Cell communication and signaling Flashcards
What must cells be able to do in order to function/survive?
- Sense their environment
- Respond to their environment
- Coordinate with other cells for overall survival (especially in multicellular organisms)
Types of cellular communication
1.) Gap junctions
2.) Plasmodesmata
3.) Juxtacrine
4.) Neuronal
5.) Paracrine
6.) Endocrine
Gap Junctions (animals)/Plasmodesmata (plants)
Direct contact (fast!)
- local cell-to-cell communication
~ Transfer both chemical and electrical signals
Juxtacrine
Transmembrane protein signaling between two neighboring cells in physical contact
(ex. developmental; delta = signal, notch = receptor)
(ex. apoptosis; death ligand, death receptor Fas)
Neuronal
Short range neurotransmitters released into synapse (gap) between cells in nervous system
- Through synaptic clefts
- Neurotransmitters
What is one important neurotransmitter?
Acetylcholine
What is the issue with neuronal?
Small fraction of cells are innervated
- Nervous system commands are very specific and short lived but many life processes are not short lived (ex. growth and reproduction)
Paracrine
Short range proteins released by neighboring cells
(ex. EGF=Epidermal Growth Factor)
(ex. Histamine and inflammation response)
Endocrine
Long range peptide or steroid hormones delivered through circulatory system
(ex. estrogen-steroid hormone)
(ex. insulin-peptide hormone)
Signal and response
Same signal can lead to diverse responses depending on the target cell
What are 3 common signal responses?
1.) Heart muscle decreased rate and force of contraction
2.) Salivary gland secretion
3.) Skeletal muscle cell contraction
Combinatorial signaling
Functional consequences: different combinations equal different outcomes
1.) survive
2.) grow and divide
3.) differentiate
4.) die (apoptotic cell)
How do cells communicate?
Signaling molecule and target cells
Signaling molecule
Chemical messenger secreted from another cell
Target cells
Specific cells that possess receptors
- Receptors needed to bind and “read” the signaling molecule
3 steps of cell signaling
1.) Reception
2.) Transduction
3.) Response
Reception
Signal is bound to receptor
- Signal relayed into cytoplasm
Transduction
Signal transduction pathway relays signal into cell
Response
Cellular responses are activated in both cytoplasm and nucleus to respond to signal
What happens during Reception?
receptors span the plasma membrane and relay signal to signal transduction pathways in cell
- Signaling molecules released by another cell bind here
What is the Signal Transduction Pathway
a series of steps by which a signal on a cell’s surface is converted into a specific cellular response
(involves both phosphorylation cascade & enzyme activation to make a second messenger)
What is the phosphorylation cascade of Transduction?
sequential activation of a series of kinases (amplifies signal at each step)
- Kinases are subsequently turned off again by phosphatases
What happens during the activation of reusable molecular switches of Transduction?
A.) Signaling by protein-phosphorylation
B.) Signaling by GTP-Binding Protein
What happens during Response?
Signal transduction pathways relay outside signals to affect intracellular responses via cytoplasmic signaling and nuclear signaling
Cytoplasmic signaling
- Changes activity of existing proteins
- Fast (and easily changed)
Nuclear signaling
- Changes gene expression to reinforce signal
- Slow (but longer lasting)
Three general types of cell surface receptors
1.) Ion-channel-linked receptor
2.) G-protein-linked receptors
3.) Enzyme-linked receptors
What does a G-protein coupled receptor (GPCRs) contain?
7-transmembrane receptors and Trimeric G protein
What makes up a Trimeric G protein?
Alpha subunit, beta subunit, and Y subunit (beta Y complex)
G protein coupled receptors (GPCRs) steps
Unstimulated –> stimulated –> GTP activation alpha subunit and beta Y complex both activated –> Activated alpha subunit and beta Y complex find target protein –> target protein activation –> GTP hydrolysis/target protein inactivation –> G protein inactive
G-proteins can activate membrane bound enzymes
ex. adenylyl cyclase
(2nd messenger, example is cAMP, amplify the signal)
Adrenaline (GPCRs)
epinephrine; signals through GPCR to break down glycogen
Cytoplasm
- Adrenaline activates adenylyl cyclase and makes cAMP
- Activates protein kinase A (PKA)
- Activates glycogen phosphorylase= glycogen breakdown
Nucleus
Signaling makes more PKA and glycogen phosphorylase
Receptor Tyrosine Kinases (RTKs)
phosphorylation cascades lead to gene activation
- Ex. EGF (Epidermal Growth Factor)
- Ligand binding causes dimerization and activation of the RTK receptor
~ Receptors phosphorylate each other (trans-phosphorylation)
~ Signaling proteins bind and are activated
What do RTKs often activate?
Ras
What does Ras activate?
a signal transduction phosphorylation cascade
- Ras activated by nucleotide exchange: GDP swapped for GTP
- Signal relayed into cell by MAP kinase cascade, which results in changing protein activity and changes in gene expression
