Lecture 11: Cell Communication Flashcards
What is cell communication?
- Cells sense changes to their environment and adjust their activities.
- Cells can communicate with other cells to form systems in multicellular organisms.
What are the two things that cell communication focuses on?
how a cell:
A. Sends a message to another cell.
B. Receives and responds to messages (cell signaling).
Why is cell communication important for the cell?
- Allows a cell to respond to its chemical and physical environment.
- Allows development programs to be carried out in multicellular organisms.
What are cell division, cell maturation, apoptosis, production of other signals, etc. examples of?
cell responses
What do cell communication systems allow multicellular organisms to do?
A. Respond to changes in its external
environment
B. Respond to its internal environment
and maintain homeostasis
C. Run other systems (e.g., immune
system)
Why study cell communication?
- Advances our knowledge of how cells and the body work as a system.
- Abnormal cell communication (overactive or underactive) is involved in several diseases
Give an example of a disease where cells are overactive.
cancer
Give an example of a disease where cells are underactive.
diabetes mellitus
What do many medicinal drugs target to treat diseases?
Many medicinal drugs target components of cell signaling pathways.
What kind of signals do cells respond to?
to internal and external signals:
Specialized cells can detect:
1. The presence of chemicals
2. Contact with other cells or the extracellular cell matrix.
3. Mechanical force
4. Gravity
5. Changes in voltage across the membrane
6. Changes in light
7. Changes in pressure
What is an example of cell signal that is a change in voltage across the membrane?
muscle cells
What is an example of cell signal that is a change of light?
vision
What can a cell do in response to a signal? Give 5 examples
What are the molecular responses to signals? (response at a molecular level)
- Enhance or silence expression of a gene.
- Activate or inactivate a protein (that is already made).
- Modify the cytoskeleton.
- Release a stored protein or other substance from the cell.
What are the three types of cell signaling in plants and animals?
- Direct Signaling
- Local (Short-Distance) Signaling
- Long Distance Signaling
What are the two types of direct signaling?
- cell junctions
- cell-cell recognition
What are the two types of local signaling?
- paracrine signaling
- synaptic signaling
What are the cell junctions in animal cells?
gap junctions
What are the cell junctions in plant cells?
plasmodesmata
Give an example of paracrine signaling
activation of an immune cell
What type of signaling do neurotransmitters do?
synaptic signaling
What are long-distance chemical messengers called?
hormones
What are the three most important actions of long distance chemical messengers?
They act:
A. In both plants and animals.
B. Over longer distances.
C. Over longer periods of time (need time to clear).
Where do long-distance signaling happen in animals and plants?
The long-distance chemical messengers circulate:
A. In the blood of animals.
B. In the sap of plants.
What is the sap of a plant?
The liquid transported by xylem and pholem
How do you call long-distance signaling?
endocrine signaling
When we talk about “endocrine” signaling, what does it imply?
its a hormonal signaling
What are the four steps of cell signaling?
Cell signaling occurs in four steps:
1. Signal reception
2. Signal transduction
3. Signal response
4. Signal deactivation
What happens during signal reception?
- Hormones and other chemical signals bind to protein signal receptors.
- The cells that have the appropriate receptor will be able to respond to a particular chemical signal (i.e., a target cell)
How can hormones coordinate the activities of cells throughout a multicellular organism?
By identical receptors in diverse cells and tissues
Is cell reception intracellular or extracellular?
either, depending on the chemical properties of the signal molecule.
What are receptors?
proteins that bind to a ligand (signal molecule) in a specific interaction.
do receptors react with ligands?
No, it is not a reaction but an interraction
What happens to a receptor after it binds with the ligand?
it changes its shape and activity
Where are receptors located?
within the plasma membrane or within the cell.
What type of binding is a receptor-ligand interraction?
non-covalent and reversible
Where are intracellular receptor proteins found?
in the cytosol or nucleus of target cells.
How do intracellular receptors get activated?
Small or hydrophobic chemical messengers can readily cross the membrane and activate intracellular receptors.
Is lipid-soluble signal binding directly or indirectly processed? What does it mean?
directly
means that it does not have to be transducted
Give two examples of hydrophobic messengers?
the steroid and thyroid hormones of animals.
Describe the actions happening in this image
an activated steroid hormone-receptor complex can act as a transcription factor, turning on specific genes in response to a signal.
Is lipid-insoluble signal binding directly or indirectly processed? What does it mean?
indirectly
it requires signal transduction (signal is transformed) at the plasma membrane
What do chemicals that cannot diffuse across the plasma membrane bind to?
to membrane receptors
What is a signal transduction pathway?
When a signal binds at the cell surface it triggers a complex series of events, which converts the extracellular signal to an intracellular signal.
How happens signal transduction and what does it result in?
Signal transduction involves an activation cascade and leads to signal amplification within the cell.
What is happening from the third to fourth step?
a protein int he activation cascade activates a transcription factor.
How do you call proteins that span the plasma membrane?
transmembrane proteins
What happens to a receptor when bound to a ligand?
a shape change that can change its properties and activate proteins to initiate a signal transduction pathway inside the cell.
What can activated receptors do?
in turn activate relay proteins.
Some act as ion channels.
What are the three types of membrane receptors?
- G protein-coupled receptors (GPCRs).
- Enzyme (kinase)- linked receptors.
- Ion channel receptors.
What is this image?
G protein-coupled receptor
How do G-protein-coupled receptors get activated?
How do proteins kinase receptors get activated?
How do ligand-gated channels get activated?
example of receptor that functions as an ion channel
In signal transduction pathways, what are the two key elements that can be initiated by relay proteins?
A. Production of second messengers
B. Phosphorylation cascades
What are second messengers?
small, nonprotein, water- soluble molecules or ions that spread throughout a cell by diffusion.
What do second messengers do in signal transduction pathways?
can be produced or released in signal transduction pathways
can activate proteins
Give me two examples of second messengers
cyclic adenosine monophosphate (cAMP)
ions such as Ca2+
What is cyclic AMP?
(cAMP): one of the most widely used second messengers in signal transduction pathways
What is adenylyl cyclase
enzymes that convert ATP to cAMP in response to an extracellular signal
Where do you find adenylyl cyclase?
in the plasma membrane
What is phosphodiesterase? What is its role?
enzyme that converts cAMP to AMP.
Ensures that a second messenger can be deactivated.
How is [Ca2+] kept low inside the cell?
by active transport
What happens when a Ca2+ channel is activated?
Ca2+ ions flow down their electrochemical gradient.
When does Ca2+ act as a second messenger?
when released into the cytosol.
Why doesn’t the Ca2+ pump require ATP in the mitochondrion? What provides the energy for this type of active transport?
because it utilizes the electrochemical gradient established by the proton pumps?
(to be verified)
What is a protein phosphorylation cascade?
a series of protein phosphorylations that serve as signal transmitters in many pathways
Phosphorylation of one kinase activates another kinase by phosphorylation that activates another kinase by phosphorylation and so on.
How do you call the enzymes that can catalyze the phosphorylation of proteins?
protein kinases
What happens during phosphorylation?
Process where protein kinases transfer phosphates from ATP to a protein
What happens during dephosphorylation?
Process where protein phosphatases remove the phosphates from proteins.
What do protein phosphatases ensure during dephosphorylation?
that proteins can be deactivated (in case phosphorylation activates it)
What acts as a molecular switch, turning activities on and off or up and down when required?
protein phosphorylation and dephosphorylation system
Is dephosphorylation the reverse reaction of phosphorylation?
No, it is a complete different reaction.
Reverse reaction of phosphorylation/dephosphorylation isn’t possible
What are scaffolding proteins? In what process are they important?
Hold together proteins involved in signal transduction to increase the organization and efficiency of cell signaling pathways (make faster and easier)
they also localize the pathway to a particular area of the cell
How do you call the overall structure of a scaffolding protein and its content?
signaling complex
What leads to signal amplification? Through what?
Signal transduction can lead to signal amplification through second messengers and phosphorylation cascades.
Are cellular responses the same in all cells?
No, the ultimate response cell signaling varies from signal to signal and from cell to cell
What are the two general categories of signal response?
- Nuclear: A change in which genes are being expressed in the target cell. Slow response.
- Cytoplasmic: Activate or deactivate a particular target protein that already exists in the cell. Fast response.
Which category of signal response is slow?
Nuclear
Which category of signal response is fast?
Cytoplasmic
What is nuclear response? What is the end target of the pathway?
it is the regulation of the synthesis of new proteins by activating or deactivating gene expression
happens in the nucleus
The last kinase of the pathway targets a transcription factor, which, (if activated), can regulate the transcription of a gene.
mRNA moves to the cytoplasm and gets translated into proteins
What is a cytoplasmic response?
signal response in the cytoplasm where the last kinase either activates an enzyme involved in the breakdown of a molecule or inactivate the enzyme involved in the synthesis of that molecule
the enzymes are the end targets of the pathway and already exist in the cytoplasm
example of epinephrine (adrenaline) where glycogen is the molecule being synthesized and broken down:
Does the activation and inactivation of the enzyme happen at the same time in cytoplasmic response? Why?
Yes since the the synthesis of the molecule needs to be stopped so the breakdown of the molecule can come to an end.
What does signal amplification do to the response?
it leads to an amplified response:
example of epinephrine
Why is there signal deactivation?
- Turning cell signals off is just as important as turning it on.
- Cells have automatic and rapid mechanisms for signal deactivation.
- These mechanisms allow the cell to stop the pathway and return the cell to a sensitive state to detect new changes.
What are the mechanisms responsible for signal deactivation?
A. Signal is no longer produced by source and removed from interstitial fluid.
B. Receptors inactivated, sequestered (hidden), or destroyed
C. Relay protein deactivation by enzymes
D. Second messenger removal from cytoplasm
What are the “off switches” that could turn the signals off in this image? name them by if they occur inside or outside of the cell
Outside of cell: Receptor can be deactivated or no more production of the signaling molecule
Inside of cell: the dephosphorylation of a second messenger protein with the help of an enzyme (example: cAMP transformed to a AMP by phosphodiesterase) or deactivation of any relay protein
How do you call when a pathway branches and lead to two or more responses?
Pathway divergence
How do you call when cross-talk occurs between two pathways?
Pathway convergence
What is a pathway communication web?
the whole of divergence and convergence of pathways
What is cross-talk of pathways useful for?
it allows for signal (+ and -) integration and fine-tuning of a response.
(for the signals to work together to create the wanted response)
What is epinephrine?
a neurotransmitter and hormone made by the adrenal glands
What are the effects of epinephrine?
Take epinephrine as an example; how can the same signal molecule lead to such varied effects on the human body?
due to pathway diversity
What is pathway diversity?
Diversity leads to different responses in different cells.
Distinct target cells in the body contain different protein receptors and corresponding signal transduction pathways that lead to different cellular responses.
