Epinephrine Receptors (HL) (HL IB Biology)

• A hormone called epinephrine (also known as adrenaline) can act to increase blood glucose concentration in response to biological stress
• Epinephrine binds to receptors on the outside of a cell and brings about an intracellular response using a mechanism of action known as the second messenger model
  • Second messengers are molecules/ions inside cells that relay signals received by cell-surface receptors

The second messenger model

• Epinephrine binds to specific receptors on the membrane of liver cells
• This causes the enzyme adenylyl cyclase to change shape and become activated
• Active adenylyl cyclase catalyses the conversion of ATP to the second messenger, cyclic AMP (cAMP)
• cAMP binds to protein kinase A enzymes, activating them
• Active protein kinase A enzymes activate phosphorylase kinase enzymes by adding phosphate groups to them
• Active phosphorylase kinase enzymes activate glycogen phosphorylase enzymes
• Active glycogen phosphorylase enzymes catalyse the breakdown of glycogen to glucose
  • This process is known as glycogenolysis
• The enzyme cascade described above results in the release of glucose by, e.g. cells in the liver, to increase blood glucose concentration

Epinephrine receptors diagram

The effect of adrenaline is amplified so that each molecule can stimulate many molecules of cAMP, which in turn activate many enzymes

NOS: Students should be aware that naming conventions are an example of international cooperation in science for mutual benefit

• The work of scientists does not take place within the confines of a laboratory, or even a single country, but can have implications for the work of other scientists around the world
• Because of the international nature of scientific research, it is essential that scientists are able to communicate with each other clearly about their work
• For scientific communication to be effective and allow collaboration, it is essential that scientific language enables scientists to be sure that they are talking about the same thing
• With this in mind, when new names are coined, there are mechanisms which are applied to construct a logical and universal term.
• In the case of adrenaline and epinephrine, the two terms were coined using the idea that the hormone is produced from the adrenal glands located just at the top of the kidneys'
  • Adrenaline comes from the Latin translating to 'at kidney'
    • 'ad' which means 'at'  
    • 'ren' which means 'kidney'
  • Epinephrine comes from ancient Greek translating to 'above kidney'
    • 'epi' which means 'above'
    • 'nephros' which means 'kidney'
• In the case of adrenaline/epinephrine, both names are in common use by scientists in different parts of the world; this is very unusual