Question

List three common transport proteins found in vertebrate blood and the compounds they carry. Are there any compounds that do not require transport proteins in circulation? Why is this the case?

Answer 1

The three types of transport proteins found in blood are:-

1. Channel proteins – These are those types of transport proteins which are able to help the movement of molecules and ions from one outside of the cell to inside and vice versa. They open as the substance it transports need to pass through it. They are designed specifically so that it enables passage of only one type of substance. An example for the same is the voltage gated ion channels which helps in passage of different ions like K+, Cl, Ca etc.
2. Carrier proteins – These kind of proteins are present only on one side of the membrane and they help in transport of the substances against their concentration gradient. They use the help of ATP for the substance to be passed against their concentration gradient. An example is the sodium potassium pump which enables the movement of 3 molecules of Na outside the cell and 2 molecules of K inside the cell.
3. Receptor proteins – They are present on the cell membrane and as they bind the molecule they want to transport, they open a gates and hence enables the movement of the molecule through it. It attaches a signal molecule and as the molecule binds to it, it signals its transport either inside or outside the cell. An example is the G-linked receptor protein which helps in transport of multiple molecules.

There are many components which do not require transport protein in blood and one of the them is CO2. The reason it does not require a transport protein is because it is able to cross the membrane through the process of diffusion. Hence it can easily pass from the area of high concentration to low concentration until it attains equilibrium.