Chemical signalling - cell signalling Flashcards
What is cell signalling?
The process by which messages are sent to cells
Why is cell signalling important?
It allows multicellular organisms to control and coordinate their bodies and respond to their environments
What do cell signalling pathways do?
Coordinate the activities of cells, even if they are far apart within the organism
What are the basic stages of a cell signalling pathway?
- A stimulus or signal is received by a receptor
- The signal is converted to a signal that can be passed on (transduction)
- The signal is transmitted to a target (effector)
- An appropriate response is made
What are signalling molecules often called?
Ligands
Give examples of ligands
- Proteins and amino acids
- Nucleotides
- Steroids
- Amines
What is the first step in the role of ligands in cell signalling?
Ligands are secreted from a cell into the extracellular space
How do ligands reach the target cell?
They are transported through the extracellular space to a target cell
What do ligands bind to on the target cell?
Surface receptors specific to that ligand
What type of molecules can be surface receptors?
Proteins with binding sites, e.g. glycoproteins
What happens after ligands bind to their receptors?
The message carried by the ligand is relayed through a chain of chemical messengers inside the cell, triggering a response
What is quorum sensing in bacteria?
A mechanism by which bacteria communicate using ligands to respond to changes in population size
What does the term quorum refer to?
The minimum number of individuals who must be present for a process to take place
How does quorum sensing work?
- Ligands released by bacteria bind to receptors on the surface of other bacteria
- The more bacteria present, the more ligands are released
- When a threshold number of receptors are occupied, a change in gene expression is triggered
What is the effect of a change in gene expression in quorum sensing?
It leads to a change in activity which signals that a quorum has been met in the bacterial colony
What is Vibrio fischeri?
A species of bacterium found in marine environments that forms mutualistic associations with some species of squid
What benefit does Vibrio fischeri provide to the squid?
Increased camouflage
How do Vibrio fischeri help the squid with camouflage?
They emit light by bioluminescence, lighting up the underside of the squid
What benefit do Vibrio fischeri gain from the squid?
Provision of amino acids and sugar from the squid’s metabolic processes
How do Vibrio fischeri produce light?
- They colonise the squid’s light organ
- Release a ligand called an autoinducer
- Autoinducer enters other bacterial cells and binds to LuxR in the cytoplasm
- When enough autoinducer-LuxR complexes form, transcription of DNA occurs, leading to luciferase synthesis
What does luciferase do?
Catalyses an oxidation reaction which releases energy as bioluminescence
When does production of bioluminescence occur in Vibrio fischeri?
Only when the colony is large enough to switch on the synthesis of luciferase
