9. Cell Signalling Flashcards
What is cell signalling
Transferring information from outside of the cell to get a response from inside the cell
What are the four essential elements of cellular communication
- signalling cell
- signalling molecule (etc. peptides, lipids, gases, varies)
- receptor protein
- responding cell
what is epinephrine, and what is its role in cellular communication
the hormone adrenaline
- signalling molecule
released from the adrenal glands (located above the kidneys
circulates through the body and acts on many cells, including your heart. this lets it beat more strongly and quickly, delivering more oxygen
How is cell signalling related to how bacteria take up DNA from the environment?
- When there is a lot of bacteria, the concentration of the signalling peptide is high
- these then bind to receptors which simulate DNA uptake
this occurs when the bacteria population reaches a certain density
called quorum sensing
What is quorum sensing?
bacteria cell-to-cell communication
- bacteria use signalling molecules to detect population density
- allow them to coordinate behaviour + regulate gene expression
What is receptor activation
when a signalling molecule binds to a receptor on a responding cell
- usually causes a conformational change in the receptor
What are the 4 steps of cell signalling
- Receptor activation
- signal binds to a receptor and activates it - Signal transduction
- signal is transmitted to the interior of the cell by a signal transduction pathway - Response
- cell responds (etc. activating an enzyme, turning on transcription of a gene) - Termination
- response is terminated so we can receive new signals
What is signal transduction
- Triggered by the activated receptor
- chain reaction; one molecule activates the next molecule, so on
- signal is usually amplified at each step
What determines whether or not a cell responds to a signalling molecule?
If it has receptors that can bind to the signalling molecule
What is endocrine signalling
Signalling using molecules that travel through the bloodstream
What type of signalling is estrogen and testoterone
endocrine;
- hormones from the ovaries and tests travel to target cells in other areas of the body during puberty
What is paracrine signalling
signalling to nearby cells (~20 cell diameters), where the signalling molecule moves using diffusion
- signals usually take form in a small, water-soluble molecule (etc. growth factor)
What is a growth factor
Type of signalling molecule that causes the responding cell to grow, divide, or differentiate
- paracrine signalling
What is autocrine signalling
When the signalling and responding cell are the same
- etc. during the development of an embryo (when cells differentiate into their specialized cell type, autocrine signalling is sometimes used to maintain this developmental decision)
What is contact-dependent signalling
When a cell communicates with another cell through direct contact; without using a signalling molecule
- two transmembrane proteins (one on signalling and one on receiver) act as signalling molecules + receptors
- etc. Brain development
What is a ligand
The signalling molecule
What is the ligand-binding site
The specific part of the receptor protein that the ligand binds to
- covalent bond, very specific
Where are the receptors for polar/non-polar signalling molecules located?
polar: cell-surface receptor
- signalling molecules cannot pass through cell membrane
- cell-surface receptor: trans membrane protein with an extracellular, transmembrane, and a cytoplasmic domain
non-polar: intracellular receptor
- small, non-polar molecules pass through cell membrane and activate cytoplasmic receptors (inside the cell)
- in cytosol or nucleus
What are the three types of cell-surface receptors?
- G protein coupled receptors
- Receptor kinases: enzymes
- Ligand-gated ion channels
What are phosphates and what do they do
enzymes that removes phosphate groups from another molecule
What are 3 common characteristics of G protein-coupled receptors
- Similar structure: a single polypeptide chain that has 7 transmembrane spanning regions, the ligand-binding site on the outside of the cell and the portion that binds to the G protein on the inside of the cell
- They associate with a G protein when activated
- Cellular responses to their activation tend to be rapid and short lived
Name the parts of the G protein, and what indicates if it is on/off
- alpha, beta, gamma
- alpha part binds to GTP if it is active, and GDP if it is off
Note: we are not removing/adding phosphates, but rather swapping the entire nucleotide when switching between GTP and GDP
Name that steps that happen during the activation of a G protein receptor
- ligand binds to the ligand-binding site, conformational change to the receptor
- G protein binds to the receptor, swaps GDP->GTP and becomes activated
3; alpha segment separates and activates a target protein
Name the steps that are involved in signal amplification for adrenaline in the cytosol
- adrenaline ligand binds to the ligand-binding site, conformational change to the receptor
- G protein binds to the receptor, swaps GDP->GTP and becomes activated
- alpha segment separates and activates a target protein (adenylyl cyclase)
- activated adenyly cyclase converts ATP to cAMP (called the “second messenger”)
- Protein kinase A is activated by cAMP
- Each protein kinase A enzyme phosphorylates many protein targets, turning ATP->ADP
At what steps in the activation of the G protein coupled receptor activation is the signal amplified
- A single activated G protein coupled receptor activates many G proteins
- Each adenylyl cyclase enzyme produces large amounts of second messenger cAMP (activating many molecules of protein kinase A)
- Each activated protein kinase A phosphorylates multiple protein targets
What is binding affinity
The time that the ligand binds to the receptor and how tightly the receptor holds it
How is the signal of a G protein receptor terminated?
- ligand detaches from binding site (no more activated G proteins)
- G proteins convert GTP->GDP (no more activated adenylyl cyclase enzyme)
- enzymes in the cytosol degrade cAMP
- phosphates remove phosphate groups from activated proteins
What is dimerization
Two proteins of the same shape (mirror images), and are side by side
- interact and become one whole protein when activated
Explain the steps in the activation of a receptor kinase
- signalling molecule attaches to inactive receptor
- dimerization of the receptor
- dimerized receptor uses a bit of ATP, each member of the receptor attaches phosphate groups to the other member
- phosphate groups provide binding sites for intracellular signalling proteins
Explain the process of wound healing with respect to cell signalling
Cell signalling with receptor kinases
