Plasma Lab 4 membrane Basic Semifluid Ribosomes features substance (make called proteins) of all cytosol cells Chromosomes (carry genes) © 2014 Pearson Education, Inc. Prokaryotic cells are characterized by having . No nucleus . DNA in an unbound region called the nucleoid . No membrane-bound organelles . Cytoplasm bound by the plasma membrane © 2014 Pearson Education, Inc. Eukaryotic cells are characterized by having • DNA in a nucleus that is bounded by a membranous nuclear envelope • Membrane-bound organelles • Cytoplasm in the region between the plasma membrane and nucleus Eukaryotic cells are generally much larger than prokaryotic cells © 2014 Pearson Education, Inc. Figure 6.8a ENDOPLASMIC RETICULUM (ER) Nuclear envelope Rough ER Smooth ER Nucleolus NUCLEUS Flagellum Chromatin Centrosome Plasma membrane CYTOSKELETON: Microfilaments Intermediate filaments Microtubules Ribosomes Microvilli Golgi apparatus Peroxisome Lysosome Mitochondrion © 2014 Pearson Education, Inc. Figure 6.8b Nuclear envelope NUCLEUS Nucleolus Rough ER Chromatin Smooth ER Ribosomes Golgi Central vacuole apparatus Microfilaments CYTOSKELETON Microtubules Mitochondrion Peroxisome Plasma Chloroplast membrane Cell wall Plasmodesmata Wall of adjacent cell © 2014 Pearson Education, Inc. © 2014 Pearson Education, Inc. © 2014 Pearson Education, Inc. © 2014 Pearson Education, Inc. Table 6.1 © 2014 Pearson Education, Inc. Cell Walls of Plants The cell wall is an extracellular structure that distinguishes plant cells from animal cells Plant cell walls Prokaryotes, are made of fungi, and cellulose fibers some embedded in unicellular other eukaryotes also polysaccharides have cell walls and protein The cell wall protects the plant cell, maintains its shape, and prevents excessive uptake of water © 2014 Pearson Education, Inc. Plant cell walls may have multiple layers • Primary cell wall: Relatively thin and flexible • Middle lamella: Thin layer between primary walls of adjacent cells • Secondary cell Plasmodesmata wall (in some are channels cells): Added between between the adjacent plant plasma membrane cells and the primary cell wall © 2014 Pearson Education, Inc. The Extracellular Matrix (ECM) of Animal Cells . Animal cells lack cell walls but are covered by an elaborate extracellular matrix (ECM) . The ECM is made up of glycoproteins such as collagen, proteoglycans, and fibronectin . ECM proteins bind to receptor proteins in the plasma membrane called integrins © 2014 Pearson Education, Inc. Plasmodesmata in Plant Cells . Plasmodesmata are channels that perforate plant cell walls . Through plasmodesmata, water and small solutes (and sometimes proteins and RNA) can pass from cell to cell Cell walls Interior of cell Interior of cell 0.5 μm Plasmodesmata Plasma membranes © 2014 Pearson Education, Inc. Tight Junctions, Desmosomes, and Gap Junctions in Animal Cells Three types of cell junctions are common in epithelial tissues At tight junctions, Gap junctions membranes of neighboring Desmosomes (anchoring (communicating junctions) cells are pressed together, junctions) fasten cells provide cytoplasmic preventing leakage of together into strong sheets channels between adjacent extracellular fluid cells © 2014 Pearson Education, Inc. Figure 6.30 Tight junctions prevent fluid from moving Tight across a layer of cells. junction TEM 0.5 μm Tight junction Intermediate filaments Desmosome Desmosome 1 μm Gap (TEM) junction Ions or small molecules Plasma Extracellular membranes of Space matrix TEM adjacent cells between cells 0.1 μm Gap junctions © 2014 Pearson Education, Inc..