Questions and Answers
Name the four major large molecules of all living things.
Lipids, Proteins, Carbohydrates, Nucleic Acids
Explain what is meant when we say a molecule is amphipathic.
It means the molecule has a hydrophobic and a hydrophilic region.
Describe the Davson-Danielli model of membrane structure. What were 2 problems with it?
A phospholipid bilayer between 2 layers of protein. Problem 1: Generalization that all membranes of the cells were identical. Problem 2: Protein placement was wrong.
Who proposed the fluid mosaic model? When? Describe.
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What is membrane fluidity? Describe movements seen in the fluid.
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Describe how decreasing temperature affects membrane fluidity.
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Describe how phospholipids with unsaturated hydrocarbon chains affect membrane fluidity.
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Describe how cholesterol affects membrane fluidity.
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Describe integral proteins.
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Describe peripheral proteins.
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What are the major functions of transport proteins?
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What is the major function of enzymatic activity in membrane proteins?
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What is signal transduction in membrane proteins?
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What is cell-cell recognition?
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What is intercellular joining?
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What is attachment to the cytoskeleton and ECM?
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Distinguish between glycolipids and glycoproteins.
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Distinguish between channel proteins and carrier proteins.
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Are transport proteins specific?
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What are aquaporins?
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How does CO2 cross the membrane?
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How does glucose cross the membrane?
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How does H+ cross the membrane?
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How does O2 cross the membrane?
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How does H2O cross the membrane?
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Define diffusion.
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Define concentration gradient.
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Define passive transport.
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Define osmosis.
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Define isotonic.
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Define hypotonic.
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Define hypertonic.
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Define turgid.
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Define flaccid.
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Define plasmolysis.
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What is facilitated diffusion?
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Why don't plant cells burst in hypertonic solutions?
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What is active transport?
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What is membrane potential?
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What are the two forces that drive diffusion of ions across the membrane?
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What is cotransport?
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Define endocytosis.
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Define phagocytosis.
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Define pinocytosis.
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Define exocytosis.
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Define receptor-mediated endocytosis.
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What is a ligand?
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Study Notes
Major Biomolecules
- Four major molecules in all living organisms: Lipids, Proteins, Carbohydrates, Nucleic Acids.
Amphipathic Molecules
- Molecules with both hydrophobic (water-repellent) and hydrophilic (water-attracting) regions.
Davson-Danielli Model
- Proposed structure: phospholipid bilayer sandwiched between two protein layers.
- Problems:
- Oversimplified all cell membranes as identical.
- Incorrect assumptions about protein placement within the membrane.
Fluid Mosaic Model
- Proposed by S.J. Singer and G. Nicolson in 1972.
- Describes membrane with proteins dispersed individually in the phospholipid bilayer, allowing for fluid movement.
Membrane Fluidity
- Membranes are flexible due to weak bonds, allowing lateral movement of components.
Effects of Temperature on Membrane Fluidity
- Decreasing temperature leads to phospholipids packing closely, solidifying the membrane.
- Phospholipids with unsaturated hydrocarbon chains maintain fluidity at lower temperatures.
- Cholesterol reduces membrane fluidity at higher temperatures.
Integral vs. Peripheral Proteins
- Integral proteins penetrate the hydrophobic core of the lipid bilayer.
- Peripheral proteins are loosely attached to the membrane surface.
Functions of Membrane Proteins
- Transport: Create hydrophilic channels or change shape to move substances across.
- Enzymatic Activity: Act as enzymes in metabolic pathways.
- Signal Transduction: Bind to external chemical messengers, triggering shape changes.
- Cell-Cell Recognition: Glycoproteins act as identification tags for cells.
- Intercellular Joining: Proteins connect adjacent cells at junctions.
- Attachment to Cytoskeleton and ECM: Link cellular structures to membrane proteins or ECM components.
Glycolipids vs. Glycoproteins
- Glycolipids are lipids with carbohydrate attachments; glycoproteins are proteins with carbohydrate attachments.
Channel Proteins vs. Carrier Proteins
- Channel proteins provide openings for specific molecules; carrier proteins change shape to transport substances.
Specificity of Transport Proteins
- Transport proteins are specific for the substances they transport.
Aquaporins
- Channel proteins that facilitate water transport across cell membranes at high rates.
Crossing Membranes
- CO2 and O2 dissolve in the lipid bilayer and rely on membrane proteins.
- Glucose uses carrier proteins that change shape to pass through.
- H+ ions require passage via hydrophilic channels.
- Water molecules predominantly pass through aquaporins.
Key Transport Concepts
- Diffusion: Movement of molecules to evenly distribute in available space.
- Concentration Gradient: Variation in chemical substance density across a region.
- Passive Transport: Movement across a membrane without energy expenditure.
- Osmosis: Passive transport of water across a membrane.
Tonicity Definitions
- Isotonic: Solutions that do not affect cell water content.
- Hypotonic: Solutions that cause cells to lose water.
- Hypertonic: Solutions that lead to water gain in cells.
Cell States
- Turgid: Swollen state of a cell due to water intake.
- Flaccid: Limp state of a cell when it loses water.
- Plasmolysis: Cellular shrinkage and membrane detachment due to excessive water loss.
Facilitated Diffusion
- Movement of molecules or ions through a membrane with the aid of specific proteins, requiring no energy.
Plant Cells in Hypertonic Solutions
- Cell walls prevent bursting even in hypertonic environments.
Active Transport
- Movement of substances against their concentration gradient, requiring energy (ATP) and involving carrier proteins.
Membrane Potential
- Voltage difference across a membrane, with the outside positively charged and inside negatively charged.
Forces Driving Ion Diffusion
- Electrical and chemical forces create the electrochemical gradient that influences ion movement.
Cotransport
- Coupling of the downhill transport of one substance with the uphill transport of another against its concentration gradient.
Endocytosis Types
- Endocytosis: Uptake of molecules through vesicle formation.
- Phagocytosis: Uptake of large molecules or particles.
- Pinocytosis: Ingestion of extracellular fluid and solutes.
Exocytosis
- The process of exporting materials out of the cell, the reverse of endocytosis.
Receptor-Mediated Endocytosis
- Specific uptake of molecules into a cell via vesicular inward budding, triggered by ligand binding.
Ligands
- Molecules that specifically bind to larger molecules, often involved in signaling and uptake processes.
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Description
Test your knowledge on the key concepts of membrane structure and function with this flashcard quiz from Biology Chapter 7. Learn about the major molecules of life, the characteristics of amphipathic molecules, and the Davson-Danielli model of membrane structure. Perfect for students preparing for exams!