26th Oct

Question 1

What is the function of guanylyl cyclases?

Answer 1

Convert GTP to cGMP

Question 2

What are the three main effectors of cGMP?

Answer 2

Cyclic nucleotide gated channels
PKG
PDE

Question 3

What are the two main families of guanylyl cyclases?

Answer 3

Particulate GC

Soluble GC

Question 4

How many mammalian isoforms are there of particulate GC?

Answer 4

7

Question 5

Outline the domain structure of particulate guanylyl cyclase

Answer 5

Extracellular binding domain
Single TM domain 
Regulatory domain with homology to protein kinases
C-terminal catalytic domain
Dimerisation domain

Question 6

Are particulate GCs homodimers?

Answer 6

Yes

Question 7

What are the three groups of particulate GCs?

Answer 7

Natriuretic Peptide Receptors
Intestinal peptide binding receptors
Orphan receptors

Question 8

What ligands activate Natriuretic peptide receptors (group of particulare GCs)?

Answer 8

Atrial naturetic peptide

Brain naturetic peptide

Question 9

What are the effects of activation of natriuretic peptide receptors?

Answer 9

Increased natriuresis (increased sodium excretion)
Decreased systemic vascular resistance

Question 10

What are the effects of activation of intestinal peptide binding receptors (group of GCs)?

Answer 10

Regulate electrolyte and water transport in intestinal and renal epithelium

Question 11

Are soluble GCs homodimers?

Answer 11

No they are heterodimers

Question 12

What are the subunits of soluble GCs?

Answer 12

Alpha and beta

Question 13

Outline the basic domain structure of each subunit of soluble GC

Answer 13

N-terminal regulatory domain - with heme and dimerisation domain
C-terminal catalytic domain

Question 14

What are the ligands that activate soluble GCs?

Answer 14

NO and CO

Question 15

Who identified NO as an active substance in 1977?

Answer 15

Murad

Question 16

When did Furchgott and Zawadzki find that the endothelial derived relaxing factor (EDRF) causes smooth muscles to relax?

Answer 16

1980

Question 17

Who found that Endothelial derived relaxing factor (EDRF) is NO?

Answer 17

Moncada and Igarro

Question 18

Who won the Nobel Prize in 1998 for their work on NO?

Answer 18

Furchgott, Ignaro and Murad

Question 19

Why must NO be made as and when needed, rather than being stored in vesicles?

Answer 19

It is a gaseous compound therefore it only remains stable for a few seconds

Question 20

What are the three major physiological functions of NO?

Answer 20

Smooth muscle relaxation
Platelet aggregation
Neurotransmission

Question 21

What are the molecular functions of NO?

Answer 21

Promote soluble guanylyl cyclase
Nitrosylate proteins such as L type calcium channels
Promote ADP-ribosylation
Be used as a non-specific immune response in high concentrations

Question 22

Which enzyme synthesises NO?

Answer 22

Nitric oxide synthase

Question 23

What are the three types of nitric oxide synthase?

Answer 23

inducible NOS
endothelial NOS
neuronal NOS

Question 24

Outline the reaction that nitric oxide synthase catalyses

Answer 24

L-arginine –> Citrulline and NO

Question 25

What ion is NO activity dependent upon?

Answer 25

Calcium

Question 26

What residues does PKG phosphorylate?

Answer 26

Serine/threonine

Question 27

What are the two maintypes of PKG?

Answer 27

Type 1 | Type 2

Question 28

Describe Type 1 PKG

Answer 28

``` Soluble homodimers present in many cell types 2 isoforms (alpha and beta) Functions = smooth muscle relaxation, vasorelaxation and platelet aggregation ```

Question 29

What are the domain sof each subunit in type I PKG?

Answer 29

Dimerisation domain 2cGMP binding domains Autophosphorylation and autoinhibitory domain

Question 30

Describe Type II PKG

Answer 30

Present in intestine, kidney and brain Generally membrane bound Functions = Intestinal secretion, bone growht, renin secretion and circadian rhythm

Question 31

Describe the conformation of inactive PKG

Answer 31

It is folded over so that the pseudosubstrate domain is blocking the kinase domain, preventing ligand from binding.

Question 32

Outline the pathway from L-arginine to PKG

Answer 32

L-arginine --> Citrulline +NO --> sGC --> cGMP --> PKG

Question 33

Outline the main physiological functions of PKG

Answer 33

``` Cardiac Protection Smooth muscle relaxation Neuronal plasticity Endothelial permeability Gene transcription Urinary tract function ```

Question 34

Outline the process of regulating vascular tone

Answer 34

Gq activated --> iP3 release --> Calcium release from ER --> Further calcium release from L-type calcium channels --> Calmodulin activation --> MLCK activation --> MLC phosphorylation --> contraction Simultaneously Galpha 12/13 activation --> RhoA --> ROCK --| MLCP

Question 35

Outline how NO causes vasorelaxation

Answer 35

ENDOTHELIAL CELL (Gq receptor --> Increase in calcium --> eNOS activation --> Citrulline and NO production), NO diffuses into SMOOTH MUSCLE CELL (Stimulates sGC --> cGMP --> PKG activation --> Potassium channel opening therefore reduction in calcium entry, RGS2 activation therefore inhibition of Galphaq, IRAG activation therfore inhibition of iP3 receptors on sarcoplasmic reticulum, inhibition of RhoA therefore stopping ROCK from inhibiting MLCP, activation of MLCP) --> MLC dephosphorylation --> Vasorelaxation

Question 36

Outline some important physiological functions of cyclic nucleotide gated channels

Answer 36

Vision, olfaction, cardiac pacemaker cells, renal collecting duct cells

Question 37

Outline the reactions catalysed by PDE

Answer 37

cAMP --> 5'AMP | cGMP --> 5'GMP

Question 38

How many different PDE families are there in mammals

Answer 38

11

Question 39

What are the three main types of PDEs?

Answer 39

Those that hydrolyse both cGMP and cAMP Those that hydrolyse cGMP Those that hydrolyse cAMP

Question 40

How can cGMP regulate PDEs?

Answer 40

They can alter the rate of hydrolysis by competition at the catalytic active site in PDE 1, 2 and 3 They can regulate enzymatic activity through direct binding to allosteric sites

Question 41

What is the chemical name of viagra?

Answer 41

Sidenafil citrate

Question 42

How does viagra work (not the molecular pathway)?

Answer 42

It causes relaxation of the smooth muscle in the penis and thus a rush of blood to the corpa cavernosum, causing it's cavernous sinuses to fill with blood causing an erection.

Question 43

Outline the pathway for an erection

Answer 43

Psychogenic/reflexogenic stimulus --> neural depolarisation --> increae in intracellular calcium --> Calmodulin activated neuronal NOS --> NO causes vasorelaxation and shear stress --> activates PI3K --> Akt --> endothelial NOS --> NO --> more relaxation

Question 44

How does viagra cause an erection?

Answer 44

It blocks PDE5, thus preventing cGMP being converted to 5'GMP, leading to increased stimulation of PKG --> decrease in calcium --> corpus cavernosal smooth muscle relaxation --> blood inflow

Question 45

How does PKG cause PDE activation?

Answer 45

PKG will phosphorylate PDE5 at ser92 if GTP is bound to PDE5's allosteric binding sites, leading to further activation

Question 46

What is another clinical use for viagra?

Answer 46

Treats pulmonary hypertension

Question 47

How does PKG1 stimulate apoptosis in response to NO?

Answer 47

PKG1 activation in colon cells results in phosphorylation and activation of MEKK1 leading to activation of SGK1 and the JNK pathway --> apoptosis