Chapter 9

Cells in multicellular organisms communicate by way of

signaling molecules that interact with specific receptors.

An example of a signaling molecule is .

hormones.

A response such as increased protein synthesis is a result from a….

a. Signaling pathway.

Steroid Hormones are non-polar signaling molecules (T/F).

True.

In order for a target to receive a signaling molecule, it must possess a specific __ to that signaling molecule.

receptor.

A Hormone with a Polar side chain will bind to its receptor on the (inside/outside) of the cell.

outside.

When we say a signal is TRANSDUCED, it means…..

e. The physical form of the signal changes as it passes from the cell membrane to the ultimate intracellular target.

What proteins form connexons in gap junctions?.

a. Connexins.

How do gap junctions help heart muscles contract?.

a. They control ion flow, coordinating electrical signals for contraction.

What is the role of plasmodesmata in plants?.

a. Allow direct communication between plant cells.

How do plasmodesmata differ from gap junctions?.

a. Plasmodesmata are more flexible, allow more different molecules to go through.

What is cell–cell recognition important for?.

a. Embryonic development and immune response.

What is the signal molecule released in local signaling called?.

a. A local regulator.

What type of regulation occurs when a local regulator affects nearby cells?.

a. Paracrine Regulation.

What is it called when a local regulator acts on the same cell that produced it?.

a. Autocrine Regulation.

Neurons communicate locally

a. Through chemical synapses.

Neurotransmitters are released and

bind to receptors on adjacent cells.

In bacterial two-component signaling, what is the primary role of the intracellular response regulator once it is activated?.

c) It attaches to DNA regulatory sequences to control gene expression.

True or False: In bacterial two-component signaling, the surface receptor (sensor kinase) is responsible for directly phosphorylating the DNA regulatory sequences.

FALSE.

Which of the following best describes the difference in response times between ligand-gated ion channels and G protein-coupled receptors (GPCRs)?.

c) Ligand-gated ion channels generate rapid, short-lived responses that last only milliseconds, while GPCRs trigger longer-lasting effects that persist for seconds to minutes.

Which of the following best describes the role of protein kinase receptors in cellular signaling?.

b) Upon activation, protein kinase receptors phosphorylate themselves or other proteins, altering their shape and function to trigger specific cellular responses, such as the insertion of glucose transporters into the plasma membrane.

Which of the following statements accurately describes the structure and function of G protein-coupled receptors (GPCRs)?.

c) GPCRs are composed of seven transmembrane alpha helices, with specific loops that form binding sites for signaling molecules on the outside and G proteins on the inside of the cell.

True or False: A G protein is activated when it switches from being bound to GTP to being bound to GDP.

FALSE.

True or False: The enzyme adenylyl cyclase converts ATP into the second messenger cAMP.

TRUE.

True or False: Second messengers like cAMP directly add phosphate groups to target proteins to trigger cellular responses.

FALSE.

What cellular responses does cAMP control?.

d. Glucose uptake, Glycogen synthesis, ion transport

What pathway does epinephrine and glucagon both activate?.

d. Gluconeogenesis.

True or false: a signal transduction cascade amplifies the signal to produce more results.

True.

_ are glucose storage units.

Glucagon are glucose storage units.

What is a phospholipase?.

b. Enzyme that breaks down membrane phospholipids.

Release of stored is the result of the IP3/DAG pathway?.

calcium.

True or false: The G protein Ras is not involved in gene regulation.

False.

What kind of gated ion channel is activated by the binding of a ligand?.

a. Ligand-gated ion channel.

What neurotransmitter is released from a ligand-gated ion channel?.

a. Acetylcholine.

Is a steroid hormone an example of an intracellular receptor?.

a. Yes.

Are steroid hormones polar?.

b. No.

Steroids are derived from proteins.

b. False.

What do steroid hormones usually bind to?.

c. Chaperone proteins.

Nitric Oxide is a first messenger in the signal transduction pathway.

b. False.

What does Nitric Oxide NOT play an important role in?.

a. Vasodilation.

Cross talk involves DIRECT channels of communication.

a. True.

Does signal amplification decrease magnitude as the signal transduction pathway continues?.

b. No.

The more enzyme catalyzed steps = The less the amplification.

b. False.

Steps in Cell Communication pathway/reaction.

1. Involves a LIGAND, a RECEPTOR, and a SIGNAL TRANSDUCTION PATHWAY that produces the cellular response.

Target cells processing the signal process/pathway/reaction.

i. Reception ii. Transduction iii. Response.

Ways cells communicate process/parts of.

i. Direct Contact ii. Local Signaling iii. Long-Distance Signaling.

Cell communication by direct contact parts of.

1. Gap junctions (in animals) 2. Plasmodesmata (in plants) 3. Cell-cell recognition (in animals).

Gap junctions parts of.

Six proteins called connexins form connexons. Connexons from adjacent cells align to form channels.

Bacterial two-component signaling parts of.

1. Surface Receptor Protein (Sensor Kinase) 2. Intracellular Response Regulator.

Bacterial two-component signaling process/pathway/reaction.

1. Signaling molecule binds and activates sensor kinase. 2. Sensor kinase phosphorylates and activates response regulator. 3. Response regulator binds to DNA sequences, turning genes on or off.

Types of cell receptors parts of.

1. Ion channels 2. G protein-coupled receptors 3. Protein kinase receptors.

Epinephrine and Glucagon cAMP pathway process/pathway/reaction.

1. Hormone binds to receptor, G protein activated, adenylyl cyclase stimulated. 2. cAMP activates PKA, which activates phosphorylase kinase and inhibits glycogen synthase. 3. Phosphorylase kinase activates glycogen phosphorylase, releasing glucose.

IP3/DAG pathway process/pathway/reaction.

1. Ligand binds to receptor, phospholipase C activates. 2. Phospholipase C cleaves IP3 from PIP2, DAG remains. 3. IP3 binds to channel-linked receptor on ER, releasing Ca^{2+}. 4. Ca^{2+} binds to calmodulin/PKC to cause a cellular response.

Receptor Tyrosine Kinase (RTK) Transduction Activation process/pathway/reaction.

1. Two receptors bind a signal molecule. 2. They form a dimer. 3. Cytoplasmic protein kinases are activated and phosphorylate tyrosines on the other receptor (autophosphorylation).

G Protein Ras pathway process/pathway/reaction.

1. RTK activates by autophosphorylation. 2. Adapter proteins bridge activated RTK to Ras (activated by GTP). 3. Ras initiates a phosphorylation cascade of 3 MAP kinases. 4. Last kinase enters nucleus and phosphorylates proteins for gene expression.

Ligand-Gated Ion Channel synaptic signaling process/pathway/reaction.

1) Acetylcholine is released from neuron. 2) Acetylcholine binds to receptor, opening ion channel. 3) Na^{+} ions enter the neuron. 4) Electrical signal is conducted down the neuron length.

Steroid hormone binding and release of chaperone process/pathway/reaction.

Hormone passes through membrane and binds to internal receptor (bound to chaperone). Binding changes receptor shape, releasing the chaperone.

Gene activation by steroid hormone receptors process/pathway/reaction.

Hormone-receptor complex translocates to nucleus and binds to steroid hormone-response elements (SREs), modulating gene expression.

Components of surface receptor signaling systems parts of.

Extracellular signal molecules, cell surface receptors, and internal response pathways.

Steroid hormone receptor domains parts of.

Hormone-binding domain and Gene activation or DNA binding domain.

Heterotrimeric G proteins parts of.

Three different subunits: \alpha, \beta, \gamma.

What is a hallmark of living things?.

Their ability to process and respond to information from their environment.

What type of cell communication is the most common means of cell communication?.

Long-distance signaling.

Why is cell-cell recognition crucial?.

For embryonic development and immune responses.

What is the significance of the evolution of cell communication?.

Mechanisms existed in unicellular organisms prior to multicellularity; some proteins (like kinases) appeared only after eukaryotes evolved.

What is the role of phosphorylation in protein kinase receptors?.

It changes the shape and function of proteins; it can either activate or inhibit enzyme activity.

What are the two types of second messengers in the second G-protein response pathway?.

Inositol triphosphate (IP_{3}) and diacylglycerol (DAG).

Why are lithium ions (Li^{+}) used to treat bipolar disorder?.

They inhibit G protein activation of phospholipase C and IP{3} synthesis, toning down the overactive IP{3}/DAG pathway.

What is the G protein Ras important for?.

Gene regulation pathways linking RTK to cell division (growth factor signaling).

What is the function of Cross Talk?.

Inter-pathway interaction that modifies cellular responses, often involving direct channels of communication.

What is the mechanism of Signal Amplification?.

Increases the magnitude of each step in the pathway; more enzyme-catalyzed steps lead to greater amplification.

Define: Ligand.

A signal molecule.

Define: Target cell.

A receiving cell that has specific receptors to recognize and respond to a signal molecule.

Define: Reception.

The binding of a signal molecule with a specific receptor on a target cell.

Define: Transduction.

Changes a signal into a form that causes a cellular response.

Define: Response.

The specific cellular activity caused by the transduced signal.

Define: Quorum sensing.

A cell–cell communication process enabling bacteria to obtain information about cell density and adjust gene expression.

Define: Autoinducers.

Signal molecules released by bacteria whose increasing concentration indicates high cell density in quorum sensing.

Define: Paracrine regulation.

Local signaling where a cell releases a local regulator that affects nearby target cells.

Define: Autocrine regulation.

Local signaling where the local regulator acts on the same cell that produced it.

Define: Endocrine signaling.

Long-distance signaling in animals where hormones enter the circulatory system and travel to distant target cells.

Define: Local regulator.

A signal molecule released in local signaling that diffuses through the extracellular fluid.

Define: Hormone.

A signaling molecule secreted by a controlling cell in long-distance signaling that affects distant target cells.

Define: Connexons.

Cylindrical structures formed by six connexin proteins in the plasma membrane that align to form gap junction channels.

Define: Chemical synapse.

A narrow gap between the plasma membranes of two cells used for local neuronal communication.

Define: Neurotransmitter.

Molecules released by a neuron that diffuse across the chemical synapse and bind to receptors on the second cell.

Define: Membrane receptors.

Transmembrane receptors for large or polar ligands that cannot cross the lipid bilayer.

Define: Intracellular receptors.

Receptors located inside the cell (cytoplasm or nucleus) that bind small or nonpolar ligands that can diffuse across the plasma membrane.

Define: G protein-coupled receptor (GPCR).

A cell-surface receptor with seven transmembrane alpha helices that works with a G protein binding GTP.

Define: G protein.

A protein that binds the energy-rich molecule GTP, functioning as a molecular switch (on/off depending on GDP/GTP).

Define: Protein kinase receptors.

Eukaryotic receptors that, when activated, catalyze the phosphorylation of themselves and/or other proteins.

Define: Ligand-gated ion channel.

A channel that opens or closes when a ligand binds, changing its conformation and controlling ion movement.

Define: First messenger.

The extracellular signal molecule that binds to the cell-surface receptor.

Define: Second messengers.

Internal, nonprotein signal molecules generated by the activated effector.

Define: Adenylyl cyclase.

The enzyme that converts ATP to the second messenger cyclic AMP (cAMP).

Define: Phosphodiesterase.

The enzyme that breaks down cyclic AMP (cAMP) to AMP.

Define: Phospholipases.

Enzymes that hydrolyze phospholipids into their component parts, forming second messengers.

Define: Phospholipase C.

The effector enzyme that produces IP{3} and DAG by breaking down a membrane phospholipid (PIP{2}).

Define: cAMP.

Cyclic AMP, a small, water-soluble molecule derived from ATP and acting as a second messenger.

Define: IP3 (Inositol triphosphate).

A lipid-derived, water-soluble second messenger that diffuses through the cytoplasm and binds to ER channels.