Cell Signalling Flashcards
What is cell signalling?
The process which cells talk to one another that controls all aspects of cell behaviour
What is a signal?
Something that comes from outside a cell + induces a response in that target cell
What is a receptor?
Proteins on/in target cell that receive the signal via binding of ligands + bring about a response
What is the simple model for cell signalling?
- Signal reception
- Signal transduction
- Response
Why does cell signalling work?
No cell exists in isolation; all cells interact with their environment + with their neighbours
What aspects of cell behaviour does cell signalling control?
Growth
Differentiation/development
Metabolism
Apoptosis
What is autocrine signalling?
A cell signalling to itself
What is paracrine signalling?
A signal inducing a response in a target cell close to the signalling cell
What is endocrine signalling?
A signal that comes via the blood from a distant site e.g. hormone signalling
Define the term ligand.
Signalling molecules are generally referred to as ligands when binding to their receptors so ligand is a generic term for molecules that bind to specific sites on proteins
What are the 2 different types of ligands?
- Agonist: active a pathway
2: Antagonists: do not activate a pathway
What are the 2 different types of signal?
- Direct contact
2. Gap junctions
What is direct contact?
Protein on one cell binds to a receptor protein on the surface of an adjacent cell + triggers a response
What is a gap junction signal?
Cells within small groups often communicate via these junctions (allow exchange of small molecules) in plasma membranes of adjacent cells to help coordinate metabolic reactions
How do gap junctions work?
Rapidly close if [Ca2+]/[H+] increases (important is neighbouring cells die as this would increase Ca2+)
Why do electrical synapses and neuronal junctions use gap junctions for coupling cells?
Allows ions to move quickly + directly from one neuron to another avoiding delay which is characteristic of chemical synapses
What can be noticed about gap junctions during embryo development?
Cells make + break gap junction connections in specific patterns indicating that they are important in signalling
How do cell surface receptors work?
- EC part binds the signal
- Binding changes conformation of IC part
- IC cascade of reactions initiated which determines cellular response
How do intracellular receptors work?
Nuclear/cytoplasmic enzymes/TFs bind a signal + alter gene expression so they are slower-acting than cell-surface receptors
What type of protein are cell surface receptors?
Transmembrane
What features can cell surface receptors have?
Ion channels
Intrinsic enzyme activity
Linked to protein kinases
Coupled to target proteins via G protein
What is an example of channel-linked receptors?
ACh in skeletal muscle contraction where ACh binds, channel opens + ions flow across membrane
What is an example of an enzyme-linked receptor?
Tyrosine-kinase activation by GFs -> leads to phosphorylation to control enzyme activity
What is an example of a GPCR?
GABA activation of K+ ion channels by directly acting on G-protein subunits in CNS neurones
What is an example of a hormone that uses an intracellular receptor?
Steroid hormones
How can cellular behaviour be changed?
- Altered gene transcription
- Altered ion balance across plasma membrane
- Altered activity level of existing enzymes
What are enzymes?
Proteins that make chemical reactions proceed w/o being altered by those reactions themselves
What do enzymes names usually end in?
‘-ase’ e.g. kinase, phosphatase
What is a single component signalling system?
A minority of signalling pathways have the receptor + effector as the SAME protein
What is the process by which single component systems work?
- EC domain binds ligand
- Cytoplasmic domain has catalytic activity
- Binding of ligand activates enzyme converting substrate to product
- Product changes cell behaviour
What is the difference between first and second signalling messengers?
1st: EC ligand that binds receptor
2nd: small diffusible IC signalling molecules that act downstream
What is the benefit of having a cascade of second messengers?
Allows for signal amplification + integration
What do enzymes of signalling systems often do?
Phosphorylation: addition of phosphate (PO4)
Why is phosphorylation/dephosphorylation a useful process?
Quick Reversible Lasting effect Energy efficient Signal amplification Signal integration
What enzymes carry out phosphorylation + dephosphorylation?
Kinases add phosphate groups (phosphorylation)
Phosphatases remove phosphate groups (dephosphorylation)
What does voltage-gated Ca2+ influx do when acting as a specific signalling event?
Promotes fusion of neurotransmitter-containing vesicles with the cell membrane in the NMJ
