Cell Signaling Signal Transduction Pathways

Cellular Signaling Autocrine Signals – Diffuse from one part of a cell to another part of the same cell Synaptic signaling – Neurotransmitter is the signaling molecule – Occurs in the animal nervous system – Paracrine signals- send messages to nearby cells by diffusion – Endocrine signals, or hormones, travel anywhere in the blood to reach their target cells.

Signal Transduction Pathways Ligands – Chemical in low concentrations that reach target cells by local diffusion or via the circulatory system Ligands bind to receptors – On cell membrane or inside the cytoplasm of the target cell Coordinates the activities within, among, and between all individual cells, which supports the entire organism Examples include ion channel receptors, G-protein –coupled receptors, and protein kinase receptors End product of the signal transduction pathway is a change in gene expression, a change in protein activity, or apoptosis (cellular death)

Secondary Messengers Once the signal is transmitted from outside the cell to the cytoplasm, a secondary messenger propagates the signal Most common example: cAMP (cyclic AMP) – The ligand, or first messenger, is not able to enter the cell

The Cascade Effect The multi-step cascade uses a small number of extracellular signal molecules to produce a major cellular response. Amplifies the signal and provides numerous opportunities for cellular control, coordination, and regulation Diversity of organisms with such similar pathways suggests that signal transduction pathways evolved from a common ancestor millions of years ago!!!

What do I NEED to know? Signal transduction pathways … – Are Characterized by a signal, a transduction, and a response – Are Highly specific and regulated – One signal molecule can cause a cascade effect – Evolved millions of years ago in a common ancestor

Can you make the connections? Imagine you just got a splinter! How does your body protect itself from the “foreign invader” and keep you healthy? Pause for discussion

The Human Immune System We live in a world of germs! We must protect ourselves, so… The three levels of the immune system are: – Nonspecific defenses, or barriers (innate) – Nonspecific defenses (inflammatory response) – Adaptive Immunity

First Line of Defenses Non-specific to help prevent pathogens from entering Like soldiers patrolling the area Skin Mucous Tears- lysozyme Stomach acid

Question to Ponder Can you think of a time in which you used any of these defenses? How do you think it worked?

Second Line of Defense Non-specific Inflammatory response – Histamines trigger vasodilation – Release of phagocytes and prostaglandins White blood cells attack invaders Prostaglandins increase blood flow – Chemokines are secreted Attracts phagocytes to site

Third Line of Defense Adaptive Immunity – B lymphocytes and T lymphocytes (both arise from stem cells) Both recognize specific antigens – Specific responses Recognition – B and T cells recognize specific antigens on APC (antigen presenting cells) Activation phase – Rapid cell division – Makes effector and memory cells The effect phase – B cells produce humoral response – T cells produce cell-mediated response

Interferons Interferons are protein signals released by cells infected by viral pathogens Interferons are protein signals released by cells infected by viral pathogens

Question to Ponder Discuss with your partner how adaptive immunity could utilize cell signaling pathways. How is your second line of defense like a signal transduction pathway? – What parts of the inflammatory response are represented in the cell signaling pathway? Can you draws parallels between the parts of this response to the parts of a signaling pathway?

Are you ready… Which of the following is directly responsible for humoral immunity?

Keep it up… Of all the following, what part does not participate in nonspecific immune defense?