Questions and Answers
Which lipids become parts of membranes?
Which lipids do not become parts of membranes?
Why do phospholipids form bilayers?
Phospholipids are amphipathic with a hydrophilic phosphate group and hydrophobic tails that shield from water.
Why do lipid bilayers form spontaneously?
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Why do lipids in a bilayer interact with one another?
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How does a lipid bilayer 'self-seal' with a small tear?
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How does a lipid bilayer 'self-seal' with a large tear?
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How are phospholipids within a bilayer fluid?
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What affects the tightness of the packing of phospholipids in a monolayer?
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The more unsaturated carbons in the hydrocarbon tails, what happens?
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What explains the alteration of lipid composition in poikilothermic organisms?
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Where and how are phospholipids synthesized?
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How does the arrangement of membrane lipids become asymmetrical?
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What do scramblases do?
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What are the three types of integral membrane proteins?
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How do integral membrane proteins differ from peripheral membrane proteins?
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Why do integral membrane proteins contain alpha-helices or beta-pleated sheet structures?
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How is an alpha-helix an energetically favorable conformation for an integral membrane protein?
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How is a beta-pleated sheet an energetically favorable conformation for an integral membrane protein?
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How would you recognize the portion of a known transmembrane protein that traverses the membrane?
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How do transport proteins create hydrophilic channels?
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What does SDS stand for?
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What happens to detergents in solution?
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How do SDS and Triton-X interact with the bilayer?
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What does the cytoskeleton add to the properties of the plasma membrane?
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How do we know that membrane proteins are usually free to move in the plane of the membrane?
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What would prevent an integral membrane protein from diffusing in the plane of the membrane?
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Why might it be important to restrict the freedom of movement of proteins in the membrane?
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How are plant cell walls and glycoalyx alike?
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What does glycoalyx form?
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How are plant cell walls and glycoalyx dissimilar?
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What cells have glycoalyx and how is it beneficial?
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What is lectin?
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What does the fact that the poison ricin is a lectin suggest about its toxic effects?
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What can we see in freeze-fracture replicas that are not visible via any other forms of microscopy?
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What is a cell membrane?
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What does a cell membrane do and how?
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What does a cell membrane define?
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Study Notes
Lipids and Membranes
- Amphipathic lipids, such as cholesterol, integrate into cellular membranes.
- Non-amphipathic lipids do not form part of membranes, lacking both hydrophobic and hydrophilic properties.
Phospholipids and Bilayers
- Phospholipids have a hydrophilic phosphate head and hydrophobic hydrocarbon tails, leading to bilayer formation.
- Bilayers shield hydrophobic tails from water, creating energetically favorable noncovalent interactions.
- Bilayers form spontaneously due to their energetically favorable conformations.
Lipid Interactions
- Nonpolar lipids aggregate to minimize exposure to water, leading to compact molecular structures.
- Lipid bilayers can self-seal after small tears by rearranging to reduce unfavorable water interactions.
- Larger tears result in foldings that create new vesicles with distinct bilayers.
Fluidity of Phospholipids
- Phospholipids within bilayers exhibit fluidity by rotating around their axes and switching places based on packing tightness.
- Packing tightness is influenced by the length and number of double bonds in the hydrocarbon tails; shorter tails increase freedom.
Membrane Dynamics
- More unsaturated carbon atoms in hydrocarbon tails enhance phospholipid fluidity.
- Organisms adjust membrane lipid composition seasonally to maintain fluidity in response to temperature changes.
Phospholipid Synthesis
- Phospholipids are synthesized in the endoplasmic reticulum using cytosolic fatty acids.
- Newly formed phospholipids are unevenly distributed across monolayers by enzymes, resulting in asymmetrical membrane arrangements.
Integral and Peripheral Membrane Proteins
- Integral membrane proteins include transmembrane, lipid-linked, and lipid-monolayer-associated proteins.
- Peripheral membrane proteins interact noncovalently and can be extracted without disrupting the bilayer.
Protein Structure and Function
- Integral proteins typically consist of α-helices or β-pleated sheets in membrane-spanning regions, facilitating favorable interactions with lipids.
- α-Helices allow hydrophobic side chains to engage with lipid bilayers, while hydrophilic residues interact with the barrel's core.
- β-Pleated sheets offer similar energetic advantages, aiding in the formation of hydrophilic channels.
Transport Proteins
- β-barrels construct hydrophilic channels, allowing polar molecules to diffuse through membranes.
- Membrane conditions affect the movement and arrangement of proteins, revealing dynamic interactions within the membrane.
Detergents and Membrane Interaction
- Sodium dodecyl sulfate (SDS) and Triton-X are amphipathic detergents that form micelles to reduce unfavorable interactions with water.
- They disrupt bilayer interactions, facilitating the extraction of integral proteins while maintaining detergent-tethered stability.
Cytoskeleton and Membrane Properties
- The cytoskeleton contributes to the plasma membrane's shape and integrity through noncovalent interactions with attachment proteins.
- Membrane domains form to organize proteins, enhancing functional specialization.
Observing Membrane Dynamics
- Fluorescence microscopy experiments demonstrate that membrane proteins can move freely within the lipid bilayer.
- Integral protein movement is restricted by cytoskeletal tethers and extracellular barriers.
Extracellular Structures
- Plant cell walls and glycoalyx share structural features like glycoproteins and provide protection and support.
- Glycoalyx creates a protective sugar coating that facilitates movement through tight spaces.
Lectins and Toxic Effects
- Lectins, like ricin, bind to specific carbohydrates, altering cellular interactions and potentially causing harm, like blood clotting.
Membrane Visualization
- Freeze-fracture microscopy allows for the detailed observation of membrane topography and protein structures, offering unique insights into membrane organization.
Cell Membrane Definition and Function
- The cell membrane is a bilayer of amphipathic lipids integrated with proteins, creating compartments for cellular functions.
- It organizes macromolecules into functional membrane domains, defining cellular activities and interactions with the environment.
Studying That Suits You
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Description
Test your knowledge on lipids and their roles in membranes with these flashcards from Chapter 11. Explore the properties of amphipathic lipids, their structure, and the energetic advantages of bilayer formation. Perfect for students reviewing cellular biology concepts.
