Identify one similarity and one difference between paracrine cell signalling and cell signalling that forms part of the endocrine system.
Explain why a neurotransmitter such as acetylcholine could be described as a paracrine signalling molecule.
Human muscle cells show paracrine signalling. After muscle cells have been exposed to a substance called palmitate they: • produce a signalling molecule • show an increase in the expression of genes involved in a stress response (stress genes). Scientists carried out three experiments to investigate the signalling molecule produced by muscle cells after exposure to palmitate. Experiment A • Muscle cells were exposed to palmitate. • The palmitate-exposed muscle cells were taken out of the medium containing palmitate and then cultured in nutrient medium for six days. • The palmitate-exposed cells were removed from the nutrient medium and fresh muscle cells were placed in this spent nutrient medium. • The expression of stress genes in the fresh muscle cells was measured after 24 hours. • A control using cells that had not been exposed to palmitate was also performed. Experiment B Experiment A was repeated, but the spent nutrient medium for the palmitate-exposed cells and the control was boiled and then cooled before the fresh muscle cells were added. Experiment C Experiment A was repeated, but the spent nutrient medium from the palmitate-exposed cells and the control was treated to separate the lipid part. This lipid part was added to fresh nutrient medium to culture the new muscle cells.
Suggest how developing muscle cells that express stress genes will be structurally different from normal muscle cells.