of all energy produced by cells is consumed by the Na+- K+ exchange pump

  26. Endocytosis Endocytosis (3 Processes) • Ingestion of material by cells • Requires energy • Phagocytosis • “Cell eating” • Plasma membrane forms a pocket that engulfs solid material • Membrane-enclosed vesicle detaches from cell surface and moves into cytoplasm • Fuses with lysosomes and contents are digested by lysosomal enzymes • Ex: Cellular debris, microbes

  27. Endocytosis • Pinocytosis • Small areas of plasma membrane invaginate forming tiny vesicles • Invaginated pits and vesicles are called calveolae • Receptors for specific molecules or ions are concentrated in calveolae • Ex: Intake of some vitamins, hormones, growth factors, and translocation of substances

  28. Endocytosis Exocytosis • Movement of material out of a cell • Membrane of a vesicle fuses with plasma membrane and extrudes contents • Requires energy • Ex: Indigestible residues, hormone secretion

  29. Mitosis and Cell Division • All cells arise from the division of preexisting cells • Cell division • Division of the nucleus (karyokinesis) • Mitosis (somatic cells) • Meiosis (sex cells) • Division of the cytoplasm (cytokinesis) • In most multicellular organisms, all cells originate from the zygote • Single cell resulting from union of an egg and a sperm (gametes)

  30. Mitosis and Cell Division • Mitosis: PMAT • Nuclear division associated with formation of somatic (body) cells • Produces daughter cells genetically identical to the mother cell • Important in growth and tissue repair in multicellular organisms • Method of transmitting genetic from parent to progeny in animals that reproduce asexually

  31. Mitosis and Cell Division • Structure of Eukaryotic Chromosomes • Chromatin • DNA and protein • Not visible in cytoplasm • Chromatin condenses prior to nuclear division • Now visible in cytoplasm as chromosomes

  32. Mitosis and Cell Division • Centromere • Constricted region of a chromosome • Location of kinetochore • Disk of proteins that bind with spindle microtubules • Each species has a characteristic number of chromosomes in the somatic cells • Humans: 46 chromosomes

  33. Mitosis and Cell Division • Phases in Mitosis (PMAT) • Artificially divided into four successive phases • Prophase • Metaphase • Anaphase • Telophase