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Term 1 > (bio) Unit 6 - Cell Communication > Flashcards

(bio) Unit 6 - Cell Communication Flashcards

1
Q

Why do cells need to communicate with eachother?

A
  • development (from single to trillions)
  • growth (coordinating with the environment)
  • day to day physiology
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2
Q

What are the four types of communication in animal cells, long or short range?

A
  1. Endocrine - long range
  2. Neuronal - long range
  3. Paracrine - short range
  4. Contact-Dependant - short range
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3
Q

What happens in endocrine signalling?

A
  • diffusion of of signal molecule (HORMONE) from endocrine cell into the blood stream
  • can reach anywhere in the body (long)
  • signal travels via blood
  • diffusing at the end to reach receptor
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4
Q

What happens in Neuronal signalling?

A
  • cell/neuron that’s sending the signal is wired to the cell that receiving the signal
  • signal travels along axon and can be long
  • synapse occurs between the neuron and target cell with the transport of NEUROTRANSMITTER
  • there’s a DIFFUSION that happens on a smaller scale where the neurotransmitter from the neuron diffuses to the receptors on the target cell
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5
Q

What happens in paracrine signalling?

(long or short?)

A
  • signalling cell releases LOCAL MEDIATOR to the receptors of TARGET CELLS
  • a short distance
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6
Q

What happens in contact-dependant signalling?

A

Membrane bound signal molecule on the signalling cell touches the receptor on target cell

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7
Q

Another word for signalling molecule

A

ligand

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8
Q

Describe the signalling pathway

A
  1. signalling molecule is synthesized and released by signalling cell
  2. the signal molecule travels to target cell
  3. signal bind to receptor protein on/in target cell
  4. signal transduction occurs where there can be activation/inactivation of protein activity, or changes in gene expression
  5. this leads to changes in cell shape, movement, metabolism, secretion
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9
Q

The location of the receptor can be predicted by the chemistry of the signal molecule, what are the the two ways receptors can exist as

A
  1. Cell surface receptors for hydrophilic signal molecule (because they cannot cross the plasma membrane)
  2. intracellular receptors for small hydrophobic signal molecule
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10
Q

What hydrophobic signal molecules can enter the cell and bind to receptors that regulate gene transcription

A

steroids
ex. cortisol, testosterone, thyroxine

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11
Q

Describe the steroid hormone mechanism of action

A

steroid receptors are ligand activated transcription factors.

they drive transcription .

they can end up upstream of steroid regulated genes after moving into nucleus

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12
Q

Intracellular signalling, what happens on the cytosolic side of cell after ligand has binded to receptor protein?

A
  1. relay (with the help of scaffold)
  2. Transduce and amplify , where 1 signal molecule and 1 receptor creates multiple small “second messenger molecules” which spreads the signals to downstream molecules in the cytosol
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13
Q

What are the two ways intracellular signal molecules can act as molecular switches?

A
  1. Signalling by protein phosphorylation
  2. Signalling by GTP - binding protein
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14
Q

What are molecular switches

A

intracellular signalling proteins that can receive signals to switch from inactive to active state.

These states can stimulate/suppress other proteins in signalling pathway

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15
Q

Explain signalling by protein phosphorylation done by kinase enzyme.

A
  1. a signal comes in (mostly ligand-receptor binding complex).
  2. it changes the shape of the protein kinase enzyme. protein kinase is supposed to phosphorylate downstream target proteins and it does that by the hydrolysis of ATP–> ADP.
    Phosphorylation cascade occursb
  3. the phosphate (PO4) sits on the target protein which activates it and changes its shape and the signal goes out.
  4. In order to turn the complex off, protein phosphatase enzyme takes the phosphate (PO4) group off.
    Target protein is now inactivated
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16
Q

What does the activity of a protein regulated by phosphorylation depend on?

A

the balance between activites of its kinases and phosphates

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17
Q

How can phosphorylation of proteins not be random? Explain by describing the two types of kinases

A
  • serine/threonine kinases: the phosphorylating hydroxyl groups of serine and threonine is done in particular sequences
  • tyrosine kinases: phosphorylate hydroxyl groups of tyrosine
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18
Q

Explain signalling by GTP binding protein

A
  1. you have a G-protein that’s bound to a GDP that’s sitting on its binding site and it’s “off”
  2. a signal comes in (mostly ligand-receptor binding complex) and it changes the shape of the protein
  3. the GDP leaves the binding site b/c of the shape change
  4. A GTP comes in and sits on the binding site of the G-protein, which activates it
  5. the G-protein has a built-in ability to cleave off the terminal PO4 of GTP. it has a GTP-ase activity. It dumps the PO4, which deactivates the G-protein
  6. the GTP reverts back to it’s diphosphate form (GDP) and the G-protein is finally inactivated
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19
Q

what is the g-protein’s activity regulated by

A

whether its bound to a GTP vs GDP

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20
Q

where is GTP most abundant

A

in the cytosol

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21
Q

what are some similarities b/w signaling by protein phosphorylation and signaling by GTP-binding protein?

A
  1. both have enzymes that assist in activating the protein
  2. Both need an extra PO4 to activate the protein
  3. both the proteins change shape when the ATP goes through hydrolysis and the GDP comes off
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22
Q

what are some differences b/w signaling by protein phosphorylation and signaling by GTP-binding protein?

A
  1. ATP goes through hydrolysis and GDP goes out and GTP comes in
  2. in signaling by protein phosphorylation, a separate protein phosphatase enzymes cleaves the PO4 to turn the protein off.
    In signaling by GTP-binding protein, the G-protein has the ability to cleave off the terminal PO4 (GTP-ase) built into it
  3. in the off stage of signaling by protein phosphorylation, there’s nothing bound to the protein and in signaling by GTP-binding protein, a GDP is bound to the off G-protein
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23
Q

Purpose of a phosphorylation cascade

A

more steps = more oppurtunity to regulate and integrate information

24
Q

What are the three classes of cell-surface receptors?

A
  1. Ion channel-coupled receptors
  2. G protein-coupled receptors (GPCR’s)
  3. Enzyme-couple receptors
25
Q

Explain ion channel-coupled receptors? How does it change voltage across membrane?

A
  • there is a binding of ligand, which opens (or closes) ion channels due changing its conformation
  • the flow of ions changes voltage
    aka ‘neurotransmitter-gated’ or ‘ligand-gated’ channels
26
Q

Explain G protein-couple receptors (GPCRs)

A

binding of ligand to receptor sends signals across the membrane and activates the trimeric GTP binding proteins on the membrane.

This is followed by the activation of an enzyme or ion channel to set off a cascade

27
Q

Explain enzyme-couple receptors

A

When two signal molecules pair up to form a dimer, they bind to the active site of a two-part inactive catalytic domain.

the cytosolic tails of both become active as they push together .

28
Q

What are the subunits of the trimeric G-protein?

A

Alpha, beta , gamma

29
Q

Importance of the alpha subunit in G protein?

A
  • decides whether the trimeric G- protein is active/will turn off
  • regulatory subunit
  • binds to GDP or GTP
  • has ATPase activity
30
Q

Describe the activation of a G-protein Couple Receptor, include the three components of the G protein

A
  1. Inactive GPCR receives signal molecule, this causes the inactive G-protein to bind to GPCR
  2. This binding changes the conformation of the G-protein , which causes GDP to dissociate from the alpha subunit
  3. This opening in the alpha subunit allows for GTP to bind to it, this binding activates the beta/gamma subunits, the trimeric G-protein breaks apart
31
Q

Characterisitcs of the beta and gamma subunits of the G protein?

A

Always binded together, but only the gamma subunit is attached to the plasma membrane

32
Q

why does the GDP dissociate once the signal molecule binds to the receptor in the activation of a G-protein coupled receptor (GPCR’s)

A

the shape of the alpha subunit changes once it is activated

33
Q

How long does a G-protein signal last?

A

As long as the alpha and beta/gamma subuunits are free

34
Q

What are the consequences of disruptions in alpha subunit of G-protein? What does this look like and give examples of consequences to this

A

When the ability to turn off a signal is hindered.

  • cholera ; prolonged secretion due to continuous activity of cell
  • whooping cough; prolonged signals that generate coughing
35
Q

What are the two downstream targets of G-proteins?

A
  1. ion channels (K+ channels in heart muscle cells)
  2. membrane-bound enzymes that catalyze synthesis of 2nd messengers
36
Q

What are the steps of how G-proteins reaching ion channels as their target?

A
  1. ligand binding , GPCR activated
  2. activated beta and gamma subunits of G-protein bind to closed K+ channel
  3. Ion channel activates through interactions from the cytosolic side
  4. Results in the net flux of ions out of the cell
37
Q

What are the steps of how G-proteins reach the membrane-bound enzymes that catalyze synthesis of 2nd messengers

A
  1. ligand binding , GPCR activated
  2. alpha subunit interacts with a membrane associated enzyme on cytosolic side of membrane.
    (all excited parts of enzyme is on the cytosolic side)
  3. enzyme will catalyze the transformation of second messengers
  4. second messengers diffuse to act on intracellular signaling proteins
38
Q

what has to happen to the PO4 group of a nucleotide to turn the nucleotide on and off (U6S33)

A

ON: on a nucleotide with 3 PO4 groups, the 2 terminal PO4 groups have to come off via ATP energy and the last one that’s remaining has to bend in a cyclic shape so that the charged O groups can be on the outside

OFF: the cyclic PO4 has to break the cyclic shape and the nucleotide has to become a 5’AMP (amino-mono-phosphate)

39
Q

What can cyclic AMP drive? How?

A

Gene transcription .
Can activate protein kinases that catalyzes the phosphorylation of a transcription regulator

Also drives glycogen breakdown by activating PKA and thus the phosphorylation of phosporylase kinases and glycogen phosphorylase

Also drives stress response

40
Q

How does epinephrine (adreneline) activate adenylyl cyclase? What second messenger does this create? What are the following proteins of this process?

A
  • Act via GPCR that activates G-protein, which activates adenylyl cyclase
  • creates CYCLIC AMP (second messengers)
  • cyclic AMP turns on inactive PKA (PROTEIN KINASE)
  • PKA transfers phosphate to target protein (PHOSPHORYLASE KINASE)
  • active phosphorylase kinase phosphorylates inactive GLYCOGEN PHOSPHORYLASE
  • leads to breakdown of glycogen
41
Q

Describe the downstream pathway of GPCR activated effector enzyme, phospholipase C

A
  1. ligand activates GPCR, which activates G-protein which activates phospholipase C (on plasma membrane)
  2. phospholipase breaks down a inositol phospholipid (on plasma membrane)
  3. this creates the second messenger inosital 1,4,5 - triphosphate (IP3)
  4. the IP3 acts as a ligand that binds to the Ca+ ion channel on the ER membrane
  5. This allows the movement of Ca2+ ions out of the ion channel
    (it acts as a second messenger which later binds to target proteins)
42
Q

Where is the inosital phospholipid abundant on?

A

cytosolic side of membrane leaflets

43
Q

What is the concentration of calcium ions in the cytosol vs outside the cell? Where can there be higher concentrations?

A

very low [ ] in the cytosol compared to outside of the cell .

Higher concentrations within storage molecules

44
Q

How can the concentrations of calcium ions increase in the cytosol?

A
  • By opening channels on plasma membrane
  • opening channels on ER membrane
45
Q

what mediates the effects of Ca+2?

A

Calmodulin (CaM). Ca+2 binds to CaM and it activates it which then changes shape when wrapping around it

46
Q

Describe the activation of a receptor tyrosine kinase (RTK)

A
  1. a ligand dimerizes, binds and brings together mobile membrane proteins
  2. tails of the membrane proteins have kinase activity (aka tyrosine kinase activity), they are now active RTK
  3. these activated, cytolslic tails act as docking places for helper proteins
47
Q

What is the largest class of enzyme coupled receptors? What do they do?

A

Receptor Tyrosine Kinase (RTK),
Kinases mediate GPCR responses

48
Q

What do signal proteins do after they are recruited to the cytosolic tails of RTK?

A

They activate other downstream signals

49
Q

What is the downstream process of activated RTK followed by?

A
  • Followed by the activation phosphorylation of tyrosine residues
  • this activates the samll G - protein Ras
  • does other things
50
Q

Ras protein, what is it? where does it attach to? how is it similar to a G alpha subunit

A
  • small, monomeric G-protein activated by binding to the cytosolic tail of RTK
  • molecular switch, set off relay of signals
  • similar to alpha subunit of trimeric G-protein, active when bound to GTP
51
Q

what’s another word for a signal molecule that’s in an RTK pathway

A

mitogen; they drive mitosis or cell division

52
Q

How can cancer be a failure of cell communication?

A

Mutations in Ras protein can lead to permanently activated protiens, where there is signalling inside cell without incoming signals

53
Q

Small, monomeric G-proteins differ from trimeric G-proteins in that monomeric G-proteins …

A

are downstream components of receptor tyrosine kinase (RTK) signalling pathways.

54
Q

What event is common to ALL signal transduction pathways?

A

Proteins change in shape.

55
Q

About the adenylyl cyclase that participates in stimulation of glycogen breakdown in skeletal muscle:

During its synthesis/installation, its active site would project from the …

A

inner surface of the plasma membrane and outer surface of the ER.

Term 1 (21 decks)

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