Question

Which of the following act as secondary messenger? (a) \(\mathrm{Ca}^{2+}\) (b) \(\mathrm{IP}_{3}\) (c) cAMP (d) All \(2 \mathrm{Ca} 3 \mathrm{IP}\)

Short answer

Out of the options, \(\mathrm{Ca}^{2+}\), \(\mathrm{IP}_{3}\), and cAMP act as secondary messengers. The last option, \(\mathrm{2Ca3IP}\), has no known role as a secondary messenger.

Step-by-step solution

Identify if \(\mathrm{Ca}^{2+}\) is a Secondary Messenger

\(\mathrm{Ca}^{2+}\) is a secondary messenger. It is used by cells to regulate various metabolic processes. Upon stimulation, the calcium level inside the cell rises, which triggers further intracellular reactions.

Identify if \(\mathrm{IP}_{3}\) is a Secondary Messenger

\(\mathrm{IP}_{3}\) is a secondary messenger. It is created in the cell from a certain type of phospholipid found in the membrane, referred to as PIP2. \(\mathrm{IP}_{3}\) is released into the cytoplasm of the cell where it binds to specific receptors and causes the release of \(\mathrm{Ca}^{2+}\) from certain cellular storage sites.

Identify if cAMP is a Secondary Messenger

cAMP is a secondary messenger. It is synthesized from ATP by an enzyme, adenylate cyclase, positioned on the internal cell membrane. cAMP participates in the regulation of glycogen, sugar, and lipid metabolism.

Assess if \(\mathrm{2Ca3IP}\) is a Secondary Messenger

The provided information contains no reference to a secondary messenger named \(\mathrm{2Ca3IP}\), hence it is not considered a secondary messenger.

Key concepts

Calcium ions

Calcium ions or \(\mathrm{Ca}^{2+}\), function as vital secondary messengers in various cellular processes. When a cell receives a signal from the outside, calcium levels within the cell often increase rapidly. This rise in calcium ions triggers specific proteins and enzymes, leading to a cascade of biochemical reactions. These reactions can affect processes such as muscle contraction, neurotransmitter release, and gene expression.

Here’s how calcium ions work:

• When a signal is received, \(\mathrm{Ca}^{2+}\) channels in the cell membrane or internal stores open.
• Calcium ions flood into the cytoplasm from extracellular space or internal compartments.
• The ions bind to proteins like calmodulin, changing their structure and function.
• These proteins can then activate or inhibit other molecules, spreading the signal further into the cell.

As a secondary messenger, \(\mathrm{Ca}^{2+}\) helps translate external signals into meaningful actions inside the cell, contributing to the cell's ability to respond to its environment effectively.

Inositol trisphosphate

Inositol trisphosphate, commonly referred to as \(\mathrm{IP}_{3}\), is another crucial secondary messenger. It plays a vital role in the signaling pathways of cells. \(\mathrm{IP}_{3}\) is synthesized from a specific phospholipid, PIP2, located in the cell membrane.

When a cell surface receptor is activated by a primary signal, an enzyme known as phospholipase C cleaves PIP2, producing \(\mathrm{IP}_{3}\) and diacylglycerol (DAG). The following steps describe what happens next:

• \(\mathrm{IP}_{3}\) enters the cytoplasm and travels to the endoplasmic reticulum (ER), a major cellular storage site for calcium.
• It binds to \(\mathrm{IP}_{3}\) receptors on the ER, prompting the release of \(\mathrm{Ca}^{2+}\) into the cytoplasm.
• This increase in \(\mathrm{Ca}^{2+}\) levels amplifies the cellular signal, leading to further physiological responses.

Thus, \(\mathrm{IP}_{3}\) plays a pivotal role in mediating the release of calcium ions inside cells, acting as a bridge between the initial signal and the ultimate cellular response.

Cyclic AMP

Cyclic AMP, or cAMP, is a prominent secondary messenger with diverse roles in cellular signaling. It is created from ATP by the enzyme adenylate cyclase, which is located on the internal side of the cell membrane. When a signaling molecule binds to a receptor, it activates adenylate cyclase, leading to the production of cAMP.

The production and functions of cAMP include the following steps:

• Once formed, cAMP activates protein kinase A (PKA), a critical enzyme in the signaling pathways.
• PKA phosphorylates target proteins, modulating their activity and influencing various cellular processes.
• These processes include the breakdown of glycogen, lipid metabolism, and regulation of ion channels.
• Eventually, the effects of cAMP are terminated by phosphodiesterases, which convert cAMP into inactive AMP.

Because it can amplify and relay signals efficiently, cAMP serves as an essential mediator, helping to ensure that the initial signal is multiplied and that cells can respond quickly and appropriately to stimuli.