1.4 - theory Flashcards
How do multicellular organisms signal between cells?
using extracellular signalling molecules.
e.g. steroid hormones, peptide hormones and neurotransmitters.
what are receptor molecules?
proteins with binding sites specific to signalling molecules.
Where are receptors found and what happens once signal molecule is bound to a receptor?
receptors may be inside or on surface of the cell.
binding to receptor triggers series of event within the cell (cascade).
How do effects of signal molecules differ?
may have different effects on different target cells due to different intracellular signals or pathways.
What are hydrophobic signalling molecules?
signalling molecules that can diffuse directly through phospholipid bilayer and therefore bind to intracellular receptors.
What are receptors for hydrophobic signals called and what do they do?
they are transcription factors; proteins that when bound to DNA can either stimulate or inhibit initiation of transcription.
How do transcription factors work?
They enhance or block the binding of DNA polymerase to specific genes, thereby controlling whether gene is transcribed or not.
Give examples of hydrophobic signalling molecules…
oestrogen and testosterone (steroid hormones)
What are Hormone Response Elements (HREs)?
they are the specific DNA sequence that the hormone-receptor complex binds to.
What is thyroxine?
a hydrophobic hormone produce by thyroid gland involved with regulating metabolic rate.
What is the effect of thyroxine when not present?
when not present its receptor protein binds onto DNA in the nucleus, inhibiting the transcription of the gene for Na/K-ATPase.
What is the effect of thyroxine when present?
when present the receptor protein undergoes a conformational change and can no longer bind to DNA, allowing the transcription of the gene for Na/K-ATPase.
results in increase in metabolic rate.
What are hydrophilic signalling molecules?
signal molecules which bind to transmembrane receptors and do not enter the cytosol.
Give examples of hydrophilic signalling molecules…
peptide hormones (insulin) and neurotransmitters.
Describe stage 1 of signal transduction…
the transmembrane receptors change conformation when ligand binds outside the cell; signal molecules does not enter cell, the signal is transduced across the membrane.
