L11 Cell Signaling

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What role do cell surface receptors play in cellular communication?

They generate energy for cellular functions.

They synthesize signaling molecules within the cell.

They transport signaling molecules across the plasma membrane.

They bind to signaling molecules and activate cellular responses. (correct)

Which of the following is NOT a type of cell-surface receptor?

Ion channels

G protein-coupled receptors

Receptor kinases

Nuclear receptors (correct)

What is indicated by a receptor being in the 'off' state?

The receptor is inhibited by a signaling molecule.

The receptor is undergoing a conformational change.

The receptor is not bound to any signaling molecule. (correct)

The receptor is activated by a signaling molecule.

Which feature is characteristic of G protein-coupled receptors?

They typically have seven transmembrane alpha helices. Signup and view all the answers

What happens during signal transduction after a signaling molecule binds to its receptor?

It initiates a series of cellular events that lead to a response. Signup and view all the answers

What role does the Kit receptor kinase play in organisms?

Responsible for pigment production Signup and view all the answers

What happens to ligand-gated ion channels when a signaling molecule binds?

The channel remains open as long as the molecule is bound Signup and view all the answers

How do signaling pathways interact within a single organism?

Different molecules can activate multiple pathways simultaneously Signup and view all the answers

What is meant by 'molecular cross-talk' in signaling pathways?

One signal can inhibit or alter another's pathway Signup and view all the answers

What is a consequence of mutations in the Kit receptor kinase?

Patterns of incomplete pigmentation Signup and view all the answers

What is the primary function of signaling receptors in cells?

To bind to ligands and initiate cellular responses. Signup and view all the answers

Which type of receptor is activated by hydrophobic signaling molecules that can pass through the plasma membrane?

Intracellular receptors. Signup and view all the answers

What is the result of a ligand binding to a receptor?

Conformational shape change in the receptor. Signup and view all the answers

Which of the following is NOT a characteristic of extracellular signaling?

Signals always act over long distances. Signup and view all the answers

What forms when a steroid binds to its receptor inside the cell?

A ligand-receptor complex. Signup and view all the answers

What type of molecules typically act as signals in cell signaling?

A variety including hormones, neurotransmitters, and other chemicals. Signup and view all the answers

In which section of the cell can you find intracellular receptors?

In the cytoplasm or nucleus. Signup and view all the answers

Which type of receptor typically undergoes phosphorylation to become activated?

Receptor kinases. Signup and view all the answers

What is the primary effect of adrenaline on heart rate?

It increases heart rate. Signup and view all the answers

How does the binding affinity of a receptor affect signal duration?

Higher affinity leads to longer signal duration. Signup and view all the answers

What happens to the G protein once the ligand unbinds?

It deactivates itself. Signup and view all the answers

What is the role of phosphatases in cellular signaling?

They inactivate proteins by removing phosphate groups. Signup and view all the answers

How do receptor kinases influence protein activity?

They add a phosphate group, activating the protein. Signup and view all the answers

What mainly determines the cellular response to a signaling molecule?

The type of receptor on the cell. Signup and view all the answers

What is produced when GTP is converted to GDP during signal termination?

The signal is turned off. Signup and view all the answers

What effect does phosphorylation typically have on proteins?

It causes a shape change or provides binding sites. Signup and view all the answers

What happens to a G protein when GDP is replaced by GTP?

The G protein is activated. Signup and view all the answers

Which subunit of the G protein binds to GDP or GTP?

α (alpha) subunit Signup and view all the answers

What is the role of cAMP in G protein signaling pathways?

It is a second messenger that amplifies the signal. Signup and view all the answers

Which types of signal molecules are utilized by G-protein-coupled receptors?

Many hormones and neurotransmitters Signup and view all the answers

What occurs after the ligand binds to the G-protein-coupled receptor?

The receptor activates the G protein. Signup and view all the answers

What is the result of the activated adenylyl cyclase in the presence of G protein signaling?

It converts ATP to cAMP. Signup and view all the answers

Which of the following processes is NOT associated with the action of G protein-coupled receptors?

Directly causing a cellular response Signup and view all the answers

How does the heart rate remain elevated when adrenaline binds to its receptor?

As long as adrenaline is bound to the receptor. Signup and view all the answers

What is the primary function of receptor kinases in cellular signaling?

To activate other proteins for long-term responses Signup and view all the answers

During receptor kinase activation, what occurs after dimerization of the receptors?

They phosphorylate each other at multiple sites Signup and view all the answers

Which role does PDGF play in wound healing?

It signals cells to initiate cell division Signup and view all the answers

What does the activation of Ras protein with GTP indicate?

Ras protein is active and can transmit signals for further kinase activation Signup and view all the answers

Which of the following processes is NOT directly associated with receptor kinases?

Immediate ion channel opening Signup and view all the answers

What is the outcome when GTP-bound Ras is converted to GDP?

Ras activity is terminated and the kinase pathway becomes inactive Signup and view all the answers

Which statement correctly describes the structure of receptor kinases?

They have both extracellular and intracellular portions Signup and view all the answers

In the context of limb formation, what role do receptor kinases play?

They are involved in the formation and elongation of limb buds Signup and view all the answers

Study Notes

Cell Signaling Lecture Notes

Required Reading:
- Morris text, Chapter 9
- Section 9.1: Principles of Cell Signaling
- Section 9.2: Distance Between Cells
Objectives:
- Signaling Receptors
- G Protein-Coupled Receptors
- Receptor Kinases
Textbook References:
- Morris text, Chapter 9 (pages 179-194)
- Section 9.3: Signaling Receptors (pages 185-188)
- Section 9.4: G Protein Coupled Receptors (pages 188-191)
- Section 9.5: Receptor Kinases (pages 191-194)

Cell Communication

All cells process environmental information.
Communication is essential for coordinated activities.
Chemical signals (hormones, neurotransmitters, CO2, H+) bind to specific receptors.
Signals can originate from outside the organism or neighboring cells, and act over short or long distances.
Examples of plant signals: ethylene
Examples of animal signals: epinephrine

Receptor Activation and Types

Receptor: A protein that receives and interprets information carried by a signaling molecule (ligand).
Ligand binds to a ligand-binding site on a receptor.
Binding causes a conformational shape change in the receptor.
Shape change activates the receptor.
Receptors can be intracellular or cell-surface receptors.

Intracellular Receptors

Located inside the cell (cytoplasm or nucleus).
Bind nonpolar signaling molecules (e.g., steroids).
Steroids are hydrophobic and pass through the plasma membrane.
Active steroid-receptor complexes act as transcriptional regulators, controlling gene expression.

Cell Surface Receptors

Located on the cell surface.
Bind polar signaling molecules (e.g., small proteins).
Polar molecules cannot cross the plasma membrane.
General structure:
- Ligand-binding site (extracellular)
- Extracellular domain
- Transmembrane domain
- Cytoplasmic domain
Types:
- G protein-coupled receptors
- Receptor kinases
- Ion channels

Cell Surface Receptors (2)

Thousands of different receptor proteins on each cell surface.
Receptors are grouped by activation mechanisms.

Cell Surface Receptors (3)

Many receptors exist in "on" or "off" states.
- "On" state: signaling molecule bound to receptor
- "Off" state: signaling molecule not bound to receptor
Examples: G protein-coupled receptors, receptor kinases, ligand-gated ion channels.

Signal Transduction, Response, and Termination

Signal transduction (and sometimes amplification) occurs after a signaling molecule binds to a receptor.
- Steps usually are similar for different ligands.

G Protein-Coupled Receptors

Structure:
- Ligand binding site (extracellular)
- 7 transmembrane α-helices
- G-protein binding site (cytoplasmic)
Molecules used:
- Small molecules
- Many hormones
- Neurotransmitters Signaling responsible for senses (sight, smell, taste).
Activation:
- ligand binds to receptor, activating receptor
- Receptor activates a G protein (in the cytoplasm)
- G proteins bind either GDP or GTP (guanine nucleotides). -G-protein + GTP = active
  - G-protein + GDP = inactive
Signal Transduction:
- Ligand binds to receptor then to G protein
- GDP replaced with GTP, activating G protein.
- Activated G protein activates other proteins in the signaling pathway.

G Protein-Coupled Receptors (3)

Some G proteins have three subunits: α, β, γ (alpha, beta, gamma).
The α subunit binds either GDP or GTP.
α subunit + GDP = a three-subunit complex (inactive).
Receptor activation replaces GDP with GTP, releasing the α from the subunit complex (activating the a subunit)
Activated α subunit interacts with target protein = activates subsequent response

Example of G Protein Activation and Amplification: Adrenaline in Heart Muscle

Adenylyl cyclase converts ATP to cAMP (a second messenger)
cAMP activates protein kinase A.
Activated protein kinase A phosphorylates heart proteins, increasing heart rate.
Signal amplification occurs at multiple steps.

Amplification of Adrenaline Signalling

A relatively small signal from adrenaline can result in a large response.
Amplification occurs at multiple steps/targets within the signal cascade.
Multiple protein targets are phosphorylated.

Termination of G Protein Signal

Signal strength depends on how tightly the receptor holds onto the ligand.
Ligand binding is not permanent.
Signal turns off once the ligand is unbound.
Deactivation of the G protein occurs (replaces GTP with GDP).
Enzymes degrade cAMP to AMP

Termination of G Protein Signal (2)

Phosphatases remove phosphate groups from proteins (dephosphorylation), inactivating them.

Receptor Kinases

Kinase: an enzyme that adds a phosphate group to another molecule (phosphorylation).
Phosphorylation typically activates a protein.
Phosphate group comes from ATP.
Shape change provided by phosphorylation gives new binding sites.
Dephosphorylation removes the phosphate group (inactivates a protein).
Phosphatases carry out dephosphorylation.

Receptor Kinase Activation

Extracellular portion of the receptor binds a signaling molecule.
Dimerization activates cytoplasmic kinase domains within the cytoplasmic tails of the receptor.
Phosphorylation of the receptor activates specific sites.
Phosphorylated sites provide docking sites for other proteins and activate them.

Receptor Kinases: Examples

Involved in limb development, wound healing, and long-term responses (including changes in gene expression).
The Kit receptor kinase is responsible for pigmentation in skin, feathers, scales, and hair.Mutations cause white patches.
The MAP kinase pathway is an example (including Ras).

Ligand-Gated Ion Channels

These receptors alter the flow of ions across the plasma membrane.
Conformational shape change opens the channel.
Channel remains open as long as the signaling molecule is bound.

Integration of Signaling Pathways

Signaling pathways are not independent.
Cells can receive and respond to multiple signaling molecules at the same time, which influences cellular response.
Some pathways can enhance, cancel, or influence each other through "molecular cross-talk".

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

Test your knowledge of cell surface receptors and their critical roles in cellular communication. This quiz covers various types of cell-surface receptors, their functions, and the implications of signaling pathways. Dive into the fascinating world of cellular signaling and molecular interactions!