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Questions and Answers
What property of membrane lipids allows them to spontaneously form bilayers in an aqueous environment?
What property of membrane lipids allows them to spontaneously form bilayers in an aqueous environment?
- They are entirely hydrophilic.
- They are amphipathic. (correct)
- They are entirely hydrophobic.
- They are composed of polysaccharides.
What primarily regulates membrane fluidity?
What primarily regulates membrane fluidity?
- The number of proteins embedded in the membrane.
- The chemical composition of fatty acid tails and the amount of cholesterol. (correct)
- The concentration of ions in the surrounding solution.
- The presence of glycoproteins on the membrane surface.
In eukaryotic cells, where are membrane lipids synthesized?
In eukaryotic cells, where are membrane lipids synthesized?
- Mitochondria
- Lysosomes
- Golgi apparatus
- Endoplasmic Reticulum (ER) (correct)
Which of the following is the primary function of flippases in cell membranes?
Which of the following is the primary function of flippases in cell membranes?
Why is membrane asymmetry important for cell function?
Why is membrane asymmetry important for cell function?
What triggers the membrane repair mechanism in cells?
What triggers the membrane repair mechanism in cells?
How does cholesterol affect the cell membrane?
How does cholesterol affect the cell membrane?
If a cell membrane contains a high proportion of unsaturated fatty acids, what characteristic will it likely have?
If a cell membrane contains a high proportion of unsaturated fatty acids, what characteristic will it likely have?
A cell needs to import a large quantity of small molecules rapidly. Which aspect of the plasma membrane is most crucial for facilitating this process?
A cell needs to import a large quantity of small molecules rapidly. Which aspect of the plasma membrane is most crucial for facilitating this process?
During the synthesis of phospholipids, which side of the ER membrane are they initially added to?
During the synthesis of phospholipids, which side of the ER membrane are they initially added to?
What is the role of scramblases in the production and shuffling of cell membrane components?
What is the role of scramblases in the production and shuffling of cell membrane components?
Which class of membrane lipids is enriched in the outer leaflet of animal cells and serves as a recognition site for interactions with the environment?
Which class of membrane lipids is enriched in the outer leaflet of animal cells and serves as a recognition site for interactions with the environment?
Why is it essential for membrane integrity to be rapidly restored after it has been damaged?
Why is it essential for membrane integrity to be rapidly restored after it has been damaged?
A researcher is studying the function of a particular membrane protein. What aspect of the cell membrane should they consider in order to understand how that protein interacts with its environment?
A researcher is studying the function of a particular membrane protein. What aspect of the cell membrane should they consider in order to understand how that protein interacts with its environment?
Membranes are critical for cellular function. Which of the following is NOT a function of cell membranes?
Membranes are critical for cellular function. Which of the following is NOT a function of cell membranes?
Flashcards
What are amphipathic molecules?
What are amphipathic molecules?
Molecules with both hydrophilic and hydrophobic regions.
What are phospholipids?
What are phospholipids?
Lipids with a polar head and two nonpolar tails; the main structural component of cell membranes.
What is membrane fluidity?
What is membrane fluidity?
The property of a membrane where lipids and proteins can move laterally within the lipid bilayer.
What are Flippases?
What are Flippases?
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What is a Glycocalyx?
What is a Glycocalyx?
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Where are membrane lipids synthesized?
Where are membrane lipids synthesized?
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What is Cholesterol?
What is Cholesterol?
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What is the structure of cell membranes?
What is the structure of cell membranes?
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Study Notes
- Chapter 11 Part 1 focuses on membrane structure
- The chapter discusses membrane structure, membrane proteins, and the glycocalyx
Learning Objectives
- Analyze the arrangement, composition, and fluidity of cellular membranes
- Explain why the distribution of membrane components is often asymmetrical
Membranes and Cellular Function
- Membranes are critical for cellular function
- The external plasma membrane is involved in receiving information, importing and exporting small molecules, and providing capacity for movement and expansion.
- Internal compartments within a cell include the nucleus, endoplasmic reticulum, Golgi apparatus, lysosomes, peroxisomes, endosomes, mitochondria, and transport vesicles
- Membranes facilitate interactions with the external environment and sequester internal compartments
Cell Membrane Composition
- Composed of oriented lipids and proteins
- Approximately 30% of the genome encodes membrane proteins
- Amphipathic membrane lipids form bilayers in water
- Membrane fluidity is regulated by chemical composition
- Membrane biosynthesis is required for cell homeostasis, growth, and division
- Membrane lipids are synthesized in the ER
Lipid Bilayers
- Cell membranes consist of lipid bilayers
- Lipid bilayers contain amphipathic phospholipids with a hydrophilic head and hydrophobic tails
- Cell membranes are largely made of phosphatidylcholine, which has a polar head (hydrophilic) and nonpolar tails (hydrophobic)
- Cell membranes exhibit dynamic flexibility due to the lateral diffusion of membrane phospholipids
- Phospholipids rarely flip-flop
- Amphipathic phospholipids form a bilayer in water, where the hydrophobic tails are shielded from water
- Membrane synthesis in bacteria and yeast is temperature-dependent
- Fatty acid (FA) tails are altered to maintain fluidity
- Unsaturated FAs provide greater fluidity at low temperatures
Membrane Lipids
- All membrane lipids are amphipathic including phospholipids, cholesterol, and glycolipids
- Cholesterol can stiffen cell membranes
- Lipid composition differs on each face of the membrane
- Mammalian plasma membranes consist of Phospatidylcholine (PC), Phosphatidylethanolamine (PE), Phosphatidylserine (PS), Sphingomyelin (SM), and Sphingosine (S)
Phospholipids
- Phospholipids are synthesized by the ER and inserted into the cytosolic monolayer of the organelle
- Scramblases flip phospholipids randomly from one side of a membrane to the other
- Flippases transfer specific phospholipids to the cytosolic monolayer
- Most membrane functions are performed by membrane proteins
- The integration of ER-derived phospholipids involves scramblase-mediated switch-up, leading to random distribution and symmetric growth of both halves of the bilayer
- Certain membrane phospholipids are confined to one face, and flippases mediate asymmetric distribution.
- Membranes retain their orientation during intracellular transfer
Membrane Repair
- Membranes can undergo damage
- Ca2+ influx triggers repair
- Mechanism involves exocytosis of internal membrane components
Summary
- Cell membranes are two-dimensional solutions of oriented lipids and proteins
- Amphipathic membrane lipids form bilayers in water
- Membrane fluidity is regulated by the chemical makeup of fatty acid tails and amount of cholesterol present
- Membrane lipid distribution is asymmetric due to flippases
- Membrane lipids are synthesized in the ER, required for cell homeostasis, growth, and division
- Membrane repair is triggered by Ca2+ influx and exocytosis
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