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Steven Brown

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Introduction to Cell Biology Discovering Cells  Robert Hooke (1665) o examined cork under microscope o cork is made up of “cells”  Anton van Leeuwenhoek (1674) – father of cell biology o examined pond water under microscope o “animalcules” – name he gave to microbes  Matthias Schleiden (1838), Theodor Schwann (1839) & Rudolf Virchow (1855) - proposed the Cell Theory: 1. All organisms are composed of one or more cells. 2. The cell is the structural unit of life. 3. Cells can arise only by division from a preexisting cell. Basic properties of cells 1. Cells are highly complex and organized. 2. Cells possess a genetic program and the means to use it. Genes  Proteins Fig A 3. Cells are capable of producing more of themselves. Ex: Mitosis and Meiosis 4. Cells can acquire and utilize energy  Photosynthesis and respiration Sun  carbohydrates  ATP 5. Cells carry out chemical reactions  “Metabolism” – sum total of chemical reactions in a cell  Enzymes aid in cellular metabolic processes (use ATP) 6. Cells engage in mechanical activities.  Transport materials inside the cell (intracellular transport)  Assemble and disassemble structures  Whole cells move! 7. Cells respond to stimuli.  use cell surface proteins for this – “receptors” 8. Cells can self-regulate - for example:  cells have DNA repair enzymes  cells can determine when they should stop or start dividing 9. Cells evolve.  genetic changes that lead to cellular changes that are beneficial, are retained in future generations. Prokaryotes and Eukaryotes Types of cells: Prokaryotes & Eukaryotes Bacterial Cell Prokaryotes [“Pro” meaning “before”; “Karyon” meaning “nucleus”]  ALL bacteria  Some unique characteristics: 1. Nucleoid - genetic material not bounded by a membrane 2. Structurally simpler 3. Less DNA than eukaryotes - typically, single circular chromosome 4. No mitosis or meiosis – “binary fission” instead (where cell literally splits into 2) Eukaryotes *“Eu” = true; “karyon” = nucleus+  protists, fungi, plants and animals  Some unique characteristics: 1. Membrane bound nucleus -nuclear membrane 2. Structurally more complex - internal organelles; complex cytoskeletal system 3. More DNA than prokaryotes - typically, several chromosomes composed of single linear DNA molecules 4. Division by mitosis or meiosis Eukaryotic Cells PLANT Cell ANIMAL Cell Similarities between PROKARYOTES + EUKARYOTES  Genetic code is identical – information encoded in DNA  Shared metabolic pathways - such as synthesis of ATP  Shared structural elements - cell membrane PROKARYOTES + EUKARYOTES: who came first? Fossil records -fossil records show that PROKARYOTES came to be early -it was another billion years after, until EURKARYOTES appeared The origin of EUKARYOTIC Cells  Prokaryotic cells arose before eukaryotic cells – observed through fossil records  Did eukaryotic cells arise from prokaryotes? o similarities noted between them (genetic code, metabolism) “Endosymbiont theory”  endosymbiont is 2 cells living together in a symbiotic relationship; one cell lives “inside” the other cell  “endo” meaning inside or within Endosymbiosis Model (1)starts out with an ANEROBIC ancestor (prokaryote), who then engulfs an AEROBIC bacterium (prokaryote)- this makes the anaerobic prokaryote to become aerobic (2)AEROBIC bacterium does funny things with its membranes and parts of it become internal to the cell and starts making the intracellular organization (3)then there is further specialization into other organelles (ie. ER) (4)it remains and differentiates further into an ANIMAL cell (5)if it engulfs a cyanobacterium, it becomes a PLANT cell Types of PROKARYOTES -2 major groups: 1. Archaea (archaebacteria) - “extremophiles”- thermophiles that grow @ 80-105°C (live in extreme heat) 2. Bacteria (eubacteria) – all other bacteria -cyanobacteria -most complex -Archaea are actually closer to eukaryotes than eubacteria! Types of EUKARYOTES 1. Unicellular – ie. protists -everything that this organism needs to survive is done by the one cell. 2. Multicellular – ie. humans -different activities are carried out by different types of specialized cells - “cell differentiation” Cell Differentiation  The process by which an unspecialized cell becomes a specialized one.  Differentiation occurs primarily through signals received by the cell from its environment.  The type of signals received depends upon the location of the cell within the embryo.  changes in cell morphology (appearance)  express “cell-specific” genes  unique proteins but “housekeeping” proteins (for cell metabolism etc.) will be the same as other cells  organelles stay the same but their number and location may differ Sizes of cells and their components Angstrom (Å = 10 mm) Nanometer-6 (nm = 10
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