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Describe the function of ion channels.
Remember that the non-polar tails of lipid molecules prevent charged molecules, like ions, from crossing the cell membrane.
Ion channels allow ions to pass down their concentration gradient (from high concentration areas to low)
Some are open all the time
Some are gated: open and close on demand.
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Describe the function of carriers proteins.
Ion is carried down its concentration gradient, it does not require energy.
Ion is carried up its concentration gradient, it does require energy.
Many molecules that cannot cross the cell membrane are "ferried"
This can occur up or down a concentration dradient (high to low, low to high)
If it occurs against a concentration gradient, energy is required.... Energy comes from ATP, other molecules that run down their concentration gradient.
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What is the most important of these carriers is a protein called
Na+/K+
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The signaling molecule that binds to the receptor is called
Ligand.
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Describe the function of receptor proteins.
Signals outside the cell can affect activities inside the cell.
The cell uses receptor proteins to detect an extracellular signal and transduce it to an intracellular signal.
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The process by which a signal outside the cell is transformed into a change inside the cell is called
Signal Transduction
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Describe the function of membrane-associated enzymes.
- Remember that enzymes are proteins that catalzye (speed up) chemical reactions.
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- Enzymes on the cell surface catalyze chemical reactions there.
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Describe the function of linker proteins.
The internal structure of the cell must be connected to the connective tissues outside the cell.
Intracellular side, linkers join integral membrane proteins to the cytoskeleton.
Extracellulare side, linkers join the same integral membrane proteins to the connective tissue matrix or to other cells.
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Describe the function of cell marker proteins.
These are a way to identify cells that belong to you, and what organ they belong to.
Sugars connected to proteins (glycoproteins) commonly used as "flags"
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Only ______ and ________ can move across the cell membrane without help.
Water; Gases
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The random motion of small particles or even molecules in a liquid or gas is called
Brownian motion
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Physical principles underlying diffusion.
Molecules in a gas or liquid can move around.
The warmer the tempertature, the more movement.
The smaller the molecule, the more movement.
This random movement is seen as diffusion: over time, the concentration of the substance will become equal in all parts of the system.
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When diffusion is limited by a semi-permeable (selectively permeable) membrane, then the process is called
Osmosis
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Define Osmotic pressure.
This increase in volume
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What is Tonicity
Describes the concentration of salts.
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Isotonic Solutions
Osmotic pressure of the solution is the same as the osmotic pressure inside the cell, and the cell remains the same shape and size.
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Hypotonic Solutions
The concentration of water is higher outside the cell than inside. (Bursting)
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Hypertonic Solutions
The concentration of soluble materials outside the cell is higher than inside. (cell shrinks)
When red blood cells shrink in a hepertonic solution, we say they crenate: they take on a spiny shape, which is not good if the RBC needs to slide easily through blood vessels.
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Passive Transport
No energy needed
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Facitlitated diffusion
protein channels or carriers in the cell membrane facilitate the diffusion of substances.
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What has to be escorted, even if the concentration is higher outside than inside.
Larger and charged molecules
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What are the critical steps in the facilitated diffusion of glucose?
Step 1: Gluscose fits into "pocket" of glucose transporter.
Step 2: Protein changes shape, closing glucose pocket.
Step 3: Glucose transporter changes shape again, forces glucose into cytoplasm.
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