Cell Signaling (session 8) Flashcards
What is cell signalling?
Communication between cells/molecules essential for all life processes
Name three key process dependent on cell signalling.
Embryonic development, homeostasis, immune response
What is the primary function of cell membranes?
To protect the cells interior and mediate selective permeability
What are the two main components of the lipid bilayer?
Phospholipids and proteins
How does the lipid bilayer allow molecules to cross?
Small hydrophobic and uncharged polar molecules pass through directly, others need transport proteins or diffusion
List the four key functions of the membrane proteins
Transporters, Anchors, Receptors, and enzymes
Why is cell signalling important?
It enables communication for cell division, differentiation, survival, and responses to external signals
What are the four main types of cell signalling?
- Endocrines (long distance signalling by hormones)
- Paracrine (local signalling)
- Neuronal (specific signalling by neurons)
- Contact-dependent (direct cell contact)
What are the first and second messengers in cell signalling?
First messenger: ligands like hormones or peptides.
Second messenger: intercellular molecules triggered by first messengers.
What are the two types of receptors in cell signalling?
Extracellular receptors: on the cell membrane, respond to hydrophilic signals
Intercellular receptors: found in the cytosol/nucleus, respond to hydrophobic signals.
How do intercellular receptors influence cell function?
They act as transcription factors, binding DNA to induce or change gene transcription.
How do intercellular receptors work?
Steroids pass through the membrane, bund ti cytosolic receptors, form a ligand-receptor complex, enter the nucleus, and alter the transcription
What types of ligands bind to extracellular receptors?
Hydrophilic and large ligands that cannot cross the lipid bilayer
Name the three main types of cell surface receptors
Ion channel coupled receptors
G protein coupled receptors
Enzyme coupled receptors
What are the five forms of ion channels?
Voltage-gated
Ligand-gated(extracellular)
Ligand-gated(intercellular)
Stress/mechanical-gated
Leaky channels
What are the two states of ion channels?
Open(active): ions pass through
Closed(inactive): ion passage blocked
What is osmoregulation?
Balancing solute concentrations across membranes, allowing water movement by osmosis
What is the function of Na+/K+ pumps
Actively transport Na+ out and K+ into the cell using ATP to maintain membrane potential
How do leaky K+ channels contribute to membrane potential?
Allow K+ to passively flow out, creating the resting membrane potential (more negative ions inside the cell)
What activates voltage-gated ion channels?
Change in membrane potential
What is the function of Node of Ranvier in neurons?
Facilitate rapid signal transmission by allowing action potential to “jump” between gaps in myelin sheath
What are the two types of ion transport?
Active transport (requires ATP)
Passive transport (does not require ATP, diffusion through leaky channels)
What maintains the resting potential of -70mV?
Na+/K+ pumps (3 Na+ out, 2K+ in) and leaky K+ channels creating a negative intercellular charge.
What triggers an action potential?
A stimulus causing the membrane to depolarise to the threshold potential (-55mV)
Describe the stages of an action potential
Depolarisation: Na+ influx
Repolarisation: K+ efflux
Hyperpolarisation: overshoot due to slow K+ channel closure
Restoration: Na+/K+ pumps reset the resting potential.
What is saltatory propagation?
Action potentials jump between nodes of ranvier, speeding up transmission along the myelinated axons.
What are the three confirmations of voltage-gated ion channels?
Close, Open, and Inactive
What is the difference between an electric and chemical synapse?
Electrical: Direct ionic current flow by gap junctions, rapid transmission.
Chemical: neurotransmitters-mediated, slower but more common.
Describe the process of synaptic transmission in a chemical synapse.
AP triggers Ca2+ entry by voltage-gated channels
Ca2+ signals vesicles to release neurotransmitters by exocytosis
Neurotransmitters bind to postsynaptic receptors, initiating a response
Name three mechanisms for neurotransmitter removal from the synaptic cleft
- Enzyme degradation (Acetylcholinesterase)
- Reuptake to the presynaptic neuron or neuroglia
- Diffusion away from the synaptic cleft
What is the role of excitatory and inhibitory neurotransmitters?
Excitatory neurotransmitters trigger action potentials, while inhibitory neurotransmitters prevent them
