Biol 266 : Unit 8-1

cAMP is formed from ATP by a ____________ reaction that removes two phosphate groups from ATP and joins the “free” end of the remaining phosphate group to the sugar part of the ATP molecule. The conversion of cAMP to AMP is performed by a ______________ enzyme that reduces one of the ester bonds.

cyclization ; phosphodiesterase

The diverse effects of cAMP in animal cells are mediated by the action of cAMP-dependent protein kinase (__________)

PKA

The inactive form of PKA is a tetramer, consisting of two regulatory (R) and two catalytic (C) subunits.

Each R subunit has two binding sites for cAMP. Upon binding of cAMP to the regulatory subunits, the catalytic subunits in their active form are _____________ and can ___________ downstream target proteins.

released ; phosphorylate

___________ binds to adrenergic receptors. b-adrenergic receptors are _____ receptors and a-adrenergic receptors are ______ receptors.

Adrenaline ; Gs ; Gi

_______________ is a polymer of glucose and is the major storage form of this sugar.

Glycogen

Glucose is coupled to ________ and then the glucose is incorporated into the polymer by _______________.

UDP ; glycogen synthase

When glucose is needed, _______________ removes the sugar as glucose-1-phosphate. It is then converted into glucose-6-phosphate and incorporated into the _______________ in muscle cells.

glycogen phosphorylase ; glycolytic pathway

In ______________, the phosphate is removed and the glucose is transported into the __________ and carried to other cells.

liver cells ; blood

Fast response (<1 second to minutes):

Signal transduction in the cytosol involving activation of _______ , ________________ of glycogen synthase, phosphorylase kinase and glycogen phosphorylase.

PKA ; phosphorylation

PKA stops glycogen synthase by ________________ it.

phosphorylating

Slow response (minutes to hours):

cAMP-inducible ______________

gene transcription

The free catalytic subunit of __________________ translocates to the nucleus through the nuclear pores. It then ______________ and activates a transcription factor called _________ (cAMP response element binding protein).

protein kinase A ; phosphorylates ; CREB

___________ then dimerizes and binds to the CRE sequence.

CREB

Turning off the adrenaline/glucagon signal :

1. Affinity between receptor and ligand _____________ in the presence of activated Gs_α , limiting the number of Gs_α proteins that are activated. 

2. Hydrolysis of GTP on Gs_α is increased by ______________ (like a GAP protein) 

3. _________________ converts cAMP to AMP, lessening the signal. 

4. The β-adrenergic receptor itself becomes a ___________ for both PKA and another kinase called BARK (β-adrenergic receptor kinase) that desensitize it.

decreases ; adenylyl cyclase ; Phosphodiesterase ; substrate

Some second messengers are derived from phosphatidylinositol. The inositol group can be phosphorylated by several kinases at either the 4 or 5 position of the ring. A _________________ enzyme can then hydrolyze the inositol ring releasing two second messengers: ________________ (DAG) and ______.

phospholipase C ; diacylglycerol ; IP3

The second messengers DAG and IP3 then trigger separate downstream events. DAG remains ______________ while IP3 is _____________ and can diffuse in the cytosol.

membrane-associated ; hydrophilic

_____________ : Activated through Gq-associated receptors via the Gqa subunit. Vasopressin, acetylcholine and thrombin signal through such receptors.

PLC-b

________ : activated through receptor tyrosine kinases (RTKs)

PLC-y

Glucose in the blood is a signal for the release of insulin from pancreatic cells

As glucose rises above 5 mM, it is imported through the _______ transporter.

This leads to an _________ in glycolysis, producing ATP and pyruvate.

ATP binds to ATP-sensitive K+ channels, ________ the channel.

The closed channels lead to a slight _________________ of the plasma membrane.

Depolarization causes the _____________ of voltage-sensitive Ca2+ channels.

The _________________ in intracellular Ca2+ triggers the __________ of secretory vesicles containing insulin.

GLUT2 ; increase ; closing ; depolarization ; opening ; increase ; release

G-protein coupled receptors also signal through phospholipids and Ca2+ :

1. ______________ activates Gqa, separating it from the By subunits.

2. Gqa activates PLC-B, leading to the release of _______________.

3. ________ diffuses through the cytosol to Ca2+ channels on the ER.

4. The Ca2+ channels _________, releasing Ca2+ into the cytosol.

5. The rise in intracellular Ca2+ allows Ca2+ to bind to ________________ causing the protein to relocate to the plasma membrane.

6. PKC at the plasma membrane associates with, and is activated by, __________.

7. Activated PKC can then _____________ numerous downstream targets to elicit different cellular responses.

Ligand binding ; DAG and IP3 ; IP3 ; open ; PKC ; DAG ; phosphorylate

_____________ is a protein that binds to Ca2+. In the Ca2+-bound state it binds to numerous CaM kinases and other proteins that elicit diverse responses.

Calmodulin (CaM)

Regulation of muscle contraction by Ca2+ and CaM

1. A rise in intracellular Ca2+ causes Ca2+ to bind to ________.

2. CaM·Ca2+ activates ____________ (a CaM kinase)

3. MLCK ___________ the light chain of myosin which then binds to actin to initiate muscle contraction.

CaM ; myosin light chain kinase (MLCK) ; phosphorylates

Regulation of CREB transcriptional activity by Ca2+ and CaM :

1.  A rise in intracellular Ca2+ causes Ca2+ to bind to _________. 

2.  CaM·Ca2+ activates ________ (a CaM kinase) 

3.  CamKII enters the nucleus through the pores and _______________. 

4.  CREB dimerizes and binds to DNA at CRE sequences, and recruits p300 and CBP to activate ______________.

CaM ; CaMKII ; phosphorylates CREB ; gene transcription

Regulation of cAMP levels by Ca2+ and CaM :

1. A rise in intracellular Ca2+ causes Ca2+ to bind to _______.

2. CaM·Ca2+ activates calcium-calmodulin dependent ________________, highly expressed in brain, heart and lung.

3. PDE1 converts _______ (produced by adenylyl cyclase) to _______, downregulating cAMP-dependent signaling pathways

CaM ; phosphodiesterase 1 (PDE1) ; cAMP ; AMP

Calcium acts to __________ glycogen synthesis and _____________ its degradation.

inhibit ; activate

PKC is activated through a _____ receptor. A downstream target is glycogen synthase. Phosphorylation of glycogen synthase ________ its activity, thereby _________ synthesis of glycogen

Gq ; inhibits ; inhibiting

An increase in intracellular Ca2+ leads to activation of _________________ which activates __________________.

Thus, a rise in intracellular Ca2+ serves to _______________ glycogen synthesis (via PKC) and _______________ glycogen degradation (via Ca2+)

phosphorylase kinase ; glycogen phosphorylase ; inhibit ;activate