Based on the information in Section 23.7, how would you expect each of these common metabolites to cross the cell membrane?


c. Ca²⁺

Verified step by step guidance

1. Identify the nature of the metabolite: Ca^{2+} is a calcium ion, which is a charged particle.
2. Understand the cell membrane structure: The cell membrane is composed of a lipid bilayer that is hydrophobic, making it impermeable to charged ions without assistance.
3. Determine the mechanism for ion transport: Charged ions like Ca^{2+} typically require specific transport proteins to cross the cell membrane.
4. Consider the types of transport proteins: Calcium ions often use ion channels or transporters, such as calcium channels, to move across the membrane.
5. Recognize the energy requirement: The movement of Ca^{2+} can be passive (through facilitated diffusion via channels) or active (requiring energy, such as ATP, for transport against a concentration gradient).

Key Concepts

Cell Membrane Structure

The cell membrane is primarily composed of a phospholipid bilayer, which creates a semi-permeable barrier. This structure allows certain molecules to pass through while restricting others based on size, charge, and polarity. Understanding this structure is crucial for predicting how different metabolites, like Ca²⁺, interact with the membrane.

Transport Mechanisms

Transport mechanisms are the processes by which substances move across cell membranes. These include passive transport (like diffusion and facilitated diffusion) and active transport, which requires energy. For ions such as Ca²⁺, active transport is often necessary due to their charge and the need to maintain concentration gradients.

Ion Channels and Pumps

Ion channels and pumps are specialized proteins that facilitate the movement of ions across the cell membrane. Ion channels allow specific ions to flow down their concentration gradient, while pumps actively transport ions against their gradient using ATP. Understanding these proteins is essential for explaining how Ca²⁺ crosses the membrane, as it typically requires specific channels or pumps.