1.4 Communication and Signalling Flashcards
How do cells Communicate?
cells use extracellular signalling molecules such as steroid hormones, peptide hormones and neurotransmitters.
Describe the process of cell signalling
Firstly, the target cell must have receptor protein molecules with a binding sight that is specific to the signalling molecule.
When binding occurs, it changes the conformation of the receptor in some way that changes the behaviour of the cell (response).
How does cell signalling differ between cell types?
Different cell types produce specific signals that can only be detected and responded to by cells with the specific receptor. Signalling molecules may have different effects on different target cell types due to differences in the intracellular signalling molecules and pathways that are involved. In multicellular organisms, different cell types may show a tissue-specific response to the same signal.
How do hydrophobic signalling molecules travel through plasma membranes? and what does this mean for their proteins?
Hydrophobic signalling molecules can diffuse directly through plasma membranes because the tails of the phospholipids in the membrane are also hydrophobic. This means that their receptor proteins can be deep in the cytoplasm or in the nucleus itself (no receptors on membrane surface).
Give an example of a hydrophobic signalling molecule
The steroid hormones
What is a transcription factor?
A transcription factor is a protein that binds to DNA and controls the rate of transcription either by stimulating or inhibiting it (they do this by enhancing or blocking the binding of RNA polymerase)
The receptor proteins for steroid hormones (such as testosterone and oestrogen) are…….
transcription factors
What are two examples of steroid hormones?
oestrogen and testosterone
Where do Steroid hormones bind?
transcription factors
What happens when a steroid hormone binds to the receptor protein
When a steroid hormone binds to the receptor protein in the cytosol or nucleus, the conformational change that occurs forms a hormone-receptor complex that is then able to bind to specific sites on DNA and affects gene expression. The hormone-receptor complex binds to DNA sequences called hormone response elements (HREs). Binding at these sites influences the rate of transcription, with each steroid hormone affecting the gene expression of many different genes.
Where are receptor molecules for hydrophilic signals required to be and why?
Hydrophilic signalling molecules, such as peptide hormones and neurotransmitters, require receptor molecules to be at the surface of the cell because they are not capable of passing across the hydrophobic plasma membrane.
Hydrophilic signalling molecules do not enter the…..
and this means……
cytosol
This means that they require the signal to be transduced within the cell
How many stages are involved in transducing a cell and what are they called?
3 stages
- reception
- transduction (of which there are two types)
- response.
Describe stage 1 of transducing a cell
- reception
When the signalling molecule (acting as a ligand) binds to the transmembrane receptor on the outside of the cell, it causes a conformational change in this protein.
What are the two types of transduction
Transduced signals can involve either G-proteins or cascades of phosphorylation by kinase enzymes.
Describe what happens in stage 2 of transducing a cell
Receptor proteins convert the extracellular lignand binding event into an intracellular signal through a signal transduction pathway.
Describe Transduction by G-proteins
G-proteins relay signals from activated receptors to target proteins such as enzymes and ion channels
Describe Transduction by phosphorylation
Phosphorylation cascades allow more than one intracellular signalling pathway to be activated. Phosphorylation cascades involve a series of events with one kinase activating the next in the sequence and so on. Phosphorylation cascades can result in the phosphorylation of many proteins as a result of the original signalling event.
Describe what happens when insulin binds to its receptors
The binding of insulin (a peptide hormone) to its receptor causes a conformational change that triggers the phosphorylation of the receptor.
This starts a phosphorylation cascade inside the cell that triggers the recruitment of GLUT4 glucose transporters (found in vesicles in the cytoplasm) to the cell membrane of fat and muscle cells.
Glucose can then be taken into the cells which lowers the blood glucose level.
What is the role of insulin?
Insulin plays an important role in allowing fat tissue and skeletal muscles to absorb glucose from the bloodstream.
What is Diabetes mellitus
A medical condition that results from the failure of some stage in the insulin-signalling pathway.
Describe Type 1 Diabetes and its treatment
Type 1 diabetes is caused by the failure to produce insulin in the pancreas. It is treated by regular injections of insulin throughout the day.
Describe Type 2 Diabetes and its treatment
Type 2 diabetes is caused by a loss of insulin receptor function. This type of diabetes is usually associated with obesity. It may be treated with medications to lower blood glucose levels along with lifestyle changes.
Exercise also triggers the recruitment of GLUT4 so can improve uptake of glucose to fat and muscle cells.
When is a membrane potential created?
A membrane potential (an electrical potential difference) is created when there is a difference in electrical charge on the two sides of the membrane.
