Chapter 3: A View of the Cell Section 1: The Discovery of Cells By Jaime Crosby, CHS
The History of Cell Theory Before the microscope was invented, people thought diseases were caused by curses. They had no idea that the microscopic world existed. Microscopes enabled scientists to view and study cells.
Scientists Involved in Discovery Robert Hooke: Invented microscope, looked at corks and saw “cells” Virchow and Louis Pasteur: disproved spontaneous generation (ostracized) Anton Van Leeuwenhoek: used compound light microscope to see microscopic life for the first time…Animalcules Schleiden and Schwann: discovered all plants and animals composed of cells, respectively
Cell Theory (Schleiden and Schwann) All organisms are composed of one or more cells. The cell is the basic unit of organization. All cells come from pre- existing cells.
Two Cell Types Prokaryotic Cells No nucleus No nucleus No membrane bound organelles No membrane bound organelles Ex. Bacteria Ex. Bacteria Eukaryotic Cells “True” nucleus “True” nucleus Various membrane bound organelles Various membrane bound organelles Ex. Plants and Animals Ex. Plants and Animals
Cell Membrane Outer layer that regulates what enters and leaves a cell (diffusion) Has a bi-layer, 2 layers with fatty tails that do not dissolve in water (hydrophobic) and phosphate heads that do dissolve well in water (hydrophilic). Selective permeability, allows things in or out in order to achieve “homeostasis” Cell membrane is fluid, constantly in motion (fluid mosaic model) 8 μm thick (12,500 = 1 piece of paper)
Additional Organelles Fluid inside cell is called cytoplasm, it provides structure and support to the cell
Nucleus Termed by Robert Brown in 1831 Termed by Robert Brown in 1831 Control center of the cell Control center of the cell Most cells only have one Most cells only have one Nucleolus Nucleolus In the center of the nucleus Contains DNA, hereditary material of cells in long strands called chromatin, which shorten and thicken into chromosomes which contain genetic information.
Mitochondria Powerhouse of the cell Powerhouse of the cell Has an inner folded membrane, cristae, where ATP, an energy storing molecule is produced from food Has an inner folded membrane, cristae, where ATP, an energy storing molecule is produced from food Found in both plant and animal cells, 1-3 μm in length Found in both plant and animal cells, 1-3 μm in length Golgi Body Packages and secretes cell products as waste Packages and secretes cell products as waste Flattened system of tubular membranes that modifies proteins Flattened system of tubular membranes that modifies proteins
Lysosomes Small sacks responsible for digestion in cells Small sacks responsible for digestion in cells Break down food particles, worn out cell parts Break down food particles, worn out cell parts Formed from golgi bodies Formed from golgi bodies
Endoplasmic Reticulum Responsible for transport in the cell, connects nuclear membrane to cell membrane Responsible for transport in the cell, connects nuclear membrane to cell membrane Rough ER Rough ER Covered with ribosomes to produce protein Site of protein production Smooth ER Smooth ER No ribosomes Numerous biochemical activities including the production and storage of lipids
Ribosomes Made in the nucleolus and on ER Made in the nucleolus and on ER Produce proteins outside the nucleus Produce proteins outside the nucleus Uses instructions from DNA Uses instructions from DNA
Plant Cells vs. Animal Cells Plant cells contain all of the previous organelles plus have a cell wall (DEAD, holds water and keep shape) and chloroplasts with GRANA stacks (for photosynthesis) as well as pigments (chromoplasts) Vacuoles store large amounts of water in plant cells 95% (allow for turgidity) Animal cells do have microtubules, microfilaments, and cytoskeletons which maintain shape and provide structure to cells
Cellular Transport and the Cell Cycle Cell Cycle and Mitosis
Mitosis Introduction Mitosis is a form of nuclear division leading to the production of two new cells with identical genetic composition. It leads to asexual reproduction when followed by division of the cytoplasm (cytokinesis). Growth and regeneration of somatic cells (cells that are not sex cells) in multicellular organisms result from mitosis. Occurs at the MERISTEM, or region of growth at end of root and stem IPMAT
Phases of Mitosis Interphase: The cell is engaged in metabolic activity and performing its preparation for mitosis. Chromosomes are not clearly discerned in the nucleus, although a dark spot called the nucleolus may be visible. G1, Synthesis, G2
Prophase: Chromatin in the nucleus begins to condense and becomes visible as chromosomes. The nucleolus disappears. Centrioles begin moving to opposite ends of the cell and fibers extend from the centromeres. Some fibers cross the cell to form the mitotic spindle. Prophase: Chromatin in the nucleus begins to condense and becomes visible as chromosomes. The nucleolus disappears. Centrioles begin moving to opposite ends of the cell and fibers extend from the centromeres. Some fibers cross the cell to form the mitotic spindle.
Metaphase: The nuclear membrane dissolves, spindles attach to the centromeres, and the chromosomes begin moving. Spindle fibers align the chromosomes along the middle of the cell nucleus.
Anaphase: The paired chromosomes separate and move to opposite sides of the cell. Motion results from a combination of movement along the spindle microtubules and through the physical interaction of polar microtubules.
Telophase: Chromatids arrive at opposite poles of cell, and new membranes form around the daughter nuclei. The chromosomes disperse and are no longer visible under the light microscope. The spindle fibers disperse, and cytokinesis or the partitioning of the cell may also begin during this stage. Cytokinesis: Results when a fiber ring composed of a protein called actin around the center of the cell contracts pinching the cell into two daughter cells.