Question

Protein hormones typically bind to receptors __________. a. in the DNA b. in mitochondria c. at the plasma membrane d. at nuclear pores

Short answer

Protein hormones bind to receptors at the plasma membrane (option c).

Step-by-step solution

Identifying the Nature of Protein Hormones

Protein hormones are large and polar molecules, meaning they cannot easily pass through cell membranes. This is an important characteristic to keep in mind when determining where these hormones are most likely to bind.

Understanding Receptor Location

Receptors for hormones are specialized proteins located on or in certain parts of the cell. Given that protein hormones cannot pass through the lipid bilayer of cell membranes, they wouldn't bind to structures inside the cell like the DNA, mitochondria, or nuclear pores.

Identifying the Correct Binding Location

Protein hormones typically bind to receptors that are located on the surface of the cell, specifically at the plasma membrane. This is because the plasma membrane can accommodate receptors that interact with molecules that cannot enter the cell.

Key concepts

Hormone Receptor Binding

Protein hormones are like tiny messengers that carry vital instructions to the cells in our body. However, these hormones do not just wander around until they bump into a cell. Instead, they bind to specific receptors. These receptors act like locks, and the hormones like keys.

Receptors specific to protein hormones are commonly found in places that the hormone can easily access. Given that protein hormones are polar and cannot pass through the cell membrane easily, the binding takes place at locations where they do not have to cross into the cells.

Thus, the binding typically happens at the plasma membrane's surface, where specialized receptor proteins wait to "catch" these signaling molecules. This setup ensures proper communication, ensuring that the hormone's signal is effectively relayed inside the cell.

Plasma Membrane

The plasma membrane can be thought of as the cell's security gate. It controls what goes in and out of the cell. Structurally, it's a thin boundary made up of a double layer of lipids, known as the lipid bilayer.

This lipid bilayer is semipermeable, meaning it allows some things to enter or exit the cell while keeping others out. Polar molecules, like protein hormones, can't pass through the lipid-rich membrane as easily as non-polar molecules can.

• It serves as a barrier, protecting the inner components of the cell.
• It facilitates cell communication by housing receptor proteins on its surface.
• It plays a role in ion transport and cell signaling.

Due to its dual nature of protection and communication, the plasma membrane ensures that protein hormones bind externally at receptors without needing to enter the cell.

Cell Signaling

Cell signaling is like the communication system of the body. It involves messages being relayed from one part of the body to the other, ensuring cells function properly.

When protein hormones bind to their respective receptors on the plasma membrane, they set off a cascade of events inside the cell. This process is known as signal transduction.

• The hormone binding activates the receptor.
• This activation often leads the receptor to change shape or state.
• The change initiates a chain of intracellular events as messengers carry the signal from the outside to the inside of the cell.

Ultimately, this results in a specific response from the cell, such as an alteration in gene expression or enzyme activity, tailored precisely to the original instruction sent by the hormone.

Polar Molecules

Polar molecules are those that have a distribution of electric charge leading to positive and negative ends, akin to the poles on a magnet. Due to their nature, they interact well with other polar compounds, but not with nonpolar ones.

• Examples of polar molecules include water and protein hormones.
• These molecules are hydrophilic, meaning they "like" water and dissolve well in it.
• They do not pass easily through lipid layers, such as the cell’s plasma membrane.

Because of these properties, when protein hormones seek to send a message to a cell, they need to locate receptors that are conveniently placed at the cell’s outer membrane. This strategy allows them to communicate their message without needing to cross the nonpolar lipid barrier."