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What effect does cholesterol have on phospholipid movement at warm temperatures?
What effect does cholesterol have on phospholipid movement at warm temperatures?
How does cholesterol help maintain membrane fluidity at cool temperatures?
How does cholesterol help maintain membrane fluidity at cool temperatures?
What type of proteins are primarily responsible for the specific functions of the membrane?
What type of proteins are primarily responsible for the specific functions of the membrane?
Which statement is true regarding peripheral proteins?
Which statement is true regarding peripheral proteins?
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What distinguishes integral proteins from peripheral proteins?
What distinguishes integral proteins from peripheral proteins?
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The fluid mosaic model of the membrane suggests that membranes are made up of which components?
The fluid mosaic model of the membrane suggests that membranes are made up of which components?
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What role does the extracellular matrix (ECM) play in relation to membrane proteins?
What role does the extracellular matrix (ECM) play in relation to membrane proteins?
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In which part of the membrane are glycolipids primarily located?
In which part of the membrane are glycolipids primarily located?
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What is the primary role of proton pumps in plant cells?
What is the primary role of proton pumps in plant cells?
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Which process allows large molecules like polysaccharides to enter a cell?
Which process allows large molecules like polysaccharides to enter a cell?
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What is the mechanism of exocytosis?
What is the mechanism of exocytosis?
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Which type of endocytosis involves cells engulfing large particles?
Which type of endocytosis involves cells engulfing large particles?
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What differentiates receptor-mediated endocytosis from other forms of endocytosis?
What differentiates receptor-mediated endocytosis from other forms of endocytosis?
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What happens during pinocytosis?
What happens during pinocytosis?
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What is a key requirement for both exocytosis and endocytosis?
What is a key requirement for both exocytosis and endocytosis?
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What happens to a plant cell placed in a hypotonic solution?
What happens to a plant cell placed in a hypotonic solution?
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How does a hypertonic environment affect plant cells?
How does a hypertonic environment affect plant cells?
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Which of the following is a function of membrane proteins?
Which of the following is a function of membrane proteins?
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How do cells primarily recognize each other?
How do cells primarily recognize each other?
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Which type of transport protein enables facilitated diffusion of water?
Which type of transport protein enables facilitated diffusion of water?
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What is the result of an isotonic environment for a plant cell?
What is the result of an isotonic environment for a plant cell?
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What is one of the key roles of carrier proteins in the cell membrane?
What is one of the key roles of carrier proteins in the cell membrane?
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What function does the extracellular matrix (ECM) serve in relation to the cell membrane?
What function does the extracellular matrix (ECM) serve in relation to the cell membrane?
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Which statement describes active transport?
Which statement describes active transport?
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Which of the following options accurately describes signal transduction?
Which of the following options accurately describes signal transduction?
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What happens to an animal cell in a hypotonic solution?
What happens to an animal cell in a hypotonic solution?
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What is the primary role of integral membrane proteins?
What is the primary role of integral membrane proteins?
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What primarily facilitates the movement of specific ions across the plasma membrane?
What primarily facilitates the movement of specific ions across the plasma membrane?
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What is a characteristic of flaccid plant cells?
What is a characteristic of flaccid plant cells?
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Which type of membrane protein is specifically involved in cell-cell recognition?
Which type of membrane protein is specifically involved in cell-cell recognition?
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What is one aspect of the hydrophobic nature of the cell membrane?
What is one aspect of the hydrophobic nature of the cell membrane?
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What occurs when ion channels open or close in response to stimuli?
What occurs when ion channels open or close in response to stimuli?
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Which function does NOT belong to the roles of membrane proteins?
Which function does NOT belong to the roles of membrane proteins?
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What is the outcome of osmotic pressure in a turgid plant cell?
What is the outcome of osmotic pressure in a turgid plant cell?
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In which process do membrane-bound enzymes primarily participate?
In which process do membrane-bound enzymes primarily participate?
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What is passive transport?
What is passive transport?
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What drives the diffusion of molecules?
What drives the diffusion of molecules?
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What is the role of the concentration gradient in diffusion?
What is the role of the concentration gradient in diffusion?
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What characterizes an isotonic solution?
What characterizes an isotonic solution?
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How does water move in osmosis?
How does water move in osmosis?
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What happens to a cell in a hypertonic solution?
What happens to a cell in a hypertonic solution?
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What is the outcome for a cell in a hypotonic solution?
What is the outcome for a cell in a hypotonic solution?
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What defines tonicity in relation to cells?
What defines tonicity in relation to cells?
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What is dynamic equilibrium in the context of diffusion?
What is dynamic equilibrium in the context of diffusion?
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Which process requires no energy to occur?
Which process requires no energy to occur?
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Study Notes
Membrane Structure and Function
- The plasma membrane separates the living cell from its surroundings.
- The plasma membrane is selectively permeable. This means it allows some substances to cross more easily than others.
- Phospholipids are the most abundant lipids in the plasma membrane.
- Phospholipids are amphipathic, meaning they have both hydrophobic (water-fearing) and hydrophilic (water-loving) regions.
- The fluid mosaic model describes the membrane as a fluid structure with a mosaic of various proteins embedded in it.
The Fluidity of Membranes
- Phospholipids can move within the bilayer.
- Most lipids and some proteins drift laterally.
- Lipid flip-flop across the membrane is rare.
- The fluidity of a membrane depends on the types of lipids, specifically whether the hydrocarbon tails are saturated or unsaturated.
- Unsaturated tails with kinks increase fluidity, while saturated tails increase membrane viscosity.
- Cholesterol has an effect on membrane fluidity that varies with temperature.
- At warmer temperatures (like 37°C), cholesterol restrains phospholipid movement.
- At cooler temperatures, cholesterol maintains fluidity by preventing tight packing.
Membrane Proteins and Their Functions
- Membranes are a collage of proteins embedded in the fluid matrix of the lipid bilayer.
- Proteins determine most of the membrane's specific functions.
- Peripheral proteins are bound to the surface of the membrane.
- Integral proteins penetrate the hydrophobic core.
Six Major Functions of Membrane Proteins
- Transport
- Enzymatic activity
- Signal transduction
- Cell-cell recognition
- Intercellular joining
- Attachment to the cytoskeleton and extracellular matrix (ECM)
The Role of Membrane Carbohydrates in Cell-Cell Recognition
- Cells recognize each other by binding to surface molecules, often carbohydrates, on the plasma membrane.
- Membrane carbohydrates may be covalently bonded to lipids (forming glycolipids) or more commonly to proteins (forming glycoproteins).
- Carbohydrates on the external side of the plasma membrane vary among species, individuals, and even cell types in an individual.
Concept 7.2: Membrane Structure Results in Selective Permeability
- Cells must continuously exchange materials with their surroundings, which the plasma membrane controls.
- Plasma membranes are selectively permeable, allowing regulation of the cell's molecular traffic.
The Permeability of the Lipid Bilayer
- Hydrophobic (nonpolar) molecules, such as hydrocarbons, can dissolve in the lipid bilayer and pass through it quickly.
- Polar molecules, such as sugars, do not cross the membrane easily.
Transport Proteins
- Transport proteins allow passage of hydrophilic substances across the membrane.
- Channel proteins have hydrophilic channels that certain molecules or ions can use as tunnels.
- Aquaporins facilitate the passage of water.
- Ion channels open or close in response to a stimulus (gated channels).
- Carrier proteins bind to molecules and change shape to shuttle them across the membrane; these proteins are specific for the substance they move.
Concept 7.3: Passive Transport
- Diffusion is the tendency for molecules to spread out evenly into the available space.
- Diffusion of a population of molecules may exhibit net movement in one direction.
- At dynamic equilibrium, as many molecules cross one way as cross in the other.
- Substances diffuse down their concentration gradient (from one area of high concentration to low concentration)
- No work is needed to move substances down their concentration gradient.
- Diffusion across a biological membrane is considered passive transport since the cell needs no energy input.
Effects of Osmosis on Water Balance
- Osmosis is the diffusion of water across a selectively permeable membrane.
- Water diffuses from the region of lower solute concentration to the region of higher solute concentration.
Water Balance of Cells Without Walls
- Tonicity is the ability of a solution to cause a cell to gain or lose water.
- Isotonic solution: solute concentration the same as inside the cell, no net water movement.
- Hypertonic solution: solute concentration higher than inside the cell, cell loses water.
- Hypotonic solution: solute concentration lower than inside the cell, cell gains water.
Water Balance of Cells with Walls
- Cell walls help maintain water balance.
- A plant cell in a hypotonic solution swells until the wall opposes further uptake (turgid; firm).
- If a plant cell and its surroundings are isotonic, there is no net water movement, the cell is flaccid, and the plant may wilt.
- In a hypertonic environment, plant cells lose water, causing the membrane to pull away from the wall (plasmolysis).
Facilitated Diffusion: Passive Transport Aided by Proteins
- Transport proteins speed the passive movement of molecules across the plasma membrane.
- Channel proteins provide corridors that allow specific molecules or ions to cross the membrane.
- Examples include aquaporins (for water) and ion channels (that open or close).
Concept 7.4: Active Transport
- Some transport proteins can move solutes against their concentration gradients.
- Active transport moves substances against their concentration gradient.
- Active transport requires energy, usually in the form of ATP.
- Active transport is performed by specific proteins embedded in the membranes.
- Active transport allows cells to maintain concentration gradients that differ from their surroundings.
- The sodium-potassium pump is an example.
Cotransport
- Cotransport is when the active transport of a solute indirectly drives the transport of another solute.
- Plants commonly use the gradient of hydrogen ions generated by proton pumps to drive the active transport of nutrients.
Concept 7.5: Bulk Transport
- Large molecules, like polysaccharides and proteins, cross the membrane in bulk via vesicles.
- Bulk transport requires energy
Exocytosis
- Transport vesicles migrate to the membrane, fuse with it, and release their contents.
- Many secretory cells use exocytosis to export their products.
Endocytosis
- In endocytosis, the cell takes in macromolecules by forming vesicles from the plasma membrane.
- It is a reversal of exocytosis, using different proteins.
- Phagocytosis: cellular eating
- Pinocytosis: cellular drinking
- Receptor-mediated endocytosis
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Description
Explore the essential concepts of membrane structure and function. This quiz covers the plasma membrane's selective permeability, the role of phospholipids, and how fluidity is influenced by lipid types. Test your knowledge on key biological principles related to cell membranes.
