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A Tour of The Cell Chapter 4
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Effect of Cell Size on Surface Area
Same total volume, but greater surface area to volume in smaller cells
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Most Cells Are Microscopic
Smaller things have a greater SA to volume ratio, allowing cells to maximize exchange across the plasma membrane Larger cells have less SA relative to their volume which is not efficient for maximizing exchange
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Scanning & Transmission Electron Microscopes
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Prokaryotic cells are Structurally Simpler than Eukaryotic Cells
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Eukaryotic Cells are Partitioned into Functional Compartments
Human cells have three basic parts: Plasma membrane—flexible outer boundary Cytoplasm—intracellular fluid containing organelles Nucleus—contains most of a cells genetic material
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NUCLEUS: Nuclear envelope Chromosomes Smooth endoplasmic reticulum
Nucleolus Rough endoplasmic reticulum Lysosome Centriole Ribosomes Figure 4.4A An animal cell. The harvard cell: Peroxisome Golgi apparatus CYTOSKELETON: Microtubule Plasma membrane Intermediate filament Mitochondrion Microfilament
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NUCLEUS: Rough endoplasmic reticulum Nuclear envelope Chromosome
Ribosomes Nucleolus Smooth endoplasmic reticulum Golgi apparatus CYTOSKELETON: Central vacuole Microtubule Chloroplast Intermediate filament Cell wall Plasmodesmata Microfilament Figure 4.4B A plant cell. Mitochondrion Peroxisome Plasma membrane Cell wall of adjacent cell
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Plasma Membrane Bimolecular layer of lipids and proteins
Plays a gynamic role in cellular activity Separates intracellular fluid (ICF) from extracellular fluid (ECF) Outside cell Inside cell
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The Nucleus is the Cell’s Genetic Control Center
Contains chromatin, a complex of proteins and DNA Genetic library with blueprints for nearly all cellular proteins Bound by a nuclear envelope with pores Contains a nucleolus, dark-staining spherical bodies w/in nucleus (ribosome assembly)
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The Endoplasmic Reticulum is a Biosynthetic Factory
Interconnected tubes & parallel membranes (cisternae) Continuous with nuclear membrane Two varieties: Rough ER -external surface studded with ribosomes Ribosomes are the platform for protein synthesis Smooth ER -lacks ribosomes; functions in lipid synthesis and detoxification of drugs, synthesis of steroid sex hormones
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Lysosomes are Digestive Compartments Within a Cell
Spherical membranous bags containing digestive enzymes (acid hydrolases) Digest unwanted material for the cell
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Mitochondria harvest chemical energy from food
Double-membrane structure with shelf-like cristae and its own DNA Provides most of cell’s ATP
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Chloroplasts Convert Solar Energy to Chemical Energy
Chloroplasts are plant organelles ; site of photosynthesis Found in all green parts of a plant; leaves are main site of photosynthesis Contain the green pigment chlorophyll involved in photosynthesis
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Chloroplasts convert solar energy to chemical energy
Stroma Inner and outer membranes Figure 4.15 The chloroplast. Granum Intermembrane space
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The Golgi Apparatus Stacked and flattened membranous sacs (cisternae)
Processing, packaging and shipping proteins Rough ER ER membrane Phagosome Plasma mem- brane Vesicle becomes lysosome Secretory vesicle Golgi apparatus Secretion by exocytosis Extracellular fluid
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The Cell’s Internal Skeleton Helps Organize its Structure and Activities
Elaborate series of rods throughout cytosol Microtubules (hollow) Microfilaments (solid) Intermediate filaments (solid)
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Intermediate filament Microtubule
Nucleus Nucleus Actin subunit Fibrous subunits Tubulin subunit Figure 4.17 Fibers of the cytoskeleton: microfilaments are stained red (left), intermediate filaments are stained yellow-green (center), and microtubules are stained green (right). 7 nm 10 nm 25 nm Microfilament Intermediate filament Microtubule
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Cilia and Flagella Move When Microtubules Bend
Flagella - whip like, tails that move an entire cell Cilia -short, hair-like structures that move substances across cell surfaces
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Membrane Junctions Three types:
Tight junctions- Prevent fluids and most molecules from moving between cells Desmosomes- Rivets” or “spot-welds” that anchor cells together Gap junctions- proteins form pores that allow small molecules to pass from cell to cell For spread of ions between cardiac or smooth muscle cells
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Tight junctions Anchoring junction Gap junctions Plasma membranes
Figure 4.21 Three types of cell junctions in animal tissues. Plasma membranes of adjacent cells Extracellular matrix
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