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Cells What is a cell? A cell is a membrane bound unit containing hereditary material and other compounds that make metabolism, growth and reproduction possible. Plasma membrane Cytoplasm Hereditary material 1 Cells Overview of cell structure Cells are surrounded by a plasma membrane. DNA the hereditary material is packaged in one or more chromosomes located in a nuclear region or nucleus. The cytoplasm contains molecules and organelles needed for cellular activities. Ribosomes are the factories in which proteins are manufactured. 2 Cells How were cells discovered? 1665 Robert Hooke Examined cork in simple microscope. Saw empty compartments and called them ‘cellulae’ (small rooms). 1650 - 1700 Anton Van Leeuwenhoek Made his own microscope that could magnify 200 X. Observed living things. Called them ‘Animacules’ (little animals). 3 Cells Formation of the cell theory 1838 Matthias Schleiden Concludes that all plants are made of cells or their derivatives. He called this theory phytogenesis 1839 Theodore Schwann All animal tissue is made of cells and within an organism these cells are identical. The theory they presented from these observations is often called the Schleiden and Schwann Cell Theory 4 Cells 1855 Rudolph Virchow Studied pathenogens and concluded ‘omnis cellula e cellua’ which means that all cells arise from pre-existing cells. Principles of the Cell Theory All organisms are composed of one or more cells. Cells are the basic unit of life. Cells arise only by division of a previously existing cell. 5 Cells Cell size Does small cell sizes have advantages? The surface area increases as the square 2 (10 )of the diameter of a sphere, but the volume increases as the cube (103 ). small cube - surface area 10 m 6 x (10 m x 10 m) = 600 m2 small cube - volume 10 m x 10 m x 10 m = 1000 m3 6 Cells big cell - surface area 2 6 x (30 m x 30 m) = 5400 m big cell - volume 30 m x 30 m x 30 m = 27000 m 3 7 Cells Comparing different sizes Surface area 1 small = 600 m 2 2 27 small = 16.200 m 2 1 big = 5400 m Volume is the same for 1 big and 27 small The ratio of surface to volume 27 small 16200/27000 = 0,6 1 big 5400/27000 = 0,2 surface area of small is 3X greater 8 Cell size Why aren´t cells larger? limitations of molecular diffusion faster passage through small cells more efficient communication limitations of surface/volume ratio with in size greater in volume interaction occurs only at surface insufficient exchange of materials at plasma membrane 9 Structure of prokaryotes Strong cell wall made of carbohydrate matrix and peptide units. Slime capsule (some times with pili), not always present. 10 Structure of prokaryotes Simple interior organization lack internal compartmentalization reactions not separated, one metabolic unit lack membrane-bound organelles infolding of plasma membrane Rotating flagella cell movement - screw like motion 11 Structure of prokaryotes Ribosomes in the cytoplasm protein synthesis Circular nuclear matter (DNA) located in the nucleoid region Plasmids small independent circular DNA Mesosome infolding of plasma membrane often associated with photosynthesis 12 Structure of eukaryotes More complex than prokaryotes They are compartmentalized possess internal membrane bound organelles ribosomes rough endoplasmic reticulum (rER) lysosomes Golgi apparatus (complex) mitochondria nucleus chloroplasts 13 Structure of eukaryotes Nucleus the largest organelle the nuclear envelope double layer of membranes, outer continuous with ER nuclear pores restrict passage of molecules to proteins and RNA chromosomes - chromatid contain hereditary material divided into linear chromosomes, associated with histone protein 14 Structure of eukaryotes the nucleolus an assembly plant for ribosomal subunits ribosomal proteins are made in the cytoplasm ribosomal RNA made in the nucleus 15 Organelles Endoplasmic reticulum Thin membrane not visible in the light microscope. Divides interior into compartments. Cytoskeleton, holds the cell shape. Rough ER covered with ribosomes manufactures proteins for export Smooth ER lacks ribosomes carbohydrate and lipid synthesis 16 Organelles Ribosomes Made of two parts. Made in the nucleus. Assist in the manufacture of proteins. Golgi apparatus 17 Organelles Mitochondrion Lysosome 18 Organelles Chloroplast 19 Cells State two similarities between prokaryotic and eukaryotic cells. State two differences between the eukaryotic nucleus and the prokaryotic nuclear material. 20 Endosymbiosis Symbiosis is two organisms living in close association. Mitochondria and chloroplasts are thought to be ancient bacteria that became incorporated into eukaryotic cells. Evidence supporting Theory: both are surrounded by double membranes mitochondria and bacteria hvae similar size mitochondrial ribosomes resemble bacterial ribosomes both have circular DNA like bacteria 21 mitochondria divide by simple fission The Plant Cell Wall 22