Download Chapter 11.1 Cell Communication

Cellular Internet
 Cell to cell communication is essential in order for
organisms to coordinate activities that develop, survive
and reproduce
 Cell communication between cells is also important
and more complicated in unicellular organisms
 Biologists have discovered some universal mechanisms
of cell regulation and these same small set of cell
signals appear repeatedly
- evidence of evolutionary relatedness of all life
Signal Conversion
 What kind of cell conversation do you think would be most
prevalent?
Sex – is the answer – reproduction
- Chemical signaling of yeast in the attraction of a
cells and alpha cells
 Signal transduction pathway – process of converting a
signal on a cell’s surface into a specific response in a series
of steps
-striking similarities between way yeast cells and animal cells
communicate
- suggests same signals used today evolved before multicellular organisms existed
Yeast Cell Communication
Local Signaling
 Cell have different ways of communicating messages
a. Direct contact – cell junctions connect
cytoplasms of adjacent cells
-signaling substances dissolved in the
cytosol pass freely in adjacent cells
-possible in plant and animal cells
b. Cell-Cell recognition – communication
between membrane bound surface molecules
(remember glycoproteins & glycolipids)
-important for embryonic development &
immune response
Local and Long Distance
 Local regulators – influence cells by
secreting messenger molecules to target
cells
- known as Paracrine signaling
- Ex: growth factors targeting
numerous cells to grow and
multiply
- Synaptic signaling – electrical
signal between nerve cells is
converted to chemical signal or
neurotransmitter, that travels across
the synapse to next nerve cell or
target nerve cell pathway
Long Distance Signaling
 Hormones – chemical messengers that are released by
specialized cells into vessels or glands to target cells in
other parts of the body.
- vary in size and type
Ex: ethylene in plants causes ripening –
only 6 atoms (C2H4)
Insulin – regulates sugar levels in bloodprotein of thousands of atoms
Stages of Cell Signaling
1. Reception – target cell’s detection of a signal molecule from
outside the cell
- usually involves binding of a receptor protein on
the surface or within cell
2. Transduction – signal molecule changes receptor protein to
initiate phase.
-converts signal to form that will evoke a cellular
response
- may occur as a single step, but most often is a series
of relay molecules
3. Response – signal triggers a cellular response
Chapter 11.2 Reception
 Most signal receptors are plasma membrane proteins
 Receptor proteins in or on the target cell all it to hear
the signal and respond to it
 Ligand – refers to a molecule specifically binding to
another molecule
-ligand binding usually causes a receptor protein
to change in shape
-signal molecule fits like a key in a lock and allows
activation and interaction with other molecules
leading to signal transduction
Membrane Receptors
 G protein linked receptors – extremely widespread and
diverse in function such as embryonic development and
sensory reception
 Examples are yeast mating factors, neurotransmitters,
hormones, and epinephrine
 Diseases such as cholera, pertussis, and botulism make
victims sick by producing toxins that block G protein
function
- G protein acts as a molecular switch on or off to
trigger certain cellular responses
- Enzyme attachment to G protein is temporary
allowing rapid shutdown to pathway
G Protein Receptor
Membrane Receptors
 Receptor tyrosine kinases – help cell regulate and
coordinate many aspects of cell growth & reproduction
 Can trigger more than one signal transduction pathway ( up
to 10) from single ligand event
 Kinase is an enzyme that catalyzes the transfer of phosphate
groups (ATP to tyrosine)
- two receptor tyrosine kinases exist close to one
another
- signal molecule binding cause association of
receptors (forming a dimer)
- each tyrosine kinase adds a phosphate from ATP to
activate receptor protein
- activated proteins attract relay proteins that trigger
transduction pathways that lead to cellular response
Tyrosine Kinase
Membrane Receptors
 Ion channel receptors – signal
molecule (ligand) has specific shape
that allows binding with receptor
channel
-binding on extracellular side
allows the opening of the
channel to certain ions
- ions flow in or out cause
rapid change in concentration
to exert cellular response
- ligand dissociates from
receptor cause gate or channel
to close
*Ex: neurotransmitter
signals between neurons
Intracellular Receptors
 Typically found in the cytoplasm or the nucleus of a
cell
 Hydrophobic nature or small size allows the
movement of these receptors into the cell
Ex: steroids – travel through the blood entering
cells all over the body.
- target cells only contain receptor molecule for
that steroid in the cytoplasm,
- binding occurs, then activation, in which
receptor molecule enters nucleus to turn on
specific genes (transcription factors)
Intercellular receptors