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What does the asymmetry of protein distribution in membranes indicate?
What does the asymmetry of protein distribution in membranes indicate?
Carbohydrate motifs in the plasma membrane are directed inwardly.
Carbohydrate motifs in the plasma membrane are directed inwardly.
False
What enzyme is responsible for the displacement of lipids from one membrane layer to another?
What enzyme is responsible for the displacement of lipids from one membrane layer to another?
flipases
The majority of phosphatidylcholine is located in the _______ leaflet of red blood cells.
The majority of phosphatidylcholine is located in the _______ leaflet of red blood cells.
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Which of the following protein types is likely to be found in the outer leaflet?
Which of the following protein types is likely to be found in the outer leaflet?
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The inner leaflet of a cell membrane tends to have a more positive charge than the outer leaflet due to lipid distribution.
The inner leaflet of a cell membrane tends to have a more positive charge than the outer leaflet due to lipid distribution.
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Name one factor that affects membrane fluidity.
Name one factor that affects membrane fluidity.
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Match the following proteins or lipids with their corresponding leaflet distribution:
Match the following proteins or lipids with their corresponding leaflet distribution:
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What did Frye and Edidin use to facilitate the formation of heterokaryon in their experiment?
What did Frye and Edidin use to facilitate the formation of heterokaryon in their experiment?
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Proteins in the membrane are fixed in precise positions and do not move laterally.
Proteins in the membrane are fixed in precise positions and do not move laterally.
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What is the maximum lateral movement speed of a phospholipid molecule in the membrane?
What is the maximum lateral movement speed of a phospholipid molecule in the membrane?
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The movement of proteins between the two layers of the membrane is almost impossible without the intervention of __________.
The movement of proteins between the two layers of the membrane is almost impossible without the intervention of __________.
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Match the following terms with their descriptions:
Match the following terms with their descriptions:
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What was observed about the distribution of membrane proteins immediately after the fusion of cells?
What was observed about the distribution of membrane proteins immediately after the fusion of cells?
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What is the primary structure of the cell membrane as described in the fluid-mosaic model?
What is the primary structure of the cell membrane as described in the fluid-mosaic model?
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Movement of membrane proteins is always random.
Movement of membrane proteins is always random.
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Integral proteins exclusively penetrate only the outer layer of the lipid bilayer.
Integral proteins exclusively penetrate only the outer layer of the lipid bilayer.
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What role do extracellular matrix and membrane proteins play in protein movement?
What role do extracellular matrix and membrane proteins play in protein movement?
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What are peripheral proteins primarily attached to?
What are peripheral proteins primarily attached to?
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What primarily stabilizes the lipid bilayer structure of cell membranes?
What primarily stabilizes the lipid bilayer structure of cell membranes?
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Integral proteins must have a stretch rich in ___________ to be stable inside the hydrophobic region of the lipid bilayer.
Integral proteins must have a stretch rich in ___________ to be stable inside the hydrophobic region of the lipid bilayer.
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The Gorter and Grindel model explains the organization of proteins in the lipid bilayer.
The Gorter and Grindel model explains the organization of proteins in the lipid bilayer.
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Which type of membrane protein is covalently attached to lipid molecules?
Which type of membrane protein is covalently attached to lipid molecules?
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Match the types of membrane proteins with their characteristics:
Match the types of membrane proteins with their characteristics:
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What appearance did Robertson observe in cell membranes using osmium tetroxide staining?
What appearance did Robertson observe in cell membranes using osmium tetroxide staining?
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The central clear lamina in Robertson's trilaminar model is referred to as the ______ lamina.
The central clear lamina in Robertson's trilaminar model is referred to as the ______ lamina.
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All membrane proteins are covalently bonded to the lipid bilayer.
All membrane proteins are covalently bonded to the lipid bilayer.
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Match the scientists with their contributions to cell membrane models:
Match the scientists with their contributions to cell membrane models:
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How many times do single-pass polytopic membrane proteins cross the membrane?
How many times do single-pass polytopic membrane proteins cross the membrane?
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Which of the following accurately describes the lipid bilayer model?
Which of the following accurately describes the lipid bilayer model?
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The average thickness of osmophilic lamina is greater than that of the osmophobic lamina.
The average thickness of osmophilic lamina is greater than that of the osmophobic lamina.
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What is the average total thickness of the trilaminar appearance in cell membranes?
What is the average total thickness of the trilaminar appearance in cell membranes?
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What structure comprises the components of gap junctions?
What structure comprises the components of gap junctions?
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Synaptic junctions involve direct contact between presynaptic and postsynaptic membranes.
Synaptic junctions involve direct contact between presynaptic and postsynaptic membranes.
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Name the neurotransmitter that is released at the synaptic junction.
Name the neurotransmitter that is released at the synaptic junction.
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Gap junctions are made up of six subunits of connexins, which form a structure called a ______.
Gap junctions are made up of six subunits of connexins, which form a structure called a ______.
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Match the following features with their correct descriptions:
Match the following features with their correct descriptions:
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Which statement about gap junctions is correct?
Which statement about gap junctions is correct?
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Gap junctions are present in nearly all tissues of the body.
Gap junctions are present in nearly all tissues of the body.
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What is the width range of the synaptic cleft?
What is the width range of the synaptic cleft?
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What is the primary component of the primary cell wall in plants?
What is the primary component of the primary cell wall in plants?
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Connexins can open and close the gap junctions permanently.
Connexins can open and close the gap junctions permanently.
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What diameter range do polar molecules need to be in order to pass through gap junctions?
What diameter range do polar molecules need to be in order to pass through gap junctions?
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The cytoplasmic bridges between adjacent plant cells for communication and nutrient exchange are known as __________.
The cytoplasmic bridges between adjacent plant cells for communication and nutrient exchange are known as __________.
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Match the following components to their functions in plant cell walls:
Match the following components to their functions in plant cell walls:
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What causes the opening of gap junctions?
What causes the opening of gap junctions?
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Gap junctions allow for selective passage of small molecules.
Gap junctions allow for selective passage of small molecules.
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What is formed when connexins assemble in gap junctions?
What is formed when connexins assemble in gap junctions?
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Study Notes
Cell Membranes
- Cell membranes, also called biomembranes, are found in all cells.
- These membranes include the plasma membrane, nuclear membrane, endoplasmic reticulum (ER) membrane, Golgi apparatus membrane, vacuole membrane, and mitochondrial membranes.
- Cytomembranes separate specific compartments within cells from their surroundings.
- Prokaryotes have less complex compartmentalization than eukaryotes.
- Plasma membranes are crucial for maintaining cell integrity.
- Damage to the plasma membrane can lead to cell death.
- Cell membranes perform various biochemical reactions and physiological processes, including signal transduction, phosphorylation, and respiration (prokaryotes).
- Cells communicate and interact with neighboring cells via their plasma membranes.
- All cell membranes have selective permeability.
- They control the passage of substances between compartments.
- Some molecules pass freely, while others require channels or transporters.
Lipid Bilayer
- The primary structure of cell membranes is a lipid bilayer.
- This is composed of phospholipids (glycerol-derived and sphingosine-derived), glycolipids, and steroids (e.g., cholesterol).
- Phospholipids arrange themselves in a bilayer to avoid contact between hydrophobic tails and water.
- This arrangement is stabilized by hydrophobic interactions.
Fluid Mosaic Model
- The fluid mosaic model describes membrane structure and properties.
- The model suggests that a membrane consists of a phospholipid bilayer with proteins embedded in a mosaic-like pattern.
Types of Membrane Proteins
- Peripheral or Extrinsic Proteins: Weakly attached to the lipid bilayer's inner or outer surfaces. Often involved in adhesion (e.g., to cytoskeleton or other proteins).
- Integral or Intrinsic Proteins: Strongly attached to the lipid bilayer. Can span the membrane completely (transmembrane) or partially (monotopic).
Membrane Asymmetry
- Protein and lipid distribution across the lipid bilayer is not uniform.
- The outer and inner leaflets (layers) differ in composition.
- This asymmetry is crucial for membrane function.
Membrane Fluidity
- Membranes are dynamic structures; molecules are constantly moving.
- Fluidity is affected by factors like temperature, fatty acid composition (saturation), and presence of cholesterol.
- Cholesterol moderates membrane fluidity at both high and low temperatures.
Membrane Polarization
- Cell membranes frequently have specialized regions with different properties and functions.
- Examples include apical and basal domains in polarized cells (e.g., epithelial cells).
Cell Junctions
- Tight junctions: Seal adjacent cells together.
- Intermediate junctions (zonula adherens): Link cells via intracellular filaments (e.g., actin).
- Desmosomes (macula adherens): Anchor cells with strong connections.
- Gap junctions (communicating junctions): Allow small molecules and ions to pass between cells.
Synaptic Junctions
- These are specialized cell-cell contacts between neurons which transmit signals (neurotransmitters).
Microdomains
- Lipid rafts are specialized regions within the cell membrane, rich in specific lipids and proteins.
Plant Cell Walls and Plasmodesmata
- Plant cells have a rigid cell wall outside the plasma membrane.
- Plasmodesmata are intercellular channels that connect plant cells, allowing cell-cell communication and transport.
Transport of Macromolecules
- Endocytosis, exocytosis, and phagocytosis are mechanisms for transporting large molecules in and out of the cell.
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Description
Test your knowledge on the asymmetry of protein distribution in membranes and the factors that affect membrane fluidity. This quiz covers key concepts related to lipid and protein localization in cell membranes, as well as experimental findings in membrane research. Perfect for students studying cell biology or biochemistry!
