Communication and Signalling Flashcards
How do multicellular organisms signal between cells?
They signal between cells using extracellular signalling molecules
Examples of extracellular signalling molecules
Steroid hormones, peptide hormones and neurotransmitters
what are receptor molecules
receptor molecules of target cells are proteins with a binding site for a specific signal molecule
What does binding do to a receptor and response
Binding changes the conformation of the receptor, which initiates a response within the cell
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 involved
Why are molecules specific to receptors
different cell types may show a tissue-specific response to the same signal
What can hydrophobic signals do?
They can diffuse directly through the phospholipid bilayers of membranes, and so bind to intacellular receptors.
What are the receptors called for hydrophobic signalling
Transcription factors
What are transcription factors?
Are proteins that when bound to DNA can either stimulate or inhibit initiation of transcription.
What do steroid hormones bind to and where
Steroid hormones bind to specific receptors in the cytosol or the nucleus
What are examples of hydrophobic signalling molecules
Steroid hormones, testosterone and oestrogen.
The hormone-receptor complex moves to the nucleus where it binds to specific sites on DNA and affects gene expression
The hormone receptor complex binds to specific DNA sequences called Hormone response elements ( HRE’s ). Binding at these sites influences the rate of transcription, with each steroid hormone affecting the gene expression of many different genes.
What can hydrophilic signals do?
They can bind to transmembrane receptors and do not enter the cytosol
What are the types of hydrophilic signals
Peptide hormones
Neurotransmitters
What happens to transmembrane proteins when a ligand binds?
They change conformation when a ligand binds
As hydrophilic signals do not enter the cytosol how does the signal get through?
The signal molecule does not enter the cell but it is transduced across the membrane.
How do transmembrane receptors act as signal transducers?
They convert the extracellular ligand-binding event into intracellular signals, which alters the behaviour of the cell.
What do transduced hydrophilic signals involve?
G-proteins or cascades of phosphorylation by kinase enzymes.
What are G-proteins and their function?
G-proteins relay signals from activated receptors (receptors that have bound a signalling molecule) to target proteins such as enzymes and ion channels.
What do phosphorylation cascades allow?
They allow more than one intracellular signalling pathway to be activated.
What brings about a phosphorylation cascade?
Phosphorylation cascades involve a series of events with one kinase activating the next in the sequence and so on.
What is a result of phosphorylation cascades?
Phosphorylation cascades can result in the phosphorylation of many proteins as a result of the original signalling event.
What is the result of the peptide hormone insulin to its receptors?
It results in an intracellular signalling cascade that triggers recruitment of GLUT4 glucose transporter proteins to the cell membrane of fat and muscle cells.
What does the binding of insulin do to the receptor?
Binding of insulin to its receptor causes a conformational change that triggers phosphorylation of the receptor. This starts a phosphorylation cascade inside the cell, which eventually leads to GLUT4 containing vesicles being transported to the cell membrane.
What are the features of type 1 diabetes?
Failure to produce insulin
What are the features of type 2 diabetes?
Loss of receptor function and is generally associated with obesity
How can exercise improve type 2 diabetes?
Exercise triggers recruitment of GLUT4, so can improve uptake of glucose to fat and muscle cells in subject with type 2.
