chapter 17

Question 1

Statements

Answer 1

Notes

Question 2

Cells rely on extracellular {{c1::signal molecules}} recognized by {{c2::receptor proteins}} to change behavior.

Answer 2

These signals can be proteins, peptides, amino acids, steroids, or gases. Reference: Lecture_17+18_229_Spring25.pdf.

Question 3

Cell-surface receptors bind hydrophilic ligands, while {{c1::intracellular receptors}} bind {{c2::hydrophobic}} ligands inside the nucleus.

Answer 3

Small, non-polar ligands can diffuse across the membrane and interact with nuclear receptors. Reference: Lecture_17+18_229_Spring25.pdf.

Question 4

In multicellular organisms, signals keep cells {{c1::alive}} or direct them to {{c2::divide}} or differentiate.

Answer 4

Without appropriate signals, many cells undergo programmed death (apoptosis). Reference: Lecture_17+18_229_Spring25.pdf.

Question 5

Ligand binding can cause changes in cell metabolism, {{c1::gene expression}}, or cell {{c2::movement}}.

Answer 5

These changes happen via distinct intracellular signaling cascades. Reference: Lecture_17+18_229_Spring25.pdf.

Question 6

Autocrine signaling occurs when a cell’s {{c1::secreted signals}} act on {{c2::itself}}.

Answer 6

This mechanism allows cells to amplify their own signals. Reference: Lecture_17+18_229_Spring25.pdf.

Question 7

Endocrine signaling uses {{c1::hormones}} to reach {{c2::distant}} target cells via the bloodstream.

Answer 7

Endocrine cells release hormones that travel systemically. Reference: Lecture_17+18_229_Spring25.pdf.

Question 8

Neuronal signaling is {{c1::fast}} because neurotransmitters cross narrow {{c2::synapses}} between neurons and targets.

Answer 8

Synaptic signaling enables rapid communication. Reference: Lecture_17+18_229_Spring25.pdf.

Question 9

Contact-dependent signaling requires a ligand on one cell’s {{c1::membrane}} binding a receptor on an {{c2::adjacent}} cell.

Answer 9

This arrangement ensures direct cell-to-cell communication. Reference: Lecture_17+18_229_Spring25.pdf.

Question 10

Gap junctions allow direct {{c1::exchange}} of small {{c2::molecules}} between adjacent cells.

Answer 10

They connect cytoplasms without large protein or nucleic acid flow. Reference: Lecture_17+18_229_Spring25.pdf.

Question 11

Nitric oxide (NO) acts as a {{c1::gas signal}}, diffusing rapidly to {{c2::activate}} intracellular enzymes.

Answer 11

It regulates smooth muscle contraction and has a short half-life. Reference: Lecture_17+18_229_Spring25.pdf.

Question 12

Steroid hormones diffuse across membranes to bind {{c1::nuclear receptors}} that control {{c2::transcription}}.

Answer 12

Examples include estrogen, testosterone, and cortisol. Reference: Lecture_17+18_229_Spring25.pdf.

Question 13

All nuclear receptors share a {{c1::DNA-binding domain}}, a transcription-activation domain, and a {{c2::ligand-binding}} domain.

Answer 13

They bind response elements on DNA after ligand attachment. Reference: Lecture_17+18_229_Spring25.pdf.

Question 14

Some nuclear receptors remain {{c1::orphan}} if their {{c2::ligands}} are unknown.

Answer 14

They were identified by sequence similarity but lack a confirmed activator. Reference: Lecture_17+18_229_Spring25.pdf.

Question 15

Nuclear receptor binding induces a {{c1::primary}} then a {{c2::secondary}} transcriptional response.

Answer 15

Early response genes encode proteins that activate or repress further gene expression. Reference: Lecture_17+18_229_Spring25.pdf.

Question 16

Ion-channel-linked receptors open or close to {{c1::regulate}} ion flow when {{c2::ligands}} bind.

Answer 16

They mediate fast synaptic signaling, e.g., neurotransmitter-gated channels. Reference: Lecture_17+18_229_Spring25.pdf.

Question 17

G-protein-linked receptors have {{c1::seven}} transmembrane domains and activate {{c2::trimeric}} G-proteins.

Answer 17

They are the largest family of cell-surface receptors. Reference: Lecture_17+18_229_Spring25.pdf.

Question 18

Enzyme-linked receptors often function as {{c1::protein kinases}} that {{c2::phosphorylate}} target proteins.

Answer 18

Many are receptor tyrosine kinases, adding phosphate groups to signaling proteins. Reference: Lecture_17+18_229_Spring25.pdf.

Question 19

Switch proteins include {{c1::GTP-binding}} G-proteins and those controlled by {{c2::phosphorylation}}.

Answer 19

Turning signals on and off requires GTP hydrolysis or dephosphorylation. Reference: Lecture_17+18_229_Spring25.pdf.

Question 20

Integrator proteins combine separate inputs so a single protein is active only if both {{c1::signals}} are {{c2::present}}.

Answer 20

Cells often require multiple signals simultaneously to produce a specific response. Reference: Lecture_17+18_229_Spring25.pdf.

Question 21

Cells can scaffold signaling proteins for {{c1::efficient}} signal transduction and reduce {{c2::random}} collisions.

Answer 21

Scaffold complexes hold intermediates close together. Reference: Lecture_17+18_229_Spring25.pdf.

Question 22

Cooperative ligand binding can generate a steep, {{c1::threshold-like}} response despite a {{c2::gradual}} rise in signal concentration.

Answer 22

Multiple ligand molecules must bind to form an active complex. Reference: Lecture_17+18_229_Spring25.pdf.

Question 23

Desensitization occurs if receptors are {{c1::internalized}}, degraded, or if an {{c2::inhibitory}} protein binds.

Answer 23

This reduces receptor sensitivity to persistent signals. Reference: Lecture_17+18_229_Spring25.pdf.

Question 24

Activated G-proteins split into {{c1::alpha}} and {{c2::beta-gamma}} subunits, each relaying signals.

Answer 24

Both subunits can interact with downstream targets. Reference: Lecture_17+18_229_Spring25.pdf.

Question 25

The G-protein {{c1::alpha subunit}} hydrolyzes {{c2::GTP}} to GDP to inactivate itself.

Answer 25

It then rebinds the beta-gamma subunits. Reference: Lecture_17+18_229_Spring25.pdf.

Question 26

Adenylyl cyclase converts {{c1::ATP}} into {{c2::cAMP}}, which is rapidly degraded by phosphodiesterases.

Answer 26

This small molecule mediator can rise quickly upon signal activation. Reference: Lecture_17+18_229_Spring25.pdf.

Question 27

{{c1::PKA}} (cAMP-dependent protein kinase) is activated by {{c2::cAMP}} binding to its regulatory subunits.

Answer 27

Active subunits then phosphorylate various target proteins. Reference: Lecture_17+18_229_Spring25.pdf.

Question 28

Phosphorylated CREB recruits coactivators to drive {{c1::gene expression}} once activated by {{c2::PKA}}.

Answer 28

This pathway influences hormone production, metabolism, and more. Reference: Lecture_17+18_229_Spring25.pdf.

Question 29

Phospholipase C cleaves lipids to form {{c1::IP3}} and DAG, with IP3 releasing {{c2::Ca2+}} from the ER.

Answer 29

DAG remains in the membrane to help activate protein kinase C. Reference: Lecture_17+18_229_Spring25.pdf.

Question 30

Calcium signals often work via {{c1::calmodulin}}, which binds Ca2+ and changes its {{c2::target}} proteins' activity.

Answer 30

Calmodulin influences muscle contraction, metabolism, and other processes. Reference: Lecture_17+18_229_Spring25.pdf.

Question 31

CaM-kinase II stores 'memory' by achieving a {{c1::partially}} or fully {{c2::autophosphorylated}} active state.

Answer 31

It remains active after Ca2+ levels drop, important in neuronal plasticity. Reference: Lecture_17+18_229_Spring25.pdf.

Question 32

Cells rapidly remove cytosolic Ca2+ via {{c1::pumps}} or {{c2::buffer}} proteins to maintain low resting levels.

Answer 32

Calcium channels only open briefly, triggering transient spikes. Reference: Lecture_17+18_229_Spring25.pdf.

Question 33

Some signals raise cytosolic Ca2+ by {{c1::IP3}} opening ER {{c2::Ca2+ channels}}.

Answer 33

This results in rapid calcium release into the cytoplasm. Reference: Lecture_17+18_229_Spring25.pdf.

Question 34

Cells integrate combinations of signals to {{c1::survive}}, {{c2::divide}}, differentiate, or undergo apoptosis.

Answer 34

No signals often means cell death. Reference: Lecture_17+18_229_Spring25.pdf.

Question 35

Acetylcholine can {{c1::slow}} heart muscle contraction or {{c2::stimulate}} skeletal muscle, depending on receptor type.

Answer 35

Different intracellular pathways cause these opposite effects. Reference: Lecture_17+18_229_Spring25.pdf.

Question 36

A single ligand may trigger distinct outcomes in different cells via unique {{c1::intracellular}} {{c2::cascades}}.

Answer 36

Context-dependent pathways influence final responses. Reference: Lecture_17+18_229_Spring25.pdf.

Question 37

cAMP levels can rise 20-fold within {{c1::seconds}} after serotonin binds a G-protein-linked {{c2::receptor}}.

Answer 37

This rapid second-messenger spike demonstrates signal amplification. Reference: Lecture_17+18_229_Spring25.pdf.

Question 38

The G-protein alpha subunit changes conformation to {{c1::exchange}} GDP for {{c2::GTP}}, then separates from beta-gamma.

Answer 38

This switching mechanism is fundamental to many signaling pathways. Reference: Lecture_17+18_229_Spring25.pdf.

Question 39

Two signals X and Z may {{c1::phosphorylate}} separate sites on integrator protein Y, activating Y only if both are {{c2::present}}.

Answer 39

Thus the cell ensures a combined input requirement. Reference: Lecture_17+18_229_Spring25.pdf.

Question 40

Calmodulin binds {{c1::four}} Ca2+ ions, wrapping around target proteins to enable {{c2::broad}} regulation.

Answer 40

Activated calmodulin modulates enzymes like CaM-kinases. Reference: Lecture_17+18_229_Spring25.pdf.

Question 41

In the absence of signals, many cells undergo {{c1::apoptosis}}, highlighting the need for {{c2::survival}} factors.

Answer 41

Cells must constantly receive life signals to remain viable. Reference: Lecture_17+18_229_Spring25.pdf.