Chapter 16 biology (real)

What is the three-step process collectively known as cell signaling?

Detecting, processing, and responding to signals.

Why is communication among cells necessary for multicellular organisms specifically regarding growth?

To coordinate growth and division with other cells rather than dividing as fast as possible.

Which signaling type involves hormones distributed widely through the bloodstream?

Endocrine signaling.

What determines if a cell has the ability to respond to a specific endocrine hormone?

The presence of a specific receptor for that hormone.

Define paracrine signaling.

Chemical signals released into the extracellular fluid that act on nearby cells.

Neuronal signaling is considered a specialized form of _____ signaling.

Paracrine

In neuronal signaling, what triggers the release of neurotransmitters at the nerve terminal?

An electrical signal transmitted along the axon.

How does contact-dependent signaling differ from other forms of chemical signaling?

The signal molecule is membrane-bound and must bind to a receptor on an adjacent neighboring cell.

Where must a signaling molecule bind if it is unable to cross the plasma membrane directly?

A cell surface receptor.

What property allows signaling molecules to diffuse through the lipid bilayer and bind to internal receptors?

Small and hydrophobic.

How can the same signaling molecule, such as acetylcholine, induce different responses in different target cells?

The response depends on the specific receptor type and the internal machinery of the receiving cell.

What is the effect of acetylcholine on heart pacemaker cells?

It decreases the rate of firing.

What response does acetylcholine induce in skeletal muscle cells?

Contraction.

What is the effect of acetylcholine on salivary gland cells?

Induces secretion of saliva.

Why is neuronal signaling typically very fast compared to other pathways?

The signal directly opens ion channels without many intermediate steps.

Which cellular processes make signaling pathways involving gene transcription significantly slower?

Transcription and translation.

In a signaling pathway, what is the term for increasing the intensity of a signal at a specific step?

Amplification.

Concept: Integration

Definition: The process of combining several different signals to generate a single cellular response.

Define positive feedback in a signaling pathway.

A downstream protein increases the activity of a protein earlier in the pathway.

In negative feedback, what is the effect of a downstream protein on the earlier steps of the pathway?

It decreases or inactivates a protein earlier in the pathway, resulting in a decreasing signal.

Which enzyme is responsible for adding a phosphate group to a protein to switch its activity?

Kinase.

What is the function of a phosphatase enzyme in a molecular switch?

It removes a phosphate group from a protein.

GTP-binding proteins are considered "on" when bound to _____.

GTP (Guanine TriPhosphate)

What state is a GTP-binding protein in when bound to GDP?

Off (inactive).

What is the role of a GAP (GTPase Activating Protein)?

It helps the GTPase hydrolyze GTP to GDP to turn the protein off.

Which factor is required to help a GTPase exchange GDP for a new GTP to turn the protein back "on"?

GEF (Guanine Exchange Factor).

What are the three major classes of cell surface receptor proteins?

Ion coupled receptors, G-protein coupled receptors (GPCRs), and enzyme coupled receptors.

Ligand-gated ion channels are also known as _____ receptors.

Ion channel coupled

How do ion channel coupled receptors change the membrane potential so rapidly?

By allowing ions to flow down their concentration gradient immediately upon ligand binding.

Describe the basic structural motif of G-protein coupled receptors (GPCRs).

They consist of seven $\alpha$ helices that span the plasma membrane.

What structural change occurs in a GPCR when an extracellular signaling molecule binds?

The protein changes conformation on the cytoplasmic side to bind a heterotrimeric G-protein.

A heterotrimeric G-protein consists of _____ different subunits.

Three

How does the $\alpha$ subunit of a G-protein eventually turn itself off?

It hydrolyzes its bound GTP back into GDP.

How does the duration of ion channel opening differ between direct ion-coupled receptors and GPCR-regulated ion channels?

GPCR-regulated ion channels remain open for much longer.

In signaling, what is the purpose of producing second messengers?

To amplify the signal by producing many diffusible molecules from a single activated enzyme.

Which enzyme produces the second messenger cyclic AMP (cAMP) from ATP?

Adenylyl cyclase.

What enzyme is responsible for the degradation of cAMP?

Cyclic AMP phosphodiesterase.

From which membrane component is inositol triphosphate ($IP_3$) cleaved?

A membrane lipid.

Which enzyme is activated by GPCRs to produce inositol triphosphate ($IP_3$)?

Phospholipase C.

What is the largest class of enzyme-coupled receptors?

Receptor Tyrosine Kinases (RTKs).

What happens to RTK monomers immediately after they bind a signaling molecule?

They dimerize.

How do dimerized RTKs activate one another?

They phosphorylate each other at multiple tyrosines.

What is the function of phosphorylated tyrosines on an activated RTK?

They serve as docking sites for proteins in a signaling pathway.

How does an RTK acting as a scaffold increase signaling efficiency?

It holds pathway components in close proximity so they can interact more easily.

RTKs can act as a _____ for the monomeric GTPase called Ras.

GEF (Guanine Exchange Factor)

What specific pathway is often activated by Ras?

A kinase cascade (a series of three kinases).

Name two functional benefits of having a three-step kinase cascade rather than a single step.

Opportunities for signal regulation and signal amplification.

Where do steroid hormones like testosterone and cortisol bind to their receptors?

Inside the cell (intracellularly).

Once a steroid hormone binds its receptor, what is the final destination and function of the complex?

It is transported into the nucleus to bind DNA and activate transcription.

Unlike animals, plants do not have blood; what system do they use to transport hormones like ethylene?

A vascular system.

In plants, is the ethylene receptor active or inactive when ethylene is absent?

Active.

What is the fate of the transcriptional regulator in a plant cell when ethylene is NOT present?

It is phosphorylated by a kinase and marked for degradation.

How does the presence of ethylene lead to the transcription of responsive genes?

It inactivates the receptor and kinase, allowing the transcriptional regulator to remain stable and active.

In pathway integration, what might be required for a single target protein to trigger a response?

Phosphorylation at multiple sites by different signaling pathways.

What typically happens to human cells if they lose access to constant incoming survival signals?

They activate programmed cell death and dismantle themselves.