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Cell communication. Premedical B iology. The plasma membrane. is fluid mosaics of lipids and proteins, it consists of double layer of phospholipids and other lipids with attached proteins. controls traffic into and out of the cell it surrounds

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cell communication

Cell communication

Premedical Biology

the plasma membrane
The plasma membrane
  • is fluid mosaics of lipids and proteins, it consists of double layer of phospholipids and other lipids with attached proteins.
  • controls traffic into and out of the cell it surrounds
  • is selectively permeable, it allows sufficient passage of oxygen a nutrients and elimination of wastes
slide3

Lipids and proteins

Phospholipids are amphipatic molecules

Proteins are embeded or attached to surface.

the fluidity

Is due to the presence of

unsaturated hydrocarbons, which increase fluidity and

cholesterol (animal cells), which reduces fluidity; helps stabilize the membrane

The fluidity
slide6

Proteinsin membrane

determine many of the membrane‘s specific functions

Integral proteins – transmembrane proteins

Peripheral proteins – are not embeded in the lipid bilayer

slide8

Active transport is the pumping of solutes against concentration gradients „uphill“

It is the major mechanism of ability of cell to maintain internal concentrations of small molecules that differ from concentrations in environment.

slide9

Cell communication – function of proteins

Direct contact between membranes by cell-surface molecules

= cell junctions = intracellular joining

= cell-cell recognition (glycolipids and glycoproteins)

slide10

Intracellular junctions(joining)

Cell walls of plant cells perforated with channels called plasmodesma.

In animals are intracellular junctions.

Tight junction

Desmosomes

Gap junctions

Adhere, interact

and communicate

slide11

Cell-cell recognition is done

also by carbohydrates(linked to proteins and lipids), which

helps to sort cell into tissues and organs in embryo and

helps to recognize and reject the foreign cells in the immune system

Carbohydrates are usually short branched oligosaccharides.

slide12

Attachment with ECM

Plant cells (some Protists, prokaryotes, fungi) encased

by cell walls

Animal extracellular matrix – ECM with

glycoproteins :

Collagen fibers are embedded in network of proteoglycans.

Fibronectins bind to receptor

protein called integrins in plasma

membrane. Integrins bind to

microfilaments (cytoskeletal pr.)

on cytoplasmatic side.

slide15

Cell communication and signal transduction function of protein

Cell responds to external signals.

A signaling molecule (ligand/first messenger) binds to a receptor protein in membrane and causes a change of his shape (enzyme). On internal side is the signal transformed in the cascade of molecular interactions with origin of second messengers. In nucleus signal leads to regulation of transcription or other cytoplasmatic activities.

cell signaling
Cell signaling
  • Reception: target cell detects a signaling molecule coming from outside
  • Transduction: change of the receptor protein initiating process of cellular response (enzymatic)
  • Response: cellular activity: catalysis, rearrangement of the cytoskeleton, activation of genes
reception
Reception

Signaling molecule + Receptor

Receptor or protein associated with get activated and it is able to transfer the signal inside the cell.

G protein coupled receptors / inhibitory or activity

Receptor tyrosine kinases have enzymatic activity and catalyze transfer of phosphate groups

Ion channel receptors withgate open or close

transduction
Transduction

Multistep pathway (cascade) of activation of proteins by addition or removal of phosphate groups or it starts by the origin of small molecules or ions that act as seconder messengers.

Phosphorylation and dephosphorylation of proteins acts as a molecular switch.

Protein kinases transfer phosphate groups from ATP to protein.

slide22

Multiple steps of signal transduction greatlyamplify the signal. In each step the number of activated products is much greater than one step before.

Multiple steps also provide different points, at which the response can be regulated and also provide a specifity of cell signaling and coordination.

small molecules and ions as second messengers
Small molecules and ions as second messengers

Nonprotein molecule, which can be spreaded by diffusion – cAMP and

calcium ions

Protein are sensitive to

the cytosolic concentration

of one or other.

s econd messengers c alcium ions and inositol triphosphate
Second messengers: calcium ions and Inositol Triphosphate

Neurotransmitters, growth factors, hormones induce cell’s responses via signal transduction pathways that increase the concentration of calcium ions.

Responses: muscle contraction, secretion of substances, cell division

Second messengers: inositol triphosphate and diacylglycerol

response s
Responses:

The end of pathway may occur in the nucleus or in the cytoplasm = the change of transcription or cytoplasmic activities.

Response in nucleus is the regulation the activity and synthesis - transcription factors

slide28

Thank you for your attention

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