Explain how the che molecules allow a bacterium to move towards or away from a chemical source

Ans.

The Che proteins (chemotaxis proteins) are cytoplasmic proteins that play an important role in signal transduction pathways between the repellent or attractant and flagellar motor switch of a bacterium. Bacterial cell membranes contain different chemoreceptors for different attractants and repellents.

When a repellent or attractant binds with a chemoreceptor, stimulation of signal-transduction pathway occurs.  It sends a signal to the cytoplasmic domain of receptor, which interacts with Che proteins, present at cytoplasm. The rate of auto-phosphorylation decreases when an attractant binds with receptor, while the rate of auto-phosphorylation increases when an attractant binds with receptor.

Thus, 'the attractant enhances smooth swimming and counterclockwise rotation towards the chemical source, which repellent enhances tumbling clockwise rotation away from a chemical source.'