Cell signalling

Question 1

Basic elements

Answer 1

• signal or signalling molecules
• receptors
• intracellular signalling and effector proteins (G proteins, kinases, phosphatases)
• second messengers: amplify a signal

Question 2

secondary messenger examples

Answer 2

• cAMP
• Ca+2
• cGMP
• IP3
• DAG
• NO

Question 3

Hydrophobic signals

Answer 3

• can cross PM
• steroids, retinoids, thyroxine
• bind cytosolic receptor
• moved to nucleus

Question 4

Hydrophilic signals

Answer 4

• require surface receptors
• signal propagated through intermediate molecules (signal transduction molecules, second messengers)
• then to effector protein. Stays in cytosol or moved to nucleus

Question 5

Nuclear Receptor superfamily

Answer 5

• hydrophobic
• bind intracellular ligands
• not a cell surface receptor
• ligand binding, DNA binding, and variable region domains
  Cyto: ER, PR, GR
  Nucleus: Thyroxine, retinoic acid

Question 6

Glucocorticoid receptor

Answer 6

• GR, found in cytoplasm
• AD: activation domain, recruits TF’s
• DBD: DNA binding domain
• Ligand binding. HSP90 bound inhibits ligands from binding. DBD then binds DNA in the nucleus

Question 7

Effector proteins

Answer 7

• metabolic enzyme: Cytoplasm. Altered metabolism
• Gene regulatory protein: altered expression
• Cytoskeleton protein: cell shape, movement

Question 8

4 types of Intracellular signalling

Answer 8

• Endocrine: distant target cell. Ex; hormone secretion into the blood. Epinephrine
• Paracrine: short distance to adjacent cell. Epinephrine EGF
• Autocrine: self-signalling, makes own ligand and receptor. EGF
• PM-attached proteins: physical contact

Question 9

Short term cellular responses

Answer 9

• cytoplasm. Metabolism, function, movement, altered protein function, altered cytoplasm machinery

Question 10

long term cellular responses

Answer 10

• nucleus. Gene expression, development, altered protein synthesis , altered cyto machinery

Question 11

types of signals for survival/death

Answer 11

• growth factor= survive
• mitogenic signal= grow and divide.
• trophic factor withdrawal= apoptosis

Question 12

Dissociation constant

Answer 12

– measure of affinity of a receptor to its ligand
Kd=ligan concentration required to bind 50% of the cell surface receptors
- Low Kd= high affinity
- want high [RL]

Question 13

Functional Expression assay

Answer 13

• identifying a cDNA encoding a cell surface receptor
• cultured cells don’t contain X ligand receptor
• isolate and make cDNA from a cell that has X receptor
• insert into a plasmid, then into the cell
• add growth factors, cells will proliferate and express X receptor

Question 14

Activation/inactivation of G proteins

Answer 14

• Active when bound to GTP. Is triggered by a signal and helped by GEF
• inactive when bound to GDP. Mediated by GTPase, GTP hydrolysis. either intrinsic of help by GAP

Question 15

GEF/GAP

Answer 15

• GEF: activator protein. Removes GDP from G protein, allows GTP binding
• GAP: inactivator protein. accelerates GTP hydrolysis.

Question 16

G protein-coupled receptor system

Answer 16

• 7 membrane-spanning domains
• coupled trimeric G proteins
• 4 exoplasmic and cytosolic domains
• don’t hind GTP/GDP directly

Question 17

Trimeric G protien

Answer 17

• GTPase superfamily of proteins
• alpha, beta, gamma subunits
• A/Y are lipid-anchored proteins at cytosolic face of PM
• Alpha-GDP=inactive
• Alpha-GTP= active

Question 18

GPCR and G protein steps

Answer 18

1. Binding of hormone induces conf change
2. activated receptor binds Galpha subunit
3. Activated receptor promotes GEF, triggers dissociation of GDP from Galpha
4. Binding of GTP to Galpha triggers dissociation from receptor and Gby
5. Hormone dissociates from the receptor, Galpha binds to the effector, activates it
6. Hydrolysis of GTP (intrinsic or by GAP) causes Galpha to dissociate from effector and reassociate with Gby