Unit 1 - Communication and Signalling Flashcards
What do multicellular organisms use to signal between cells?
Extracellular signalling molecules.
Give 3 examples of extracellular signalling molecules.
Steroid hormones, peptide hormones and neurotransmitters.
What are receptor molecules of target cells and how do they initiate a response within the cell?
They 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.
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.
What are hydrophobic molecules?
Molecules that are repelled by water. Also known as non-polar.
What type of signalling molecules can diffuse directly through phospholipid bilayers?
Hydrophobic signalling molecules.
What type of receptors do hydrophobic signalling molecules bind to?
Intracellular receptors called transcription factors.
What are transcription factors?
Proteins that when bound to DNA can either stimulate or inhibit initiation of transcription.
Give 2 examples of hydrophobic signalling molecules.
Steroid hormones oestrogen and testosterone.
Where do steroid hormones bind to specific receptors?
In the cytosol or the nucleus.
What happens to a steroid hormone after it has bound to its specific receptor?
The hormone-receptor complex moves to the nucleus where it binds to specific sites on DNA and affects gene expression.
What are the specific sites on DNA that the steroid hormone-receptor complex binds to?
Specific DNA sequences called hormone response elements.
What does binding of a hormone-receptor complex to hormone response elements (HREs) affect?
Influences the rate of transcription, with each steroid hormone affecting the gene expression of many different genes.
What are hydrophilic molecules?
Molecules that are attracted to water and tends to be dissolved by water. Also known as polar molecules.
What type of receptors do hydrophilic signalling molecules bind to?
Transmembrane receptors.
Give 2 examples of hydrophilic extracellular signalling molecules.
Peptide hormones and neurotransmitters.
What happens when hydrophilic signalling molecules bind to transmembrane receptors?
Transmembrane receptors change conformation. The signal molecule does not enter the cell but the signal is transduced across the plasma membrane.
What is transduction?
Process by which a chemical or physical signal is transmitted through a cell by a series of molecular events resulting in a cellular response.
How do transmembrane proteins 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.
