Signal Transduction and G-Proteins

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Questions and Answers

What is the primary function of cyclic AMP in signal transduction involving Gs-proteins?

It binds to β-Adrenoreceptors.

It activates protein kinase A (PKA). (correct)

It directly inhibits glycogen synthesis.

It metabolizes fats in liver cells.

What are the effects of adrenaline on liver cells during glycogen metabolism?

No effect on glycogen metabolism or synthesis.

Activation of glycogen metabolism and inhibition of synthesis. (correct)

Activation of glycogen metabolism and activation of synthesis.

Inhibition of glycogen metabolism and activation of synthesis.

What role do phosphodiesterases play in the signal transduction process of cyclic AMP?

They bind to Gs-proteins.

They metabolize cyclic AMP. (correct)

They inhibit adenylate cyclase.

They activate cyclic AMP.

How does the αI subunit in Gi-proteins affect adenylate cyclase?

It inhibits adenylate cyclase, reducing cyclic AMP levels. Signup and view all the answers

What determines the overall effect of cyclic AMP signaling in a cell?

The dominant alpha subunit activated by different receptors. Signup and view all the answers

What is the primary function of the αs subunit in the Gs-protein complex?

Carrying messages to the next stage Signup and view all the answers

What occurs when GDP departs from the Gs-protein?

GTP binds to the α subunit Signup and view all the answers

What process allows for the signal amplification in Gs-protein signaling?

One ligand activates several G-proteins Signup and view all the answers

Which of the following describes the interaction of the receptor with the Gs-protein?

Induced fit alters the G-protein shape Signup and view all the answers

What is the role of the β and γ subunits in the Gs-protein complex?

Stabilizing the G-protein structure Signup and view all the answers

How does GTP binding affect the state of the G-protein?

It leads to fragmentation and release Signup and view all the answers

What effect does ligand binding have on the Gs-protein signaling pathway?

It activates cascade amplifications Signup and view all the answers

Which of the following is true regarding the G-protein's GDP and GTP binding sites?

GTP binding distorts the GDP binding site Signup and view all the answers

What is the primary role of cyclic AMP (cAMP) in signal transduction involving Gs-proteins?

To act as a secondary messenger Signup and view all the answers

Which component of protein kinase A (PKA) is activated by cyclic AMP?

Catalytic subunits Signup and view all the answers

What type of kinase is protein kinase A (PKA)?

Serine-threonine kinase Signup and view all the answers

What is produced when ATP is utilized by protein kinase A during phosphorylation?

Phosphorylated proteins Signup and view all the answers

What happens to the catalytic subunits of protein kinase A when cyclic AMP binds?

They are released and activated Signup and view all the answers

How many subunits make up protein kinase A (PKA)?

Two regulatory and two catalytic Signup and view all the answers

What is the consequence of αs-GTP deactivation in the context of signal amplification?

Hundreds of ATP molecules are converted Signup and view all the answers

Which residue types are primarily phosphorylated by protein kinase A?

Serine and threonine Signup and view all the answers

What is the primary action of diacylglycerol (DG) in signal transduction?

Activates protein kinase C (PKC) Signup and view all the answers

What role does inositol triphosphate (IP3) play in signal transduction involving Gq proteins?

It releases calcium ions from storage. Signup and view all the answers

How does inositol triphosphate (IP3) affect intracellular calcium levels?

It opens calcium ion channels, mobilizing calcium release from storage Signup and view all the answers

Which molecule is activated by the binding of calcium ions to calmodulin?

Active protein kinase Signup and view all the answers

Where does protein kinase C (PKC) move after being activated by diacylglycerol?

To the membrane to interact with enzymes Signup and view all the answers

What is the result of enzyme-catalyzed reactions in signal transduction involving calcium?

Phosphorylation of specific substrates. Signup and view all the answers

Which of the following is NOT a consequence of the action of protein kinase C (PKC)?

Inhibition of inflammation processes Signup and view all the answers

What effect do lithium salts have in the context of PIP2 resynthesis?

They inhibit the resynthesis of PIP2. Signup and view all the answers

What characterizes inositol triphosphate (IP3) in terms of its physical properties?

It is hydrophilic and can move into the cytoplasm Signup and view all the answers

What is the role of calcium ions released by inositol triphosphate (IP3) in the cell?

They activate protein kinases that subsequently alter cell chemistry Signup and view all the answers

What is synthesized from IP3 and diacylglycerol (DG)?

PIP2 Signup and view all the answers

In signal transduction, which function does tyrosine kinase perform?

Phosphorylates specific tyrosine residues on proteins. Signup and view all the answers

Which statement correctly describes the action of diacylglycerol in signal transduction?

It acts as a membrane anchor for protein kinases Signup and view all the answers

Which of the following statements about the signal transduction process involving Gq proteins is true?

Inositol triphosphate and diacylglycerol are both products of phospholipase C (PLC) activity. Signup and view all the answers

What occurs when a ligand binds to a receptor in the presence of tyrosine kinase?

Activation of signaling proteins. Signup and view all the answers

What is the fate of the inactive enzyme in the presence of calcium and calmodulin?

It becomes phosphorylated. Signup and view all the answers

What is crucial for the activation of receptor tyrosine kinases?

Dimerisation of the receptor Signup and view all the answers

What role do phosphorylated regions play in receptor tyrosine kinases?

They serve as binding sites for further proteins and enzymes. Signup and view all the answers

Which of the following represents a key step in the signaling pathway initiated by growth factors?

Binding of Grb2 and SoS Signup and view all the answers

What is directly activated as a result of the phosphorylation in receptor tyrosine kinases?

Signaling proteins and enzymes Signup and view all the answers

What change occurs upon the binding of a growth factor to its receptor?

Conformational change in the receptor Signup and view all the answers

Which of the following statements about tyrosine kinase-linked receptors is incorrect?

They directly phosphorylate lipids. Signup and view all the answers

What occurs with the tyrosine residues on one half of a dimerized receptor?

They phosphorylate the corresponding residues on the other half. Signup and view all the answers

Which molecule acts as a second messenger in the signaling pathway activated by tyrosine kinase-linked receptors?

IP3 Signup and view all the answers

Study Notes

Chapter 5: Drug Targets and Signal Transduction

Drug targets are the molecules within a biological system that a drug interacts with to produce its effect.
Signal transduction is the process by which a cell converts a signal from outside the cell to a response inside the cell.

Signal Transduction Involving G-Proteins

G proteins are membrane-bound proteins with three subunits (α, β, γ).
The α subunit binds GDP, and when a signal binds to the receptor, the G-protein releases GDP and binds GTP, activating the subunit.
The activated α subunit dissociates from the βγ subunits, each initiating a separate signal transduction pathway.
Adrenaline acts as a chemical messenger.

Interaction of Receptor with G-protein

A ligand binds to the receptor, inducing a conformational change in the receptor, causing a conformational change in the G protein.
The G protein changes shape, causing the α subunit to release GDP and bind GTP, activating it.
This activation leads to the dissociation of the G protein into α and βγ subunits.
The separated subunits interact with their target proteins, initiating different downstream effects in the cell

Interaction of α with Adenylate Cyclase

Several 100 ATP molecules are converted before a-GTP deactivated.
Cyclic AMP becomes a secondary messenger.
Cyclic AMP enters the cell's cytoplasm with messages.
The process repeats for as long as the ligand is bound to the receptor.

Interaction of Cyclic AMP with Protein Kinase A

Protein kinase A (PKA) is a serine/threonine kinase activated by cyclic AMP.
Catalyses the phosphorylation of serine and threonine residues on protein substrates.

Glycogen Metabolism

Adrenaline triggers a series of events in liver cells that result in glycogen activation, and glycogen synthesis inhibition.
Adrenaline has different effects on different cells (e.g., activating fat metabolism in fat cells).

Drugs Interacting with Cyclic AMP Signal Transduction

Theophylline and caffeine are phosphodiesterase inhibitors, prolonging cyclic AMP activity.

General Notes about G-Proteins

G proteins interact with different receptors than other G proteins.
The mechanism of activation is identical.
The α subunit binds to adenylate cyclase and inhibits it.
Adenylate cyclase is under dual control (brake/accelerator).
Background activity is due to constant levels of α and α.
The overall effect depends on the dominant alpha subunit, and this depends on the activated receptor.

Phosphorylation Reactions

Phosphorylation is prevalent in enzyme activation or deactivation.
Phosphorylation radically alters intracellular binding.
This leads to altered conformations.

Interaction with Phospholipase C (PLC)

Gq proteins interact with different receptors.
The mechanism of their activation is similar to that of Gs proteins.
The α subunit activates PLC (membrane-bound enzyme).
Reaction is catalysed for as long as α is bound.

Action of Diacylglycerol (DG)

Activates protein kinase C (PKC).
PKC moves from cytoplasm to the membrane.
PKC phosphorylates Ser and Thr.
Linked to inflammation, tumor propagation, smooth muscle activity.

Action of Inositol Triphosphate (IP₃)

IP₃ is hydrophilic and enters the cell cytoplasm.
Releases Ca²⁺ in cells by opening Ca²⁺ ion channels.
Ca²⁺ activates protein kinases.
Protein kinases activate intracellular enzymes.
Alters cell chemistry leading to biological effects.

Resynthesis of PIP₂

IP₃ and DG combine in several steps to inhibit PIP₂.
Lithium salts can inhibit this process.

Tyrosine Kinase Linked Receptors

Tyrosine kinase is an enzyme that phosphorylates tyrosine residues on other proteins.
Ligand binding causes receptor dimerization.
Phosphorylation regions act as binding sites for further proteins.
Promotes the activation of signaling proteins and enzymes.
Message is carried to the cell.

Signalling Pathways

Tyrosine kinases, 1-TM receptors, guanylate cyclase and cAMP are part of signaling pathways.

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Description

This quiz covers key concepts related to cyclic AMP and its role in signal transduction involving Gs-proteins. Participants will explore the effects of adrenaline on liver cells, the functions of various G-protein subunits, and the mechanisms of signal amplification. Test your knowledge on these critical biochemical pathways!