how do carrier proteins recognize substances to transport in active transport?

Proteins have unique shapes: Look at them here https://www.google.com/search?q=protein+shapes&oe=utf-8&rls=org.mozilla:en-US:official&client=firefox-a&um=1&ie=UTF-8&hl=en&tbm=isch&source=og&sa=N&tab=wi&ei=k5UxT-LmO9KFsAKFsImbBw&biw=1280&bih=799&sei=l5UxT6yDIsz0sQL3-Mn-Bg

The protein receptors have a mirror image shape, at least for a portion of the protein, which allows it to "latch" on and hold the protein. Other proteins cant latch on, as they are different shapes, and wont fit.

http://www.google.com/search?q=protein+shapes&oe=utf-8&rls=org.mozilla:en-US:official&client=firefox-a&um=1&ie=UTF-8&hl=en&tbm=isch&source=og&sa=N&tab=wi&ei=k5UxT-LmO9KFsAKFsImbBw&biw=1280&bih=799&sei=l5UxT6yDIsz0sQL3-Mn-Bg

Thank you Bobpursley.

And Ms.Sue.

Carrier proteins in active transport recognize substances based on specific binding sites and conformational changes. Here's a step-by-step explanation of how carrier proteins recognize substances to transport in active transport:

1. Binding Site Recognition: Carrier proteins have specific binding sites that can selectively recognize and bind to certain substances. These binding sites are often complementary in shape and charge to the substance they transport.

2. Substrate Binding: When a substance (substrate) that matches the carrier protein's binding site comes in contact, it binds to the protein. This binding occurs through non-covalent interactions, such as hydrogen bonds, van der Waals forces, and electrostatic interactions.

3. Conformational Changes: Upon substrate binding, the carrier protein undergoes conformational changes. This means that the shape of the protein changes, facilitating the translocation of the bound substrate across the cell membrane.

4. Translocation: The conformational changes in the carrier protein allow the substrate to be transported across the cell membrane. In active transport, this translocation occurs against the concentration gradient, requiring the expenditure of energy (usually in the form of ATP).

5. Release of Substrate: Once the substrate reaches the other side of the membrane, the carrier protein undergoes further conformational changes, resulting in the release of the substrate into the intracellular environment.

It's important to note that carrier proteins are highly specific in recognizing the substances they transport. The specificity arises from the molecular structure and characteristics of both the carrier protein and the substrate. This specificity ensures that only the desired substances are transported across the membrane, contributing to the regulation of cellular processes and maintaining homeostasis.