Hormones: Answer to H-01


Original Question



The answer is  (a)


The mechanism of the “second messenger” is used by hormones that can not cross the plasma membrane, like peptides hormones and hormones derived from amino acids (T3 is an exception, since it has a hydrophobic lateral chain). Since these hormones can not cross the plasma membrane, they interact with a receptor located in the membrane, like this transmembrane protein:







The interaction between the receptor (a membrane protein that frequently has seven intramembrane domains) and the hormone provokes the activation of one of the G-Proteins, a family of amphipatic proteins associated to the inner surface of the plasma membrane.


In this graphic, the receptor is represented as a transmembrane protein in blue, and the G-Protein is represented in pink color:








The interaction between the hormone and the receptor provokes changes in conformation of the G-Protein associated to the receptor, facilitating the release of GDP and the binding of GTP in the alpha subunit of the G-Protein.  The alpha subunit-GTP complex dissociates from the Beta-Gamma subunits, and it can produce activation of membrane associated enzymes like Adenyl Cyclase, Phospholipase C or other enzymes, depending on the specific Hormone-Receptor-G Protein system.


If the GTP-alpha subunit complex released in the Hormone-Receptor-G Protein System activates Adenyl Cyclase, then this enzyme catalyses the transformation of ATP to cAMP; if the system activates Phospholipase C, then it produces the hydrolysis of phosphatidyl inositol diphosphate, releasing Inositol triphosphate (IP3) and diacylglycerol, that act as second messengers.


Molecules as different as cAMP, IP3, diacylglicerol,  Ca++ and Nitric Oxide can function as second messengers.


More information about this topic can be found in the following links:


Kimball, J.K. :Second Messengers


King, M.W. : The Medical Biochemistry Page





Q: Hormones, Receptors and Second Messengers



Question H-01


A typical characteristic of hormones that use the second messenger mechanism is that:


a)     they can not pass through the plasma membrane

b)     the receptor is located in the cytosol

c)      the receptor is located in the nucleus

d)     the receptor is not necessary

e)     the receptor binds to the hormone to allow it to enter the cell



      Answer to H-01



Question H-02


Receptors for steroid hormones can be found:


a)     in the plasma membrane

b)     in the cytosol

c)      in the mitochondria

d)     in the ribosomes

e)     in the Golgi apparatus


 Answer to H-02



Question H-03


The binding of insulin to the insulin receptor triggers:


a)     the interaction of the receptor with a protein G

b)     the activation of  adenyl ciclase

c)      the activation of phospholipase C

d)     a decrease of GLUT4 in the plasma membrane

e)     tyrosine kinase activity


      Answer to H-03



Question H-04



Which of the of the following hormones use cAMP as second messenger?


a)     Insulin

b)     Thyroxin

c)      Progesterone

d)     Aldosterone

e)     Glucagon


Answer to H-04



Question H-05


Hormones that act through Phospholipase C activation, in fact are using three second messengers:



a)     cAMP, Diacylglycerol and Ceramide

b)     cAMP, , Ca++ and Diacylglycerol

c)      cAMP , Ca++ and Inositol 1,4,5 triphosphate

d)     cAMP, Diacylglycerol and Inositol 1,4,5 triphosphate

e)     cAMP, Ca++ and ceramide

f)       Ca++, Diacylglycerol and ceramide

g)     Ca++, Diacylglycerol and Inositol 1.4.5 triphosphate

h)    Ca++, Ceramide, Inositol 3,4,5 triphosphate

i)       Ceramide, Diacylglycerol and Inositol 1,4,5 triphosphate.


  Answer to H-05