Questions and Answers
A phospholipid has a 'head' made up of a glycerol molecule attached to a single ___________, which is attached to another small molecule.
phosphate group
Because the phosphate group and its attachments are either charged or polar, the phospholipid head is _____, which means it has an affinity for water.
hydrophilic
A phospholipid also has two 'tails' made up of two ______________ molecules, which consist of a carboxyl group with a long hydrocarbon chain tail.
fatty acid
Because the C-H bonds in the fatty acid tails are relatively nonpolar, the phospholipid tails are __________, which means they are excluded from water.
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Answer the following about nonpolar molecules:
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Answer the following about polar molecules:
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Answer the following about ions:
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A red blood cell placed in a hypertonic solution will shrink in a process called crenation. A red blood cell placed in a hypotonic solution will swell and potentially burst in a process called hemolysis. To prevent crenation or hemolysis, a cell must be placed in an isotonic solution such as 0.9% (m/v) NaCl or 5.0% (m/v) glucose. Indicate whether crenation, hemolysis, or neither will occur in the following solutions. Solution A: 3.21% (m/v) NaCl, Solution B: 1.65% (m/v) glucose, Solution C: distilled H2O, Solution D: 6.97% (m/v) glucose, Solution E: 5.0% (m/v) glucose and 0.9% (m/v) NaCl.
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What happens when a cell is in a hypertonic solution?
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What happens when a cell is in a hypotonic solution?
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What happens when a cell is in an isotonic solution?
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What name is given to the process by which water crosses a selectively permeable membrane?
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If a red blood cell is placed in a salt solution and bursts, what is the tonicity of the solution relative to the interior of the cell?
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The water-soluble portion of a phospholipid is the polar head, which generally consists of a glycerol molecule linked to a phosphate group.
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Which of the following particles could diffuse easily through a cell membrane?
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What property of dishwashing liquid (detergent) makes it useful to wash grease from pans?
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Osmosis is a type of diffusion.
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How can a lipid be distinguished from a sugar?
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What factors affect the membrane permeability?
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Molecules always move independently from other types of molecules when passing through a membrane.
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When do concentration gradients exist that drive diffusion of two different types of molecules?
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When is there a net movement of particles from one side of the membrane to the other?
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Will one type of particle only move from one side to the other?
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When is there no net movement of particles?
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Which of the following molecules can cross the lipid bilayer of a membrane easily, without a transport protein or other mechanism? Select all that apply.
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When talking about protein channels and carriers, Only Channels:
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When talking about protein channels and carriers, Only Carriers:
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When talking about protein channels and carriers, Both Channels and Carriers:
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When talking about endocytosis and exocytosis, Only exocytosis:
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When talking about endocytosis and exocytosis, Only endocytosis:
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When talking about endocytosis and exocytosis, Both exocytosis and endocytosis:
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Endocytosis moves materials _____ a cell via _____.
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A white blood cell engulfing a bacterium is an example of _____.
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Study Notes
Phospholipids
- Composed of a glycerol "head" linked to a phosphate group, which is charged or polar and hydrophilic.
- Two "tails" consist of fatty acid molecules with long hydrocarbon chains, making them hydrophobic and excluded from water.
Molecular Properties
- Non-polar molecules are hydrophobic, easily crossing lipid bilayers without transport proteins.
- Polar molecules are hydrophilic, struggle to cross lipid bilayers, and require transport proteins for efficient passage.
- Ions are also hydrophilic, facing similar challenges as polar molecules when crossing membranes.
Tonicity and Cell Behavior
- Hypertonic solutions cause red blood cells to shrink (crenation) due to water loss.
- Hypotonic solutions result in swelling and potential bursting of cells (hemolysis).
- Isotonic solutions maintain cell integrity with no net water movement; solutions like 0.9% NaCl or 5% glucose exert equal osmotic pressure as the cell interior.
Water Movement
- Osmosis is the process by which water crosses selectively permeable membranes.
- A red blood cell in a salt solution that bursts is in a hypotonic environment.
Membrane Permeability Factors
- Factors influencing membrane permeability include temperature, saturation of hydrocarbon tails, and cholesterol levels in the membrane.
- Lipids are mostly non-polar, whereas sugars are polar, serving as key differentiators between these two classes of biomolecules.
Diffusion and Equilibrium
- Concentration gradients exist pre-equilibrium, driving the diffusion of different types of molecules.
- There is net particle movement from one side of the membrane to another only before equilibrium is reached.
- No net movement of particles occurs at equilibrium, with independent movement of different molecules.
Protein Transport Mechanisms
- Channels provide continuous pathways for small ions and water to cross membranes quickly.
- Carriers change shape to transport small polar organic molecules across the membrane.
- Both channels and carriers offer hydrophilic pathways, serve as integral membrane proteins, and facilitate transport down gradients.
Endocytosis and Exocytosis
- Exocytosis secretes large molecules out of cells, increases plasma membrane surface area, and involves vesicle fusion with the membrane.
- Endocytosis decreases plasma membrane surface area and creates vesicles through inward folding.
- Both processes require energy and do not involve the physical crossing of substances through the plasma membrane.
Special Cases
- Endocytosis can bring materials into cells via membranous vesicles.
- An example of phagocytosis is a white blood cell engulfing a bacterium.
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