Lecture 14 - Signaling 1

Question 1

Describe ligands and receptors

Answer 1

Signaling requires activation of a receptor, usually through interaction w/ another molecule called a ligand

Ligands take many forms, receptors are proteins

Ligand - receptor interactions are non-covalent (reversible)

Ligand binding induces confirmational change in receptor or induces dimerization of receptor - causes change in activity (if receptor is an enzyme) or change in affinity

Information passed on by 2ndary messangers

Question 2

What is the process that amplifies the signal in the cell?

Answer 2

Secondary messangers!

Question 3

How is signal concentration controlled?

Answer 3

Concentration depends on balance between how fast the molecule is synthesized or released and how fast it’s degraded or removed.

Removal rate is often constant, concentrations often changed by manipulating rate of production

Fast degradation = quick acting molecules (adrenaline)

Slow degradation = slower effect molecules (steroids)

Question 4

How do cellular responses depend on a particular signal?

Answer 4

Signaling molecule concentration

of available receptors

Receptor affinity for signal

Expression of secondary messangers

Question 5

What is cellular adaption and what are 3 ways it occurs?

Answer 5

It is a changing in the response to a constant concentration of a ligand

Ex.

1. Prolonged receptor activation desensitizes receptors (reduces response to ligand binding)
2. Endocytosis removes receptors from cell surface
3. Secondary messangers may change rate of transcription of receptor gene, leading to changes in # of receptors on cell surface

Question 6

Do cells having the same receptors mean they will have the same response?

Answer 6

NO! Bindings of the same ligand to the same receptor in 2 diff cells can activate different second messanger systems.

One ligand can bind to different receptors in diff cell types and cause different reactions

Question 7

Rank the routes of signal delivery (endocrine vs paracine/autocrine vs neuronal)

Answer 7

Endocrine - transmitted through blood over long distances, need low [] and high receptor affinity

Paracrine/autocrine - intermediate affinity for receptor

Neuronal - need high [] of ligands and have lowest receptor affinity

Question 8

What are the classes of signaling molecules?

Answer 8

1. Small, diffusable molecules (CO, NO) - pass into cells and alter enzyme activity directly, very short half life (ex. nitroglycerin relaxes smooth muscle)
2. Hydrophobic molecules (steroids, retinoids, thyroid hormones) usually carried by binding proteins, pass directly through membranes and bind to cytoplasmic or nuclear receptros.
3. Hydrophobic (eicosinoids) - bind to surface receptors, derived from phospholipids, include prostaglandins, etc (involved w/ inflammatory signaling)
4. Hydrophilic molecules - peptides, amino acid derivatives, etc. - bind to receptor on cell surface
5. Sensory signals - ex. light or sound

Question 9

Describe the signal transduction mechanism of steroid hormones

Answer 9

Nuclear receptors for steroids activate gene transcription - activated receptor/steroid complex moves into nucleus.

Activated receptor-steroid complex binds to regulatory region of target gene and activates transcription, removing the inihbitory complex present

Question 10

Do all transcription factors work alone?

Answer 10

No, activation of some genes may require “partner” transcription factors - partners that a cell makes determines its response to the hormone

Question 11

What are the types of surface receptors for hydrophilic molecules and eicosinoids?

Answer 11

1. Ion-channel linked receptors
2. G-protein coupled receptors
3. Enzyme-linked receptors