Cell Signalling Flashcards
How do cells communicate with other cells over short distances?
Make physical contact
- Cell junctions
Send chemical signal to adjacent cells
How do cells communicate with other cells over long distances?
Hormones go through the bloodstream then reaches another cell. Hormones is a cell signaling molecule.
How is the process of distance communication different from the process of communicating during cell-cell contact?
Structural modifications of the cells membrane and cell wall (plasmodesmata & gap junctions) allow cells to send chemical signals.
What is a signal transduction pathway?
Binds signalling molecules to receptors located on the cell surface or inside the cell that invokes a response
Why do cells use signal transduction pathway?
Link reception with cellular response
How does a signal transduction pathway begin?
Receptor or ligands binds to an external receptor or an intracellular receptor
What is the role of protein modification in signal transduction pathways?
Conformational shape(receptor shape) changes due to ligand binding. AN intracellular response is activated which causes a second messenger to be activated.
What is the role of phosphorylation cascades in signaling transduction pathways?
Signalling pathways where one enzyme phosphorylates another causing an amplification of the reaction, leading to the phosphorylation of thousands of proteins
How can mutations in the receptor protein or any component of the signalling pathway affect the transduction of a signal?
Alters the ligand/receptor specificity can lead to incompatibility which can alter the signal transduction pathway. The receptor will not underdog proper conformational shape change, resulting in an inactive internal pathway.
What is the effect of chemicals activating a pathway?
Amplification of the pathway
What is the effect of chemicals inhibiting a pathway?
Lead to the pathway not occurring
What are the 2 types of signalling?
Long distance signalling and short distance signalling (local)
Describe long distance signalling
Endocrine signaling → involves hormones (typical messenger of long-distance signaling)
Describe how hormones travel through the body
Hormones typically get sent throught the bloodstream which gets picked up by a cell by attaching to a receptor
What are the two types of local signalling and describe each?
1.Autocrine Signalling: molecule goes back to same cell e.g. growth
E.g. molecule gets sent back as a message for the cell to multiply and divide
2.Paracrine Signalling: sending signals to nearby cells
Define synaptic signalling
type of paracrine signalling but have to do w/ neurotransmitter
What are the cell junctions in animal cells called and define it?
Gap Junctions: In animal cells→ protein channels in between 2 animal cells which allow for ions and electricity to pass
What are the cell junctions in plant cells called and define it?
Plasmodesmata: part of cell wall- allows molecules to pass; typically small and hydrophilic; sugars, amino acids and ions
What does the ability of the cell to respond to that signal depend on?
whether or not they have the receptor specific to that signal
What are the 3 major stages of signalling?
reception, transduction and response
define reception
Detection of a signal coming from outside of the cell
Steps of reception
- A signaling molecule attaches to the receptor which causes a conformation change of the receptor (which is a protein)
- Stimulates a series of relay molecules in signal transduction pathway
- Activates a cellular response
Define what a ligand is
signal molecule
define transduction
links reception and response together including amplifying a signal by activating many molecules in a complex pathway
Define what a phosphorylation cascade is?
acts as a molecular switch turning activities on or off as required
Phosphorylation
Protein kinases transfer phosphates from ATP to protein, a process called phosphorylation; amplification
Dephosphorylation
Protein phosphatases remove phosphates from proteins
When do dephosphorylation occur?
when signaling molecule concentration falls
define response
specific cell response to the signal molecule
nuclear and cytoplasmic responses- alteration of cytosolic activity or changes in transcription of genes
Describe G-protein coupled receptors mechanism of action
1.G-protein coupled receptor is activated by signalling molecule (ligand)- Epinephrine or could be any other molecule (yeast mating as well) . Receptor is activated and changes shape
2.G protein with GDP attaches to the cytoplasmic side of the receptor.
4.GDP becomes phosphorylated and becomes GTP by GTPase.
5. G protein is activated
6.The G-protein leaves and bind to 1st enzyme, changing the shape of the enzyme
7.triggers next step to cell response
8.G protein functions acts as a GTPase enzyme, which hydrolyzes its bound GTP to GDP, thereby inactivating the G protein, allows rapid shutdown of pathway when signalling molecule is not present
9. G protein is available for reuse
Describe receptor tyrosine kinase mechanism of action
1.Signalling molecule (ligand) attached to the two separate inactive monomers resulting in the two monomers becoming dimers. This activates the tyrosine kinase region.
2.Activated tyrosine kinases are fully activated through phosphorylation through ATP (phosphate leaves ATP and goes to tyrosine and ATP→ADP)
4. Specific relay proteins will bind to a specific phosphorylated tyrosine resulting in a structural change that activates the protein. Activated inactive relay proteins that will conduct the cellular responses
Describe the mechanism of action for ligand gated channels
1.A signalling molecule (ligand) attaches causing a conformational change in the protein causing it to open
2.Intiates a cellular response in which the ions pass through changing the concentrations of ions inside the cell
3.Ligand leaves, the gate is closed and no ions enter the cell.
Describe the mechanism of action for testosterone
1.Testosterone diffuses through the membrane
2.Forms a hormone receptor complex by binding to the receptor
3.Goes inside the nucleus
4.Acts as a transcription factor to transcribe DNA into mRNA=protein
Describe what initiates transduction
a shape of the first protein and the rest of the molecules will be activated and their shapes will be changed until the one protein producing the response is activated
Define tyrosine kinases
enzyme that catalyzes the transfer of a phosphate group from ATP to the amino acid tyrosine.
What is cylclic AMP?
Acts as a 2nd messenger for protein kinase A- cell response
What is the relationship between adenylyl clyclase and cAMP?
Adenylyl cyclase: enzyme in plasma membrane that converts ATP to cAMP in response ot an extracellular signal
What is the relationship between phosphodiesterase and clyclic AMP?
Phosphodiesterase: can turn cAMP into AMP
Describe the steps of a cAMP pathway
- The ligand epinephrine binds to plasma membrane receptor of cell.
- plasma membrane protein receptor activates adenylyl cyclase
- adenylyl cyclase converts ATP to cAMP
4.cAMP concentration in cytosol increases - cAMP activates another protein, usually a protein kinase “A”
6.protein kinase “A” begins phosphorylation cascade of other proteins
Define calcium ions as 2nd messengers
gated channels
describe the steps of calcium ions of IP3 pathway
1.Signaling molecule binds to membrane receptor
2.Phospholipase C is activated
3.Plasma membrane phospholipids is broken down into DAG and IP3.
4.IP3 binds to IP3 gated calcium channel receptors in ER, causing channel to open.
5. Calcium ions flow out of ER.
6. Calcium levels in cytosol increase
7. Calcium ions activate next protein in signal pathway.
Describe signal transduction and mating in yeast Sacchromyces cerevisiae
- A and a; a factor binds to proteins of nearby a cells and vice versa. Causes the cell to grow towards each other an dbring other cellular changed
- Results in fusion
-Received signal is converted to a specific cellular response= signal transduction pathway
Describe plasma membrane protein receptors
signaling molecules are hydrophilic so they cannot diffuse through the membrane thus the receptors are outside
Describe intracellular receptors
signaling molecules are hydrophobic so they can diffuse through the membrane and attach to the receptor
E.g. steroid and thyroid hormones (testosterone)
Examples of termination of the signalling
- decrease in number of receptors
- relay molecules return to inactive forms
- hydrolysis of GTP bound to G-protein
- phosphodiesterase converts cAMP back to AMP
- inactivation of phosphorylated kinases
What factors depend on what pathway will be activated?
Cell type, signalling molecule and receptor
Define crosstalk
pathways can diverge and converge
What does the hormone-receptor complex serve as?
transcription factors
What are transcription factors?
little units often protein that help transcript a gene
Define scaffolding proteins
attract protein kinases to them at the same time= multiple signalling pathway
What role does CED-4 and CED-3 play in apoptosis?
shut off CED-9; the death signalling molecule binds to CED-9 which becomes inactive so CED-4 and CED-3 could become active and perform apoptosis
