Ch. 6 - Lipids, Membranes, and the First Cells

Freeman - Biological Science 8th Edition

Freeman8th EditionBiological ScienceISBN: 9780138276263Not the one you use?Change textbook

Freeman 8th Edition

Ch. 6 - Lipids, Membranes, and the First Cells

Problem 7

Chapter 6, Problem 7

In terms of structure, how do channel proteins differ from carrier proteins?

Verified step by step guidance

Step 1: Understand the basic function of proteins. Proteins are large, complex molecules that play many critical roles in the body. They do most of the work in cells and are required for the structure, function, and regulation of the body's tissues and organs.

Step 2: Define channel proteins. Channel proteins are integral membrane proteins that form a channel to allow specific molecules or ions to pass through the cell membrane. They have a hydrophilic channel that certain molecules or atomic ions use as a tunnel through the membrane.

Step 3: Define carrier proteins. Carrier proteins are integral membrane proteins that bind to a specific molecule, change shape, and flip the molecule across the membrane. They are involved in the facilitated diffusion and active transport of molecules across the cell membrane.

Step 4: Compare the structures. Channel proteins have a pore for molecules to pass through, while carrier proteins do not have a pore but change shape to transport molecules across the membrane.

Step 5: Summarize the differences. In terms of structure, channel proteins form a tunnel that allows molecules to simply pass through, while carrier proteins bind to a molecule and change shape to shuttle them across the membrane.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Channel Proteins

Channel proteins are integral membrane proteins that form pores or channels in the cell membrane, allowing specific ions or molecules to pass through by diffusion. They are typically selective, meaning they only permit certain substances to enter or exit the cell based on size and charge. This process is passive and does not require energy, making channel proteins crucial for maintaining cellular homeostasis.

Carrier Proteins

Carrier proteins, unlike channel proteins, bind to specific molecules and undergo a conformational change to transport these substances across the cell membrane. This process can be passive (facilitated diffusion) or active, requiring energy input to move substances against their concentration gradient. Carrier proteins are essential for the uptake of nutrients and the removal of waste products from the cell.

Membrane Transport Mechanisms

Membrane transport mechanisms refer to the various ways substances move across the cell membrane, including passive transport (like diffusion and facilitated diffusion) and active transport. Understanding these mechanisms is vital for distinguishing how channel and carrier proteins function, as they represent two different strategies for regulating the internal environment of the cell and responding to changes in external conditions.

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Related Practice

Textbook Question

Which of the following groups of amino acid residues would likely be found in the portion that crosses the lipid bilayer?

a. Acidic

b. Basic

c. Polar uncharged

d. Nonpolar

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Textbook Question

Cooking oil lipids consist of long, unsaturated hydrocarbon chains. Would you expect these molecules to form membranes spontaneously? Why or why not? Describe, on a molecular level, how you would expect these lipids to behave in water.

Textbook Question

Draw and label the plasma membrane of a cell that is placed in a solution with concentrations of calcium ions and lactose that are greater than those on the inside of the cell. Use arrows to show the relevant gradients and the activity of the following membrane proteins:

(1) A pump that exports protons

(2) A calcium channel

(3) A lactose carrier

Textbook Question

Suppose a cell is placed in a solution with a high concentration of potassium and no sodium. How would the cellular sodium–potassium pump function in this environment?

a. It would stop moving ions across the membrane.

b. It would continue using ATP to pump sodium out of the cell and potassium into the cell.

c. It would move sodium and potassium ions across the membrane, but no ATP would be used.

d. It would reverse the direction of sodium and potassium ions to move them against their gradients.

Textbook Question

In an experiment, you create two groups of liposomes in a solution containing 0.1 M NaCl—one made from red blood cell membranes and the other from frog egg cell membranes. When the liposomes are placed in water, those with red blood cell membranes burst more rapidly than those made from egg membranes. What could explain these results? Select True or False for each of the following statements.

a. T/F The red blood cell liposomes are more hypertonic relative to water than the frog egg liposomes.

b. T/F The red blood cell liposomes are more hypotonic relative to water than the frog egg liposomes.

c. T/F The red blood cell liposomes contain more aquaporins than the frog egg liposomes.

d. T/F The frog egg liposomes contain ion channels, which are not present in the red blood cell liposomes.

Textbook Question

Examine the experimental chamber in Figure 6.8a. Explain what would occur by osmosis if you added a 1-M solution of sodium chloride on the left side and an equal volume of a 1.5 M solution of potassium ions on the right. How might the addition of the CFTR protein to the lipid bilayer impact the direction of water movement?