Cell signalling and communication

connexons

units in the membrane of each cell are lined up with one another to form the dodecameric gap junction

connexins

Each connexon is made up of six protein subunits called

neural communication

neurotransmitters are released at synaptic junctions from nerve cells and act across a narrow synaptic cleft on a postsynaptic cell

endocrine communication

hormones and growth factors reach cells via the circulating blood or the lymph

paracrine communication

which the products of cells diffuse in the ECF to affect neighboring cells that may be some distance away

autocrine communication

cells secrete chemical messengers that in some situations bind to receptors on the same cell, that is, the cell that secreted the messenger

downregulation

when a hormone or neurotransmitter is present in excess, the number of active receptors generally decreases

upregulation

presence of a deficiency of the chemical messenger, there is an increase in the number of active receptors

internalization

ligands bind to their receptors, and the ligand-receptor complexes move laterally in the membrane to coated pits, where they are taken into the cell by endocytosis

desensitization

receptors are chemically modified in ways that make them less responsive

first messengers

extracellular ligands are called

secondary messengers

intracellular mediators are called

cell signaling pathway

provides amplification of the primary signal and distribution of the signal to appropriate targets within the cell.

phosphorylation

the most predominant posttranslation modification of proteins

kinase

enzymes that catalyze the phosphorylation of tyrosine or serine and threonine residues in proteins (or in some cases, in lipids;

phosphatases

proteins that remove phosphates from proteins (or lipids

phosphate timer

The close relationship between phosphorylation and dephosphorylation of cellular proteins allows for a temporal control of activation of cell signaling pathways

GTPase activating proteins (GAPS)

tend to inactivate small G-proteins by encouraging hydrolysis of GTP to GDP in the central binding site

Guanine exchange factors (GEFs)

tend to activate small G-proteins by encouraging exchange of GDP for GTP in the active site.

carriers

bind ions and other molecules and then change their configuration, moving the bound molecule from one side of the cell membrane to the other

down chemical gradient

Molecules move from areas of high concentration to areas of low concentration

down electrical gradient

cations move to negatively charged areas whereas anions move to positively charged areas

uniports

transport only one substance

symports

transport requires the binding of more than one substance to the transport protein and the substances are transported across the membrane together

antiports

exchange one substance for another

Phagocytosis

process by which bacteria, dead cells, or other bits of microscopic material are engulfed by cells such as the polymorphonuclear leukocytes of the blood

Pinocytosis

similar process with the vesicles much smaller in size and the substances ingested are in solution.

patch clamp technique

The technique is used to measure and study ionic currents through membrane ion channels and via electrogenic membrane transporters in isolated living cells and tissue section

inside-out patch

to record single-channel currents

whole-cell recording

to record the whole-cell currents from the entire cell and to record electrical potentials (eg, the resting membrane potential and action potentials) in the whole cell

filtration

The capillary wall separating plasma from interstitial fluid is different from the cell membranes separating interstitial fluid from intracellular fluid because the pressure difference across it makes ___ a significant factor in producing movement of water and solute

oncotic pressure

The colloid osmotic pressure due to the plasma colloids is called the

secondary messengers

bring about many short-term changes in cell function by altering enzyme function, triggering exocytosis, and so on, but they also can lead to the alteration of transcription of various genes.