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Questions and Answers
What is the primary mechanism by which phospholipids move within the same monolayer of the cell membrane?
What is the primary mechanism by which phospholipids move within the same monolayer of the cell membrane?
What does not significantly affect the fluidity of the cell membrane?
What does not significantly affect the fluidity of the cell membrane?
Which of the following describes the 'flip-flop' movement of phospholipids?
Which of the following describes the 'flip-flop' movement of phospholipids?
How do tightly packed hydrocarbon tails affect the movement of phospholipids?
How do tightly packed hydrocarbon tails affect the movement of phospholipids?
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What is the primary type of movement that occurs in the lateral diffusion of phospholipids?
What is the primary type of movement that occurs in the lateral diffusion of phospholipids?
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What is the primary function of carbohydrates in the cell membrane?
What is the primary function of carbohydrates in the cell membrane?
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Which statement about the lipid bilayer structure is correct?
Which statement about the lipid bilayer structure is correct?
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What is the approximate percentage composition of proteins in the cell membrane?
What is the approximate percentage composition of proteins in the cell membrane?
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What role does cholesterol play in the cell membrane?
What role does cholesterol play in the cell membrane?
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Which of the following statements about membrane transport mechanisms is false?
Which of the following statements about membrane transport mechanisms is false?
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What determines the fluidity of the cell membrane?
What determines the fluidity of the cell membrane?
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Which organelles have a double lipid bilayer structure?
Which organelles have a double lipid bilayer structure?
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How do membrane lipids behave in relation to water?
How do membrane lipids behave in relation to water?
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What is a primary characteristic of channels in transport proteins?
What is a primary characteristic of channels in transport proteins?
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Which type of channel opens in response to voltage changes?
Which type of channel opens in response to voltage changes?
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What triggers ligand-gated channels to open?
What triggers ligand-gated channels to open?
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What is the typical resting membrane potential range?
What is the typical resting membrane potential range?
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How do passive transport mechanisms function?
How do passive transport mechanisms function?
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What is the purpose of the concentration gradient in diffusion?
What is the purpose of the concentration gradient in diffusion?
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Which of the following statements about transporters is correct?
Which of the following statements about transporters is correct?
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Which ion concentration is typically higher outside the cell?
Which ion concentration is typically higher outside the cell?
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Which type of channel is influenced by mechanical forces?
Which type of channel is influenced by mechanical forces?
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What happens to diffusion when the concentration is equal on both sides of a membrane?
What happens to diffusion when the concentration is equal on both sides of a membrane?
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What is the main role of cholesterol in cell membranes?
What is the main role of cholesterol in cell membranes?
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Which type of fatty acids can create more space between fatty acid chains in phospholipids?
Which type of fatty acids can create more space between fatty acid chains in phospholipids?
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Which statement is true about saturated fatty acids?
Which statement is true about saturated fatty acids?
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How do trans-unsaturated fatty acids differ from cis-unsaturated fatty acids?
How do trans-unsaturated fatty acids differ from cis-unsaturated fatty acids?
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What happens to membrane fluidity at high temperatures?
What happens to membrane fluidity at high temperatures?
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What is the primary function of membrane transport proteins?
What is the primary function of membrane transport proteins?
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Which of the following molecules can cross the cell membrane rapidly?
Which of the following molecules can cross the cell membrane rapidly?
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What role does the hydrophobic interior of the lipid bilayer play in membrane permeability?
What role does the hydrophobic interior of the lipid bilayer play in membrane permeability?
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What is a characteristic of peripheral proteins in cell membranes?
What is a characteristic of peripheral proteins in cell membranes?
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What is the effect of short hydrocarbon chain lengths on membrane fluidity?
What is the effect of short hydrocarbon chain lengths on membrane fluidity?
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What type of interactions occur between saturated fatty acid chains in phospholipids?
What type of interactions occur between saturated fatty acid chains in phospholipids?
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Why is cell membrane fluidity important for cell division?
Why is cell membrane fluidity important for cell division?
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Which proteins are embedded in the hydrophobic core of the lipid bilayer?
Which proteins are embedded in the hydrophobic core of the lipid bilayer?
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What happens to phospholipids at low temperatures due to cholesterol?
What happens to phospholipids at low temperatures due to cholesterol?
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What is the main reason that large polar molecules require transporter proteins to cross cell membranes?
What is the main reason that large polar molecules require transporter proteins to cross cell membranes?
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What type of molecules can directly cross the lipid bilayer through simple diffusion?
What type of molecules can directly cross the lipid bilayer through simple diffusion?
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What primarily determines the direction of passive transport for uncharged or polar molecules?
What primarily determines the direction of passive transport for uncharged or polar molecules?
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Which two forces determine the direction of passive transport for charged molecules?
Which two forces determine the direction of passive transport for charged molecules?
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What is the net force driving the direction of passive transport for charged molecules called?
What is the net force driving the direction of passive transport for charged molecules called?
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What type of transport requires energy to move molecules from low concentration to high concentration?
What type of transport requires energy to move molecules from low concentration to high concentration?
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What specialized proteins facilitate the movement of water across the membrane?
What specialized proteins facilitate the movement of water across the membrane?
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In osmosis, water moves from an area of __________ solute concentration to an area of __________ solute concentration.
In osmosis, water moves from an area of __________ solute concentration to an area of __________ solute concentration.
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What role does ATP hydrolysis play in membrane transport?
What role does ATP hydrolysis play in membrane transport?
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Which of the following statements about facilitated diffusion is true?
Which of the following statements about facilitated diffusion is true?
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Which ions would likely be attracted into the cell due to the resting membrane potential?
Which ions would likely be attracted into the cell due to the resting membrane potential?
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Study Notes
Cellular and Molecular Biology MD105
- Dr. C. Michaeloudes teaches at the European University Cyprus, School of Medicine.
- The course covers Cellular & Molecular Biology.
Cell Membrane Structure and Transport
- The cell membrane is a protective layer surrounding all cells.
- It's composed of lipids, proteins, and carbohydrates.
- The membrane is semi-permeable, allowing some molecules to pass through while blocking others.
Lecture Objectives
- Understanding the basic structure and composition of the cell membrane.
- Understanding the structure of the lipid bilayer and factors influencing fluidity.
- Understanding the various mechanisms of molecular transport across the cell membrane.
Cell Membrane Structure and Composition
- Lipids (40%): Phospholipids and cholesterol form a bilayer.
- Proteins (50%): Embedded in the bilayer, performing diverse functions.
- Carbohydrates (10%): Attached to proteins (glycoproteins) and lipids (glycolipids), extending from the membrane surface.
Organelle Membranes
- Intracellular organelles also possess lipid bilayer membranes.
- These membranes have slightly different compositions compared to the cell membrane.
- Nucleus and mitochondria have two lipid bilayers; ER, Golgi, and lysosomes have one.
Lipid Bilayer Structure
- Phospholipids and cholesterol are the major components.
- Phospholipids have a hydrophilic head and hydrophobic tails.
- The hydrophobic tails aggregate away from water, while the hydrophilic heads face water.
Phospholipids and Cholesterol
- Phospholipids are the primary component of cell membranes.
- Cholesterol is embedded within the lipid bilayer.
- Both have hydrophobic tails and hydrophilic heads.
Cell Membrane Lipid Bilayer
- Membrane lipids are exposed to two opposing forces: attraction to water (hydrophilic heads) and repulsion from water (hydrophobic tails).
- The bilayer forms due to these forces.
- Hydrophilic heads face water on both sides of the bilayer; hydrophobic tails reside in the bilayer's interior.
Cell Membrane Fluidity
- Membrane lipids and proteins can move freely within the membrane.
- This creates a fluid mosaic model for the cell membrane.
- Fluidity depends on factors such as temperature, phospholipid composition, and cholesterol levels.
Cell Membrane Phospholipid Movement
- Phospholipids move laterally within a monolayer (lateral diffusion).
- Enzymes catalyze this movement.
- Flip-flop movement (from one monolayer to another) is rare.
- Lipids flex their tails and rotate.
- Fluidity depends on how tightly hydrocarbon tails are packed.
Factors Determining Cell Membrane Fluidity
- Temperature: High temperatures increase fluidity; low temperatures decrease fluidity.
- Phospholipid tail structure: Saturated tails decrease fluidity; unsaturated tails increase fluidity.
- Cholesterol level: Cholesterol acts as a buffer, maintaining fluidity at both high and low temperatures.
Effect of Temperature on Cell Membrane Fluidity
- High temperatures: Phospholipids have more energy, leading to increased movement and spacing between them; increasing fluidity.
- Low temperatures: Phospholipids have less energy, packing more tightly together, decreasing fluidity.
Saturated vs. Unsaturated Fatty Acids
- Saturated fatty acids have only single bonds between carbons in their hydrocarbon chain, resulting in a straight structure and often being solid at room temperature.
- Unsaturated fatty acids have one or more double bonds, creating kinks or bends in their hydrocarbon chains, leading to less interaction between the chains, which result in liquid state at room temperature.
- Cis-unsaturated have hydrogen atoms on the same side of the double bond, whereas trans-unsaturated have hydrogen atoms on opposite sides of the double bond.
Phospholipid Tails
- Phospholipid tails consist of two fatty acids; can be saturated or unsaturated.
- Cis-unsaturated fatty acids are bent, preventing close packing.
- This results in more space between the tails and increased fluidity.
Effect of Phospholipid Structure on Cell Membrane Fluidity
- Length of hydrocarbon chain: Shorter chains reduce interactions, increasing fluidity.
- Double bonds: Double bonds create bends, increasing space between hydrocarbon tails and increasing fluidity.
Effect of Cholesterol on Cell Membrane Fluidity
- Cholesterol fits between phospholipid molecules.
- It regulates membrane fluidity.
- It acts as a buffer to prevent extreme changes in fluidity at low and high temperatures.
- Low temperatures: Increases fluidity, preventing freezing.
- High temperatures: Reduces fluidity, preventing melting.
Importance of Cell Membrane Fluidity
- Cell shape and movement adapt to various conditions.
- Membrane proteins can diffuse and interact—crucial for cell signaling.
- Ensures even distribution between daughter cells during cell division.
Membrane Proteins and Carbohydrates
- Membrane proteins are embedded within the lipid bilayer (integral or transmembrane) or situated on the membrane surface (peripheral).
- Functions: Transporters, receptors, enzymes, and anchors.
- Carbohydrates: Sugars attached to lipids (glycolipids) or proteins (glycoproteins).
- Crucial for cell recognition, damage protection, and lubrication.
Membrane Transport Proteins
- Cells and organelles need to transport hydrophilic molecules.
- Transport proteins—channels and transporters—facilitate this movement.
The Cell Membrane is Semi-permeable
- Hydrophobic interior prevents most hydrophilic molecules from passing through directly.
- The membrane is selective: Small nonpolar molecules and small uncharged polar molecules cross relatively quickly; large polar molecules and charged molecules cross slowly or not at all.
Types of Ion Channels
- Voltage-gated channels: Open in response to changes in membrane potential.
- Ligand-gated channels: Open in response to the binding of a chemical messenger (ligand).
- Mechanically-gated channels: Open in response to a mechanical force.
Resting Membrane Potential
- Differences in ion concentration create a voltage difference across the membrane.
- The inside of the cell is slightly more negative than the outside.
- This stored energy is essential for cell function.
Mechanisms of Membrane Transport
- Concentration gradient: Difference in concentration of a substance across a membrane.
- Diffusion: Driven by a concentration gradient.
- Passive transport: Movement along a concentration gradient, requiring no energy input.
Passive Transport
- Simple diffusion: Small, non-polar molecules directly cross the membrane.
- Facilitated diffusion: Large molecules use transporter proteins across the membrane.
Passive Transport of Charged Molecules
- Two forces driving passive transport of charged molecules: resting membrane potential and concentration gradient.
- The net force is called the electrochemical gradient.
Active Transport
- Movement against the concentration gradient.
- Requires energy input (usually from ATP hydrolysis).
- Facilitated by transporter proteins (pumps).
Summary of Membrane Transport
Osmosis
- Movement of water across a semi-permeable membrane.
- Driven by a concentration gradient of solutes.
- Water moves from low solute concentration to high solute concentration.
- Specialized channels—aquaporins—facilitate water's movement.
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Description
This quiz explores the fundamental aspects of cell membrane structure and transport mechanisms. You will learn about the lipid bilayer, protein functions, and the roles of carbohydrates in the cell membrane. Test your understanding of how these components contribute to cellular protection and transport processes.
