U1: KA4 Communication and signalling Flashcards
(50 cards)
Multicellular organisms signal between cells using what?
Extracellular signalling molecules.
What are examples of extracellular signalling molecules?
Steroid hormones, peptide hormones and neurotransmitters.
What are receptor molecules of target cells?
Proteins with a binding site for specific signal molecules.
What initiates a response within the cell?
Binding changes conformation of receptor
Why may signalling molecules have different effects on different target cell types?
Differences in intracellular signalling molecules and pathways that are involved.
Hydrophobic signalling molecules can…
Diffuse directly through phospholipid bilayers of membranes and so bind to intercellular receptors.
The receptors of hydrophobic signalling molecules are transcription factors. What are transcription factors?
Proteins that when bound to DNA either stimulate or inhibit initiation of transcription. They can enhance or block the binding of RNA polymerase to specific genes thereby controlling whether the gene is transcribed and therefore expressed.
Examples of Hydrophobic signals are?
Thyroxine
Steroid hormones - testosterone and oestrogen
Steroid hormones bind to specific receptors in the cytosol or ……
The nucleus forming hormone-receptor complex. The hormone-receptor complex moves to the nucleus where it binds to specific sites on DNA.
The specific DNA sequences that the hormone-receptor complex binds to are called?
Hormone response elements (HREs)
Binding at HREs influences what?
Rate of transcription with each steroid hormone affecting the gene expression of many different genes.
Hydrophilic signalling molecules bind to …..
Transmembrane receptors and do not enter the cytosol.
Why do hydrophilic signals not enter cytosol?
Because they are not capable of passing across the hydrophobic plasma membrane.
When do Transmembrane receptors change conformation?
When ligand binds to extracellular face; the signal molecule does not enter the cell.
What happens after the transmembrane receptor changes conformation?
Signal is transduced across plasma membrane, they act as signal transducers by converting the extracellular ligand-binding event into intracellular signals, which alters the behaviour of the cell.
What do transduction hydrophilic signals often involve?
G-proteins
Cascade of phosphorylation by kinase enzymes.
How do G-proteins work?
Relay signals from activated receptors (receptors that have bound a signalling molecule) to target proteins such as enzymes and ion channels.
Enzymes then catalyse reactions in cell
Ion channels will then either open or close to control ion movement.
Phosphorylation cascades involve a series of events with?
One kinase activating the next
Phosphorylation cascades can result
In?
The phosphorylation of many proteins as a result of the original signaling event.
Phosphorylation allows more than one what?
Intracellular signalling pathway to be activated.
What 2 hormones control levels of glucose?
Insulin
Glucagon
Features of insulin?
Made when there is increase in blood glucose concentration
Made by cells in the pancreas
Hydrophilic peptide hormone
Allows fat tissue and skeletal muscles to absorb glucose from the bloodstream.
How does glucose pass into the cells?
Travelling through a transporter protein called GLUT4 by facilitated diffusion.
Describe type 1 diabetes.
Failure to produce insulin in pancreas. Treated with regular injections throughout the day
