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

• http://www.dnaftb.org/35/animation.html

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?

A. Cytotoxic T-cellsB. Helper T-cells

C. Macrophages

D. B cells

Keep it up…

• Of all the following, what part does not participate in nonspecific immune defense?

A. ImmunoglobulinsB. Macrophages

C. SkinD. Natural Killer Cells