Chapter 9 Cell Communication

What is a ligand in cell communication?

A ligand is the signaling molecule that carries messages between cells.

What is the role of a receptor protein in cell communication?

The receptor protein binds to the ligand to receive the signal and trigger a response in the cell.

Where can receptor proteins be located?

Receptor proteins can be on the plasma membrane or within the cell.

What happens when a ligand binds to a receptor protein?

The receptor protein sends a signal inside the cell to initiate a response.

Why is cell communication important?

Cell communication allows cells to coordinate actions like growth, healing, and immune responses.

Give an example of a ligand.

Insulin is a ligand that signals cells to absorb glucose from the blood.

What is the plasma membrane?

The plasma membrane is the outer boundary of the cell where some receptor proteins are located.

What is direct contact in cell communication?

when molecules on the surface of one cell are recognized by receptors on an adjacent cell.

How do cells recognize each other in direct contact communication?

through receptors on their plasma membranes that detect surface molecules from neighboring cells.

What part of the cell is involved in direct contact communication?

The plasma membrane.

Why is direct contact communication important?

It provides fast and specific communication between neighboring cells.

What is an example of direct contact communication?

Gap junctions, which allow molecules to move directly between cells.

What does the diagram of direct contact show?

Two adjacent plasma membranes with connecting proteins and molecules passing between them.

What is cell–cell recognition in animal cells?

It is when membrane-bound surface molecules dock, initiating communication between cells.

What is the function of gap junctions in animal cells?

allow ions and small molecules to move directly between adjacent cells.

What is plasmodesmata in plant cells?

channels through the cell walls that allow ions and small molecules to move between plant cells.

What is the difference between gap junctions and plasmodesmata?

Gap junctions are found in animal cells, while plasmodesmata are found in plant cells.

What do gap junctions and plasmodesmata have in common?

Both allow direct movement of ions and small molecules between cells.

How do animal cells use direct contact for recognition?

Through docking of membrane-bound surface molecules.

What part of the plant cell contains plasmodesmata?

The cell wall.

Why are gap junctions important in animal cells?

They enable fast communication, such as synchronized heart contractions.

What is local signaling in cell communication?

when cells communicate with nearby cells through signaling molecules.

What is paracrine signaling?

when a cell releases signaling molecules that affect nearby target cells.

What is an example of paracrine signaling?

Growth factors that help cells grow and divide.

What is synaptic signaling?

communication between neurons where electrical signals trigger neurotransmitter release.

What is the role of neurotransmitters in synaptic signaling?

carry the signal across the synapse to the next neuron.

What is the synapse?

gap between two neurons where neurotransmitters are released.

What is autocrine signaling?

when a cell releases a signal that acts on itself.

Why is autocrine signaling important?

It helps cells like immune cells amplify their own responses.

What triggers neurotransmitter release in synaptic signaling?

An electrical signal.

In paracrine signaling, where do signaling molecules act?

On nearby target cells.

What is long-distance signaling in cell communication?

Long-distance signaling is when a controlling cell secretes hormones that travel far to target cells.

What molecule is commonly used in long-distance signaling?

Hormones.

How do hormones travel in animals?

Hormones travel through the circulatory system to reach target cells.

How do hormones travel in plants?

through cells or diffuse through the air as gases.

Why is long-distance signaling important?

It is the most common means of cell communication, coordinating functions throughout the body.

Give an example of long-distance signaling in animals.

Insulin traveling from the pancreas to regulate blood sugar.

What does long-distance signaling control?

Processes like growth, metabolism, stress responses, and reproduction.

In plants, what is a function of ethylene gas?

It helps ripen fruit.

What is the first step in long-distance signaling?

The secreting cell releases hormone molecules.

How do hormones travel to target cells in animals?

Hormones travel through the circulatory system.

What is a target cell in long-distance signaling?

A cell with receptors that specifically bind to the hormone.

What is the function of receptors on the target cell?

bind to hormones and trigger a response in the target cell.

What happens after a hormone binds to its receptor?

The target cell produces a specific response.

What is the role of the circulatory system in long-distance signaling?

It transports hormones from the secreting cell to the target cells.

What ensures hormones reach the correct target cell?

Specific receptors on the target cell that match the hormone.

What are hormones in long-distance signaling?

signaling molecules released by secreting cells to communicate with distant cells.

What is reception in cell communication?

the binding of a signal molecule to a specific receptor on a target cell.

What are polar signal molecules?

Molecules like epinephrine that cannot cross the cell membrane and bind to receptors on the cell surface.

Where are receptors for polar signal molecules located?

On the surface of the cell.

What are nonpolar signal molecules?

Molecules like steroid hormones that can cross the cell membrane and bind to receptors inside the cell.

Where are receptors for nonpolar signal molecules located?

Inside the cell.

Why do polar molecules bind to surface receptors?

Because they cannot pass through the cell membrane.

Why do nonpolar molecules bind to internal receptors?

Because they can easily cross the cell membrane.

What is signal transduction?

It is the process of converting a signal into a form that produces a cellular response.

What triggers the start of transduction?

The binding and activation of the receptor by the signal molecule.

What is a signaling cascade?

A series of steps where molecules inside the cell activate each other to pass the signal along.

What is the role of proteins in transduction?

Proteins help pass the signal along in the signaling cascade.

What are second messengers?

Small molecules that help amplify and spread the signal inside the cell.

Give an example of a second messenger.

cAMP (cyclic AMP).

Why is transduction important in cell communication?

It amplifies the signal and ensures the whole cell prepares to respond.

What happens to the receptor during transduction?

The receptor changes shape or state and initiates the signaling cascade.

What is the outcome of transduction?

The signal is spread inside the cell, preparing it for a response.

What is the response in cell communication?

It is the specific action taken by the cell after the signal is processed.

What does the cell’s response depend on?

It depends on the signal and the receptors on the target cell.

Who studied the response involving glycogen phosphorylase?

Earl Sutherland.

What is glycogen phosphorylase?

An enzyme that breaks down glycogen into glucose.

Why is the activation of glycogen phosphorylase important?

It provides the cell with quick energy by converting glycogen into glucose.

How can different cells have different responses to the same signal?

They have different receptors and internal pathways.

What happens after the signal is transduced in the cell?

The cell triggers a specific response.

What is the final step in cell communication?

Response.

What are surface receptors?

Proteins on the cell membrane that detect external signals.

Do surface receptor combinations change over time?

Yes, they change as cells develop or transform.

Why is the change in surface receptors important?

It allows cells to respond to different signals during development or disease.

Name the three subclasses of membrane surface receptors.

Channel-linked receptors, enzymatic receptors, G protein-coupled receptors.

What is the function of channel-linked receptors?

They open ion channels in response to ligand binding.

Give an example of a process using channel-linked receptors.

Neuron signaling.

What is the function of enzymatic receptors?

They act as enzymes activated by ligand binding.

Give an example of an enzymatic receptor.

Receptor tyrosine kinases (RTKs).

What is the function of G protein-coupled receptors (GPCRs)?

They use G-proteins to help transmit the signal inside the cell.

What does the G-protein do in GPCRs?

It assists in transmitting the signal.

What kind of signals use GPCRs?

Signals for senses like smell and taste, and many hormone responses.

What is a G-protein?

An intracellular switch molecule that is activated by GPCRs.

How many subunits does a trimeric G-protein have?

Three: alpha, beta, and gamma.

What molecule is bound to an active G-protein?

GTP

What molecule is bound to an inactive G-protein?

GDP

Where does the guanine nucleotide bind in a G-protein?

To the alpha subunit.

What is Ras?

A monomeric G-protein involved in growth signaling.

What happens when a signal molecule binds to a GPCR?

The receptor activates the G-protein.

What does the activated G-protein do?

It activates an effector protein, usually an enzyme.

What is an effector protein?

A membrane-bound enzyme activated by the G-protein to start the signaling cascade.

What is the function of GPCRs?

To bind to signal molecules outside the cell and activate G-proteins inside the cell.

Where are GPCRs located?

In the plasma membrane of the cell.

What is the first messenger in a GPCR pathway?

The extracellular signal molecule that binds to the receptor.

What activates a G-protein?

Binding of the first messenger to the GPCR.

What causes a G-protein to switch from inactive to active?

The exchange of GDP for GTP on the alpha subunit.

What happens when the G-protein is activated?

The GTP-bound alpha subunit breaks off and activates the effector protein.

What is an effector in a GPCR pathway?

A membrane-associated enzyme activated by the G-protein.

What are second messengers?

Internal, nonprotein signaling molecules produced by the effector enzyme.

What do second messengers do?

They activate protein kinases.