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Questions and Answers
What is the main function of linker proteins?
What is the main function of linker proteins?
Which type of membrane transport does not require energy?
Which type of membrane transport does not require energy?
Which process is characterized by the transport of two different molecules in the same direction?
Which process is characterized by the transport of two different molecules in the same direction?
What type of ion channels opens in response to a change in membrane potential?
What type of ion channels opens in response to a change in membrane potential?
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What distinguishes facilitated diffusion from simple diffusion?
What distinguishes facilitated diffusion from simple diffusion?
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Which of the following conditions is caused by abnormal carrier proteins leading to kidney stones?
Which of the following conditions is caused by abnormal carrier proteins leading to kidney stones?
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Aquaporins are specialized channels for the transport of which substance?
Aquaporins are specialized channels for the transport of which substance?
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What is the primary consequence of cystic fibrosis related to NaCl transport?
What is the primary consequence of cystic fibrosis related to NaCl transport?
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What primarily drives active transport in cells?
What primarily drives active transport in cells?
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What happens to a red blood cell when placed in a hypotonic solution?
What happens to a red blood cell when placed in a hypotonic solution?
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Which process involves the engulfment of solid particles by a cell?
Which process involves the engulfment of solid particles by a cell?
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What is the role of ATP-binding cassette (ABC) transporters in eukaryotic cells?
What is the role of ATP-binding cassette (ABC) transporters in eukaryotic cells?
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Which type of secretion involves a response to an extracellular signal?
Which type of secretion involves a response to an extracellular signal?
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What is the main consequence of placing plant cells in a hypertonic solution?
What is the main consequence of placing plant cells in a hypertonic solution?
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Which active transport mechanism involves the simultaneous transport of glucose and Na+ in the same direction?
Which active transport mechanism involves the simultaneous transport of glucose and Na+ in the same direction?
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What defines receptor-mediated endocytosis?
What defines receptor-mediated endocytosis?
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Which statement accurately describes transmembrane proteins?
Which statement accurately describes transmembrane proteins?
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What is the primary role of glycocalyx?
What is the primary role of glycocalyx?
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Which type of protein primarily uses energy for transport?
Which type of protein primarily uses energy for transport?
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Which statement is true about the protein to lipid ratio in cell membranes?
Which statement is true about the protein to lipid ratio in cell membranes?
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What is the function of channel proteins in the membrane?
What is the function of channel proteins in the membrane?
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Which type of integral protein spans the lipid bilayer and might loop several times?
Which type of integral protein spans the lipid bilayer and might loop several times?
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What distinguishes non-transmembrane proteins from transmembrane proteins?
What distinguishes non-transmembrane proteins from transmembrane proteins?
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What role do Siglecs play in relation to immune cells?
What role do Siglecs play in relation to immune cells?
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What is the primary reason the plasma membrane is considered 'fluid'?
What is the primary reason the plasma membrane is considered 'fluid'?
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Which component of the plasma membrane is primarily responsible for its structural integrity?
Which component of the plasma membrane is primarily responsible for its structural integrity?
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In the fluid mosaic model, what role do integral proteins play?
In the fluid mosaic model, what role do integral proteins play?
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What is the characteristic of the hydrophilic head of phospholipids?
What is the characteristic of the hydrophilic head of phospholipids?
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How does temperature affect the fluidity of the plasma membrane?
How does temperature affect the fluidity of the plasma membrane?
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Which type of protein is found on the outer or inner surfaces of the plasma membrane?
Which type of protein is found on the outer or inner surfaces of the plasma membrane?
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What is the main function of cholesterol in the plasma membrane?
What is the main function of cholesterol in the plasma membrane?
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What distinguishes glycolipids in the plasma membrane?
What distinguishes glycolipids in the plasma membrane?
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Study Notes
Cell Membrane Structure
- The cell membrane (also called the plasma membrane or plasma lemma) is approximately 7.5 nm thick.
- It's a phospholipid bilayer with integral (intrinsic) and peripheral (extrinsic) proteins embedded within.
- Lipids and proteins may be attached to carbohydrates.
- The inner leaflet faces the cytoplasm (P-face), and the outer leaflet faces the extracellular matrix (E-face).
- Under electron microscopy, the membrane appears trilaminar.
Cell Membrane Composition
- The membrane is primarily composed of phospholipids (lipid + phosphate group).
- It also contains glycolipids (lipid + carbohydrate) and cholesterol, a sterol.
- Phospholipids are amphipathic, with a polar (hydrophilic) head and two nonpolar (hydrophobic) fatty acid tails.
- Cholesterol is present in both leaflets, comprising only 2% of plasma membrane lipids.
- The membrane is more fluid when temperature is high and fatty acid tails are unsaturated.
- Fluidity decreases with higher cholesterol content.
Cell Membrane Proteins
- Membrane proteins are categorized into peripheral (extrinsic) and integral (intrinsic) types.
- Peripheral proteins are located on the external or internal surfaces and associate with the hydrophilic head of the lipid bilayer.
- Integral proteins are embedded within the phospholipid bilayer, interacting with hydrophobic tails.
- The protein-to-lipid ratio typically is 1:1, but can be 1:4 in myelin cells.
- Many integral proteins are transmembrane, spanning the entire bilayer.
- Transmembrane proteins can be single-pass or multi-pass.
- Single-pass proteins pass once, while multi-pass proteins pass multiple times through the lipid bilayer.
Cell Membrane Functions
- Maintain cell integrity.
- Act as a semipermeable barrier.
- Enables molecule recognition and transport.
- Facilitate signal transduction.
- Allow cell-to-cell contact and communication.
- Maintain potential difference in nervous tissue.
- Attach to the cytoskeleton and extracellular matrix.
Cell Membrane Transport
- Membrane transport moves substances across the cell membrane.
- There are passive (no energy required) and active (energy required) processes.
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Passive transport occurs down the concentration or electrochemical gradient.
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Simple diffusion is a nonspecific process through the phospholipid bilayer, with little specificity.
- Small, nonpolar (e.g., O2, N2) and small, uncharged, polar (e.g., H₂O, CO2, glycerol) molecules are able to move through the membrane by simple diffusion.
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Facilitated diffusion is a specific process through protein channels or carriers.
- Ion channels (e.g., K⁺ leak channels, voltage-gated channels, mechanically gated channels, and ligand-gated channels) and aquaporins (water channels) increase the rate of transport across the membrane. - Carrier proteins (e.g., glucose transporters) undergo conformational changes to transport specific molecules.
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Simple diffusion is a nonspecific process through the phospholipid bilayer, with little specificity.
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Active transport moves substances against their concentration or electrochemical gradient, requiring energy (ATP).
- Primary active transport (e.g., Na⁺-K⁺ pump) directly utilizes ATP to move molecules.
- Secondary active transport (e.g., glucose transport) couples the movement of one molecule down its gradient to the movement of another molecule against its gradient.
- ATP-binding cassette (ABC) transporters use ATP to move substances across the cell membrane.
Glycocalyx
- The glycocalyx is a carbohydrate-rich layer on the outer surface of the plasma membrane.
- It's composed of oligosaccharides covalently connected to proteins (glycoproteins) and lipids (glycolipids).
- Functions include cell-cell recognition, communication, binding to extracellular matrix molecules, and protection.
Examples of Ion Channels & Diseases
- Ion channels are integral membrane proteins that regulate the movement of ions across the cell membrane.
- Types include K⁺ leak channels, voltage-gated channels, mechanically gated channels, and ligand-gated channels.
- Examples of diseases involving ion channel malfunction include cystic fibrosis (malfunctioning chloride channel proteins) and cystinuria (abnormal carrier proteins).
Endocytosis and Exocytosis
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Endocytosis is the process of taking substances into the cell. It involves a portion of the plasma membrane engulfing the substances.
- Types of endocytosis include phagocytosis, pinocytosis, and receptor-mediated endocytosis
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Exocytosis is the process of releasing substances out of the cell. It involves secretory granules fusing with the plasma membrane.
- Types of exocytosis include regulated secretion and constitutive secretion
Other important concepts
- In the case of poisonous snake bites, the venom often targets acetylcholine receptors, leading to muscle paralysis.
- Graves' disease is an autoimmune disease in which antibodies stimulate thyroid-stimulating hormone receptors, resulting in hyperthyroidism.
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Description
Explore the intricate details of cell membrane structure and composition. This quiz covers the phospholipid bilayer, the types of proteins involved, and the role of cholesterol in membrane fluidity. Test your understanding of important concepts regarding the cellular barrier that protects and organizes cellular contents.
