Lecture 8.docx

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Biology - Biological Sciences
Course Code
BSC 2010

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Lecture 8 Concept 4.3 Eukaryotic Cells Have A Nucleus and Other Membrane Bound Compartments  Plant and algae cells contain plastids that can differentiate into organelles—some are used for storage.  A chloroplast contains chlorophyll and is the site of photosynthesis.  Photosynthesis converts light energy into chemical energy.  A chloroplast is enclosed within two membranes, with a series of internal membranes called thylakoids.  A granum is a stack of thylakoids.  Light energy is converted to chemical energy on the thylakoid membranes.  Carbohydrate synthesis occurs in the stroma—the aqueous fluid surrounding the thylakoids.  Other organelles perform specialized functions.  Peroxisomes collect and break down toxic by-products of metabolism, such as H2O2, using specialized enzymes.  Glyoxysomes, found only in plants, are where lipids are converted to carbohydrates for growth.  Vacuoles occur in some eukaryotes, but mainly in plants and fungi. Functions of vacuoles includes: o Storage of waste products and toxic compounds; some may deter herbivores o Structure for plant cells—water enters the vacuole by osmosis, creating turgor pressure o Reproduction—vacuoles in flowers and fruits contain pigments whose colors attract pollinators and aid seed dispersal o Catabolism—digestive enzymes in seeds’ vacuoles hydrolyze stored food for early growth  Contractile vacuoles in freshwater protists get rid of excess water entering the cell due to solute imbalance.  The contractile vacuole enlarges as water enters, then quickly contracts to force water out through special pores. Concept 4.4 The Cytoskeleton Provides Strength and Movement  The cytoskeleton: o Supports and maintains cell shape o Holds organelles in position o Moves organelles o Is involved in cytoplasmic streaming o Interacts with extracellular structures to anchor the cell in place  The cytoskeleton has three components with very different functions: o Microfilaments o Intermediate filaments o Microtubules:  Microfilaments: o Help a cell or parts of a cell to move o Determine cell shape o Microfilaments are polymers made from the protein (monomer) actin o Microfilaments are dynamic and often change organization and length in a cell. o Actin polymer (filament) ⇌ Actin monomers o Dynamic instability allows quick assembly or breakdown ofthe cytoskeleton. o In muscle cells, actin filaments are associated with the “motor protein” myosin; their interactions resul
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