Receptors and Signalling

Question 1

Receptors

Answer 1

sensing elements of chemical communication within the body being the targets of: neurotransmitters (eg. acetylcholine); hormones (‘endocrines’ eg. adrenaline, insulin, glucocorticoid and reproductive steroids); other mediators (eg. peptide growth factors, chemokines and cytokines of the immune system); therapeutic agents that act as agonists, antagonists, or allosteric modulators.

Question 2

Due to a receptors ligand selectivity it

Answer 2

responds to one, or more, of the signalling molecules in the chemically-rich extracellular, or intracellular, environment

Question 3

Autocrine

Answer 3

cell signals to itself

Question 4

Paracrine

Answer 4

cell signals to its close neighbours

Question 5

Endocrine

Answer 5

cell signals via signalling molecules which entered the circulation and are transported by the blood to the target distant cell

Question 6

Ligand-gated Ion Channels (LGICs) - ionotropic receptors

Answer 6

located at plasma membrane, targeted by hydrophilic signalling molecules - action on a millisecond time scale, consist of separate glycoprotein subunits forming a central ion conducting channel, rapid change in permeability of the membrane to certain ions

Question 7

G protein-coupled receptors (GPCRs) - metabotropic receptors

Answer 7

located at plasma membrane, targeted by hydrophilic signalling molecules - signal on a second time scale. Linked to a cell-membrane-located effector by intermediary G proteins. Contain 7 transmembrane alpha helical spans, joined by 3 extracellular and 3 intracellular connecting loops

Question 8

Kinase-linked receptors (enzyme linked receptors)

Answer 8

located at plasma membrane, targeted by hydrophilic protein mediators - work on an hour time scale

Question 9

Nuclear receptors

Answer 9

located intracellularly in the nucleus, targeted by hydrophobic signalling molecules - very slow action on an hours/day time scale. Are ligand-gated transcription factors.

Question 10

Ion channels

Answer 10

transmembrane pores formed by glycoproteins that span the membrane to create an ion conducting pathway for selected ions

Question 11

regulation of ion channels

Answer 11

signals cause cycle to change reversibly between a closed and open conformation

Question 12

Enzyme effectors

Answer 12

may increase or decrease rate of synthesis of second messenger molecules affecting the activity of targets within the cell.