Question

• Opposite charges attract; like charges repel.
• Like dissolves like.
• “Stable” means “low energy” and unreactive, while “unstable” means “high energy” and reactive; and all things spontaneously become more stable over time (unless there is an input of energy), and in becoming more stable they release energy.

Explain how one or more of those principles apply to each of the following:

1. A signaling ligand/first messenger is always attracted to a particular receptor. (2.5 points)
2. Motor proteins tails determine what cargo they will carry. (2.5 points)

Answer 1

Ligands are signaling molecules that cause modulation of processes inside cells by binding to receptors. Intracellular ligands, such as nitric oxide and estrogen are small and hydrophobic and diffuse directly through the cell membrane to activate proteins. The ligands crosses the plasma membrane and binds to the receptor in the cytoplasm. The receptor then moves to the nucleus, where it binds DNA to regulate transcription. Many signaling pathways involving both intracellular and cell surface receptors, cause changes in the transcription of genes.

Motor proteins are a class of molecular motors that can move along the cytoplasm of animal cell. They convert chemical energy into mechanical work by the hydrolysis of ATP. Retrograde transport carries survival signals from the synapse back to the cell body, such as the TRK, the nerve growth factor receptor. Some pathogens exploit this process to invade the nervous system. They enter the distal tips on an axon and travel to the soma by retrograde transport.

Motor proteins fulfill the role of transporting large cargo about the cell to their required destinations. Kinesis are motor proteins that transport such cargo by walking uniditectionally along microtubule tracks hydrolysing one molecule of adenosine triphosphate (ATP) at each step.