The Cell Membrane Also known as a “plasma membrane”
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Transcript of The Cell Membrane Also known as a “plasma membrane”
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The Cell Membrane
Also known as a
“plasma membrane”
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Plasma Membrane
• Controls materials entering and leaving the cell
• Helps regulate homeostasis
• Plasma membrane has selective permeability
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similar to a window screen
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Made of phospholipids with embedded proteins.
Phospholipid
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Types of proteins in cell membrane
1. Cell-surface marker: identifies cell type and identifies cells as “self”.
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2. Receptor Protein: recognizes and binds to substances outside the cell
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3. Enzyme: Assists chemical reactions inside the cell
Example: sucrase and
maltase are embedded
into cells of the
small intestine,
where they digest
disaccharides
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4. Transport protein: Helps substances move across cell membrane.
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Cellular Transport
Sections 3-4 and 3-5
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I. Passive Transport• Materials move across membranes
because of a concentration gradient.
• Does not require energy.
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Diffusion is a type of passive transport.
• Molecules move from an area of high concentration to an area of low concentration.
A. Diffusion
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• Continues until equilibrium is reached
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B. Osmosis
• How is osmosis different from diffusion?
• It only deals with movement of water
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• Isotonic: same concentration of dissolved particles inside and outside of cell; cell stays the same size
Three Types of Solutions
• Hypotonic: less dissolved particles outside cell than in
cell; cell gains water and swells
• Hypertonic: more dissolved particles outside cell than in cell; cell loses water and shrinks
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• Osmosis in Plant cells
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• Practice Problem:
• Sea water has a higher concentration of salt than human body cells have.
• Why might drinking large amounts of sea water be dangerous for humans?
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• Facilitated diffusion is passive transport of materials across the plasma membrane with the aid of transport proteins .
• Molecules such as sugars or amino acids enter the cell through facilitated diffusion
• Channel protein shown at right – provides a tubelike opening for small molecules
C. Facilitated Diffusion
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• Carrier proteins change shape to let larger molecules into the cell
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Cells use energy to transport materials against the concentration gradient
II. Active Transport
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• Active transport is powered by chemical energy (ATP).
Active Transport
• Active transport occurs through transport proteins
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A cell can import large materials in vessicles during the process of endocytosis.
• Cells use energy to transport material in vessicles.
Endocytosis
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Exocytosis
•Exocytosis is the process of expelling material from the cell.
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