4.1,2,3,4 Cell Communication Flashcards
Why is cell-to-cell communication critical? (2)
Critical for the function and survival of cells
What is cell-to-cell communication responsible for? (2)
-the growth and development of multicellular organisms
What are the three general ways that cells communicate?
- direct contact
- Local Signaling
- Long-distance signaling
What is the direct contact way of cells communicating?
Communication through cell junctions
What occurs in direct contact?
- signaling substances and other material dissolved in the cytoplasm can freely move between adjacent cells
Which gap junctions do animals and plants use in direct contact?
- animals use gap junctions
- plants use plasmodesmata
An example of direct contact would be immune cells. What occurs in this process?
- antigen (protein markers on cell surface) presenting cells (APCs, ex. macrophages) communicate to T cells through direct contact
- (see diagram page 4)
What are happens in local signaling?
- A secreting cell will release chemical messages (local regulators/ligands) that travel a short distance through the extracellular fluid (outside cell)
What is a ligand?
- A term used for a molecule that specifically binds to another larger molecule (a signal)
How do local regulators/ligands work?
The chemical messages will cause a response in a target cell
What are two examples of local signaling?
paracrine and synaptic signaling
What is paracrine signaling (local)?
- secretory cells release local regulators (ie. growth factors) via exocytosis to adjacent cell
What is synaptic signaling? (2)
- occurs in animal nervous system
- Neurons secrete neurotransmitters, which diffuse across the synaptic cleft
What is the synaptic cleft?
The space between the nerve cell and target cell
What do animals and plants use for long-distance signaling?
hormones
How does long-distance signaling occur in plants?
- plants release hormones that travel in the plant vascular (vessel) tissue (xylem and phloem) or through the air to reach target tissues
What is xylem?
transports water and nutrients from roots
What is phloem?
- transports sugars and other metabolic products down from leaves
How do animals do long-distance signaling? (2)
- use endocrine signaling
– specialized cells release hormones into the circulatory system where they reach target cells
(slow b/c rely on circ. system for transport)
The mechanism of insulin regulation is an example of long-distance signaling. How does it work? (2)
- insulin is released by the pancreas into the bloodstream where it circulates through the body and binds to target cells
- insulin decreases blood sugar, promoting cellular respiration
What are the three stages of cell-to-cell signaling?
- reception (ligand binds to receptors)
- transduction (signal is converted)
- response (a cell process is altered)
What is reception?
The detection and receiving of a ligand by a receptor in the target cell
What are receptors?
macromolecule that binds to a signal molecule (ligand)
What do all receptors have, in terms of ligands? (2)
- have an area that interacts with the ligand
- an area that transmits a signal to another protein
Ligand and receptor binding is highly _____?
specific
What happens when the ligand binds to the receptor?
- the receptor activates via conformational change and allows the receptor to interact with other cellular molecules
- initiates a transduction signal
Where can receptors be found? (2)
in plasma membrane or intracellular space (cytoplasm)
What are plasma membrane receptors, and what do they bind to?
- most common type of receptor involved in signal pathways
- Binds to ligand that are polar, water-soluble, and large
What are two examples of plasma membrane receptors?
- G Protein couple receptors (GPCRs)
- ligand-gated ion channels
What are G Protein coupled receptors (stated in chart)?
- these proteins act as an “inbox”
- They receive messages in the form of light energy (autotrophs) and as nutrients from the environment
What are ligand-gated ion channels in terms of the nervous system?
- in the nervous system, neurotransmitters are the ligand that a receiving dendrite binds to, so the Na+ gates will open and a continuation of action potential occurs
Where can intracellular receptors be found, and what do they bind to?
- found in cytoplasm or nucleus or target cells
- bind to ligands that can pass through the plasma membrane (hydrophobic molecules)
What are examples of ligands that can pass through intracellular receptors?
- steroid hormones (type of lipid ex. estrogen, testosterone, cholesterol)
- thyroid hormones
- gasses like nitric oxide
What is transduction?
- The conversion of an extracellular signal to an intracellular signal that will bring about a cellular response
What does transduction require?
- A sequence of changes in a series of molecules known as a signal transduction pathway
What does the signal transduction pathway regulate?
- protein activity
How does a signal transduction pathway regulate protein activity?
- through phosphorylation and dephosphorylation
What does the enzyme protein kinase do?
- relays signal inside the cell (activates signal by gaining phosphate group)
What does the enzyme protein phosphatase do?
- shuts off pathway as dephosphorylation occurs, shutting down the pathway
During transduction, the signal is amplified by second messengers. What are second messengers? (2)
- small, non-protein molecules and ions that help relay the message and amplify the response
- cyclic AMP (cAMP, adenosine monophosphate) is a common second messenger
What is stage 3 response?
- The final molecule in the signaling pathway that converts the signal to a response that will ALTER a cellular process
What are three examples of response?
- Protein that can alter membrane permeability (ex. insulin increases glucose uptake)
- Enzymes that will change a metabolic process (Promote or shut it down)
- proteins that turn genes on or off
What can signal transduction pathways influence?
- how a cell responds to its environment
What can signal transduction pathways cause changes in? (2)
- gene expression and cell function
- (what protein will be made/not made) - can alter phenotypes (characteristics such as physical appearance or making that protein) or result in cell death
What are mutations, and what do mutations to receptor proteins or any component of the signaling pathway result in? (2)
- mutations are changes in nucleotide sequence of DNA or mRNA
- change to the transduction pathway of the signal
What are the two main categories of cell membrane receptors in eukaryotes?
- G protein couple receptors (GPCRS)
2. Ion channels
What are G protein couple receptors? (3)
- Largest category of cell surface receptors
- important in animal sensory systems
- Binds to G protein that can bind to GTP, which is an energy molecule similae to ATP
The GPCR, enzyme, and G protein are inactive until _____
ligand binding to GPCR on the extracellular side (see pg 16)
When the ligand binds to GPCR, what does it cause, and allow for? (7)
- cytoplasmic side to change shape
- allows G protein to bind to GPCR
- Activates the GPCR and G protein
- GDP becomes GTP
- Part of the activated G protein can then bind to the enzyme
- enzyme activated
- amplifies signal and leads to a cellular esponse
What is the polarity of ligand gated ion channels, and what type of transport does this indicate?
- hydrophilic, therefore facilitated diffusion or active transport
Where are ligand gated ions channels located, what are they important for, and what do they act as? (3)
- located in the plasma membrane
- important in the nervous system
- receptors that act as a gate for ions
What happens when a ligand binds to the receptor/ion channel? (2)
- the “gate” opens or closes, allowing diffusion of specific ions
- initiates a series of events that lead to a cellular response
EXAMPLE ACTION POTENTIAL
