Ch11 Cell Communication

What’s the purpose of internal and external signals?

Regulate a variety of physiological responses that synchronize with environmental cycles and cues.

describe a type of communication between unicellular organisms

Slime molds produce a chemical signal cAMP which guides the cells together based on concentration. They then form a multicellular slug like structure that find a place appropriate for attach and form a fruiting body

Ligands

Small molecules that bind specifically to a larger molecule (a protein that changes shape, initiating transduction of the signal)

Three stages of cell signaling

Reception, transduction, response

Reception

Chemical signal binds to a cellular protein, typically at the cells surface (signal can be proteins, small chemicals, or peptides)

Transduction

Binding leads to change in shape of enzyme that triggers a series of changes along a signal transduction pathway where one molecule phosphorylates another until a cellular response is produced

Response

Transduced signal triggers a specific cellular activity (gene turns on or off)

Transduction pathway

Phosphorylation (phosphate group added to a protein) and modification (functional group added to a protein)

Major types of receptors

G-protein-linked, tyrosine-kinase, ion-channel

G-protein-linked receptor

Receptor protein associated with a G protein on the cytoplasmic side -when GDP is bound the protein is inactive and when GTP is bound the protein is active. Continues to phosphate proteins until something happens (chemical response)

GDP vs GTP

GDP = INACTIVE and GTP = ACTIVE

Tyrosine-kinase receptor system

Triggers more than one pathway at once (6), transfers a phosphate group from ATP to a protein. Activated relay proteins trigger many different transduction pathways and responses.

Tyrosine-kinase receptor structure

Extra cellular signal-binding site, single alpha helix spanning membrane, intercellular tail with several tyrosines.

Ligand-gated ion channel

Protein pores that open or close in response to a chemical signal. Binding of ligand to extra cellular side changes proteins shape and open channel. When ligand dissociates, the channel closes.

What cells are ligand-ion channels important to?

Nerve cells and muscle cells

Why are signaling systems so complicated

More opportunities for coordination and regulation than simpler systems AND signal amplification (small number of signals can result in major cell responses)

Secondary messengers

small non-protein molecules or ions: cAMP, Ca2+, DAG, IP3 - can rapidly spread throughout cell via diffusion. Commonly found in pathways initiated by G-protein linked receptors and tyrosine-kinase receptors.

Response examples

Cell growth, secretion of molecules, gene expression

example of same hormone with different effects

Testosterone: in muscles = makes more muscle cells, in skin = makes hair grow

What causes signaling pathways to NOT function properly and what are results

Mutations or toxins that result in blocked signaling pathways and lead to diabetes, neurological diseases, and cholera

How are signals terminated

Degradation of ligand, removal of ligand (neurons), removal of ligand-receptor complex

Messengers that pass through plasma membrane

Hydrophobic steroid and thyroid hormones of animals - nitric oxide (NO)