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The cellular level of organization.docx

6 Pages

Biological Sciences
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Kenneth Welch

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The Cellular Level of Organization An Introduction to Cells The cell theory states: • Cells are the building blocks of all plants and animals • Cells are produced by the division of preexisting cells • Cells are the smallest units that perform all vital physiological functions • Each cell maintains homeostasis at the cellular level • Homeostasis at higher levels reflects combined, coordinated action of many cells Cell biology • Cytology, the study of the structure and function of cells • The human body contains both somatic and sex cells A typical cell • Is surrounded by extracellular fluid, which is the interstitial fluid of the tissue • Has an outer boundary called the cell membrane or plasma membrane The Cell Membrane Cell membrane functions include: • Physical isolation • Regulation of exchange with the environment • Structural support • The cell membrane is a phospholipid bilayer with proteins, lipids and carbohydrates. Membrane proteins include: • Integral proteins • Peripheral proteins • Anchoring proteins • Recognition proteins • Receptor proteins • Carrier proteins • Channels Membrane carbohydrates form the glycocalyx • Proteoglycans • Glycolipids • Glycoproteins The Cytoplasm The cytoplasm contains: • The fluid (cytosol) • The organelles the cytosol surrounds Organelles • Nonmembranous organelles are not enclosed by a membrane and always in touch with the cytosol • Cytoskeleton, microvilli, centrioles, cilia, ribosomes, proteasomes • Membranous organelles are surrounded by lipid membranes • Endoplasmic reticulum, Golgi apparatus, lysosomes, peroxisomes, mitochondria Cytoskeleton provides strength and flexibility • Microfilaments • Intermediate filaments • Microtubules • Thick filaments Microvilli  increase surface area Centrioles • Direct the movement of chromosomes during cell division • Organize the cytoskeleton • Cytoplasm surrounding the centrioles is the centrosome Cilia • Is anchored by a basal body • Beats rhythmically to move fluids across cell surface Ribosomes • Are responsible for manufacturing proteins • Are composed of a large and a small ribosomal subunit • Contain ribosomal RNA (rRNA) • Can be free or fixed ribosomes Proteasomes • Remove and break down damaged or abnormal proteins • Require targeted proteins to be tagged with ubiquitin Endoplasmic reticulum • Intracellular membranes involved in synthesis, storage, transportation and detoxification • Forms cisternae • Rough ER (RER) contains ribosomes • Forms transport vesicles • Smooth ER (SER) • Involved in lipid synthesis Golgi Apparatus • Forms secretory vesicles • Discharged by exocytosis • Forms new membrane components • Packages lysosomes Lysosomes and Peroxisomes • Lysosomes are • Filled with digestive enzymes • Responsible for autolysis of injured cells • Peroxisomes • Carry enzymes that neutralize toxins Membrane flow • Continuous movement and recycling of membranes • ER • Vesicles • Golgi apparatus • Cell membrane Mitochondria • Responsible for ATP production through aerobic respiration • Matrix = fluid contents of mitochondria • Cristae = folds in inner membrane The Nucleus The nucleus is the center of cellular operations • Surrounded by a nuclear envelope • Perinuclear space • Communicates with cytoplasm throu
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