signalling via intracellular receptors

Question 1

chemistry of NO

Answer 1

L-arginine —-> N-hydroxyarginine —> L-citrulline + NO

Question 2

cNOS

Answer 2

constitutive expression
Ca2+/calmodulin activates enzymatic activity 
transient activity 
eNOS and nNOS 
produces picomoles of NO

Question 3

where is eNOS located in the cell?

Answer 3

bound at cell membrane

Question 4

where is nNOS located in the cell?

Answer 4

cytosol

Question 5

iNOS

Answer 5

inducible expression - in response to stimuli produced by pathogens active all the time
produces nanomoles of NO

Question 6

what stimuli do pathogens produce?

Answer 6

LPS
IFN-γ
IL-1

Question 7

describe how NO causes vasodilation

Answer 7

1. autonomic nerves innervate endothelial cells + release ACh
2. ACh activates eNOS in endothelial cells
3. eNOS oxidises arginine twice to produce NO
4. NO diffuses into smooth muscle and activates guanylyl cyclase
5. guanylyl cyclase converts GTP to cGMP
6. cGMP binds to PKG
7. PKG activates myosin light chain phosphatase
8. myosin light chain phosphatase inhibits myosin light chain
9. smooth muscle relaxes

Question 8

describe how NO is involved in synaptic plasticity

Answer 8

1. presynaptic terminal produces glutamate
2. glutamate binds to NMDA glutamate receptors on post-synaptic membrane
3. ca2+ release into cell
   nNOS is tethered close to NMDA receptors
4. ca2+ activates nNOS
5. nNOS produces NO
6. NO diffuses into pre-synaptic terminal and increases glutamate production in pre-synaptic terminal = positive feedback loop
7. creates long-term potentiation

Question 9

describe how NO is involved in the immune system

Answer 9

in inflammatory cells, iNOS produces higher quantities of NO –> required to damage pathogens (cytotoxic) and trigger cell death (cytostatic)
also triggers inflammatory diseases when overproduced

Question 10

how is nitroglycerine used as an angina treatment?

Answer 10

1. nitroglycerine breaks down in vivo to produce NO
2. NO activates guanylyl cyclase
3. guanylyl cyclase converts GTP to cGMP
4. cGMP activates PKG
5. blood vessel smooth muscle relaxation –> vasodilation
   - decrease BP
   - decrease load of heart
   - increase heart blood supply

Question 11

phosphodiesterase-5

Answer 11

converts cGMP back to GMP
GMP is made into GTP
maintains cGMP levels

Question 12

viagra

Answer 12

inhibits phosphodiesterase-5 –> smooth muscle relaxes —> increased blood flow

Question 13

list some steroid hormones

Answer 13

• testosterone
• estradiol
• cortisol

Question 14

which part of the structure of nuclear signalling molecules makes them hydrophobic?

Answer 14

carbon ring

Question 15

how are nuclear receptors activated

Answer 15

1. inactive? -> binds inhibitory proteins = inactivates receptor
2. ligand binding releases inhibitory proteins from receptor resulting in a conformational change
3. coactivator proteins bind to receptor to form a complex on DNA
4. complex directs transcription of target genes

Question 16

describe nuclear receptor homodimers

Answer 16

• glucocorticoid and estrogen receptors
• bind as symmetric homodimers to palindromic sequence separated by 3 nucleotides
• no hormone? - anchored in cytoplasm by hsp90 = inhibitory proteins
• hormone present? - inhibitory proteins released. receptors translocate to nucleus

Question 17

describe nuclear receptor heterodimers

Answer 17

• vitamin D, thyroid & RA receptors
• bind to common cofactor = RXR as heterodimers to tandem repeats separated by nucleotides
• located in nucleus
• no hormone? - act as repressors by recruiting histone deacetylases
• hormone? - act as activators by recruiting histone acetylases to open up DNA

Question 18

early primary response of nuclear receptors

Answer 18

nuclear receptor/hormone complex directly activates transcription of primary response genes

Question 19

delayed secondary response of nuclear receptors

Answer 19

primary response genes code for TFs activating secondary response genes which produce secondary response proteins