Cell Membrane Transport
Cell Membrane
l Also called the plasma membrane
l Is a semi-permeable lipid bilayer
l Semi—only some
l Permeable—passes through
l Lipid—made of fats
l Bi—two
l Layer—flat sheets
Structure of Cell/Plasma Membrane
l Composed of two phospholipid layers (bilayer)
l There are other molecules embedded in the membrane (proteins, carbohydrates)
l The fluid mosaic model describes the membrane
Function: Plasma/Cell Membrane
l Forms a boundary between inside and outside of the cell
l Controls passage of materials include:
l Water
l Glucose
l Nutrients
l Protects and supports the cell
l Transmits chemical signals across cell Chemical signals are transmitted across the cell membrane
l Receptors bind with ligands and change shape
Characteristics of Cell/Plasma Membrane
l The cell membrane is selectively permeable
l Some molecules can cross the membrane while others cannot
l The cell membrane is a double layer of membranes of fat that only let certain things get in and out of a cell.
l Also called the “gatekeeper” of the cell because it does in essence choose what enters or does not
l There are two types of receptors
l Intracellular receptor
l Membrane receptor
Cell Transport Osmosis and Diffusion
l Materials move across membranes because of concentration differences/gradient.
l Substances move from high to low concentration.
Passive transport does not require energy input from cell.
l Molecules can move across cell membrane through passive transport.
l There are two types of passive transport:
l Diffusion
l Osmosis
Diffusion and osmosis are types of passive transport.
l Molecules diffuse down a concentration gradient.
l From High to Low
Diffusion
l Movement of molecules, other than water, from an area of HIGH concentration to an area of LOW concentration
l No ATP energy is used.
l Example:
l Spraying air freshener in a room and eventually smelling it across the other side
l Some molecules cannot easily diffuse across the cell membrane
l Substances that are not soluble in lipids, like glucose and amino acids, must have help getting across the membrane.
l Facilitated diffusion is diffusion through transport proteins
l Does not require energy
Factor Affect Diffusion
l Size of the molecules
l Large molecules do not pass through easily
l Temperature
l The warmer the water or atmosphere the faster the reaction of diffusion
l Size of concentration gradient
l The greater the concentration difference the faster the reaction
Does diffusion ever stop?
l NO… because particles are in constant motion
l When the # of particles is equal on both sides of the membrane then equilibrium is reached
l When particles reach equilibrium the rate of diffusion is equal across the membrane
Osmosis
l There are three types of solutions:
l Isotonic
l Hypertonic
l Hypotonic
l Osmosis is the diffusion of water molecules across a semipermeable membrane.
l Water molecules move from high to low concentration.
l Example:
l Water moving from your small intestine to the bloodstream
Active Transport, Endocytosis, and Exocytosis
l Cells also use energy to transport materials that cannot diffuse across a membrane
l Active Transport requires energy input from a cell and enables a cell to move a substance against its concentration gradient.
l Active transport is powered by chemical energy (ATP)
l Remember:
l Passive transport requires no energy from the cell
l Active transport occurs through transport protein pumps.
l Cells use active transport to maintain homeostasis.
l Two types of Active Transport:
l Endocytosis
l Exocytosis
l A cell can import and export large materials or large amounts of materials in vesicles during the processes of Endocytosis and Exocytosis.
Endocytosis
l Process of taking material into the cell
l Phagocytosis is a type of Endocytosis.
l Cells require energy to transport material in endocytosis.
Exocytosis
l Process of expelling materials from the cell
l Cell requires energy to transport materials in endocytosis.
Cell Membrane Transport PPT
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