Cell Communication
What is cell communication? (cellular signalling)
Cells communicate using chemical signals to coordinate actions and respond to their environment.
Why is cell signallinf important across different species?
Because the same basic signalling mechanisms exist in many species, shwoinf they evolved early and are essential for life.
What is quarum sensing?
Its how bacteria detect their population density by releasing and sensing signalling molecules.
How do bacteria use quarum sensing to firm biofilms?
When signal molecule concentration is high, bacteria recognise a crowd and form protective communities called biofilms
What is a biofilm?
A group of bacterial cells stuck to a surface and to each other, forming a protective community
What is the topic of yeast cell communication?
Yeast cells communicate to find and mate with a compatible partner.
What are the 3 main steps in yeast mating communication?
Exchange of mating factors
Mating
Formation of new a/A cell
What us signal transduction?
Its the process where a cell converts a received signal into a specifc cellular response
What are the four forms of intercellular signalling?
1. Direct contact
2. Paracrine signalling
3. Endocrine signalling
4. Synaptic signalling
What is direct contact signalling?
Its when neighbouring cell communicate through physical connections, such as gap junction
What is paracrine signalling?
Cells release local messengers molecules that affect nearby cells only
What is synaptic signalling?
Its a type of paracrine signalling that happens in the nervous system when neurotransmitters are released in response to an electrical signal
What is hormonal (endocrine) signalling?
Specialised cells release hormone that travel long distances through the bloodstream to reach target cells
What are the three stages of cell signalling?
1. Reception
2. Transduction
3. Response
What is signal reception?
Is when a cell detects and binds a signalling molecule using specifc receptor proteins.
Where are most receptor proteins found?
Most receptors are bound to the cell surface, though some are inside the cell.
What is a G protein linked receptor? (GPCR)
Its a cell surface receptor that activates G protein when a signal molecule bikds to it
What do G proteins do in signalling?
They act as molecular switches that turn signals on and off by bknding and hydrolyzing GTP
What is an enzyme linked receptor?
A receptor that activates an enzyme function when a signal molecule binds to it
What is a receptor tyrosine kinase?
Its an enzyme linked receptir that activates multiple signal transduction pathways at once
What is an Ion-channel linked receptor?
Its a receptor that opens and closes an ion channel in response to a signal molecule binding
What are intracellular receptors?
They are receptor proteins located inside the cell, either in the cytoplasm or the nucleus
What types of molecules can activate intracellular receptiors?
Small or hydrophobic chemical messenger, such as steroid pr thyroid hormones
What is nitric oxide? NO
NO is a simple gas that acts as a biological messenger in the body.
How does nitric oxide cause smooth muscle relaxation?
In response to nerve signals, cells lining arteries produce NO, which diffuses into surrounding smooth muscle cells and causes them to relax.
What is guanylyl cyclase and what role does it play?
It is an enzyme that acts as a receptor for NO and produces cyclic GMP (cGMP) from GTP.
What does cyclic GMP (cGMP) do in this process?
It acts as a secondary messenger and caused smooth muscle relaxation and increased blood flow
What is a signal transduction pathway?
Its a series of molecular interactions that relay and amplify a signal from a receptor to produce a specifc cellular response
What happens during phosphorylation and dephosphorylation?
Phosphorylation activates proteins, and dephosphorylation deactivates them - controlling signal flow in a cell.
What are second messengers?
Small non protein molecules or ions that carry and amplify signals inside a cell
What is cAMP and how is it made?
Its a second messenger made from ATP by the enzyme adenylyl cyclase
Main steps in the cAMP signalling pathway?
Signal binds to G-protein linked receptor
G protein activated
G protein activates adenylyl cyclade
Adenylyl cyclase converts ATP into cAMP
cAMP activates protein kinase A
Protein kinase A acts on target proteins to produce a cellular response
What role do calcium ions (CA^2+) play in cell signalling?
They act as important second messengers in many signalling pathways
Why can calcium ions function effectively as second messengers?
Because their normal cytosolic concentration is much lower than outside the cell so small changes can have large effects
What is inositol triphosphate and what does it do?
Its a secondary messenger that helps release calcium ions from internal stores into the cytosol
What is the role of diacyglycerol?
DAG acts alongside inositol triphosphate as a second messenger, often activating protein kinase C and helping transmit the signal inside the cell
What are the 4 key aspects of signal regulation?
1. Amplification of signal
2.Specificity of response
3. Overall efficiency of response
4. Termination of the signal
What happens during glycogen breakdown in response to adrenaline?
Adrenaline triggers a signal pathway that leads to glycogen being broken down into glucose for energy
Why is there further complexity in cell signalling?
Because different cells have different proteins and pathways, the same signals can produce different effects in different cell types
What are scaffolding proteins and what do they do?
They are large relay proteins that organise and hold together other proteins in a signalling pathway
Why is signal termination important?
As once the job is done the signal must be stopped so the cell doesnt keep signalling unnecessarily.