Cell signaling

Cells communicate by releasing __________ signaling molecules that bind to receptor proteins located in the __________, cytoplasm, or nucleus.

extracellular; plasma membrane

This signal is transduced into the __________, or inactivation, of one or more intracellular messengers.

activation

Receptors interact with a variety of intracellular signaling proteins, including __________, phosphatases, and __________ proteins.

kinases; GTP-binding (G proteins)

Target proteins modulated by signaling pathways include ion channels and __________ proteins, metabolic enzymes, and __________ proteins.

transport; gene regulatory

Signaling pathways are characterized by multiple, __________ steps and __________ of the signal-receptor binding event.

hierarchical; amplification

Feedback mechanisms in signaling pathways provide __________ control over these pathways.

tight regulatory

Cells secrete hundreds of chemicals, including peptides, __________ hormones, and __________.

steroid; amines

The ability of a cell to respond to a signaling molecule depends on the expression of __________ that bind the signaling molecule.

receptors

Contact-dependent signaling is important during development, in __________ responses, and in __________.

immune; cancer

Molecules that are released and act locally are called __________ or __________ hormones.

paracrine; autocrine

Autocrine signaling involves the release of a molecule that affects the __________ cell or other cells of the same type.

same

In __________ signaling, neurons transmit electrical signals along their axons and release __________ that affect the function of other cells.

synaptic; neurotransmitters

Endocrine signals are hormones that are secreted into the __________ and are widely dispersed in the body.

blood

Gap junctions allow intracellular signaling molecules to diffuse from the cytoplasm of one cell to an __________ cell.

adjacent

The permeability of gap junctions is regulated by cytosolic __________, [H+], and cyclic adenosine monophosphate (cAMP).

[Ca++]

The speed of response to an extracellular signal depends on the mechanism of __________.

delivery

Endocrine signals are relatively slow because time is required for __________ and blood flow to the target cell.

diffusion

A signaling molecule can have many different effects that depend on the cell type and the expression of the __________ receptor.

cognate

All signaling molecules bind to specific receptors that act as signal __________, thereby converting a ligand-receptor binding event into intracellular signals.

transducers

Receptors can be divided into four basic classes: ligand-gated ion channels, __________ receptors, enzyme-linked receptors, and nuclear receptors.

G protein–coupled (GPCRs)

Ligand-gated ion channels mediate direct and rapid synaptic signaling between __________ cells.

electrically excitable

G protein–coupled receptors regulate the activity of other proteins such as enzymes and __________ channels.

ion

Enzyme-linked receptors usually function as enzymes or are associated with and regulate __________.

enzymes

Nuclear receptors bind to regulatory sequences in __________ and increase or decrease gene transcription.

DNA

Cyclic adenosine monophosphate (cAMP) is a second messenger that is produced in response to __________ signaling.

hormone

Calmodulin (CaM) is a __________ binding protein that regulates various signaling proteins.

calcium

Phosphodiesterases facilitate the breakdown of cAMP and __________ to AMP and GMP, respectively.

cGMP

Phosphatases dephosphorylate effector proteins that were phosphorylated by kinases such as __________.

PKA

Guanylyl cyclase converts GTP to __________, which relaxes smooth muscle.

cGMP

Binding of TGF-β to its receptor induces phosphorylation of the type __________ subunit.

I

Activation of insulin receptors causes autophosphorylation of __________ residues in the catalytic domains.

tyrosine

Tyrosine kinase–associated receptors have no intrinsic kinase activity but associate with proteins that do have __________ activity.

tyrosine kinase

Nuclear receptors can regulate gene expression by acting as transcriptional __________.

repressors

When activated by hormone binding, nuclear receptors bind to specific DNA sequences called __________ response elements.

hormone

Activated PKA phosphorylates CREB, which recruits __________, activating transcription.

coactivator CBP

G proteins are composed of 3 subunits: α, __________, and __________.

β; γ

GTP binding activates GTP-binding proteins, whereas hydrolysis of GTP to __________ inactivates them.

GDP

Cholera toxin catalyzes the ADP ribosylation of the G-protein αs subunit, leading to an increase in __________ levels.

cAMP

Phototransduction in rod cells of the eye involves the activation of the G protein __________.

transducin

Protein kinase C (PKC) is activated by __________ and regulates various signaling pathways.

diacylglycerol

Arachidonic acid can be metabolized to form __________ and __________ that regulate inflammatory responses.

prostaglandins; leukotrienes

Ca++ is an intracellular messenger that elicits cellular effects via Ca++-binding __________ such as calmodulin.

proteins

Nuclear receptors regulate gene expression in response to __________ and thyroid hormones.

steroid

Ligand binding to __________ stimulates the transcription of many genes, including those that code for hormones.

cAMP

Activation of Ras proteins is important for cellular responses to various __________ factors.

growth

Binding of ligands to their receptors can create multiple pathways that amplify and integrate the __________.

signal

Signal transduction

The process by which a cell responds to substances outside the cell and converts these signals into cellular responses.

Ligands

Molecules that bind to receptors to initiate a signaling pathway.

Receptors

Proteins that receive and respond to signaling molecules.

Second messenger

Intracellular signaling molecules that relay signals received at receptors on the cell surface.

Amplification

The process through which a small number of signaling molecules can produce a large response in the target cell.

Feedback regulation

Mechanisms that regulate the output of a signaling pathway to maintain homeostasis.

Autocrine signaling

A type of signaling where a cell produces a signal that binds to receptors on its own surface, influencing its own activity.

Paracrine signaling

A form of cell signaling where the target cell is close to the signal-releasing cell.

Endocrine signaling

Hormonal signaling where hormones are secreted into the bloodstream and affect distant target cells.

Ion channels

Proteins that allow the passage of ions across the cell membrane, often involved in signal transduction.

Transcription factors

Proteins that help regulate the transcription of specific genes by binding to nearby DNA.

G proteins

Molecular switches that transmit signals from receptors to intracellular targets.