Cell Signalling

Question 1

autocrine

Answer 1

Autocrine: affects the cells that made them

Question 1

what are the different chemical signals

Answer 1

Different chemical signal:
Autocrine
Juxtacrine
Paracrine
Hormones

Question 2

juxtacrine

Answer 2

Juxtacrine: signals only affect adjacent cells

Question 3

paracrine

Answer 3

Paracrine: signals only affect nearby cells

Question 4

hormones

Answer 4

Hormones: travel to distant cells, usually via the circular system

Question 5

Is feedback inhibition considered a type of regulation?

Answer 5

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

Question 6

what is the purpose of cell to cell communication?

Answer 6

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

Question 7

what are the three types of cell to cell communication

Answer 7

information can come in a variety of forms, and communication frequently involved converting the signals that carry that information from one form to another

1. signal perception
2. intracellular signal transduction
3. cellular response

Question 8

what is signal perception?

Answer 8

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

Question 9

what is intracellular signal transduction

Answer 9

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

Question 10

what is cellular response?

Answer 10

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.

Question 11

what is an example of signals used by animals

Answer 11

1. endocrine
   
   • Endocrine
   • Can be widely distributed
   • Endocrine glands production- distributed blood
2. paracrine
   
   • Localised
   • Extracellular fluid
   • Only effects cells that share that fluid, hence the local nature of this
3. synaptic
   
   • Neurotransmitters
   • Neuronal transmission
   • Electronically along nerve axal cells until it’s reaches its terminal
4. 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

Question 12

what is signal detection?

Answer 12

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

Question 13

how do small hydrophobic extracellular signal molecules interact with cell receptors?

Answer 13

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

Question 14

how do plant cell signalling molecules work?

Answer 14

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

Question 15

How can cells restrict the types of signals they receive?

Answer 15

• 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

Question 16

what are enzyme-linked receptors?

Answer 16

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

Question 17

what is a GPCR?

Answer 17

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

Question 18

what is a ligand-gated ion channel?

Answer 18

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

Question 19

what is an intracellular receptor?

Answer 19

it turns on the transcription of specific genes

it is located in the cytosol or nucleus

example: estrogen receptor

Question 20

what are intracellular receptors?

Answer 20

• 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

Question 21

what are extracellular receptors?

Answer 21

• 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)

Question 22

what are the steps in the signal transduction pathway

Answer 22

• 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

Question 23

How does insulin lower BG levels?

Answer 23

• 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

Question 24

what are photoreceptors? what are their benefits?

Answer 24

photoreceptors is another word for an electronic signal

photoreceptors are used because they are quicker than chemical signals

Question 25

how many classes of plant hormones are there? what are their characteristics?

Answer 25

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

Question 26

how does glucagon increase BG levels?

Answer 26

• 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)

Question 27

what are the purpose of alpha islets?

Answer 27

produce glucagon in response to low BGL

Question 28

what are the purpose of beta islets?

Answer 28

produce insulin in response to high BGL

Question 29

what are action potentials?

Answer 29

• 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

Question 30

how to action potentials work (neuron)?

Answer 30

• 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

Question 31

what is a resting potential?

Answer 31

• The electrical difference between the inside and the outside of the cell membrane of neurons at rest
  
  • When they aren’t being stimulated
  • -70mV

Question 32

How does resting potential work (neuron)?

Answer 32

• 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

Question 33

How do neurons communicate?

Answer 33

• 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

Question 34

what is a synapse? what are the types of synapses?

Answer 34

• 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

Question 35

what are soma?

Answer 35

where signals are combined in a neuron
and then the cell determines whether or not to pass the message further