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Chapter 12: Problem 10

List the following compounds in order of decreasing lipidbilayer permeability: RNA, \(\mathrm{Ca}^{2+}\), glucose, ethanol, \(\mathrm{N}_{2}\), water

Short Answer

Expert verified
Order: \(\mathrm{N}_2\), ethanol, water, glucose, \(\mathrm{Ca}^{2+}\), RNA.

Step by step solution

01

Understanding Lipid Bilayer Permeability

Lipid bilayers are selectively permeable, allowing small and non-polar molecules to diffuse more easily than large or charged ones. Therefore, molecules like gases and small nonpolar substances pass through more easily than ions or large polar molecules.
02

Analyzing Each Compound

- **RNA** is large and polar, with a negative charge, making it poorly permeable.- **\(\mathrm{Ca}^{2+}\)** is a charged ion, highly impermeable.- **Glucose** is polar and relatively large, decreasing its permeability.- **Ethanol** is small and polar but with a nonpolar region, increasing its permeability.- **\(\mathrm{N}_{2}\)** is nonpolar and small, giving it high permeability.- **Water** is small and polar, somewhat permeable.
03

Ranking Compounds by Permeability

From most to least permeable:1. \(\mathrm{N}_{2}\) (nonpolar, small)2. Ethanol (small, polar with nonpolar region)3. Water (small, polar)4. Glucose (polar, larger)5. \(\mathrm{Ca}^{2+}\) (charged ion)6. RNA (large, polar, charged)

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Selective Permeability
The idea of selective permeability is like having a filter that only lets certain things pass through. It is a crucial feature of the lipid bilayer of cell membranes. This helps maintain the internal environment of a cell by controlling what enters and exits its surroundings. Not every substance can pass through easily.
  • Small, nonpolar molecules get the green light to diffuse freely.
  • Large, charged, or polar molecules may struggle to pass through without assistance.
Imagine selective permeability as a clubhouse that requires a special pass for entry. Only specific individuals can walk in effortlessly. In the same manner, selective permeability allows essential molecules needed for cellular function to move in and out while keeping unwanted substances out. This ensures that the cell can live and function properly in its environment.
Molecular Diffusion
Molecular diffusion is the process by which molecules move from an area of higher concentration to an area of lower concentration. Think of it as a natural balancing act. Molecules are in constant motion, spreading out evenly over time. This process doesn't require energy input because molecules move due to their kinetic energy.
  • Small, nonpolar molecules like \(\mathrm{N}_{2}\) diffuse quickly across the lipid bilayer.
  • Polar molecules may need help or channels to aid in their diffusion.
This process is essential for maintaining cellular homeostasis. For cells to function correctly, they rely on diffusion to acquire nutrients and expel waste materials, ensuring a balanced internal environment.
Cell Membrane Structure
The structure of the cell membrane is remarkably sophisticated and gives rise to various crucial functions. The primary component is the lipid bilayer, made up of phospholipids. These phospholipids have a dual nature:
  • They have hydrophilic (water-attracting) heads.
  • They also have hydrophobic (water-repelling) tails.
These phospholipids arrange themselves uniquely: their heads face outward to interact with water, while their tails hide away, avoiding water. This arrangement forms a stable barrier, which is essential for maintaining the integrity of the cell. Other components, like proteins, integrate into or associate with the bilayer, contributing to its functionality:
  • Embedded proteins assist in transporting substances that cannot diffuse freely.
  • These also help in cell communication and recognition.
The structure of the cell membrane is not just a wall, but a dynamic and interactive boundary that plays a pivotal role in a cell's ability to sustain life.

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Most popular questions from this chapter

Amino acids are taken up by animal cells using a symport in the plasma membrane. What is the most likely ion whose electrochemical gradient drives the import? Is ATP consumed in the process? If \(s o,\) how?

The neurotransmitter acetylcholine is made in the cytosol and then transported into synaptic vesicles, where its concentration is more than 100 -fold higher than in the cytosol. When synaptic vesicles are isolated from neurons, they can take up additional acetylcholine added to the solution in which they are suspended, but only when ATP is present. \(\mathrm{Na}^{+}\) ions are not required for the uptake, but, curiously, raising the \(\mathrm{pH}\) of the solution in which the synaptic vesicles are suspended increases the rate of uptake. Furthermore, transport is inhibited when drugs are added that make the membrane permeable to \(\mathrm{H}^{+}\) ions. Suggest a mechanism that is consistent with all of these observations.

Which of the following statements are correct? Explain your answers. A. The plasma membrane is highly impermeable to all charged molecules. B. Channels have specific binding pockets for the solute molecules they allow to pass. C. Transporters allow solutes to cross a membrane at much faster rates than do channels. D. Certain \(\mathrm{H}^{+}\) pumps are fueled by light energy. E. The plasma membrane of many animal cells contains open \(\mathrm{K}^{+}\) channels, yet the \(\mathrm{K}^{+}\) concentration in the cytosol is much higher than outside the cell. F. A symport would function as an antiport if its orientation in the membrane were reversed (i.e., if the portion of the molecule normally exposed to the cytosol faced the outside of the cell instead). G. The membrane potential of an axon temporarily becomes more negative when an action potential excites it.

One thousand \(\mathrm{Ca}^{2+}\) channels open in the plasma membrane of a cell that is \(1000 \mu \mathrm{m}^{3}\) in size and has a cytosolic \(\mathrm{Ca}^{2+}\) concentration of \(100 \mathrm{nM}\). For how long would the channels need to stay open in order for the cytosolic \(\mathrm{Ca}^{2+}\) concentration to rise to \(5 \mu \mathrm{M} ?\) There is virtually unlimited \(\mathrm{Ca}^{2+}\) available in the outside medium (the extracellular \(\mathrm{Ca}^{2+}\) concentration in which most animal cells live is a few millimolar), and each channel passes \(10^{6} \mathrm{Ca}^{2+}\) ions per second.

The ion channels that are regulated by binding of neurotransmitters, such as acetylcholine, glutamate, GABA, or glycine, have a similar overall structure. Yet each class of these channels consists of a very diverse set of subtypes with different transmitter affinities, different channel conductances, and different rates of opening and closing. Do you suppose that such extreme diversity is a good or a bad thing from the standpoint of the pharmaceutical industry?
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