Cell Signalling Flashcards
Scientists have hypothesized that signalling mechanisms first arose in?
Prokaryotes
Paracrine signalling acts on?
Nearby cells (growth factors)
Synaptic signalling acts on?
Neurons
Hormones are an example of what type of cell signalling?
Endocrine signalling (Long distance)
What are the 3 stages of signal transduction?
- Reception
- Transduction
- Response
What is reception?
A signalling molecule binds to a protein receptor and makes it do stuff (change shape/chemical modifications)
What is transduction?
A series of relay molecules carry the signal into the cell via signal transduction pathways
What is a response?
The signal transduction triggers a response (gene expression, catalysis of enzymes, etc.)
Is ligand/receptor binding specific or vague?
Specific (A specific signal molecule will only bind and activate one specific receptor protein)
What types of proteins can receptors be found in, in the plasma membrane?
Integral proteins
How do G protein-coupled receptors work?
When a signalling molecule binds to the binding site, the domain shifts, changing the loops inside the cell, revealing a site inside the cell that can bind proteins
What are GPCRs composed of?
- A specific receptor that binds a specific ligand
- A G protein
- An enzyme that transfers the signal to the signal transduction pathway
What is the “on” state for a G protein?
GTP
What is the “off” state for a G protein?
GDP
What initiates the signal transduction inside the cell?
Cyclic AMP (cAMP)
When activated, what are the steps that the G protein takes?
- Detach from the receptor and activates the enzyme
- Makes cyclic AMP to initiate the signal transduction inside the cell
- G protein hydrolyses the GTP to GDP + inorganic phosphate, inactivating the G protein
Is ligand binding reversible?
Yes
What are receptor tyrosine kinases? (RTKs)
Catalyzes the transfer of phosphate groups from ATP to the amino acid tyrosine
Where is the ligand binding site?
The outside of the cell
Describe the off state of RTKs
Single proteins that are embedded in the membrane by a single alpha helix
What happens when a ligand binds to the receptors? (RTKs)
The two monomers come together to form dimers in a process called dimerization
What does dimerization cause?
Activates the receptor
What does the area of cytoplasmic domains with the phosphorylated tyrosines act as?
Docking sites for proteins to bind and become activated
What does each activated relay protein trigger?
A transduction pathway, leading to cellular response
What are the function of RTKs in humans?
- Triggering cell division
- Differentiation of cells into different cell types
- Survival of the cell: deciding if it will go into apoptosis or not
What is apoptosis?
Programmed cell death
What are ligand-gated ion channels?
A channel that allows or blocks the flow of specific ions through a channel in the receptor
How do ligand-gated ion channels work?
The ligand binds to the receptor, changing its shape, allowing ions to flow through via the concentration gradient. When the ligand dissociates from the receptor, the channel reverts to its original shape, blocking the ions
What is intracellular receptor signalling?
Ligands that cross the plasma membrane to bind to receptors in the cytosol
What are transcription factors?
Proteins that bind DNA at specific nucleotide sequences and turn on the transcription of specific genes
How does apoptosis work?
Genes ced-3 and ced-4 encode for the cell death proteins
When a cell death signal is received, it deactivates ced-9 which no longer inhibits ced-4. Ced-4 activates ced-3 which activates other enzymes that break down the cell
What is the name of proteases that break up proteins?
Caspases
In humans, apoptosis is controlled by how many caspases?
Around 15
What are the types of receptors?
G protein-couple receptors
Receptor tyrosine kinases
Ion channel receptors
Taste and smell signalling is done through?
GPCR’s
