Communication and Signalling Flashcards
How do multicellular organisms signal between cells ?
-Multicellular organisms signal between cells using extracellular signalling molecules
-Steroid hormones, peptide hormones, and neurotransmitters are examples of extracellular signalling molecules.
-There are two main forms of communication; nervous and hormonal
What are receptors ?
-Receptor molecules of target cells are proteins with a binding site for a specific signal molecule
-Binding changes the conformation of the receptor, which initiates a response within the cell
Explain the specificity between signal and cells
-Different cell types produce specific signals that can only be detected and responded to by cells with the specific receptor
How can signals cause different responses ?
-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 a multicellular organism, different cell types may show a tissue-specific response to the same signal
Also links to specificity between signal and receptors
What are the two types of signalling molecules ?
1) Extracellular hydrophobic
2) Extracellular Hydrophilic
What are examples of extracellular hydrophobic signalling molecules ?
-The steroid hormones oestrogen and testosterone are examples of hydrophobic signalling molecules
-Steroid hormones bind to specific receptors in the cytosol or the nucleus
What are examples of extracellular hydrophilic signalling molecules ?
Peptide hormones (such as insulin) and neurotransmitters
Explain hydrophobic signals and control of transcription
1) Hydrophobic signalling molecules can diffuse directly through the phospholipid bilayers of membranes, and so bind to specific intracellular receptors, in the cytosol or the nucleus
2) The receptors for hydrophobic signalling molecules are transcription factors; proteins that when bound to DNA can either stimulate or inhibit initiation of transcription.
3) The hormone-receptor complex moves to the nucleus where it binds to specific sites on DNA and affects gene expression
4) 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 (HREs). Binding at these sites influences the rate of transcription, with each steroid hormone affecting the gene expression of many different genes.
Why might not all cells respond to testosterone ?
-Testosterone is a steroid hormone, and an extracellular hydrophobic signalling molecule.
-All cells might not respond to testosterone as only target cells possess the appropriate regulatory proteins.
What do hydrophilic signalling molecules require to transmit a signal into a cell ?
Hydrophilic signalling molecules require receptor molecules at the surface of the cells because they are not capable of passing across the hydrophobic plasma membrane.
Describe hydrophilic signal transduction ?
1) Hydrophilic signalling molecules bind to transmembrane receptors and do not enter the cytosol
2) 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 across the plasma membrane
3) Transmembrane receptors act as signal transducers by converting the extracellular ligand-binding event into intracellular signals, which alters the behaviour of the cell
4) Transduced hydrophilic signals often involve G-proteins or cascades of phosphorylation by kinase enzymes
How do G-proteins relay signals in a cell ?
G-proteins relay signals from activated receptors (receptors that have bound a signalling molecule) to target proteins such as enzymes and ion channels.
-G-proteins possess quaternary structure (made of connected polypeptide subunits)
How do phosphorylation cascades (phosphorylation cascades by kinase enzymes) relay a signal in a cell ?
-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; allow more than one intracellular signalling pathway to be activated
How does insulin promote cell glucose uptake ?
Triggers recruitment of GLUT4 (does facilitated diffusion)
-Binding of the peptide hormone insulin (hydrophillic) to its receptor causes a conformational change which tirggers phosphorylation of the receptor. This causes an intracellular phosphorylation signalling cascade, which eventually leads to GLUT4-containing vesicles being transported to the cell membrane of fat and muscle cells.
What causes type 1 diabetes and how is it treated ?
-Diabetes mellitus can be caused by failure to produce insulin (type 1)
-Also known as insulin-dependent diabetes or juvenile diabetes
-Treated with regular insulin injections throughout the day