Cell Communication and Signaling Flashcards
Yeast Mating Types
Two types of haploid yeast (mating types)
1) Type a –> Secretes a-factor
2) Type alpha –> Secretes alpha-factor
Type-a yeast
Secretes a-factor
Has receptors for alpha-factor
Type-alpha yeast
Secretes alpha-factor
Has receptors for a-factor
Yeast Mating Process
1) a and alpha yeast cells bind to each others’ particles
2) a and alpha cells begin to fuse
3) creates a new cell with both a/alpha genes
Signal-Transduction Pathway
1) Signal reception
2) Signal transduction
3) Cell response
Types of communication in multicellular organisms (2)
1) Local communication
2) Long-distance communication
Types of local communication (3)
1) Paracrine
2) Direct Contact
3) Synaptic
Direct Contact Communication (and types)
Signals pass through intercellular connections OR through cell-cell recognition
1) Gap junctions
2) Plasmodesmata
3) Cell-cell recognition (involves glycoproteins)
Paracrine Communication
Signals released into the extracellular fluid (Signal is available to all neighboring cells)
–> Signal only impacts those target cells with the necessary receptor
Synaptic Communication
In NEURONS
–> Signals are released into a synapse (region between two neuron terminals)
–> Signal goes ONLY to interact with that one neuron (no other cells can interact with it)
Long Distance Communication (and its one type)
Occurs between cells that are farther apart (usually within an organism) –> BUT it can occur between organisms
1) Endocrine/Hormonal Signaling
Endocrine/Hormonal Communication
Signals are released by an endocrine cell and travel a long distance through a vascular system (or possibly through the air)
–> Only target cells with necessary receptors will respond
Fruit ripening when next to other ripe fruit is an example of…
(and explain its cause)
Long distance communication BETWEEN organisms
–> The ripening agent ETHYLENE (gas) that spreads to other fruits nearby a ripening fruit (gets them to ripen as well)
The ability of a cell to respond to a signal is dependent upon…
Whether it has the specific receptor molecule that can bind a given signal
Main stages of cell signaling (3)
1) Reception
2) Transduction
3) Response
Reception
The detection (by a target cell) of a signal which binds to a receptor molecule –> The RECEIVING of a signal
Receptor
Molecule that a signal binds to
Ligand
Signal Molecule
Main types of receptors (4)
1) G-protein linked receptor
2) Tyrosine-kinase receptor (enzyme receptor)
3) Ligand-Gate Ion Channel
4) Internal/Intracellular Receptor
G-Protein Linked Receptor
Cell surface transmembrane receptor that works WITH the help of G-protein
G-Protein
A protein that binds to GTP
G-Protein Linked Receptor: Extracellular Domain is ________
The receptor: Interacts with the ligand
G-Protein Linked Receptor: Cytoplasmic Domain is ________
Initiator of transduction: Interacts with the G-protein molecule
G-Protein Linked Reception Process
1) No ligand = Inactive state = G-Protein bound to GDP
2) Ligand binds to receptor: receptor changes shape
3) Inactive G-protein binds to receptor which causes GTP to displace GDP
4) Activated G-protein dissociates from receptor and diffuses along membrane
5) G-protein binds to an enzyme, activates it = triggers cascade
6) G-protein hydrolyzes GTP to form GDP and returns to inactive state
G-Protein Active vs Inactive states
Active State = Bound to GTP
Inactive State = Bound to GDP
Enzyme Receptors
Receptors that function as BOTH a receptor and an enzyme
(Not linked to an enzyme, it IS an enzyme)
Tyrosine-Kinase Receptor
Protein kinase receptor that phosphorylates tyrosine
Tyrosine-kinase receptor has ______ subunits
2 subunits
Tyrosine-Kinase Receptor Process
1) Signals bind to receptors of the TKR subunits
2) The subunits dimerize (come together to form one unit)
3) Subunits phosphorylate each other (their tyrosine components)
4) TK receptor FULLY activates
5) Relay proteins bind to the TKR and become activated = begins cascade
Protein Kinase
An enzyme that catalyzes the transfer of phosphate groups from ATP to another protein
Where do protein kinases get their phosphate group from?
Take it from ATP to give to other molecule
Tyrosine-Kinase Receptors are associated with what disease? Why?
Cancer
–> TKRs are involved with a lot of growth factors so any issues with these receptors could cause uncontrolled growth = cancer
Ligand-Gated Ion Channel
A type of membrane channel receptor which contains a region that can act as a “gate”
–> Channel “opens” when ligand binds
–> Channel is “closed” when no ligand binds
How does Ligand-Gated Ion Channel lead to a cell response?
The channel allows for the passage of ions (if activated)
–> So a change in ion concentration when activated leads to the cellular response mechanisms
Internal Receptors
(AKA intracellular receptors)
–> Receptors found INSIDE the cell
Internal receptors only work if…
the signal can get INTO the cell
Internal receptor signals include: (2)
1) Hydrophobic molecules (Ex: steroids/hormones)
2) Small gaseous molecules (Ex: ethylene)
Testosterone signaling is an example of what…
Internal Receptor Signaling
–> Testosterone is a hormone that can enter the cell
–> Its receptor is found within specific cells which when activated lead to the development of male sex characteristics
Transduction
Change to the receptor due to the binding of a signal which begins a sequence of biochemical events (pathway/cascade) which ultimately leads to a cellular response
Analogy for transduction
Signal = Mailman
–> Signal “knocks on the door, leaves a letter, and then goes away”
Relay Molecules
The molecules that relay a signal from a signal-receptor to the response
2 main types of transduction pathways:
1) Membrane receptors
2) Internal receptors
Membrane receptors vs internal receptors (transduction differences)
Membrane Receptors = Multi-step pathway that carries info from outside to inside the cell (usually contains a longer cascade)
Internal Receptors = Can carry out the transduction THEMSELVES (as they are already in the cell)
–> Usually less steps in the cascade
Advantages of multi-step signal-transduction pathways
1) Amplification of signal = 1 signal can transmit info to multiple molecules at each step of the cascade
2) Regulation = Provide more opportunities for control and coordination (“more checkpoints”)
Transduction mechanism =
= Conformational change: Signal causes switch between active and inactive forms of cellular proteins
One main mechanism of transduction is… (most common)
phosphorylation
The 2 potential substrates of protein kinases are…
1) The protein kinase itself (autophosphorylation)
2) Other proteins
Phosphorylation Cascade
1) Signal binds to receptor
2) Activates relay molecule
3) Activates 1st protein kinase
4) Activates 2nd protein kinase
…
5) Final protein kinase activates a cell response
Protein Phosphatases
THE INHIBITORS of phosphorylation
They DE-phosphorylate –> Remove phosphate groups
(Undo the work of protein kinases)
Second Messengers
Small, non-protein, water soluble ions/molecules that cause relay proteins to react
(Second because “first messenger” is said to be the original signal)
Major second messengers (4)
1) Ca2+
2) cAMP –> Cyclic AMP
2.1) IP3 –> Inositol Triphosphate
2.2) DAG –> Diacyl glycerol
Cyclic AMP (cAMP)
A small molecule produced from ATP (second messenger of mainly G-Protein reception pathways)
Adenylyl Cyclase
Enzyme that CREATES cAMP from ATP
(Closes ATP in on itself to create a cyclic molecule)
Phosphodiesterase
Enzyme that breaks the third carbon bond of cAMP to get rid of the cyclic shape =
cAMP –> AMP
–> Deactivates cAMP
cAMP in G-Protein Signal Pathway PROCESS
1) 1st messenger (signal) binds to G-Protein coupled receptor, activating it
2) Receptor binds to G-protein causing GTP to replace GDP, activating the protein
3) G-protein binds to Adenylyl Cyclase = triggers conversion of ATP –> cAMP
4) cAMP goes off and activates another protein = cascade begins
Ca2+ Messenger
Functions in signaling through both G-protein and TKR reception
Ca2+ cellular gradient
Inside cell [Ca2+] < Outside Cell [Ca2+]
–> cell wants less Ca2+ inside of it
Processes that maintain the Ca2+ gradient
1) Cell is always pumping Ca2+ OUT of cell
2) Cell is always pumping Ca2+ INTO the ER
3) When [Ca2+] is suddenly greater inside cell: the cell will pump Ca2+ into MITOCHONDRIA
The ER is a ________ for Ca2+
Repository for Ca2+ –>Stores it for when the cell needs it
Ca2+ does not act alone, it uses assistance from…
1) IP3
2) DAG
3) Calmodulin
Creation of IP3 and DAG
The signal activates the phospholipidase-C enzyme
–> Cleaves PIP2 (phospholipid) into IP3 and DAG
Phospholipidase-C
Creates IP3 and DAG through cleaving PIP2
PIP2 –> IP3 + DAG
DAG function
Remains in the membrane to activate a kinase
IP3 function
Ligand for an ion-gate channel in the ER membrane
–> Causes the channel to open and begin releasing Ca2+ from the ER repositories
Calmodulin function
Ca2+ binding protein –> Ca2+ binds to it and then this protein goes and binds to the next step of the cascade
Ca2+ can activate the cascade in two ways:
1) Indirectly –> Using calmodulin
2) Directly –> Doing it itself
Cellular Response
The “final destination” –> What the cell does due to transduction
Two types of cell responses =
1) Cytoplasmic response
2) Nuclear response
Cytoplasmic response
Regulates enzyme activity
–> Does not affect gene expression
Nuclear response
Causes a change in gene expression
–> Activates/inactivates transcription factors
Isolated pathway
Some signals only activate ONE specific cell/pathway
1 signal = 1 response
Branched pathway
Some signals elicit MULTIPLE responses
1 signal = 2+ responses
Crosstalk
Transduction pathways overlap: Interactions between pathways
–> DIFFERENT signals elicit the SAME response
Glycogen Phosphorylase
Enzyme that breaks down glycogen
Epinephrine induced breakdown of glycogen in liver pathway
Epinephrine –> Activates glycogen phosphorylase –> Breaks down glycogen = Energy production for body
Epinephrine-glycogen pathway only occurs in LIVING CELLS: Why is this important?
Because it shows us that epinephrine does not directly activate glycogen phosphorylase (as when put into a test tube nothing happens) which signifies that there are other steps that occur in between to activate the pathway
