Week 6 (cell Signalling) Flashcards
Describe cellular communication
- no cell exists in isolation
- signals must be received and processed from the environment and from other cells
- signals are generally transmitted across the environment in the form of soluble molecules
- these molecules must be detected and appropriate responses produced
What are the different modes for the cell to receive stimuli (cell signalling)?
- Contact dependent
- Paracrine
- Synaptic
- Endocrine
- Autocrine
What is autocrine signalling?
Self signalling
Why are receptors on the cell membranes necessary?
- membrane is impermeable to large soluble molecules
- some are transported across the membrane
- others are detected outside of the cell nd a signs, transmitted into the cell
- this is the role of receptors
What is a ligand?
A molecule that binds to a receptor
Describe the relationship between receptors and ligands
- Some receptors have one ligand whereas others have many
- Different ligands produce different responses at the same receptor e.g agonist/antagonist
Receptors detect a vast array of signals:
Dissolved gases Amino acids Peptides/proteins Retinoids Fatty acids Nucleotides
describe the plasma membrane in relation to being an interaction surface with the surrounding of a cell
- receptors are generally integral (transmembrane) proteins
- the extracellular region detects ligands
- the intracellular region interacts with effectors
Where can receptors be located?
- receptors can be either on the cell surface (peripheral proteins) or intracellular (integral proteins)
How do receptors modify cellular responses?
Signalling cascades
What 3 main domains do receptors have?
Extracellular domain
Transmembrane domain
Intracellular domain
What are intracellular mediators?
Proteins that transmit the signal from the receptor to the effector enzymes
What are effector enzymes
Bring about changes in cell resulting in, and affected by the production of second messenger
For a receptor to be able to detect a signal it must contain?
- contains at least one binding site for a ligand
What are the 4 main types of receptors?
- Ligand gated ion channels (cell surface receptor)
- G protein coupled receptors (cell surface receptor)
- Receptor tyrosine kinase (cell surface receptor)
- Intracellular receptor
What are receptor tyrosine kinases?
- transmembrane proteins
- bind extracellular ligand (comes as a dimer or has 2 binding sites)
- the dimer (consists of two of the same proteins that come together)
- extracellular ligand binding domain
- intracellular kinase domain (possesses enzymatic activity- can phosphorylate proteins)
What is the function of Kinases?
- kinases add phosphate group to amino acids in proteins using ATP
- kinases phosphorylate proteins
Explain phosphorylation in signalling
- often used as a signalling mediator
- phosphorylation can cause either protein activation or inactivation
- phosphorylation is reverses by phosphatases
Explain receptor tyrosine kinases (RTK)
- RTK phosphorylates tyrosine residues on a variety of target proteins in response to ligand binding
- ligand binding site formed from both molecules of the dimer
- the two molecules come together and trap the ligand
- this results in two intracellular domains coming together
What does phosphorylation do in receptor tyrosine kinases?
-Changes the properties of the kinase domain and allows it to interact with other molecules because phosphorylation sites are recognised by cyosolic proteins and bind to them thus conveying the signal further
How can RTK use monomeric GTPases as molecular switches?
- The GTPase protein is “off” when GDP is bound
- Then it receives a signal and GTP replaces GDP
- GTPase protein now bound to GTP and is now “on” in its activated state allowing it to pass the signal on
- GTP is hydrolysed by the GTP which converts the protein back to its inactivated state