cAMP as a Second Messenger in Signal Transduction Pathways

Cell Signaling

• cAMP acts as a 2nd messenger, which is a cytoplasmic signal molecule involved in signal transduction pathways.
• 1st messenger: signal molecule (ligand) binds to receptor to initiate cellular response.
• Examples of 2nd messengers: cAMP, Ca2+, phosphatidylinositol triphosphate, nitric oxide.

Signal Transduction Pathways

• PKA (protein kinase A) is inactive when bound to glycogen.
• When cAMP binds to PKA, it becomes active and stimulates glycogen breakdown.
• Phosphatase removes Pi (inorganic phosphate) to inactivate the protein.
• GTPase (G-protein) is active when bound to GTP and inactive when bound to GDP.

Cell Signaling Types

• Juxtacrine signaling requires physical contact between the signaling cell and receiving cell.
• Autocrine signaling: a cell responds to its own signal molecules.
• Paracrine signaling: a cell responds to signal molecules from nearby cells.
• Endocrine signaling: a cell responds to signal molecules from distant cells.

Caffeine

• Caffeine is a competitive inhibitor of adenosine.
• It does not activate drowsiness.

Nervous System

Brain Anatomy

• Cerebrum: largest part of the brain.
• Pons and cerebellum: structures in the brainstem.
• Neural tube: precursor of the brain that develops over time.
• Structures to know: cerebrum, glands, midbrain, pons, cerebellum, medulla, spinal cord.

Central and Peripheral Nervous Systems

• CNS (Central Nervous System): brain and spinal cord.
• PNS (Peripheral Nervous System): nerves outside the brain and spinal cord.
• Neuron: a single electrically excitable cell with long axons.
• Afferent neurons: transmit signals from sensory receptors to the CNS.
• Efferent neurons: transmit signals from the CNS to muscles or glands.

Neuron Structure

• Dendrites: receive input from other neurons.
• Cell Body: contains organelles.
• Axon Hillock: at the cell body/axon border.
• Axon: conducts the signal.
• Synapse: connects the axon terminus to dendrites of the postsynaptic neuron.

Glial Cells

• Support and protect neurons.
• Types of glial cells: astrocytes, oligodendrocytes, Schwann cells.
• Astrocytes: link axons to capillaries (blood flow).
• Oligodendrocytes: found in CNS axons.
• Schwann cells: found in PNS axons.

Neuronal Signaling

• Voltage-gated channels: Na+ and K+ channels.
• Resting potential: -60 mV.
• Threshold: -50 mV.
• Action potential: +50 mV.
• Sodium/potassium pump: reestablishes the Na+ and K+ gradients.

Muscle Structure

• Skeletal muscle: made up of many muscle fibers.
• Muscle fiber: contains many myofibrils.
• Myofibril: contains many sarcomeres.
• Sarcomere: unit of contraction apparatus.

Muscle Contraction

• Sliding filament model: actin and myosin filaments slide past each other.
• Actin filaments: 2 strings of pearl beads wrapping around each other.
• Myosin filaments: 2 ropes wrapping around each other.
• Ca2+ increase in sarcoplasm triggers muscle contraction.
• ATP hydrolysis is required for contraction.