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Questions and Answers
What is the primary framework of a cell membrane composed of?
What is the primary framework of a cell membrane composed of?
What aspect of the cell membrane is described by the fluid-mosaic model?
What aspect of the cell membrane is described by the fluid-mosaic model?
What role do carbohydrates play in the structure of the cell membrane?
What role do carbohydrates play in the structure of the cell membrane?
What distinguishes the two leaflets of a phospholipid bilayer?
What distinguishes the two leaflets of a phospholipid bilayer?
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Which type of lipid is primarily found in animal cell membranes and contributes to membrane fluidity?
Which type of lipid is primarily found in animal cell membranes and contributes to membrane fluidity?
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What is the primary function of an ATP-driven pump?
What is the primary function of an ATP-driven pump?
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How does secondary active transport function?
How does secondary active transport function?
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What does the Na+/K+ pump primarily do?
What does the Na+/K+ pump primarily do?
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What is a characteristic of an electrogenic pump?
What is a characteristic of an electrogenic pump?
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Which of the following statements about the H+/sucrose symporter is true?
Which of the following statements about the H+/sucrose symporter is true?
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What are the primary functions of membrane proteins?
What are the primary functions of membrane proteins?
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Which of the following statements about transmembrane proteins is true?
Which of the following statements about transmembrane proteins is true?
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How does the length of phospholipid tails affect membrane fluidity?
How does the length of phospholipid tails affect membrane fluidity?
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What is the role of double bonds in phospholipid tails?
What is the role of double bonds in phospholipid tails?
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What effects does cholesterol have on membrane fluidity at high temperatures?
What effects does cholesterol have on membrane fluidity at high temperatures?
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Which method of transport across membranes does not require energy?
Which method of transport across membranes does not require energy?
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What happens to cells in a hypotonic environment?
What happens to cells in a hypotonic environment?
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What are the roles of transport proteins?
What are the roles of transport proteins?
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What characterizes channel proteins?
What characterizes channel proteins?
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Which class of transporters binds two or more different ions and transports them in the same direction?
Which class of transporters binds two or more different ions and transports them in the same direction?
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What type of transport moves solutes from low to high concentration using energy?
What type of transport moves solutes from low to high concentration using energy?
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What effect does a hypertonic environment have on animal cells?
What effect does a hypertonic environment have on animal cells?
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What is the primary reason membranes are selectively permeable?
What is the primary reason membranes are selectively permeable?
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Study Notes
Membrane Structure, Synthesis, and Transport
- This chapter covers the structure, synthesis, and transport of biological membranes.
- The cell membrane holds the contents of a cell together, allowing life processes to occur.
- The plasma membrane is a biomembrane that separates the internal contents of the cell from its external environment.
- It regulates the traffic of substances into and out of the cell.
- It is an interface for many vital cellular activities.
Chapter 5 Outline
- Membrane Structure: Includes the fluidity of membranes and the synthesis of membrane components in eukaryotic cells.
- Overview of Membrane Transport: Explains the general mechanisms of membrane transport.
- Proteins that Carry Out Membrane Transport: Discusses the proteins involved in transporting molecules across membranes.
- Exocytosis and Endocytosis: Details the processes of exporting and importing materials through the membrane.
Membrane Structure
- The framework of the membrane is a phospholipid bilayer.
- Phospholipids are amphipathic.
- Membranes also contain proteins and carbohydrates.
- Carbohydrates are attached to proteins (forming glycoproteins) and lipids (forming glycolipids).
- Other lipids, like cholesterol (in animal cells) or phytosterols (in plant cells), are also present.
Fluid-Mosaic Model
- The plasma membrane is a mosaic of lipids, proteins, and carbohydrates.
- The membrane is fluid, as lipids and proteins can move.
- The phospholipid bilayer has two leaflets; each facing a different region of the cell (e.g., cytoplasm or cell exterior).
- The two leaflets are asymmetrical, meaning their composition differs, with glycolipids primarily on the extracellular leaflet.
Membrane Proteins
- Membrane proteins participate in many cellular processes, including transport, energy transduction, cell signaling, secretion, cell recognition, and cell-to-cell contact.
- They are important targets of medications.
- Transmembrane proteins span the membrane.
- Lipid-anchored proteins attach to the membrane via lipid anchors.
- Peripheral proteins attach non-covalently.
Membranes are Semifluid
- Biomembranes are semifluid.
- Lipid and protein movement are primarily lateral and rotational.
- Fatty acyl tails stay within the hydrophobic interior.
- Movements are energetically favorable.
Bilayer Fluidity
- The optimal level of bilayer fluidity is essential for normal cell function, growth, and division.
- Membrane fluidity depends on temperature.
- Fluidity is influenced by phospholipid tail length, the presence of double bonds in tails, and cholesterol.
Lipid Tails of Phospholipids
- Lipid tails are typically 14–24 carbon atoms long.
- 16–18 carbon atoms are common.
- Shorter tails lead to a more fluid membrane.
Double Bonds in Phospholipid Tails
- Double bonds in tails create kinks.
- Unsaturated fatty acids have double bonds.
- Double bonds reduce interactions between adjacent tails, leading to more fluid membranes.
Membrane Cholesterol
- Cholesterol's polar head group associates with hydrophilic heads of phospholipids.
- Its nonpolar tail associates with hydrophobic tails.
- The rigid ring structure limits dense packing.
- It affects membrane fluidity depending on temperature.
Cholesterol & Fluidity
- Cholesterol tends to stabilize membranes.
- Its effect depends on temperature.
- At higher temperatures, cholesterol reduces fluidity.
- At lower temperatures, cholesterol increases fluidity.
Membranes are Selectively Permeable
- Membranes are selectively permeable.
- They prevent uncontrolled transport, ensuring proper regulation of cellular contents.
- Proteins are needed for selective transport given that a membrane composed only of phospholipids wouldn't be permeable enough.
Ways to Move Across Membranes
- Passive transport does not require energy.
- Molecules move down a concentration gradient.
- Simple diffusion occurs without a transport protein, directly through the phospholipid bilayer.
- Facilitated diffusion uses transport proteins to move molecules down their concentration gradient.
- Active transport moves molecules against their concentration gradient, using energy.
Movement Across a Biological Membrane
- Simple diffusion is passive transport.
- Facilitated diffusion is passive transport with the help of a transport protein.
- Active transport is the movement against a concentration gradient with a transport protein and energy.
Simple Diffusion
- The hydrophobic interior of the membrane blocks ions and hydrophilic molecules from diffusing easily.
- Factors affecting diffusion are size, polarity, charge, and concentration.
- Gases and small, uncharged molecules diffuse easily.
Artificial Bilayer
- Illustrates different permeabilities of molecules through membranes.
- Permeability is affected by size, polarity, and charge.
Membrane Gradients
- Living cells maintain internal environments distinct from the outside.
- Chemical gradients and electrochemical gradients exist across membranes.
Osmosis
- Osmosis is water movement across a membrane in response to solute concentration gradients.
- The membrane is somewhat permeable to water.
- Solute concentration can determine the direction of water movement.
Osmosis
- In a hypertonic environment, cells lose water and shrink.
- In a hypotonic environment, cells take up water and swell or lyse.
Effects of Osmosis
- Osmosis in animal cells versus plant cells can show different effects.
Transport Proteins
- Transport proteins provide pathways for specific ions and hydrophilic molecules.
- These proteins help biological membranes function via selective permeability.
- Two types are channels and transporters.
Channels
- Channels form passageways for ions and molecules across a membrane.
- Most channels are gated (opening and closing in response to signals).
- Movement through open channels is rapid.
Transporters
- Transporters bind to a solute and change conformation to move the solute across the membrane.
- Their movement is slower than channels.
Categories of Transporters
- Uniporters transport one molecule.
- Symporters transport two or more molecules in the same direction.
- Antiporters transport molecules in opposite directions.
Active Transport
- Active transport moves molecules against a concentration gradient.
- Primary active transport uses energy directly (e.g., ATP).
- Secondary active transport uses a pre-existing gradient (e.g., H+/sucrose symporter).
Na+/K+ Pump
- The Na+/K+ pump is an antiporter.
- It actively maintains sodium and potassium ion gradients.
- It generates an electrochemical gradient.
Mechanism of Pumping
- Steps of Na+/K+ pump activity are shown, from binding to release. (Involved conformations shown)
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Description
This quiz focuses on Chapter 5 of biological membranes, covering their structure, synthesis, and transport mechanisms. Dive into topics like membrane fluidity, transport proteins, and the processes of exocytosis and endocytosis. Test your understanding of how the cell membrane regulates substance traffic essential for life processes.
