cell signals

Question 1

What is a transducer in the context of signal transduction?

Answer 1

A transducer is any device that converts variations in one physical quantity into variations in another, such as from an external signal into an intracellular response.

Question 2

What is the basic process of signal transduction?

Answer 2

• A receptor is activated by a signal.
• The activated receptor triggers a cascade of reactions inside the cell.
• The cascade leads to an end reaction and a physiological response.

Question 3

What factors influence signal perception?

Answer 3

• Presence and abundance of the signal.
• Presence and abundance of the receptor.

Question 4

What are the two main functions of receptors in signal transduction?

Answer 4

• Perception of the signal.
• Triggering a reaction that initiates a signaling cascade.

Question 5

What are common types of receptors in signal transduction?

Answer 5

• G-protein coupled receptors (GPCR)
• Receptor-like kinases (RLK)
• Ion channel receptors (ICRs)
• Cytoplasmic receptors (CRs)
• Sensor molecules (e.g., phytochrome for light perception)

Question 6

What is the structure of G-protein coupled receptors?

Answer 6

• Located in the plasma membrane.
• Composed of:
  N-terminal receptor domain
  Seven trans-membrane domains
  C-terminal intracellular extensions.

Question 7

What is the structure of receptor-like kinases (RLK)?

Answer 7

• Composed of:
  Extracellular N-terminal receptor domain.
  Transmembrane region.
  C-terminal protein kinase in the cytosol.
• Binding of ligand activates the kinase.

Question 8

How do ion channel receptors work?

Answer 8

• Ion channels associated with receptors open and close in response to:
  Physical signals: light, sound, stretching, charge difference.
  Chemical signals: hormones, metabolites.
• Movement of ions triggers a signaling cascade.

Question 9

How do cytoplasmic receptors function?

Answer 9

• These receptors bind to small ligands capable of diffusing across the plasma membrane.
• Ligand binding causes a conformational change, leading to the release of the receptor from a chaperone protein and its movement into the nucleus or other compartments.

Question 10

What are secondary messengers in signal transduction?

Answer 10

• Small molecules that relay and amplify the signal within the cell.
• Examples include cyclic nucleotides, calcium ions, nitric oxide (NO), and reactive oxygen species (ROS).

Question 11

What is the role of calcium in signal transduction?

Answer 11

• Calcium is a major secondary signaling component.
• Calcium ions move into the cytosol, triggering signaling cascades and activating calcium-dependent enzymes with EF hands calcium-binding domains.

Question 12

What is the role of nitric oxide in signal transduction?

Answer 12

• Nitric oxide (NO) is produced from arginine by NO synthase and activated by calcium ions.
• It induces signaling cascades, such as the relaxation of the endothelial layer of arteries.

Question 13

What role do reactive oxygen species (ROS) play in signal transduction?

Answer 13

• ROS are major secondary signals.
• At high concentrations, they can damage DNA and proteins, but they also serve in normal signaling.

Question 14

What are some common signaling effectors?

Answer 14

• G-proteins and phospholipase C.
• Protein kinases: Phosphorylate substrates, including serine PK and tyrosine PK.
• Calcium-activated protein kinases: CDPK, calmodulin-activated CPK.

Question 15

What is the function of protein phosphatases?

Answer 15

• Protein phosphatases catalyze the opposite reaction of protein kinases, removing phosphate groups.
• They work in pairs with protein kinases, but usually only one is regulated.

Question 16

What are the output responses of signal transduction?

Answer 16

• Activation or derepression of pathways.
• Deactivation or repression of pathways.
• Changes in enzyme activities, modulation of translation, transport processes, protein interactions, and chaperoning/ubiquitination.