Questions and Answers
Which of the following membrane visualization techniques allows for the study of the inside of the membrane?
What is the main function of cell surface markers?
What is the polar and hydrophilic part of a phospholipid?
How do unsaturated fatty acids affect membrane fluidity compared to saturated fatty acids?
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What is the function of sterols like cholesterol in membranes?
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What is the main difference between integral membrane proteins and peripheral membrane proteins?
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What is the term for the model of membrane structure that describes it as a mosaic of proteins floating in a fluid lipid bilayer?
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What is the function of fatty acid desaturases in bacteria that are cold-tolerant?
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What is the primary function of anchoring molecules in peripheral proteins?
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What type of proteins have extensive nonpolar regions that create a pore through the membrane?
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What is the primary function of facilitated diffusion?
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What type of transport requires energy and moves substances from low to high concentration?
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What is the function of the sodium-potassium pump?
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What is the term for the net diffusion of water across a membrane toward a higher solute concentration?
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What is the function of aquaporins?
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What is the term for the force needed to stop osmotic flow?
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What type of transport uses the energy released from a molecule moving by diffusion to supply energy to active transport of a different molecule?
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What is the term for the movement of substances into the cell?
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Study Notes
Membrane Structure
- Phospholipids are arranged in a bilayer with globular proteins inserted in the lipid bilayer, forming a fluid mosaic model
- The fluid mosaic model describes proteins floating in or on the fluid lipid bilayer, like boats on a pond
Cellular Membrane Components
- 4 main components of cellular membranes:
- Phospholipid bilayer (flexible matrix, barrier to permeability)
- Transmembrane proteins (integral membrane proteins)
- Interior protein network (peripheral membrane proteins)
- Cell surface markers (glycoproteins and glycolipids)
Phospholipid Structure
- Consists of:
- Glycerol (a 3-carbon polyalcohol)
- 2 fatty acids attached to the glycerol (nonpolar and hydrophobic)
- Phosphate group attached to the glycerol (polar and hydrophilic)
- Spontaneously forms a bilayer with fatty acids on the inside and phosphate groups on both surfaces
Membrane Fluidity
- Bilayers are fluid due to hydrogen bonding between water molecules, allowing individual phospholipids and unanchored proteins to move through the membrane
- Environmental influences on membrane fluidity:
- Saturated fatty acids make the membrane less fluid than unsaturated fatty acids
- Warm temperatures make the membrane more fluid than cold temperatures
- Sterols like cholesterol can increase or decrease membrane fluidity depending on the temperature
Membrane Proteins
- Various functions:
- Transporters
- Enzymes
- Cell-surface receptors
- Cell-surface identity markers
- Cell-to-cell adhesion proteins
- Attachments to the cytoskeleton
- Structure relates to function:
- Diverse functions arise from diverse structures of membrane proteins
- Common structural features related to their role as membrane proteins
- Types of membrane proteins:
- Peripheral proteins (anchoring molecules attach membrane protein to surface)
- Integral membrane proteins (span the lipid bilayer, with nonpolar regions embedded in the interior and polar regions protruding from both sides)
Passive Transport
- Movement of molecules through the membrane without energy input
- Diffusion: movement of molecules from high to low concentration
- Diffusion will continue until concentration is equal in all regions
- Factors affecting permeability:
- Hydrophobic interior of the membrane repels polar molecules but not nonpolar molecules
- Limited permeability to small polar molecules
- Very limited permeability to larger polar molecules and ions
- Facilitated diffusion:
- Molecules that cannot cross the membrane easily move through proteins
- Channel proteins: hydrophilic channel when open
- Carrier proteins: bind specifically to molecules they assist
Osmosis
- Net diffusion of water across a membrane toward a higher solute concentration
- Osmotic concentration:
- Hypertonic solution: higher solute concentration
- Hypotonic solution: lower solute concentration
- Isotonic solution: same osmotic concentration as the cell
- Osmotic pressure:
- Force needed to stop osmotic flow
- Cell in a hypotonic solution gains water, causing cell to swell and creating pressure
Active Transport
- Requires energy input (ATP) to move substances from low to high concentration
- Uses highly selective carrier proteins
- Types of carrier proteins:
- Uniporters: move one molecule at a time
- Symporters: move two molecules in the same direction
- Antiporters: move two molecules in opposite directions
- Sodium-potassium (Na+-K+) pump: direct use of ATP for active transport, moving 3 Na+ out of the cell and 2 K+ into the cell against their concentration gradient
Bulk Transport
- Endocytosis:
- Movement of substances into the cell
- Phagosytosis: cell takes in particulate matter
- Pinocytosis: cell takes in only fluid
- Receptor-mediated endocytosis: specific molecules are taken in after binding to a receptor
- Exocytosis:
- Movement of substances out of the cell
- Requires energy
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Description
Learn about the structure and components of cellular membranes, including phospholipid bilayers and globular proteins, and the fluid mosaic model.
