A Tour of the Cell

Surface Area to Volume Ratio * Metabolic requirements imposes limits on the size of a practical cell * Cells need a large enough surface area to adequately exchange materials * As any cell increases in size, its volume grows proportionately more than its surface area * Area – n2 * Volume – n2 * Where n = linear dimension Need for surface area explains the elongated nerve cells * Microvilli – long, thin projections (animal only) that increases SA and not volume Nucleus * Contains most of genes (other genes are located in mitochondria and chloroplast) * Nuclear envelope (lipid bilayer, double membrane): encloses nucleus and separates its contents from the cytoplasm * Pore complex: regulates entry/exit of proteins, RNAs and macromolecules * Nucleoplasm: the cytoplasm of the nucleus Nuclear lamina: a netlike array of protein filaments that maintains the shape of the nucleus * Nuclear matrix: fibres extending throughout the nuclear interior *

Primary cell wall: young plant cell’s thin wall Middle lamella: thin layer rich in sticky polysaccharides called pectins, acts as a glue for adjacent cells Extracellular Matrix (ECM) of Animal Cells * Contain glycoproteins secreted by the cells, the most abundant being collagen which forms strong fibers outside the cells * Proteoglycans – woven network of collagen fibers * Fibronectin – a type of glycoprotein found in ECM * Integrins – receptor protein attached to plasma membrane Intercellular Junctions Plants * Plasmodesmata: on cell walls, cytosol passes through the plasmodesmata and connects the chemical environments of adjacent cells, water and small solutes can pass Animals Tight junctions: plasma membranes tightly pressed against each other forming a continuous seal and prevents leakage (e.

g. skin cells make us watertight by preventing leakage between cells in our sweat glands) * Desmosomes: anchors cells together in strong sheets, made of intermediate filaments (e. g. muscle tears involve the rupture of desmosomes) * Gap junctions: cytoplasmic channels where small molecules pass, communication between cells (e. g. heart muscle and animal embryos)