Key Area 4 Flashcards
What does it mean multicellular organisms show division of labour?
That different cells carry out different functions within defined areas of the body
What do multicellular organisms use to signal between cells?
Extracellular signalling molecules
I hate are examples of extracellular signalling molecules?
- steroid hormones
- peptide hormones
- neurotransmitters
What are receptor molecules of target cells?
They are proteins with a binding site for a specific signal molecule.
How are different cell types that produce specific signals detected and responded to by?
Detected and responded to by cells with the specific receptor
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 a multicellular organism, what response might different cell types show to the same signal?
Tissue-specific response
What do hydrophobic signals do?
They can diffuse directly through the phospholipid bilayers of membranes and therefore bind to intracellular receptors.
What are the receptors for hydrophobic signalling molecules?
They are transcription factors
What are transcription factors?
They are proteins that when bound to DNA can either stimulate or inhibit initiation of transcription.
What are examples of hydrophobic signals?
- thyroxine
- steroid hormones (examples are testosterone and oestrogen)
What is the action of steroid hormones?
They bind to specific receptors in the cytosol or the nucleus forming a hormone-receptor complex.
Why does the hormone-receptor complex move to the nucleus?
To bind to specific sites on DNA
What are the specific DNA sequences that the hormone-receptor complex binds to called?
Hormone response elements
What do binding to these sites influence?
They influence the rate of transcription, with each steroid hormone affecting the gene expression of many different genes.
