Cell communication Premedical biology. The plasma membrane fluid mosaics of lipids and proteins -...

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

• phospholipids are

amphipatic molecule

membrane

• 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

Campbell, Neil A., Reece, Jane B., Cain Michael L., Jackson, Robert B., Minorsky, Peter V., Biology, Benjamin-Cummings Publishing Company, 1996 –2010.

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