Cell signalling

What is the general purpose of signalling molecules in a multicellular organism?

They facilitate communication between cells, which may or may not be immediately adjacent.

Which type of cell signalling acts over long distances, often using the bloodstream?

Endocrine signalling.

What is the term for local signalling that affects nearby cells?

Paracrine signalling.

When a cell releases a signal that targets itself, this is known as _ signalling.

autocrine

Which form of cell signalling requires direct physical contact between adjacent cells?

Juxtacrine signalling.

In cell signalling, what is the general term for a molecule, like a hormone or neurotransmitter, that binds to a specific receptor protein?

A ligand (or primary messenger).

What are the channels that allow molecules to pass readily between adjacent animal cells without crossing plasma membranes?

Gap junctions.

What are the channels that serve a similar function to gap junctions but are found between adjacent plant cells?

Plasmodesmata.

What is the process by which a signal is converted from one form to another and amplified within a cell?

Signal transduction.

The epinephrine signalling pathway shows that one molecule of epinephrine can lead to the production of $10^8$ molecules of glucose 1-phosphate. What key principle does this illustrate?

Signal amplification.

What are intracellular signalling molecules released by a cell in response to extracellular signalling molecules called?

Second messengers.

In a signalling pathway, the extracellular ligand is often referred to as the ____ messenger.

first

A cellular response to a signal can include changes in gene expression, which occurs in what part of the cell?

The nucleus.

What type of receptor opens or closes in response to a ligand binding, allowing ions like $Ca^{2+}$ to pass through?

A ligand-gated ion channel.

What does the acronym GPCR stand for?

G protein-coupled receptor.

What type of receptor often functions as a dimer and has an intrinsic enzymatic activity, such as a tyrosine kinase?

Enzyme-coupled receptor.

Hormones like steroids are lipids and can pass through the cell membrane to bind to what type of receptor?

A nuclear or cytoplasmic receptor (intracellular receptor).

When a GPCR binds its ligand, it activates an associated intracellular protein called a _.

G protein

In its resting, inactive state, the $\alpha$ subunit of a heterotrimeric G protein is bound to what molecule?

Guanosine diphosphate (GDP).

What event causes the G protein to become active, releasing GDP and binding GTP?

The binding of a ligand to the associated GPCR.

Upon activation and binding of GTP, what happens to the heterotrimeric G protein?

The $G\alpha$ subunit separates from the $G{\beta\gamma}$ subunits.

How does an activated G protein become inactive again?

The $G\alpha$ subunit hydrolyzes its bound GTP to GDP, becoming inactive and reassociating with the $G{\beta\gamma}$ subunits.

In one major GPCR pathway, the activated G protein stimulates which membrane-bound enzyme?

Adenylyl cyclase.

What molecule does adenylyl cyclase synthesize?

Cyclic AMP (cAMP).

From which precursor molecule is cAMP synthesized by adenylyl cyclase?

ATP (adenosine triphosphate).

In the GPCR pathway involving adenylyl cyclase, what is the role of cAMP?

It acts as a second messenger.

What is the primary downstream target that is activated by cAMP?

Protein Kinase A (PKA).

How does cAMP activate Protein Kinase A (PKA)?

cAMP binds to the regulatory subunits of PKA, causing them to dissociate from and activate the catalytic subunits.

What is the primary function of activated PKA?

It phosphorylates many different target proteins within the cell.

In another major GPCR pathway, an activated G protein stimulates the enzyme Phospholipase C (PLC). What molecule does PLC cleave?

Phosphatidylinositol-4,5-bisphosphate ($PIP_2$).

The cleavage of $PIP_2$ by Phospholipase C produces which two important second messengers?

Inositol-1,4,5-trisphosphate ($IP_3$) and diacylglycerol (DAG).

What is the primary function of the second messenger $IP_3$?

It is released into the cytosol and triggers the release of calcium ($Ca^{2+}$) from the endoplasmic reticulum (ER).

What type of protein in the ER membrane does $IP_3$ bind to in order to release calcium?

An $IP_3$ receptor, which is a ligand-gated calcium channel.

What is the primary function of the second messenger diacylglycerol (DAG)?

It remains in the plasma membrane and, along with $Ca^{2+}$, activates Protein Kinase C (PKC).

What is another name for enzyme-coupled receptors, reflecting their common function?

Protein kinase receptors.

Activation of many receptor tyrosine kinases, like the EGF receptor, involves the ligand inducing the receptors to form a ____.

dimer

After dimerization, what process do the cytoplasmic tails of receptor tyrosine kinases undergo to become fully active?

Autophosphorylation (they phosphorylate each other on tyrosine residues).

The insulin receptor is a key example of what type of enzyme-coupled receptor?

A tyrosine kinase receptor.

Steroid hormones, such as estradiol and testosterone, are derived from what type of molecule?

Lipids (specifically, steroids).

Because steroid hormones are lipid-soluble, where are their receptors typically located?

Inside the cell, either in the cytoplasm or the nucleus.

Nuclear receptors typically have two key functional domains. What are they?

A ligand-binding domain (LBD) and a DNA-binding domain (DBD).

Upon binding their ligand, what is the primary function of most activated nuclear receptors?

They bind to specific DNA sequences and act as transcription factors to regulate gene expression.

What is the name of the steroid hormone that controls molting and metamorphosis in insects?

Ecdysone.

The ecdysone receptor (EcR), which mediates the molting process in insects, is an example of what class of receptor?

A nuclear receptor.

In the epinephrine cascade, one active G protein activates one adenylyl cyclase, which can produce many molecules of what second messenger?

Cyclic AMP (cAMP).

What is the target cell in endocrine signalling?

A distant cell that is reached via the bloodstream.