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Transcript
Cell communication
Premedical Biology
Plasma membrane
• half-fluid mosaic of lipids and proteins, it consists
of double layer of phospholipids and incorporated
proteins
• controls traffic into and out of the cell
• is selectively permeable, it allows sufficient
passage of oxygen and nutrients, and elimination
of wastes
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
Proteins in membrane
determine many of the membrane‘s specific functions
Integral proteins – transmembrane proteins
Peripheral proteins – are not embeded in the lipid bilayer
Transport
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.
Cell communication – function of proteins
Direct contact between membranes
through molecules on the cell surface
= cell junctions = intracellular joining
= cell-cell recognition (glycolipids and
glycoproteins)
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
Cell-cell recognition
- 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.
Attachment with ECM
Plant cells (some Protists, prokaryotes, fungi) are 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.
Signal transduction pathways
Cell communication: Local and long-distance
signaling
Cell communication and signal
transduction function of protein
Cell responds to external signals.
Signal molecule (ligand/first messenger) binds to a
receptor protein in membrane and causes change of
its shape (enzyme). On internal side is the signal
transformed into the cascade of molecular
interactions (second messengers). The signal leads
to regulation of transcription in nucleus or some
cytoplasmatic activities.
Cell signaling
1. Reception: target cell detects 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 + receptor
Receptor or protein associated with it gets activated
and is able to transfer the signal inside the cell.
G protein associated receptors – on/off
Tyrosine kinase receptors have enzymatic activity
and catalyze transfer of phosphate groups
Ion channel receptors - gate open or close
Intracellular receptors for steroid and thyroid
hormones, nitric oxide
Transduction
Multistep pathway (cascade) of activation of proteins
by addition or removal of phosphate groups or it
starts by formation of small molecules or ions that
act as second messengers.
Phosphorylation and dephosphorylation of proteins
acts as molecular switch.
Protein kinases transfer phosphate groups from ATP
to protein.
A phosphorylation cascade
Multiple steps of signal transduction greatly
amplify 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
Nonprotein molecule, which can be spreaded by
diffusion – cAMP and
calcium ions
Proteins are sensitive to
cytosolic concentration
of the molecule.
Second messengers: calcium ions
Neurotransmitters, growth factors, hormones induce
cell response 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
Responses:
End of the pathway may occur in the nucleus or
in the cytoplasm = change of transcription or
cytoplasmic activities.
Response in nucleus is the regulation of gene
activity - transcription factors
Nuclear
response to
a signal
Cytoplasmic
response to
the signal
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.
Repetition
5. Molecular base of DNA inheritance
1. Describe the molecular structure of DNA
2. What is hybridization?
3. Describe the process of DNA replication in eukaryotic cells
4. What are the types of chromatin?
5. What are telomeres and what is their function?
6. How does the human karyotype look like?
7. What are the types of human chromosomes?
8. What is NOR?
9. Describe spiralisation of DNA, what does it serve for?
10. What nucleotides do you know and where you could find
them?