Cell communication Flashcards
Why do multi-cellular organisms need to be able to communicate between cells?
To co-ordinate, not just a local response, a whole organism response, e.g. fight or flight requires entire body to react quickly
How do chemical signals transfer information throughout the organism?
Travel throughout the organism to target cells
What are the step involved in intercellular signalling via chemicals?
Signal reception
Signal procession/transduction
Signal response
Signal deactivation
Explain the steps involved in the intercellular signalling via chemicals
A signalling molecule attaches to a receptor protein on the plasma membrane (Reception), this creates relay molecules in a signal transduction pathway (Transduction), this activates a cellular response (Response)
What are intracellular signal typically?
Hormones
What are the types of hormones?
Small peptides (produced by the brain FYI) Steroids
What are hormones? How much hormone is needed to create a stimulus?
Small molecules that bind to specific receptors
Only small concentration are needed for large impact
What is the general role of a hormone?
Coordinating cell activity in response to information from outside or inside the body
What kind of signal is a hormone?
An intercellular signal
How do intercellular signals create intracellular signals?
Intercellular signal bind to receptor protein in membrane which causes change in their conformation activating the protein. This creates an intracellular signal
What generally happens to intracellular signals?
They are amplified
Do steroid hormones go into the cell?
Yes
What do steroid hormones do inside the cell?
They attach to a large receptor protein in the cytosol
What is the parent molecule of steroids?
Cholesterol
How are steroids able to get into the cell?
They are lipid soluble
How does the steroid affect the cell?
It alter the gene expression at it makes the receptor protein synthesise steroid sections of the DNA
What are ligand gated ion channels?
An ion channel that requires a signalling molecules to allow for ion movement
What are ligands?
The signalling molecules which opens ligand gated ion channels
How do ligand gated ion channel receptors work?
They are normally closed preventing ions from moving across plasma membrane, however when a ligand attaches to the binding site of the ion channel it temporarily opens and allows either free flowing or facilitated ion movement (depends on ion channel), once the ligand disassociates the gate closes
Do signalling molecules affect every cell in the body? Why/why not?
No
Only cells which have the target receptors on them will respond to the signal receptor and activate signal transduction pathways
What kind of receptors are there?
Cytosolic/nuclear receptors, Membrane bound/cell surface receptors
What kind of signalling molecules do cytosolic/nuclear membranes receive? give an example. Where do these signalling act in/on a cell?
They are generally small and/or hydrophobic, e.g. hormones (they are lipid soluble, not water soluble FYI)
Normally it will get through the membrane and and on the inside of the cell
What kind of signalling molecules do membrane bound/cell surface receptors receive? give an example. Where do these signalling act in/on a cell?
They are generally large and/or hydrophilic, e.g. ligand gated ion channel, G protein coupled receptor, receptor tyrosine kinase
Normally act on the outside of the cell activating transduction pathway
Where does signal transduction occur? What kind of parties does it normally involve?
Happes on the plasma membrane
Involves G proteins or receptor protein kinases
What are G proteins?
Cytosolic proteins that bind to the receptor that produce intracellular signals
What are the activated and deactivated G proteins?
GDP is deactivated, GTP is activated
How does the deactivated G protein go to activated G protein and what does it do?
When a signal protein (primary messenger) binds to a receptor, the receptor changes shape and GDP splits off and binds GTP, the G protein dissociates from the receptor protein, in this activated form it binds to another enzyme on the plasma membrane and stimulates the production of secondary messenger (e.g. starts signal transduction)
What kind of signalling do G proteins stimulate?
On off signalling where either no secondary messenger is produced or lots of secondary messenger is produced (amplification)
What is the process of the secondary messenger producing a cellular response using cyclic AMP?
Adenylyl cyclase (enzyme that catalyses cyclic AMP) and ATP produces cAMP which then initiates a response from protein kinase A resulting in a cellular response
What need to happen once the cellular response from a secondary messenger has achieved its purpose? Why
It needs to be de activated
You don’t want the secondary messenger to be constantly on
How can the cAMP pathway be overstimulated and disrupted?
Overstimulated = caffeine Disrupted = cholera toxin
What is an example of a very potent cellular signal? What is its relative concentrations inside and outside the cell? Why is it like this?
Calcium ion (Ca2+)
10,000 times higher concentration outside cell
Ca2+ is very potent so very little needed
How does the cell maintain a low Ca2+ conc inside the cell? When do these operate?
Using three different ion pumps: pump into the mitochondria (bound and stored), pump out of the cell (removed from cell) and one into the endoplasmic reticulum (it is bound and stored)
Always operate
What is phospholipase C? What is the function of phospholipase C?
It is a membrane bound enzyme
Attracts and then cleaves phospholipids in the plasma membrane
Explain the pathway of how Ca2+ is activated and used as a messenger signal?
- First messenger activated G protein (with GTP) then activates phospholipase C
- This enzyme then cleaves PIP2 (component of phospholipid bilayer) into DAG and IP3
- The IP3 is a secondary messenger which then disperses in the cell and opens IP3 gated calcium channels in the ER releasing Ca2+ into the cell
- Ca2+ now becomes the secondary messenger and activates various proteins and cellular responses
Is the activation processes for Ca2+ signalling fast? Does it last long? Why/why not? What happens when Ca2+ isn’t removed from the cytoplasm?
It is fast
The Ca2+ is not present in the cell for long as it activates many cellular responses which if left for extended times will kill the cell
If Ca2+ isn’t removed (e.g. leaky mitochondria or ER) then cell will undergo apoptosis
Explain the overall signalling process from the primary messenger to cellular response
Primary messenger binds to receptor molecule on the plasma membrane (reception)
This activates an enzyme which produces intracellular messenger molecules, e.g. secondary messengers (transduction)
This secondary molecules then activates a signal transduction pathway to activate cellular responses (response)
What are receptor tyrosine kinases?
Transmembrane proteins that is a hormone receptor
What is the function of receptor tyrosine kinases?
They begin a phosphorylation cascade
What is the final product of a phosphorylation cascade? What does it do?
An active protein that is translocated into the nucleus to activate transcription of target genes
What kind of proteins are phosphorylated?
Kinase proteins
What hormone initiates a fight or flight response?
Adrenaline/Epinephrine
What receptor does epinephrine bind to?
Beta - Adrenergic receptor
What must happen to glucose before it is used in cellular respiration?
It must be phosphorylated into glucose 1 - phosphate then phosphorylated again into glucose 6 - phosphate
Explain the phosphorylation cascade with cyclic AMP. What can the final product do?
- ATP is catalysed into Cyclic AMP by Adenylate cyclase
- AMP then phosphorylates protein kinase A therefore activating it
- this active version then phosphorylates Phosphorylase kinase into its active version
- this phosphorylase kinase phosphorylates Phosphorylase β (inactive) into phosphorylase α (active),
- from here phosphorylase α can phosphorylate multiple different reactions
How does phosphorylase α enable glycolysis from glycogen? explain the process
Glycogen is phosphorylated by phosphorylase α which produces glucose 1 - phosphate which is then phosphorylated by phophoglucomutase into glucose 6 - phosphate and is ready for glycolysis
Is signal deactivation controlled by the nervous system? Does it make it fast and automatic or slow and controlled?
Signal deactivation is done automatically and rapidly with no input from the nervous system
What is the purpose of signal deactivation?
It enables the cell to remain sensitive to future hormone signals (doesn’t have to die to stop signal)
What is the end results of cell sensitivity to hormone signals?
It is an integrated whole organism response to changing conditions both inside and outside the organism
What are some examples of cellular responses? What is a common feature of all signalling types
Gene expression
altering protein function to gain or lose activity
opening or closing ion channels
altering cellular metabolism
–All of these signals are on for a limited time
When is deactivation promoted?
Deactivation is promoted normally by the activation of the signal so that the moment it is started it begins to stop therefore only on for a limited time
What does the rapid signalling response ensure?
Homeostatic equilibrium
