Cell Communication: Chapter 9

Intracellular signaling

Within one cell

Intercellular signaling

Between different cells

Intercellular signaling can occur between what?

Between cells in a multicellular organism

Occurs between different single-celled organisms

What are the three stages of cell signaling and describe them?

Reception - chemical signal (ligand binds receptor proteins in/on target cell

Transduction - receptor protein changes shape; sequence of changes in series of molecules inside the cell

Response - transduced signal triggers specific cellular response

What are 3 types of chemical signaling in multicellular organisms and briefly describe them?

Local Signaling - Signaling other cells throughout a short range or to itself

Paracrine Signaling - Cell targets a nearby cell

Long-distance signaling - Signaling through a long distance such as to other parts of the body

What are the types of local signaling and describe them.

Autocrine signaling - signaling itself

Direct contact - Signaling directly through gap junctions

Direct contact: Cell-cell recognition - The ligand is on the surface while the target cell has a receptor

What is a type of paracrine signaling and describe it?

Synaptic signaling: Signaling through the synapse

What is a type of long-distance signaling?

Hormonal (endocrine signaling): A cell targets distant cell through the bloodstream

A ligand is _ in shape to receptor.

Complementary

Ligand binding causes what to happen to the receptor?

Causes the receptor to change shape (conformation)

Receptors can be associated with _ or be .

The plasma membrane; found inside the cell

What does the location of the receptor tell you?

If the ligand is hydrophilic or hydrophobic

If the receptor is with the cell membrane than the ligand is hydrophilic

If the receptor is inside the cell than the ligand is hydrophobic

What are the three major types of cell-surface (transmembrane) receptors?

Ion channel receptors

G-protein-linked (coupled) receptors (GPCR)

Enzyme-linked receptors (receptor tyrosine kinases

Cell surface (transmembrane) receptors bind to what?

Water-soluble signal molecules

What are ion channel receptors?

It is a receptor that lets ions through the cell membrane

Through a ligand the shape changes and its gate opens

What are G-protein linked receptors?

They bind G protein (inside of cell)

Have seven alpha helices that span membrane

The G protein is made of three subunits: alpha, beta and gamma

What is an example of a GPCR (G-protein coupled receptors) activity?

Why is GPCR limited?

Because the G-protein will hydrolyze the GTP to GDP

What is cholera?

A toxin produced by Vibrio Cholerae

It modifies a G protein making it unable to hydrolyze GTP

Causes diarrhea so there would be a lot of water loss

What are enzyme-linked receptors (receptor tyrosine kinases)

Can trigger several pathways at once (coordination of responses)

Kinases catalyze transfer of phosphate group

Protein phosphatases

Rapidly remove phosphate groups (dephospho rylation) and usually inactive proteins

Where are internal receptors?

Either in the cytoplasm or the nucleus

Internal receptors bind to signal molecules that are what?

Hydrophobic/small non-polar molecules

Give an example of an internal receptor.

Testosterone turns on transcription factors

Multistep processes allow for what?

Amplification

Coordination

Regulation
(The more steps the more control you have)

Signaling pathway

Signal-activated receptor activates another protein, which activates another molecule, etc. (“cascade”)

Like dominoes, relay

Amplification of signal

When 1 row of dominoes goes to more than 1 (“domino effect”)

Like 1 epinephrine leads to 10,000 Active glycogen phosphorylase

Conformation changes often result from what?

Phosphorylation/ dephosphorylation

Protein kinases

Transfer phosphate groups from ATP to another molecule

Cytoplasmic kinases are usually what?

Phosphorylate serine or threonine

What is usually the active form of proteins?

Phosphorylated proteins

How can all these molecules find each other in the cell?

Through collision

What are scaffolding proteins?

Large relay proteins to which several other relay proteins are simultaneously attached

What are second messengers?

Small, non-protein, water-soluble molecules or ions involved in signal transduction; signal amplification

What was the first messenger?

The ligand

Ca²⁺

Calcium ions

Widely-used second messenger (important in muscle contraction and cell division)

Used in both G-protein and receptor tyrosine kinase pathways

Typically low concentration in cytoplasm; stored in cytoplasmic vesicles or enters from outside of cell

Moves through gated channels

Cyclic AMP

Second messenger in G-protien-signaling pathways

Activates cAMP-dependent kinase (A-kinase)

cGMP is also a second messenger

What Is viagra (sildenafil)?

It inhibits the hydrolysis of cGMP to GMP

Inositol phospholipids

Lipids that can be converted to second messengers (by phospholipase)

Found in membranes

Signal transduction pathways lead to regulation of cellular activities. What are these cellular activities

Gene expression

Energy metabolism

Cell growth

Cell death