Activated

Activated

Activated is a term used in various scientific and medical contexts to describe a state in which a molecule, cell, or system is in a heightened state of activity or responsiveness. This term is often used in biochemistry, immunology, and physiology to denote a change from a resting or inactive state to one that is functionally active.

Biochemistry

In biochemistry, activation often refers to the process by which enzymes or other proteins are converted from an inactive form to an active form. This can occur through various mechanisms, such as:

• Proteolytic cleavage: Many enzymes are synthesized as inactive precursors called zymogens or proenzymes. These precursors are activated by the cleavage of specific peptide bonds, which results in a conformational change that exposes the active site of the enzyme.

• Phosphorylation: The addition of a phosphate group to a protein can activate or deactivate its function. This is a common regulatory mechanism in signal transduction pathways.

• Allosteric regulation: Some enzymes are activated by the binding of an effector molecule at a site other than the active site, known as an allosteric site. This binding induces a conformational change that increases the enzyme's activity.

Immunology

In immunology, activation refers to the process by which immune cells, such as T cells and B cells, become capable of responding to a pathogen. This process involves several steps:

• Antigen recognition: Immune cells recognize specific antigens through their receptors. For T cells, this involves the T cell receptor (TCR) recognizing a peptide presented by major histocompatibility complex (MHC) molecules on the surface of antigen-presenting cells.

• Co-stimulation: In addition to antigen recognition, immune cells require additional signals from co-stimulatory molecules to become fully activated. This ensures that the immune response is appropriately regulated.

• Proliferation and differentiation: Once activated, immune cells proliferate and differentiate into effector cells that can carry out immune functions, such as cytotoxic T cells that kill infected cells or plasma cells that produce antibodies.

Physiology

In physiology, activation can refer to the process by which cells or tissues become more active in response to stimuli. For example:

• Muscle activation: The process by which muscle fibers are stimulated to contract. This involves the release of calcium ions from the sarcoplasmic reticulum and the interaction of actin and myosin filaments.

• Neuronal activation: The process by which neurons become more active, often measured by changes in electrical activity or neurotransmitter release. This can occur in response to sensory input or other stimuli.

Also see

• Enzyme activation
• Signal transduction
• Immune response
• Cell signaling