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Cell communication (Smit)

30 important questions on Cell communication (Smit)

What are four types of cell communication?

  • Endocrine
  • Paracrine
  • Neuronal
  • Contact-dependent

What is endocrine cell communication?

Endocrine cell communication is cell communication via the blood stream. The cells that communicate with each other are 'far' away.

What is neuronal cell communication?

Neuronal cell communication happens in the neurons, in the synapse a neurotransmitter is released which is the communication messenger.
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What is contact-dependent cell communication?

Contact-dependent cell communication is membrane bound signalling.

A single signal molecule can cause different effects in specific organs. Explain this using acetylcholine.

When acetylcholine binds to a heart muscle cell, the heart rate is determined, it gets slower. When acetylcholine binds to a salivary gland cell, the cell secretes more mucus. When it binds to a skeletal muscle cell the skeletal muscle contracts.
This is the case because it binds to different receptors that activate different intracellular proteins.

What causes different actions of the same cell?

A combination of signal molecules.

What is the difference between intracellular and cell-surface receptors?

Intracellular receptors are inside the cell. The molecules that bind to these receptors go through the cell membranes.
Cell-surface receptors are on the membrane of the cell. Big or hydrophilic molecules bind to these receptors.

What are examples of molecules that bind to intracellular receptors?

Steroid hormones such as cortisol, estradiol, testosterone, and the thyroid hormones such as thryoxine.

What happens when cortisol binds to a receptor protein?

A steroid like cortisol, binds to a receptor protein and induces a conformational change. After this conformation change the activated receptor can move into the nucleus, bind DNA and start the transcription process.

What are the functions of the components of the intracellular signaling pathway?

  • They can relay the signal onward and thereby help spread it through the cell
  • They can amplify the signal received, making it stronger, so that a few extracellular signal molecules are enough to evoke a large intracellular response
  • They can detect signals from more than one intracellular signaling pathway and integrate them before relaying a signal onward
  • They can distribute the signal to more than one effector protein, creating branches in the information flow diagram and evoking a complex response

What are the functions of protein kinases and protein phosphatases?

Protein kinases attach a phosphate group to a molecule, protein phosphatases remove this attached phosphate group.

Why is phosphorylation (besides activation of the protein) important?

The phosphates are added to keep the signals from the surroundings low so the signal from this cell can be 'heard'.

There are a lot of different kinases, just a few phosphatases. What does this imply?

Kinase is specific, phosphatase is nog specific so they can remove all the phosphates that are bound to the enzymes. This implies that a body always tries to turn enzymes off to keep the signals low.

What are the two types of protein switches?

  • Phosphorylation
  • GTP-binding

What is the effect of phosphorylation?

By adding a negatively charged phosphate on a protein it will attract positive charge, either on a different protein (leading to protein interaction) or within the same protein (leading to a conformational change).

How does the ion-channel-coupled receptor work?

An ion-channel-coupled receptor opens in response to binding an extracellular signal molecule. These channels are also called transmitter-gated ion channels.

How does the activation of a G-protein-coupled receptor work?

When an extracellular signal molecule binds to the receptor, the GDP will be changed into GTP. This activates the α-subunit which then activates the β-γ-subunit.

What is an example of a G-protein?

GPCR

What happens after a G-protein has been activated?

After a G-protein has been activated the α-subunit will activate the target protein. When GTP undergoes hydrolysis this inactivates the α-subunit and causes it to disassociate from the target protein. The target protein is inactivated again. The α-subunit then reassembles with the β-γ-subunit to form an inactive G-protein again.

Describe the activation of the K+-channel by a G-protein.

Acetylcholine binds to the receptor protein. The GDP on the α-subunit gets replaced by a GTP, this activates the α-subunit and β-γ-subunit. The activated β-γ-subunit activates the K+-channel. After GTP gets hydrolyzed, the α-subunit gets inactive which reassembles with and inactivates the β-γ-subunit.

How is cyclic AMP synthesized and degraded?

Cyclic AMP is formed from ATP by a cyclization reaction that removes two phosphate groups from ATP and joins the "free" end of the remaining phosphate group to the sugar part of the AMP molecule The degradation reaction beaks this bond, forming AMP. Cyclic AMP is degraded by cyclic AMP phosphodiesterase.

What is the proces of glycogen breakdown that starts with a G-protein-coupled receptor?

The hormone adrenaline binds to a protein receptor. This activates the G-protein. The α-subunit binds to adenylyl cyclase which is then activated. ATP is now converted into cyclic AMP. cAMP activates PKA. The active PKA plus ATP activates phophorylase kinase. Active phophorylase kinase plus ATP activates glycogen phophorylase, which breaks down glycogen.

What is the process of gene transcription activation caused by adrenaline?

Adrenaline binds to a receptor protein. The α-subunit gets activated and binds to adenylyl cyclase which also gets activated by this binding. ATP is now converted into cyclic AMP. cAMP activates PKA. The active PKA moves into the nucleus and phosphorylates specific transcription regulators. Once phosphorylated, these proteins stimulate the transcription of a whole set of target genes.

Which two signaling pathways are shown here?

G-protein-coupled signaling and ion-channel-linked signaling.

What are the three main classes of cell-surface receptors?

  • Ion-channel-coupled receptors
  • G-protein-coupled receptors
  • Enzyme-coupled receptors

What is the process of activation of receptor tyrosine kinases (RTKs)?

A signal molecule in the form of a dimer binds to the extracellular domain of the RTK. The kinase domains on both receptors get into contact with each other. This activates the kinases to phosphorylate the adjacent tail on several tyrosines. Each phosphorylates tyrosine serves as a specific docking site for a different intracellular signaling proteins, which then helps to relay the signal to the cell's interior.

Describe the Ras-Map-kinase pathway.

After the RTK is activated an adaptor protein will bind to it. The RAS-activation protein binds to the adaptor protein. RAS-activation protein activates the Ras protein by changing bound GDP to GTP. Activated Ras protein activates MAP kinase kinase kinase. With help of ATP, activated MAP kinase kinase kinase is formed into activated MAP kinase kinase. Again with the help of ATP, activated MAP kinase kinase is formed into activated MAP kinase. Activated MAP kinase phosphorylates various downstream signaling or effector proteins.

How is the order of the proteins in the Ras-Map-kinase pathway defined?

Introducing specific mutations.
Mutations made in different proteins of the signaling cascade help to dissect their role. Some of the mutations may occur naturally in the cell leading to highly disturbed signaling, that might lead to cell division (cancer).

What is the process of cytokine signaling?

A cytokine binds to cytokine receptors, this causes a conformational change. The tyrosines come into contact and phosphorylate each other. When activated the tail also get phosphorylated. Two STAT gene regulatory proteins can bind to this phosphor on the tails. The STAT gets activated by binding to each other. It goes into the nucleus and DNA is transcribed into RNA.

What is the process of growth factor signaling?

A TGF-β binds to a TGF-β-receptor. The tail gets activated because of phosphorylation. One SMAD gene regulatory protein binds to get phosphorylated, then it binds to another SMAD gene regulatory protein and it becomes activated. When it's activated it goes into the nucleus and the DNA is transcribed into RNA.

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The question on the page originate from the summary of the following study material:

Cell biology - Histology

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