plasma membrane. i. maintaining balance how do cells maintain balance? – cells need to maintain a...
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Plasma Membrane
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I. Maintaining Balance
• How do cells maintain balance?–Cells need to maintain a
balance by controlling material that move in and out of the cell –> HOMEOSTASIS.
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I. Maintaining balance
• Small molecules like water, oxygen, and carbon dioxide can move in and out of the cell freely.• Large molecules like proteins and
carbohydrates cannot.• Eliminating wastes.
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I. Maintaining balance
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Structure of the Plasma (cell) membrane
• All cells are surrounded by a plasma membrane
• Functions like a GATE, controlling what ENTERS and LEAVES the cell.
• The cell membrane is semipermeable or selectively permeable.
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Structure of the Plasma (cell) membrane
• A semipermeable membrane only allows certain molecules to pass through.–Some substances easily cross the
membrane, while others cannot cross at all.
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Structure of the Plasma (cell) membrane
• Made of a thin layer of lipids and proteins – Made mostly of
phospholipid molecules (phosphate + lipid).
– Phospholipids are a kind of lipid that consists of 2 FATTY ACIDS (tails), and PHOSPHATE GROUP (heads).
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Structure of the Plasma (cell) membrane
• Cell membranes consist of TWO phospholipid layers called a LIPID BILAYER.
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Structure of the Plasma (cell) membrane
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Structure of the Plasma (cell) membrane
• Water molecules surround both sides of the cell membrane.–Polar phosphate heads sticking
TOWARD the water (hydrophilic)–Nonpolar lipid tails pointing AWAY
from the water (hydrophobic)
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Structure of the Plasma (cell) membrane
• The cell membrane is constantly being formed and broken down in living cells.
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III. Lipid bilayer• Moving with and among the
phospholipids are cholesterol, proteins, and carbohydrates.–Cholesterol:•Nonpolar, found among the
phospholipids to help prevent the fatty acid tails from sticking together•Helps with structure and
homeostasis.
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III. Lipid bilayer
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III. Lipid bilayer• Proteins:–Found on the surface of the plasma
membrane = transmit signals to the inside of the cell.–Embedded in the plasma
membrane = structure and support of cells shape, and move large substance in and out of the cell.
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III. Lipid bilayer
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III. Lipid bilayer• Carbohydrates:–Attached to proteins, helps cells identify
chemical signals.– Ex.: help disease fighting cells recognize and
attack a potentially harmful cell.