Cell Receptors and Transduction Pathways

Question 1

Cell junctions in plants and animals

Answer 1

Directly connect the cytoplams of adjacent cells

• Animals: gap junctions
• Plants: plasmodesmata

–> signaling substances in the cytosol can pass freely between adjacent cells

Question 2

Growth Factors

Answer 2

Class of local regulators that stimulate nearby target cells to grow and divide

Question 3

Paracrine signaling

Answer 3

Multiple cells recieve and respond to a signal sent by one cell

• local signaling

Question 4

Synaptic Signaling

Answer 4

One cell receives and responds to a signal sent directly to that cell

• Occurs in animal nervous system
• Electric signal moving along a nerve cell triggers the secretion of neurotransmitter molecules carrying a chemical signal
• Molecules diffuse across a synapse (space between nerve cell and target cell)–> triggers a response in the cell
• local signaling

Question 5

Endocrine signaling

Answer 5

Hormonal signaling, long distance

Cells release hormones that travel via the circulatory system to responsive target cells in other parts of the body

• Plant hormones travel mostly through vascular tissue (xylem / phloem), but some travel through air as gas
• Common animal hormone: epinephrine

Question 6

Three stages of cell signaling

Answer 6

1. Reception- target cell’s detection of a signaling molecule coming from outside the cell
2. Transduction- a step or series of steps that converts the signal that causes a specific cellular response
3. Response- transduced signal triggers cellular response

Question 7

Ligand

Answer 7

A molecule that specifically binds to another molecule, usually causing the receptor to change shape, which activates the receptor

• Signaling molecules generally act as ligands to receptor proteins on target cells

Question 8

G protein-coupled receptor (GPCR)

Answer 8

A cell surface transmembrane receptor that makes use of a G protein (protein that binds GTP)

• After receptor protein binds and changes shape, its cytoplasmic side binds and activates a G protein
• Activated G protein carries a GTP molecule
• Leaves the receptor, diffuses along the membrane, and then binds to an enzyme that triggers the rest of the reaction

Question 9

Ligand-gated ion channel

Answer 9

A membrane receptor that has a region that can act as a “gate” for ions when the receptor assumes a certain shape

• Regulates passage of specific ions across membrane
• Example: sodium potassium pump

Question 10

Transcription factors

Answer 10

Proteins that control which genes are turned on / transcribed into mRNA

• Receptors act as transcription factors that turn on other genes

Question 11

Steroid hormone

Answer 11

Chemical messenger that passes through the cell membrane to reach a receptor

• Hydrophobic (nonpolar) enough to cross the cell membrane
• Example: testosterone

Question 12

Protein kinase

Answer 12

An enzyme that transfers phosphate groups from ATP to a protein

• Participates in signaling pathways in animals, plants, and fungi
• Many relay molecules in signal transduction pathways are protein kinases, often acting on other protein kinases in the pathway

Question 13

Protein phosphatases

Answer 13

Enzymes that quickly remove phosphate groups from proteins (dephosphorylation)

• By dephosphorylating and thus inactivating protein kinases, phosphates turn off the signal transduction pathway when the initial signal is no longer present

Question 14

Second messengers

Answer 14

Small, nonprotein water-soluble (polar) molecules or ions involved in signaling pathways

• Small size allows them easily spread throughout the body by cell division
• Calcium Ions
  
  • ​A signal relayed by a signal transduction pathway may trigger an increase in calcium in the cytosol
• Cyclic AMP
  
  • Epinephrine binds to the plasma membrane of a liver cell, heightening the cytosolic concentration of cAMP
  • cAMP broadcasts signal to cytoplasm
  • Does not exist for long without the hormone because another enzyme converts cAMP back to AMP