Question

Choose one of the four forms of cell signaling and describe it in detail using examples.   Relate the development of such systems with the evolution of multicellularity and apply this to an explanation of why this would be advantageous in complex organisms.

Answer 1

Cell signaling is part of a complex system of communication that governs basic cellular activities and coordinates cell actions.The ability of cells to perceive and correctly respond to their micro environment is the basis of development, tissue pair,and immunity as well as normal tissue homeostasis. Errors in cellular processing are responsible for diseases such as cancer, autoimmunity, and diabetes. By understanding cell signaling, disease may be treated effectively and, theoretically, artificial tissues may be created.

Cell signaling is about communication between different groups of cells and tissues how one group of cells what to do.

Signal transduction refers to how the presence of an extra cellular signal can produce a change in the intracellular state of the cell without the initial signal crossing the membrane.

The cells communicate when

• During development, cells differentiate to adopt specialized roles.
• cells need to know whether to live, die, or divide.
• Neurotransmission
• Regulation of metabolism.
• Contraction- expansion.
• Secondary sexual characteristics.

There are four types of cell signaling found in multicellular organisms. They are paracrine signaling, autocrine signaling, endocrine signaling and signaling by direct contact.

An example is the conduction of an electric signal from one nerve cell to another to a muscle cell. In this case the signaling molecule is a neurotransmitter.

Autocrine: cells respond to substances which they themselves release and thus changes takes place in the cell itself.

Example

• tumour cells: release growth factors for their own survival and proliferation.

Endocrine:

• Signaling over long distance.
• Sgnal molecules( hormones) secreted by glands.
• Bloodstream carries hormones far and wide may lie anywhere in the body.

Example

• Epinephrine
• amino acid derivative(of tyrosine)
• hydrophilic signaling molecule ( bind to G protein coupled receptor)
• Released from Adrenal medulla.

Paracrine: Signaling molecules released by a secretory cell affect only those target cells in close proximity..

• For paracrine signals to act locally, secreted molecules must not be allowed to diffuse so far.
• Rapidly taken up by neighboring target cells or immobilized by ECM.

Examples

• conduction by a neurotransmitter of a signal from one nerve cell to another or from a nerve cell to a muscle cell.
• Mostly studies neurotransmitters.

Multicellular organisms thus have the competitive advantages of an increase in size without its limitations. They can have longer lifespans as they can continue living when individual cell die. Multicellularity also permits increasing complexity by allowing differentiation of cell types with in one organism.