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Questions and Answers
What type of membrane proteins span the entire membrane?
What type of membrane proteins span the entire membrane?
What characteristic of amphipathic molecules allows them to form bilayers in aqueous environments?
What characteristic of amphipathic molecules allows them to form bilayers in aqueous environments?
What characterizes peripheral proteins in relation to membrane interaction?
What characterizes peripheral proteins in relation to membrane interaction?
Which of the following correctly describes the role of the hydrophobic core in a lipid bilayer?
Which of the following correctly describes the role of the hydrophobic core in a lipid bilayer?
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How are transmembrane proteins associated with the lipid bilayer?
How are transmembrane proteins associated with the lipid bilayer?
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What role do membrane proteins play in the cell membrane?
What role do membrane proteins play in the cell membrane?
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What is one major consequence of the amphipathic nature of phospholipids in biological membranes?
What is one major consequence of the amphipathic nature of phospholipids in biological membranes?
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Which statement about non-covalent interactions involving hydrophilic molecules is accurate?
Which statement about non-covalent interactions involving hydrophilic molecules is accurate?
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Which of the following statements about lipid-anchored proteins is true?
Which of the following statements about lipid-anchored proteins is true?
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Why do fats and oils typically float on the surface of water when mixed?
Why do fats and oils typically float on the surface of water when mixed?
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What is the primary role of flippases in the membrane?
What is the primary role of flippases in the membrane?
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Which lipid is typically found on the inner leaflet of the bilayer?
Which lipid is typically found on the inner leaflet of the bilayer?
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What contributes to the asymmetry of the lipid bilayer?
What contributes to the asymmetry of the lipid bilayer?
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What is the typical rate of flip-flop movement for lipids in a membrane?
What is the typical rate of flip-flop movement for lipids in a membrane?
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Why is lipid bilayer asymmetry considered functionally important?
Why is lipid bilayer asymmetry considered functionally important?
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What mainly influences the lateral mobility of lipids and proteins in the cell membrane?
What mainly influences the lateral mobility of lipids and proteins in the cell membrane?
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During which cellular process is new membrane synthesized?
During which cellular process is new membrane synthesized?
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Which lipid is typically involved in creating asymmetry due to its location preference?
Which lipid is typically involved in creating asymmetry due to its location preference?
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What function does the glycocalyx serve in relation to cells?
What function does the glycocalyx serve in relation to cells?
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Which statement accurately describes the structure of phospholipids in the cell membrane?
Which statement accurately describes the structure of phospholipids in the cell membrane?
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What role do cholesterol molecules play in the membrane?
What role do cholesterol molecules play in the membrane?
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Which type of protein in the cell membrane specifically facilitates the passage of polar molecules and ions?
Which type of protein in the cell membrane specifically facilitates the passage of polar molecules and ions?
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What is the primary characteristic of the Fluid Mosaic Model of the cell membrane?
What is the primary characteristic of the Fluid Mosaic Model of the cell membrane?
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What is the role of glycoproteins in the cell membrane?
What is the role of glycoproteins in the cell membrane?
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In what way do carrier proteins function differently from channel proteins?
In what way do carrier proteins function differently from channel proteins?
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Which statement best describes the hydrophobic and hydrophilic regions of membrane proteins?
Which statement best describes the hydrophobic and hydrophilic regions of membrane proteins?
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Which function is NOT performed by membrane proteins?
Which function is NOT performed by membrane proteins?
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Which component directly contributes to the formation of the glycocalyx?
Which component directly contributes to the formation of the glycocalyx?
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What is the main limitation on the lateral movement of membrane proteins?
What is the main limitation on the lateral movement of membrane proteins?
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What type of interactions can peripheral membrane proteins have with transmembrane proteins?
What type of interactions can peripheral membrane proteins have with transmembrane proteins?
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Which of the following statements about integral proteins is correct?
Which of the following statements about integral proteins is correct?
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How do glycoproteins primarily aid in cellular interactions?
How do glycoproteins primarily aid in cellular interactions?
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What structural characteristic do proteoglycans primarily possess?
What structural characteristic do proteoglycans primarily possess?
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Which of the following is NOT a mechanism for restricting protein movement in membranes?
Which of the following is NOT a mechanism for restricting protein movement in membranes?
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Which protein type is primarily responsible for transporting Na+ across the cell membrane?
Which protein type is primarily responsible for transporting Na+ across the cell membrane?
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What is the primary role of carbohydrates attached to membrane lipids and proteins?
What is the primary role of carbohydrates attached to membrane lipids and proteins?
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Study Notes
Lipid Bilayer Asymmetry
- The two layers of the lipid bilayer have different compositions of phospholipids and glycolipids.
- Membrane proteins are embedded into the membrane with specific orientation.
- The asymmetry of the lipid bilayer is functionally important.
Membrane Synthesis
- Membrane synthesis occurs in the endoplasmic reticulum (ER).
- New membrane is exported to other membranes by vesicles (budding and fusion).
- Lipid asymmetry occurs during manufacture.
- Flippases selectively transfer specific phospholipids, resulting in asymmetric distribution in each monolayer.
Phospholipid Mobility
- Weak hydrophobic interactions in the interior of the membrane allow lipids and proteins to move laterally.
Flip-Flop
- The two leaflets of a bilayer membrane tend to differ in their lipid composition.
- Flip-flop of lipids (from one half of a bilayer to the other) is normally very slow.
- Flip-flop would require the polar head-group of a lipid to traverse the hydrophobic core of the membrane, which requires a large amount of energy.
- Some membranes contain enzymes that actively transport particular lipids from one monolayer to the other.
- Flippases catalyze flip-flop in membranes where lipid synthesis occurs.
Amphipathic Molecules
- Contain both a hydrophilic and a hydrophobic portion.
- Examples include steroids, glycolipids, and phospholipids.
Hydrophilic and Hydrophobic Interactions
- Hydrophilic molecules can dissolve in water due to the polarity of both molecules.
- Hydrophobic molecules will be "caged" by the polar molecules, requiring energy.
The Lipid Bilayer
- Membrane lipids are amphipathic molecules that spontaneously form bilayers.
- Phospholipid bilayers are two molecules thick and form the cell membrane.
- The hydrophobic core prevents the diffusion of water-soluble molecules and is regulated by specific membrane proteins.
- Stability is maintained by hydrophobic and van der Waals interactions between the lipid chains.
Enclosed Compartment Formation
- The spontaneous closure of a phospholipid bilayer forms a sealed compartment.
- The formation of a sealed compartment is fundamental to the creation of a living cell.
Cell Membrane Proteins
- Membrane proteins can be associated with the lipid bilayer in various ways.
- Transmembrane proteins span the entire membrane.
- Peripheral proteins interact with transmembrane proteins noncovalently and are linked by lipids on either surface of the membrane.
Functions of Membrane Proteins
- Carry out the functions of the membrane.
- Transporters (e.g., Na+ pump) move ions across the membrane.
- Linkers (e.g., integrins) connect intercellular components to extracellular ones.
- Receptors bind a compound that sends a signal to the rest of the cell.
- Enzymes perform chemical reactions in the membrane.
Peripheral Membrane Proteins
- Proteins that are attached to either surface of the bilayer.
- Those attached to lipids are covalently linked.
- Those that interact with other transmembrane proteins are attached by noncovalent interactions.
Protein Movement
- Proteins can move through the layer of the membrane similar to lipids.
- However, they cannot flip from one side to the other.
Fluorescence Recovery After Photobleaching (FRAP)
- A technique used to study protein movement in the membrane.
Fluorescence Loss in Photobleaching (FLIP)
- A technique used to study protein movement in the membrane.
Restriction by Location
- Proteins can be restricted in their lateral movement within the membrane due to various factors:
- Cell Cortex Attachment
- Interaction with the Cytoskeleton
- Extracellular Attachment
- Attachment to Other Cells
Membrane Domains
- Cells can restrict the movement of proteins by:
- Cell cortex attachment
- Interaction with the cytoskeleton
- Extracellular attachment
- Attachment to other cells
Protein Glycosylation
- Many membrane proteins are glycosylated and have intrachain or interchain disulfide bonds.
Carbohydrates
- Some phospholipids have carbohydrates attached to them - glyCOLIPIDS.
- Some proteins have carbohydrates attached to them - GLYCOPROTEINS.
- Many of the plasma membrane proteins have sugars attached to them.
- Short Oligosaccharides - glycoproteins
- Long Polysaccharides - proteoglycans
Glycocalyx
- The carbohydrate-rich zone on the cell surface.
- Functions include:
- Protection against mechanical and chemical damage.
- Keeping foreign objects and other cells at a distance.
Transport Proteins
- Channel proteins create a hydrophilic channel that allows certain polar molecules or ions to pass through.
- Carrier proteins bind to their "passengers" and undergo a conformational change to shuttle them across the membrane.
Other Membrane Protein Functions
- Attachment to the cytoskeleton and extracellular matrix.
- Receptor sites (e.g., Insulin) bind to specific molecules without entering the cell.
- Enzymes speed up chemical reactions in the membrane.
- Intercellular joining (adhesion).
- Cell-to-cell recognition (glycoproteins).
Key Membrane Components and Their Functions
- Phospholipids: Form the bilayer, acting as a barrier to most water-soluble substances.
- Cholesterol: Regulates membrane fluidity, provides mechanical stability, and helps prevent ions from passing through the membrane.
- Proteins: Act as transport proteins to allow substances to move into or out of the cell. Some act as membrane enzymes, and others have important roles in the membranes of organelles.
- Glycolipids and Glycoproteins: Stabilize membrane structure. Some act as receptor molecules (e.g., for hormones and neurotransmitters) or as antigens for other cells to recognize them.
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Description
Explore the intricate concepts of lipid bilayer asymmetry and the mechanisms behind membrane synthesis. This quiz covers the composition differences in lipid layers, the role of membrane proteins, and lipid mobility within membranes. Test your understanding of how these elements work together in cellular function.
