1. Key Area 4- Communication and Signalling Flashcards
How do multicellular organisms signal between cells?
Using extracellular signalling molecules
What are 3 examples of extracellular signalling molecules?
Steroid hormones, peptide hormones and neurotransmitters
What are receptor molecules of target cells?
They are proteins with a binding site for a specific signal molecule
What effect does binding have on the receptor molecule?
Changes the conformation of the receptor which initiates a response within the cell
Why might signalling molecules have different effects on different target cell types?
Due to differences in the intracellular signalling molecules and pathways that are involved
In multicellular organisms, what might different cell types show?
A tissue specific response to the same signal
What are hydrophobic signalling molecules?
They can diffuse through the phospholipid bilayers of membranes and so bind to intracellular receptors
What are the receptors for hydrophobic signalling molecules?
Transcription factors
What are transcription factors?
They are proteins that when bound to DNA can either stimulate or inhibit initiation of transcription
What are 2 examples of hydrophobic signalling molecules?
The steroid hormones: oestrogen and testosterone
Where do steroid hormones bind to specific receptors?
Steroid hormones bind to specific receptors in the cytosol or the nucleus.
Describe the hormone-steroid complex in terms of steroid hormones?
The hormone-receptor complex moves to the nucleus where it binds to specific DNA sequences called hormone response elements (HREs) and affects gene expression. Binding at these sites influences the rate of transcription, with each steroid hormone affecting the gene expression of many different genes
Where do hydrophilic signalling molecules bind to?
They bind to transmembrane receptors and do not enter the cytosol
What are 2 examples of hydrophilic signalling molecules?
peptide hormones and neurotransmitters
When do transmembrane receptors change conformation?
When the ligand binds to the extracellular face. The signal molecule does not enter the cell but the signal is transduced (converted into another form) across the plasma membrane
How do transmembrane receptors act as signal transducers?
By converting the extracellular ligand-binding event into intracellular signals which alters the behaviour of the cell
What do transduced hydrophilic signals often involve?
G-proteins or cascades of phosphorylation by kinase enzymes
What is the function of G proteins?
Relay signals from activated receptors to target proteins such as enzymes and ion channels
What is an advantage of phosphorylation cascades?
They allow more than one intracellular signalling pathway to be activated
What does phosphorylation cascades involve?
They involve a series of events with one kinase activating the next in the sequence and so on which can result in the phosphorylation of many proteins as a result of the original signalling event
What does phosphorylation cascades involve?
They involve a series of events with one kinase activating the next in the sequence and so on which can result in the phosphorylation of many proteins as a result of the original signalling event
What does binding of the peptide hormone insulin to its receptor result in?
Binding of the peptide hormone insulin to its receptor causes a conformational change that triggers phosphorylation of the receptor
What does phosphorylation at the receptor of the peptide hormone insulin create?
It starts a phosphorylation cascade inside the cell, which eventually leads to GLUT4 containing vesicles being transported to the cell membrane of fat and muscle cells.
