Download Cell Signaling and Receptors

Cell Signaling and Receptors
To function in a biological system, cells communicate with others
cells and respond to the external environment.
The language of cells is in the form of chemicals = signals
 There are two general types of signal transmission:
1. Intercellular (inside the cell)
2. Intracellular (between cells)
 Cell signal transduction pathways affects:
a. Function of an organisms as a whole
b. Overall cellular function
c. Gene expression
d. Protein activity
 Cells may communicate by direct contact; signaling molecules in
cytosol pass freely through:
- Animals = gap junctions
- Plants = plasmodesmata
Important for development &
immune response in both plants
& animals
- &/OR –
- Animal cells = cell-cell recognition via cell receptor
molecules (proteins & glycoproteins) [ECM].
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 Local vs. Long Distance Signaling:
 Local signaling (short distance) by local regulators ~ effect
cells in localized area.
1. Paracrine signaling:
o Ex. growth factors = stimulate nearby target cells to
divide.
2. Synaptic signaling (animal nervous system) = chemical
signals (neurotransmitters) created by one nerve cell is
sent across the gap (synapse) to a second nerve cell to
stimulate target tissue
 Long distance signaling ~ once released by the signaling cell,
signal travel in blood stream to target tissue or affect the
organism as a whole.
Ex. hormones
o Animals – signals travel in blood via vessels (ex. insulin,
estrogen, testosterone)
o Plants – signals travel
1. Vessels
2. Cell to cell via diffusion
3. As a gas through stomata (ex. ethylene speeds up
growth, fruit ripening, death)
Other plant signals:
- light
- water stress
- viruses
- growth factors
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- damage
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So, how does it happen?
 3 Stages of Cell Signaling: (KNOW THIS!)
1. Reception - The receiving cell must have a specific protein
receptor to the signaling substance (messenger)
2. Transduction – Where the message carried by the
signaling molecule is converted into a form for…
3. Response – the transduced response triggers a specific
response in target cell(s)
 Reception:
 Communication can cause of stimulatory (or inhibitory) signals
from
a. Other cells – cell to cell contact; ex. growth hormones
b. Organisms – ex. pheromones
c. The environment – ex. ethylene (ripening of fruit)
ex. drugs to inhibit pain
Types of Reception:
1. (Chemo)receptors embedded in plasma membrane
- Ligand = signal molecule that are too big &/or chemically
unable to enter the cell (too big or polar/fully charged);
attaches to a protein receptor imbedded in membrane.
Ex. Epinephrine
2. Intracellular receptors located in the cytoplasm &/or nuclear
membrane.
o Signal (small and non-polar) crosses the cell membrane
and attaches to receptor protein inside the cell.
Ex. Testosterone and Estrogen hormones
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 Signal Transduction (ST) & Response: The process where a
signal on a cell’s surface is converted into a specific cellular
response.
From the viewpoints of the two types of reception:
1. Receptors embedded in the cell membrane.
- Causes conformational change of the membrane protein
receptor
o This change in shape causes a cellular response
 Can be amplified (one signal molecule = many
product molecules [see cascading])
a) Single celled organisms = ST pathways influence how the cell
responds to environments.
Ex. Yeast cell “sex”
Mating pheromone (signal) triggers mating; gene expression
Genes turned on (expressed) = produce a &  factors
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b) Multicellular organisms
Ex #1: Ligand gated ion channels (e.g. muscle contraction)
Ex #2. Phosphorylation cascades = after the ligand attaches, a
series of enzymes (kinases) add a phosphate group to the next
protein in the cascade sequence
o Protein in an inactive form
adding phosphate
group changes it to active form. (sometimes – other
way around)
o Signal is transduced along the way.
 Cascading benefits:
1. To amplify the message the signal is delivering.
2. Contribute to the specificity of the response.
…In regulating and coordinating the complexity of the cell’s
function.
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2. Intracellular receptor = on inside of cell and/or nuclear
membrane. Affects:
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Both types of reception can affect gene expression
 Termination of the Signal:
- ST’s are reversible
- Dependent on concentration of signal
- When signal is no longer present, receptor molecules
revert back to inactive forms.
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 Understanding signaling pathways allows humans to modify and
manipulate biological system and physiology.
3. Ex. understanding of human endocrine system (hormones)
allowed:
1. The development of birth control methods
2. Medicines that control depression.
3. Blood pressure and metabolism.
4. Other examples:
4. Ability to control ripening of fruit
5. Agricultural production (growth hormones)
6. Biofilm control
Biofilms are associations of complex microbial communities present in all
aqueous environments. In biofilms microbes surround themselves with a
slimy coating that protects them from their environment, making them hard
to remove or kill with traditional chemical or mechanical methods.
Due to this durability, biofilms are responsible for a wide range of
industrial and health problems. They are associated with persistent
infections and can cause fouling and corrosion in fluid processes;
undesirable taste and odor issues in the water industry; pipe corrosion
within oil and gas industries and souring of oil in pipelines and storage
facilities.
These problems can lead to significant infrastructure replacement or
operational costs, and highlight the need for effective strategies to
control or minimize biofilm formation.
Biofilms also have beneficial impacts, for example in wastewater treatment
processes. Thus, strategies to enhance the activity of useful biofilms as
well as remove biofilms are of critical importance.
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