ch.9 Flashcards
(28 cards)
Purpose of Cell-Cell Signaling in Unicellular Organisms
Allows unicellular organisms to detect and respond to environmental changes, find nutrients, or coordinate actions (e.g., mating, quorum sensing in bacteria).
mechanism of cell-signaling in unicellular organisms
Signaling molecules bind to receptors on other cells, triggering specific responses.
Molecules Involved: Small peptides, ions, and other chemical signals.
Cell-Signaling Molecules in Multicellular Organisms
Examples:
Hormones: Insulin, adrenaline.
Neurotransmitters: Dopamine, serotonin.
Growth Factors: Epidermal growth factor (EGF).
Cytokines: Interleukins used in immune responses.
Types of Cell Signaling
- local signaling
- long distance signaling
Local Signaling:
Paracrine Signaling: Cells release molecules that affect nearby cells (e.g., growth factors).
Autocrine Signaling: Cells respond to signals they themselves release (e.g., some immune cells).
Synaptic Signaling: Specialized signaling in neurons where neurotransmitters cross synapses to target cells.
Long-Distance Signaling
Endocrine Signaling: Hormones are released into the bloodstream and reach target cells throughout the body (e.g., insulin regulating blood sugar).
Four Main Stages of Cell-Signaling
- reception
- transduction
- response
- termination
Reception
Signaling molecule binds to a receptor on the target cell
Transduction:
Signal is relayed through a series of molecules (often involving phosphorylation).
Response:
The cell activates a specific function, like gene expression or enzyme activation.
Termination:
The signal is deactivated, restoring the cell to its pre-signal state.
Signal Receptors and Their Activity Function:
Receptors bind specific signaling molecules and trigger intracellular responses.
Signal Receptors and Their Activity
Types
Intracellular Receptors: Located inside the cell; bind small, nonpolar molecules (e.g., steroid hormones).
Extracellular Receptors: Located on the cell surface; bind larger, polar molecules.
Signal Receptors and Their Activity
Characteristics
Intracellular: Nonpolar, hydrophobic signaling molecules that diffuse across the membrane.
Extracellular: Polar, hydrophilic signaling molecules interact with receptors that typically contain α-helices.
Main Types of Membrane Receptors
- G Protein-Coupled Receptors (GPCRs)
- Tyrosine Kinase Receptors (TKRs
G Protein-Coupled Receptors (GPCRs)
Function: Bind signaling molecules, activate G-proteins, which hydrolyze GTP to GDP to trigger responses.
Tyrosine Kinase Receptors (TKRs):
Function: Binding leads to dimerization (joining of two receptors), activating kinase activity, which phosphorylates tyrosine residues, triggering downstream signals.
Second Messengers
Definition: Small, non-protein molecules that relay signals inside the cell.
Second Messengers
Examples:
cAMP (cyclic AMP): Produced from ATP by adenylyl cyclase; levels increase in response to GPCR activation.
Calcium Ions (Ca²⁺): Released from intracellular stores or enter through channels, triggering various responses.
Phosphorylation Cascade
Definition: A series of protein activations where each protein in the pathway is phosphorylated, activating the next.
Key Enzymes: Protein kinases that phosphorylate other proteins, leading to signal amplification.
Signal Amplification
Definition: Each activated molecule in a signaling cascade activates multiple downstream molecules, amplifying the original signal.
Purpose: Enables a small signal to produce a large response, increasing efficiency and response speed.
Cellular Responses to Signals
Types:
Cytoplasmic Response: Activation of enzymes or proteins, usually fast.
Nuclear Response: Changes in gene expression, often slower and long-lasting.
Examples: Enzyme activation (cytoplasmic), activation of transcription factors for gene expression (nuclear).
Signal Deactivation
Purpose: Essential to stop the response once the signal is no longer needed.
Mechanisms:
Dephosphorylation: Phosphatases remove phosphate groups from proteins.
GTP Hydrolysis: G-proteins hydrolyze GTP to GDP, inactivating the protein.
Second Messenger Degradation: Enzymes degrade molecules like cAMP to reset signaling pathways.
Signaling Webs:
Complex networks formed by interconnected pathways
