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Questions and Answers
What characteristic of phospholipids allows them to form a bilayer in the cell membrane?
What characteristic of phospholipids allows them to form a bilayer in the cell membrane?
Which of the following best describes the permeability of the cell membrane?
Which of the following best describes the permeability of the cell membrane?
What role do proteins play in the uptake and extrusion of specific molecules in the cell membrane?
What role do proteins play in the uptake and extrusion of specific molecules in the cell membrane?
What is the thickness of the typical cell membrane?
What is the thickness of the typical cell membrane?
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Which statement is true regarding the separation provided by the cell membrane?
Which statement is true regarding the separation provided by the cell membrane?
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What primarily drives secondary active transport in cells?
What primarily drives secondary active transport in cells?
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What is the function of antiporters in active transport?
What is the function of antiporters in active transport?
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In the context of active transport, symporters are used to...
In the context of active transport, symporters are used to...
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Which process connects the active transport of one solute to the transport of other solutes?
Which process connects the active transport of one solute to the transport of other solutes?
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What role do proton pumps play in the active transport of nutrients in plants?
What role do proton pumps play in the active transport of nutrients in plants?
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The Na+-glucose co-transport system primarily exemplifies which type of transport mechanism?
The Na+-glucose co-transport system primarily exemplifies which type of transport mechanism?
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What is the outcome of phosphorylation during active transport?
What is the outcome of phosphorylation during active transport?
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Which statement best describes the role of carrier proteins in active transport?
Which statement best describes the role of carrier proteins in active transport?
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What primarily characterizes a semi-permeable membrane in a cell?
What primarily characterizes a semi-permeable membrane in a cell?
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What is the function of aquaporin in bacteria?
What is the function of aquaporin in bacteria?
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Which of the following correctly describes passive transport?
Which of the following correctly describes passive transport?
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What distinguishes facilitated diffusion from simple diffusion?
What distinguishes facilitated diffusion from simple diffusion?
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What is required for active transport to occur?
What is required for active transport to occur?
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Which type of transport directly uses energy from ATP?
Which type of transport directly uses energy from ATP?
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How does a protein channel function during facilitated diffusion?
How does a protein channel function during facilitated diffusion?
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Which of the following best defines osmosis?
Which of the following best defines osmosis?
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What role do protein pumps play in the cell membrane?
What role do protein pumps play in the cell membrane?
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Which statement about diffusion is true?
Which statement about diffusion is true?
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Study Notes
Membranes and Receptors - Session 2
- Lecture Objectives: Describe the function of membranes as permeability barriers to small, hydrophilic molecules. Explore protein-mediated mechanisms allowing the uptake and extrusion of specific water molecules and ions.
Body Fluids
- Intracellular Fluid: Fluid within cells.
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Extracellular Fluid: Fluid outside of cells.
- Intravascular fluid: Blood plasma.
- Interstitial fluid: Fluid surrounding cells.
The Cell Membrane
- Structure: The cell membrane is a thin barrier (8nm thick) that separates the living cell from the aqueous environment. It's primarily composed of a phospholipid bilayer with embedded proteins.
Phospholipids
- Structure: Phospholipids have a hydrophilic head (attracted to water) and hydrophobic tails (repelled by water).
- Arrangement: These arrange themselves as a bilayer, with hydrophobic tails facing inwards and hydrophilic heads facing outwards.
Phospholipid Bilayer
- Boundary: This structure serves as a border defining the cell.
- Impermeability: The bilayer is largely impermeable to polar molecules (e.g., water, sugar, ions) but permeable to nonpolar molecules (e.g., lipids).
Cell Membrane Function
- Separation: The cell membrane separates the interior of the cell from its surroundings.
- Regulation: The cell membrane controls what enters and exits the cell. Hydrophobic (nonpolar) molecules can pass through more readily than hydrophilic (polar) molecules.
- Thickness: The membrane is approximately 8 nanometers thick.
Permeability to Polar Molecules
- Semi-permeable: The membrane becomes semi-permeable due to protein channels.
- Specific Channels: Specific protein channels allow the passage of specific materials across the membrane (e.g., water, ions, amino acids).
Cell Membrane Components
- Transmembrane Proteins: Transmembrane proteins embedded in the bilayer create semi-permeable channels.
- Lipid Bilayer Membrane: The foundation of the cell membrane.
Examples of Membrane Proteins
- Aquaporins: Water channels found in bacteria.
- Porins: Channels in bacterial outer membranes.
- Proton Pump (channels): Found in photosynthetic bacteria, these proteins facilitate movement of ions by changing shape.
Movement Across the Cell Membrane
- Diffusion: Movement of substances from high to low concentration. This can be both simple (through the lipid bilayer) or facilitated (through protein channels). Water moves through osmosis.
- Lipid Diffusion: Fats and other lipids can cross directly without the help of a protein.
- Facilitated Diffusion: Movement of polar or charged molecules through channels that require no energy input.
- Active Transport: Movement of molecules against their concentration gradient, which requires ATP.
Types of Active Transport
- Primary Active Transport: Requires ATP directly for transport, such as the sodium-potassium pump.
-
Secondary Active Transport (Cotransport): The energy is derived secondarily from ionic concentration gradients created by primary active transport. In this process, two or more molecules move together.
- Symport: Two molecules move in the same direction.
-
Antiport: Two molecules move in opposite directions.
- Examples: Na+-glucose co-transport or Na+-Ca2+ exchange
Uniport, Symport and Antiport
- Uniport: Moves one molecule across the membrane.
- Symport: Moves two molecules in the same direction across the membrane.
- Antiport: Moves two molecules in opposite directions across the membrane.
Additional Notes
- Diffusion: Movement of molecules from high to low concentration. This occurs naturally across a membrane.
- Concentration Gradient: Difference in the concentration of a substance across a membrane.
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Description
This quiz covers the function of membranes as barriers to hydrophilic molecules and the mechanisms for the uptake and extrusion of water and ions. It includes details about intracellular and extracellular fluids, as well as the structure of cell membranes and phospholipids.
