Signal Transduction Pathway

Question 0

Types of hormones

Answer 0

• amino acid derivatives: small, made in advance, water soluble (hydrophillic), travel in blood stream
• steroid hormones: lipid molecules (hydrophobic), made on demand, transported in blood by carrier proteins
• peptide and protein hormones: chains of amino acids, made in advance, water soluble (hydrophillic)

Question 1

Signal transduction

Answer 1

• once hormones enter the cell they trigger a cascade of events leading to a response
• signal transduction pathway is the mechanism which links a stimulus with a cellular response

Question 2

Hydrophillic signalling molecules

Answer 2

• unable to pass through cell membrane
• bind with specific receptors on the surface of the cell membrane of the target cell
• stored in vesicles and secreted from the cell by exocytosis

Question 3

Binding specificity

Answer 3

High binding specificity between the ligand (signalling molecule) and the receptor is due to complementary groups of atoms and shape

Question 4

Types of cell membrane bound receptors

Answer 4

• ion channel receptor: takes milliseconds, binding of ligand causes a shape change that opens the channel so ions enter or leave the cell
• G protein-coupled receptor: takes seconds, binding of ligand activates a G protein which activates or inhibits an enzyme or modulates an ion channel that generates secondary messengers
• tyrosine kinase-linked receptor: can take hours, binding of ligand to TK causes a shape change that activates enzymes within the cell

Question 5

Signal transduction pathway for hydrophillic signals

Answer 5

• signal binds to receptor molecule
• receptor molecule changes shape
• initiates a molecular cascade of secondary messenger molecules to an effector molecule (signal transduction)
• effector initiates the cellular response
• response can lead to the production of proteins or more hormones

Question 6

Receptors for hydrophobic signalling molecules

Answer 6

• able to pass through cell membrane
• bind with their specific receptor within the cytoplasm of the target cell
• require a carrier protein for transport in the blood (blood is water based)
• leave the secretory cell by simple diffusion

Question 7

Signal transduction pathway for hydrophobic signals

Answer 7

Steroid hormones regulate gene expression

• steroid hormone moves across cell membrane
• signal binds with intracellular protein receptor
• ligand-receptor complex moves into the nucleus to bind with DNA to regulate gene expression
• proteins are the products of gene expression

Question 8

How is the signal amplified

Answer 8

• each successive step in the transduction pathway may activate multiple molecules in the next step
• pathways may branch to produce multiple responses from the initial signal

Question 9

Types of cellular responses

Answer 9

Effector molecule brings about the cellular response
- regulate the expression of proteins by switching genes on or off
- open or close protein channels
- activate or inhibit enzyme action
- move transport vesicle to cell membrane to secrete cellular products
Once a signalling molecule has delivered the message to a cell and the cell response is initiated, the signalling molecule is degraded by cell enzymes so it doesn’t keep stimulating a response