Cell Signaling

Question 1

Are all hormones hydrophobic?

Answer 1

no

some like peptide-hormones are hydrophilic and have a hard time passing the cell membrane

Question 2

Signal transduction

Answer 2

any process by which a cell converts one kind of signal or stimulus into another

sequence of linked reactions by enzymes within the cell

accomplished through secondary messengers

Question 3

Secondary messengers

Answer 3

molecules that relay signals received at receptors on the cell surface to target molecules in the cytosol/nucleus

amplify the strength of the signal

Question 4

Example of signal amplification

Answer 4

lots of cAMP secondary molecules are created through one ligand molecule of epinephrine

Question 5

Categories of secondary messengers

Answer 5

cyclic nucleotides (ex: cAMP), ions, and lipids

anything but proteins

Question 6

Two classes of extracellular molecules? Which one is larger class?

Answer 6

1. Intracellular receptors

2. Extracellular receptors (larger class)

Question 7

What types of extracellular molecules trigger intracellular receptors?

Answer 7

small and hydrophobic molecules can move through the plasma membrane

ex: steroid hormones (cortisol) and nitric oxide

Question 8

What types of extracellular molecules trigger extracellular receptors?

Answer 8

signals that are too hydrophilic to cross the plasma membrane

ex: insulin

Question 9

What controls blood pressure?

Answer 9

degree of contraction of smooth muscle is important for blood flow and controls BP

Question 10

What types of cells line every blood vessel?

Answer 10

endothelial cells

Question 11

Where is nitric oxide produced?

Answer 11

endothelial cells from arginine

Question 12

What does NO trigger?

Answer 12

moves from endothelial cells to smooth muscle and activates guanylyl cyclase

Question 13

Guanylyl cyclase

Answer 13

stimulates formation of cGMP which triggers relaxation of smooth muscle

Question 14

Phosphodiesterase

Answer 14

PDE

within smooth muscle tissues, breaks down cGMP and causes the smooth muscle to constrict

Question 15

Viagra

Answer 15

inhibits PDE and results in prolonged cGMP signaling and prolonged relaxation

Question 16

Steroid hormones

Answer 16

hydrophobic hormones that bind to receptors in the cytoplasm or nucleus

these complexes then act as promoting factor to regulate gene transcription

Question 17

Cortisol example

Answer 17

example of a steroid hormone that forms a complex that supresses the immune system

Question 18

3 types of extracellular receptor models

Answer 18

G-protein linked receptors

Ion-channel linked receptors

Enzyme linked receptors

Question 19

G-protein linked receptors overview

Answer 19

several different types of G-proteins that each bind a specific type of receptor and set of downstream targets

all G-proteins have alpha, beta, gamma subunits and operate similarly

Question 20

What is the largest family of extracellular receptor models?

Answer 20

g-protein linked receptors

Question 21

trimeric G-proteins

Answer 21

alpha, beta, gamma subunits of g-protein

Question 22

Inactive G-proteins

Answer 22

bound by GDP at the alpha-subunit

Question 23

What happens when a hydrophilic signal binds to the extracellular receptor?

Answer 23

shape change on the cytoplasmic side of the membrane that allows a g-protein to bind to the receptor

Question 24

What happens when a g-protein binds to the receptor?

Answer 24

alpha-subunit swaps GDP nucleotide to GTP to activate the g-protein

Question 25

Does the alpha-subunit catalyze the swap of GDP to GTP?

Answer 25

NO

Question 26

What happens when the g-protein is activated?

Answer 26

alpha subunit can detatch from beta and gamma subunits g-protein can move around the cell and roam plasma membrane activated alpha and beta-gamma subunits can interact directly with target proteins in the plasma membrane to trigger amplification

Question 27

How do alpha and beta-gamma subunits become unactivated?

Answer 27

alpha-subunit hydrolyses the bound GTP to GDP alpha subunit rejoins with the beta-gamma subunit and becomes inactive

Question 28

Cholera

Answer 28

caused by inability to hydolysize GTP to GDP *review how to treat this on a molecular level

Question 29

What does Gs type of g-protein activate?

Answer 29

Adenylyl cyclase

Question 30

Adenylyl cyclase

Answer 30

catalyzes cAMP formation

Question 31

cAMP

Answer 31

secondary messenger that activates the enzyme Protein Kinase A PKA phosphorylates specific gene transcription facts which then trigger specific gene expression

Question 32

What degrades cAMP?

Answer 32

phosphodiesterase caffeine inhibits phosphodiesterase

Question 33

What does Gq type of g-protein activate?

Answer 33

Phospholipase C activates through phosphylation from the alpha-subunit

Question 34

Phospholipase C

Answer 34

hydrolyses phospholipid, PIP2 into IP3 and DAG DAG = lipid tails IP3=soluble sugar

Question 35

DAG

Answer 35

comes from hydrolysis of PIP2 secondary messenger that moves around plasma membrane DAG works with calcium to activate PKC

Question 36

IP3

Answer 36

comes from hydrolysis of PIP2 moves into cystoplasm, since soluble, and binds to calcium channels on the smooth ER

Question 37

Why are calcium channels on the smooth ER?

Answer 37

calcium deposits are stored there

Question 38

What happens when IP3 binds to calcium channels?

Answer 38

the channels allow calcium to diffuse from the smooth ER to the cytoplasm

Question 39

Calcium

Answer 39

once released from the smooth ER, acts as a secondary messenger with DAG to activate PKC

Question 40

Ion-channel linked receptors

Answer 40

convert chemical signals into electrical signals can be opened to let certain ions in or out of a cell and are responsible for rapid transmission of signals across synapses in the nervous system

Question 41

example of ion-channel linked receptors

Answer 41

Acetylcholine is a neurotransmitter that opens up acetylcholine receptor to Na+ ions makes the inside of cell have positive charge

Question 42

example of enzyme linked receptor

Answer 42

Epidermal Growth Factor Receptor (EGFR)

Question 43

What happens when EGF signal molecule binds to EGFR?

Answer 43

it triggers dimerization

Question 44

what happens once receptors are dimerized?

Answer 44

Tyrosin Kinase phosphylates attached tyrosines on the cytosolic tail

Question 45

Why is the phosphorylation of EGFR trans-?

Answer 45

left-hand kinase phosphorylates right-hand tyrosines and vice versa

Question 46

What binds to the phospho-tyrosine residues?

Answer 46

downstream cytoplasmic proteins

Question 47

What do downstream cytoplasmic proteins do?

Answer 47

build a bridge between the receptor tyrosine kinase (RTK) and the Ras protein, which is subsequently activated

Question 48

Ras protein

Answer 48

small protein bound by a lipid tail to the internal plasma membrane RAS protein is a single subunit GTP-binding protein Ras protein activates a phosphorylation cascade in which a series of protein kinases phosphorylate and activate one another (MAPKKK -> MAPK)

Question 49

How is the Ras protein activated?

Answer 49

by exchange of GDP to GTP

Question 50

What is the last protein that the Ras- protein stimulates?

Answer 50

MAP-kinase

Question 51

MAP kinase

Answer 51

phosphorylates regulatory proteins on serine and theronine leads to growth (epidermal GROWTH factor receptor)

Question 52

Mutant Ras proteins

Answer 52

unable to dissociate GTP and are always activated leads to cancer because promotes unregulated growth

Question 53

what is meant by the term "always on?"

Answer 53

indicates that an enzyme is on regardless of what is happening before it for example, it can bypass phosphorylzation step means that to reduce its effects you have to turn off DOWNSTREAM constituents

Question 54

Are signaling pathways independent of one another?

Answer 54

No there is often crosstalk between pathways

Question 55

How is cell response to extracellular signals determined?

Answer 55

Determined by the total number of signals that the cell can interpret

Question 56

autrocrine

Answer 56

self signaling

Question 57

juxtacrine

Answer 57

signaling touching cells

Question 58

paracrine

Answer 58

signaling nearby cells

Question 59

endocrine

Answer 59

signaling cells far away through the bloodstream