Cell Signalling Flashcards
autocrine
Autocrine: affects the cells that made them
what are the different chemical signals
Different chemical signal:
Autocrine
Juxtacrine
Paracrine
Hormones
juxtacrine
Juxtacrine: signals only affect adjacent cells
paracrine
Paracrine: signals only affect nearby cells
hormones
Hormones: travel to distant cells, usually via the circular system
Is feedback inhibition considered a type of regulation?
Yes, Feedback can be considered a type of intracellular communication
Feedback from the presence or absence of molecules can also provide information and regulate processes
what is the purpose of cell to cell communication?
unicellular organisms need to communicate with each other, as well as sense and respond to their environments
- track down nutrients, tell the difference between light and dark, avoid poisons, toxins and predators
- reproduce and have relationships (working together to live in colonies), they also have to be able to communicate
- Helps to make sure the proper processes are occurring at the right time, and in smooth conjunction with other process in the cell/general cellular area
what are the three types of cell to cell communication
information can come in a variety of forms, and communication frequently involved converting the signals that carry that information from one form to another
- signal perception
- intracellular signal transduction
- cellular response
what is signal perception?
signal is detected by a target cell. The signalling molecule comes from outside the cell and binds to a receptor on the surface or inside of the target cell. These signals are usually chemical
what is intracellular signal transduction
Signalling molecule binds and changes the tertiary structure of the target cell’s receptor and initiates this process.
This transduction phase converts the signal from that molecule to a form that can bring about specific cellular processes/responses.
Can occur in a single step or in a transduction pathway
Signal transduction is when one signal is converted to another type of signal
e.g. when you receive a phone call the phone is converting your call to radio waves which trave to your phone, and then sound waves, which you hear
what is cellular response?
after the signal is received the cell responds to it. This is the final stage. Response could be anything, catalysis or rearrangement of the cytoskeleton etc.
what is an example of signals used by animals
- endocrine
- Endocrine
- Can be widely distributed
- Endocrine glands production- distributed blood
- paracrine
- Localised
- Extracellular fluid
- Only effects cells that share that fluid, hence the local nature of this
- synaptic
- Neurotransmitters
- Neuronal transmission
- Electronically along nerve axal cells until it’s reaches its terminal
- contact-dependent
- The signal is on the membrane of one cell, and the receptor is on the membrane of another
They knock into each other lol
- The signal is on the membrane of one cell, and the receptor is on the membrane of another
what is signal detection?
for an extracellular signal molecule to influence a target cell it must interact with a receptor protein in or in a target cell that is specific to the signaling molecule
how do small hydrophobic extracellular signal molecules interact with cell receptors?
Small hydrophobic, extracellular signal molecules, such as steroid hormones and nitric oxide, can cross the plasma membrane and activate intracellular proteins, which are usually either transcription regulators or enzymes
how do plant cell signalling molecules work?
Plants, like animals, use enzyme-coupled cell-surface receptors to recognise the extracellular signal molecules that control their growth and development; these receptors often act by relieving the transcriptional repression of specific genes
How can cells restrict the types of signals they receive?
- Receptors are specific to a specific signal
- Without the appropriate receptor the cell will be deaf to the signal and won’t be able to receive it, and therefore the cell won’t be able to have a response or change
- A cell therefore can also restrict the type of signals that effect it through the types of receptors it has- this is also good for specialised cells
what are enzyme-linked receptors?
receptors that link to enzymes
they are located in the plasma membrane
they cause phosphorylation of an intracellular protein
example: EGF receptor
- Activate a wide range of intracellular signalling pathways
- Receptors can even phosphorylate themselves
what is a GPCR?
it is a receptor that binds to a G protein
it is located in the plasma membrane
example: epinephrine receptor
- Hormone binds to the receptor and activates a protein
- This causes a change reaction (as above)
- Lots of different downstream effects can be caused by lots of different things
what is a ligand-gated ion channel?
it opens an ion channel
it is located in the plasma membrane
example: acetylcholine receptor
- When a signal is intercepted, the channel opens and allows for ions/molecules to be transported across the membrane that aren’t usually allowed across
what is an intracellular receptor?
it turns on the transcription of specific genes
it is located in the cytosol or nucleus
example: estrogen receptor
what are intracellular receptors?
- These are inside the cell
- Interact with physical or chemical signals
- Non-polar signals can diffuse directly across the plasma membrane of the cell membrane and interact with the receptor on the cytoplasm or nucleus
- Example: above (cortisol)
- Cell-surface receptors relay extracellular signals via intracellular signalling pathways
- they can relay a signal, increase its strength, detect and then relay signals from other pathways or distribute it to more than one protein
what are extracellular receptors?
- If the signal is large or polar the receptor must be imbedded in the plasma membrane (as the signal cannot pass through the plasma membrane via diffusion and what’s the point of transporting something across and expending energy when you can just intercept it at the point of contact instead)
what are the steps in the signal transduction pathway
- extracellular signal molecule interacts with a receptor protein
- intracellular signalling molecule produced
- effector proteins actuate the signal
- targeted cell responses occur
- if extracellular signalling molecule that can diffuse it directly diffuses and then interacts with a receptor inside the cell instead
How does insulin lower BG levels?
- insulin is secreted when BG is high
- binds to receptor and phosphorylates a molecule
- this triggers glycogen synthase to make glycogen from glucose
- insulin binding also increases the number of glucose transporters in the membrane which also increases the rate of glyocogen production
what are photoreceptors? what are their benefits?
photoreceptors is another word for an electronic signal
photoreceptors are used because they are quicker than chemical signals
how many classes of plant hormones are there? what are their characteristics?
6 major classes of plant hormones
- All small organic molecules
- All pretty different, except one which is a steroid
- One is a gas
- They can control many important roles
- They can have overlapping roles
- Some work synergistically and others work antagonistically
how does glucagon increase BG levels?
- glucagon is released when BG levels are low in order to convert glycogen into glucose
- glucagon activating its receptor has two effects
1. activation of glycogen phosphorylase (to begin breaking down glycogen)
2. inactivtion of glycogen synthase (to stop the further production of glycogen)
what are the purpose of alpha islets?
produce glucagon in response to low BGL
what are the purpose of beta islets?
produce insulin in response to high BGL
what are action potentials?
- Specific change in charge across a cell membrane
- Primary way electrical signals are propagated in the nervous system
- Hyperpolarised or decrease
- Depolarise or increase
- Sits at the resting potential
how to action potentials work (neuron)?
- Sits at the resting potential
- When a neuron is depolarised to the threshold potential the voltage gates sodium pumps open
- Threshold potential
○ The point where the action potential is triggered - There is a greater concentration of NA outside the neuron
- Greater concentration of K inside neurons
- When sodium channels open, sodium rushes in
- This causes the membrane potential to increase/depolarise further due to the increase in positive charge from the Na+ ions
- This occurs until the peak of the action potential is reached at about 40 Mv
- Na will then inactivate, stopping the flow of Na+
- Then the voltage gated K+ channels will open, allowing K+ to flow out
- Then the membrane potential will drop
- The refractory period occurs: when the membrane becomes hyperpolarised
- This greatly reduces the chances of a new action potential until the resting potential is restored
what is a resting potential?
- The electrical difference between the inside and the outside of the cell membrane of neurons at rest
- When they aren’t being stimulated
- -70mV
How does resting potential work (neuron)?
- Neuron at rest- potassium ion channel
- Sodium potassium pump- moves sodium out and potassium in
- This creates a higher concentration gradient
- This causes the potassium to move out of the cell through the potassium ion channel
- This creates a negative charge inside the membrane, or a negative potential, because of the lack of positive charge
How do neurons communicate?
- Neurons communicate with cellular signals known as action potentials
- Originate in the cell body
- Travel through the axon to the axon terminal
- Where they are then passed on to the next cell
what is a synapse? what are the types of synapses?
- Synapse
○ The point where two neurons meet - Electrical synapse
○ Allow direct communication between cells using gap junctions - Chemical synapses
○ Contain a synaptic cleft
○ A space between the cell sending the signal and the one receiving it
○ Cell sending the signal- presynaptic cell
○ The cell receiving the signal- postsynaptic cell
○ Action potential cannot travel cross this synaptic cleft, therefore the electrical signal is converted into a chemical signal so it can cross
○ This is accomplished by the release of neurotransmitters
○ Voltage gates calcium channels, calcium rushes in, and this triggers the fusion of vesicles with the cell wall to release transmitters into the synaptic cleft
○ They bind to receptors on the post synaptic cells
○ This can result in an increase or decrease in the postsynaptic cell’s action potential
This then results in an increased likelihood of an action potential occurring
what are soma?
where signals are combined in a neuron
and then the cell determines whether or not to pass the message further
