A Tour of the Cell, Part 2 Lecture 2, Part 2 Fall 2008

Cytoskeleton Network of fibers extending throughout the cytoplasm 1 Network of fibers extending throughout the cytoplasm Three types: Microtubules Microfilaments Intermediate filaments Fig. 6.20

Cytoskeleton Microtubules Hollow rods Protein: tubulin 2 Microtubules Hollow rods Protein: tubulin Largest diameter (25 nm) Actively assembled & disassembled Function Maintain cell shape Compression-resisting Cell division (centrioles) Tracks for organelle movement Cell motility (cilia & flagella) Fig. 6.21 Table 6.3

Cilia & Flagella Microtubular containing extensions from a cell 3 Fig. 6.23 Microtubular containing extensions from a cell Flagella Typically one or two, long Undulating motion Cilia Typically many, short Back & forth motion Functions: Mobility of cell Movement of fluid past a cell Attachment (some cilia) Signal-receiving (specialized cilia)

Cytoskeleton Microfilaments Solid rods Protein: actin 4 Microfilaments Solid rods Protein: actin Smallest diameter (7 nm) Actively assembled & disassembled Function Maintain cell shape Tension bearing Change cell shape Cell motility (pseudopodia) Cell division (cleavage furrow) Muscle contraction Cytoplasmic streaming Table 6.3

Cytoskeleton Intermediate filaments Supercoiled cables 5 Intermediate filaments Supercoiled cables Proteins: keratin family Intermediate & variable diameter (8-12 nm) Permanent structures Function: Maintain cell shape (tension bearing) Anchor nucleus, some organelles Forms nuclear lamina Table 6.3

Extracellular Matrix (ECM): Animal Cells 6 Collagen Glycoproteins (protein + carbohydrate) Proteoglycan complex Core protein with many carbohydrate chains Fig. 6.30

Extracellular Matrix (ECM): Animal Cells 7 Fibronectin Attaches ECM to integrins Integrins Cell surface receptor proteins Fig. 6.30

Intercellular Junctions: Animal Cells 8 Tight junctions Continuous seal around cell Prevent fluid leakage Desmosomes Attach cells together Gap Junctions Cytoplasmic channels Proteins Fig. 6.32

Cell Walls in Plants Cell walls 9 Cell walls A protective layer external to the plasma membrane Plants (also bacteria, archaea, fungi, some protists) Functions: Protection Maintain shape Prevent excessive water uptake Fig. 6.28

Cell Walls in Plants 10 Matrix of cellulose, other polysaccharides & proteins What is cellulose?

Carbohydrates Function Energy source 11 Function Energy source used in cellular respiration to create ATP What are some sources of carbohydrates? Carbon skeleton “building block” for other organic molecules Cell identity Fibrous structural material Cellulose, chitin, peptidoglycan Sugars, starchs (pasta, bread, potatoes) Ribose and other monosachharides could have been formed in the prebiotic chemical soup of early earth

Carbohydrates Monomer small molecule Polymer 12 Monomer small molecule Polymer large molecule made up of many smaller monomers Macromolecules “Big molecule” Synthesis & Breakdown of Polymers Dehydration reaction Hydrolysis Fig. 5.2

Carbohydrates Monosaccharides Simple sugar (CH2O) Disaccharides 13 Monosaccharides Simple sugar (CH2O) E.g., glucose, fructose Disaccharides Double sugar (complex carbohydrate) E.g., sucrose, maltose, lactose Polysaccharides Complex carbohydrates Long chains of sugar E.g., glycogen, starch, cellulose, chitin Storage molecules Sucrose = glucose + fructose, maltose = 2 glucose, lactose = glucose + galactose Starch – glucose molecules strung together Glycogen = glucose polymer – stored in liver & muscle cells “carb loading” Cellulose – dietary fiber, roughage – need special anaerobic bacteria to break it down

Cellulose Structural polysaccharide Polymer of glucose 14 Fig. 5.8 Structural polysaccharide Polymer of glucose Most abundant organic compound on earth Not digestible by most organisms Beta glucose Unbranched & straight Forms microfibrils Fig. 5.7

Intercellular Junctions – Plant Cells 15 Plasmodesmata Channels between adjacent cells Cytosol is continuous between connected cells Fig. 6.31