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Cell communication
Premedical biology
The plasma membrane
• fluid mosaics of lipids and proteins - consists a
double layer of phospholipids and other lipids,
proteins
• controls traffic into and out of the cell it
surrounds
• selective permeability - allows sufficient passage
of oxygen a nutrients, elimination of wastes
membrane
• phospholipids are
amphipatic molecule
• proteins are embeded or
attached to surface
The fluidity
- drift in the plane of the membrane
- switch from one phospholipid layer to the
other
- protein move slowly
- unsaturated hydrocarbons – remain fluid
- cholesterol (animal cells) reduces membrane
fluidity; helps stabilize the membrane
Proteins
determine most of the membrane‘s specific functions
Integral proteins – transmembrane proteins
Peripheral proteins – are not embeded in the lipid bilayer
Intracellular junctions
Cell walls perforated with channels called plasmodesma
In animals are intracellular junctions.
Tight junction
Desmosomes
Gap junctions
Adhere, interact
and communicate
Carbohydrates
Cell-cell recognition – sorting cell into tissues and organs
in embryo
- rejection of foreign cells by the immune system
- usually short branched oligosaccharides
- covalently bonded
to proteins
Cell surfaces
Plant cells (some protist, prokaryotes, fungi) encased
by cell walls
the extracellular matrix - ECM
Glycoproteins :
Colagen fibers embedded in network of proteoglycans
fibronectins bind to receptor
protein called integrins are built
into plasma membrane
and bind to microflaments
on cytoplasmatic side
Cell communication
• Cell respond to external signals
• A signaling molecule binds to a receptor
protein, causing to change shape
• transduction: cascades of molecular
interactions
• Response: signaling lleads to regulation of
transcription or cytoplasmatic activities
• signal transduction pathways
Signal transduction pathways
Cell communication
• Direct contact between membrane-bound cell-surface
molecules – cell junctions
- cell-cell recognition
Embryo development, immune response
Local regulators - paracrine signaling
Synaptic signaling - animal nervous system
• Long distance signaling – chemicals called
hormones
Local and long-distance signaling
Cell signaling
1. Reception: target cell’s detection of a
signaling molecule coming from outside
2. Transduction: change of the receptor protein
initiating process of cellular response
3. Response: cellular activity: catalysis,
rearrangement of the cytoskeleton, activation
of genes
Reception
Signaling molecule - ligand
Change of shape – activation and ability to transfer
of signal
G protein coupled receptors / inhibitory or activity
Receptor tyrosine kinases enzymatic activity,
catalyse transfer of phosphate groups
Ion channel receptors gate open or close
Intracellular receptors for steroid and thyroid
hormones, nitric oxide
Transduction
Multistep pathway of activation of proteins by
addition or removal of phosphate groups or other
small molecules or ions that act as messegers –
greatly amplifying a signal
Phosphorylation and dephosphorylation of proteins
system acts as a molecular switch
Protein kinase / transfer phosphate groups from ATP
to protein
A phosphorylation cascade
Small moleculer and ions as
second messengers
Nonprotein molecule, can readily spread by
diffusion – cAMP and
calcium ions
Protein are sensitive to
the cytosolic concentration
of one or other
Calcium ions and Inositol Triphosphate
Neurotransmitters, growth factors, hormones induce
cell’s responses via signal transduction pathways
that increase the concentration of calcium ions
Muscle contraction, secretion of substances, cell
division
Second messengers: inositol triphosphate and
diacylgylcerol
Response
Regulation of transcrption or cytoplasmic activities
The end of pathway may occur in the nucleus
or in the cytoplasm
Regulation of synthesis / a transcription factors
Regulate the activity or synthesis
Nuclear
response to
a signal
Cytoplasmic
response to a
signal
Multiple steps of signal transduction
• amplify the signal, in each step the number of
activated products is much greater
• provide different points at which response can
be regulated
• Specifity of cell signaling and coordination
Thank you for your attention
Campbell, Neil A., Reece, Jane B., Cain Michael L.,
Jackson, Robert B., Minorsky, Peter V., Biology, BenjaminCummings Publishing Company, 1996 –2010.