Cell Membrane Structure and Composition

Questions and Answers

What is the primary function of Gq proteins in cellular signaling?

Stimulates phospholipase C (correct)

Regulates cAMP levels

Activates adenylate cyclase

Inhibits phospholipase C

Which G-protein is responsible for inhibiting adenylate cyclase?

Transducin

Gi (correct)

What happens to Gq proteins after they activate their target?

They remain permanently active

They stimulate cGMP levels

They hydrolyze their bound GTP (correct)

They promote IP3 accumulation

As hormone concentrations decrease, what happens to the active Gq-GTP complex?

It decreases in concentration Signup and view all the answers

Which second messenger is primarily associated with Gs stimulation?

cAMP Signup and view all the answers

What effect does vasopressin have on renal collecting duct membranes?

It increases water permeability. Signup and view all the answers

Which pathway is activated by oxytocin to regulate genes involved in cell division?

Mitogen-activated protein kinase pathway Signup and view all the answers

What is the role of nitric oxide in vascular endothelial cells?

It activates guanylate cyclase. Signup and view all the answers

Which of the following receptors undergo autophosphorylation upon hormone binding?

Monomeric tyrosine kinase receptors Signup and view all the answers

What does cyclic guanosine monophosphate (cGMP) do in smooth muscle cells?

It induces relaxation of smooth muscle. Signup and view all the answers

What is primarily found in the exterior monolayer of the red blood cell plasma membrane?

Sphingomyelin and phosphatidylcholine Signup and view all the answers

Which statement about membrane proteins is correct?

Membrane proteins typically make up 40% to 50% of a membrane. Signup and view all the answers

What is a primary function of the membrane carbohydrate?

Determine immune recognition of cells Signup and view all the answers

What role does cholesterol play in the plasma membrane?

It helps maintain membrane fluidity. Signup and view all the answers

What generates chemical and electrical signals in cell membranes?

Ion pumps and facilitated transport Signup and view all the answers

What occurs when a hormone binds to a G-protein-linked receptor?

The G-protein activates adenylate cyclase. Signup and view all the answers

How is the asymmetry of membrane composition maintained?

By the addition of new membrane structures Signup and view all the answers

Which molecule is produced as a result of adenylate cyclase activation?

cAMP Signup and view all the answers

Which lipids are considered a part of membrane lipids?

Phospholipids, sphingolipids, and cholesterol Signup and view all the answers

What happens to the G-protein's α-subunit after it binds GTP?

It dissociates from the β and γ subunits. Signup and view all the answers

What characteristic is true for integral membrane proteins?

They span the entire membrane and are often hydrophobic. Signup and view all the answers

What does the receptor kinase do in the signal transduction process?

Inactivates G-protein-linked receptors. Signup and view all the answers

Which of the following is a role of cAMP in signal transduction?

Serves as a second messenger in the pathway. Signup and view all the answers

What is the function of the β and γ subunits in G-protein signaling?

To stabilize the inactive G-protein complex Signup and view all the answers

How is GDP involved in the activation of a G-protein?

It is released when GTP binds. Signup and view all the answers

In the absence of hormone binding, what state is the G-protein primarily in?

Inactivated with GDP bound Signup and view all the answers

What is the role of the a-subunit of the Gs protein after hormone binding?

It releases GDP and binds GTP. Signup and view all the answers

What happens to the a-subunit of the Gs protein after it activates adenylate cyclase?

It hydrolyzes GTP to GDP. Signup and view all the answers

What effect does constant stimulation of epinephrine have on the sensitivity of the receptor?

It decreases receptor sensitivity. Signup and view all the answers

What are the products of phosphatidylinositol 4,5-bisphosphate (PIP2) hydrolysis?

Inositol 1,4,5-trisphosphate and diacylglycerol. Signup and view all the answers

Which hormone is known to stimulate the action of phospholipase C?

Angiotensin II. Signup and view all the answers

What is the function of ca+2 released by inositol 1,4,5-trisphosphate (IP3)?

To bind to calmodulin and regulate cellular activity. Signup and view all the answers

What initiates the activation of adenylate cyclase in the signaling process?

The interaction of the a-subunit–GTP complex with adenylate cyclase. Signup and view all the answers

What is the consequence of spontaneous GTP hydrolysis in G-proteins?

It provides an automatic deactivating mechanism. Signup and view all the answers

Study Notes

Key Points About Membrane Structure and Composition

The red blood cell plasma membrane consists of phospholipid monolayers: the exterior mainly has sphingomyelin and phosphatidylcholine, while the interior features phosphatidylserine and phosphatidylethanolamine.
Membranes are crucial for compartmentalization, hormone signal recognition, chemical and electrical signal generation, selective transport, and cell adhesion.
Membrane composition is a fluid mosaic bilayer with lipids, proteins, and carbohydrates, which varies according to the specific function.
Integral membrane proteins (40%-50% of membrane composition) are hydrophobic and cannot be isolated without membrane disruption, while peripheral proteins are surface-associated and removable.
Membrane carbohydrates, predominantly on the external surface, anchor to proteins and lipids, playing a role in immune recognition.

Hormone Interaction and Signal Transduction

Hormone binding to plasma membrane receptors induces a change in the intracellular domain, facilitating interaction with G-proteins.
The Gs protein releases GDP and binds GTP, activating adenylate cyclase through its alpha subunit.
One hormone molecule can generate many active Gs protein subunits, amplifying the cellular response.
Gs alpha subunit inactivates by hydrolyzing GTP to GDP, returning to the inactive complex with the beta-gamma dimer.

Phosphoinositide Cascade

Hormones like angiotensin II, epinephrine, and vasopressin activate phospholipase C, stimulating the phosphoinositide pathway.
Phospholipase C hydrolyzes PIP2 into IP3 and diacylglycerol, leading to calcium release and subsequent cellular responses.
IP3 opens calcium channels in the endoplasmic reticulum, and cytosolic calcium binds to calmodulin, which regulates various cellular activities.

Tyrosine Kinase Receptors and Their Effects

Oxytocin and vasopressin operate through the phosphoinositide pathway; oxytocin contracts smooth muscles, while vasopressin increases water permeability in renal ducts.
Monomeric tyrosine kinase receptors aggregate upon hormone binding, activating the MAP kinase pathway and promoting gene regulation for cell division.
Nitric oxide (NO) activates guanylate cyclase, raising cGMP levels leading to smooth muscle relaxation and vasodilation.

General Notes on G-Protein Types

G-protein types include:
- Gs: Stimulates adenylate cyclase, increasing cAMP levels.
- Gi: Inhibits adenylate cyclase, decreasing cAMP levels.
- Gq: Stimulates phospholipase C, activating the phosphoinositide pathway.
G-proteins possess an automatic inactivation mechanism through GTP hydrolysis, ensuring transient signaling.

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Description

This quiz explores the key points about the structure and composition of plasma membranes, focusing on the specific phospholipid composition of red blood cells. Gain insights into the functions of membranes and their importance in cellular compartmentalization.