mechanisms of hormone action

Question 1

Endocrine system consists of organs that secrete hormones… what organ is this?

Answer 1

glands

Question 2

hormones

Answer 2

signaling molecules that are secreted directly into the bloodstream to travel to a distant target tissue

Question 3

At the tissue, hormones bind to

Answer 3

receptors

Question 4

Hormones can be subdivided into 3 categories:

Answer 4

peptides
steroids
amino acid derivatives

Question 5

PEPTIDE HORMONES

Answer 5

• made up of amino acids that are derived from a larger precursor that are cleaved during post translational modification
• are polar and cannot pass through the plasma membrane
• bind to extracellular receptors, where they trigger the transmission of a second messenger
• have rapid onset but are short lived
• travel freely in the blood stream but not require a special carrier
• each step of the signaling cascade can demonstrate amplification of the signal

Question 6

common second messengers are

Answer 6

cyclic adenosine monophosphate (cAMP)
inositol triphosphate (IP3)
calcium

Question 7

The binding of a peptide hormone triggers the receptor to either activate or inhibit an enzyme called ____, raising or lowering the levels of cAMP

Answer 7

adenylate cyclase

Question 8

Protein kinase A

Answer 8

can modify other enzymes as well as transcription factors , thus it can have a rapid or slow effect on the cell

Question 9

overall mechanism of action of a peptide hormone:

Answer 9

peptide hormones bind to membrane - bound receptors to initiate a signal cascade, using second messengers like cAMP

Question 10

STEROID HORMONES

Answer 10

• derived from cholesterol
• minimally polar and can pass through the plasma membrane
• bind to intracellular or intranuclear receptors, where they promote conformation change and bind to DNA, affecting the transcription of a particular gene (causing alterations in the amount of mRNA and protein in the cell)
• effects are slower but are long - lived
• cannot dissolve in the blood stream and must be carried by specific proteins

Question 11

AMINO ACID - DERIVATIVE HORMONES

Answer 11

• modified amino acids
• share some chemical features with peptide hormones and some features with steroid hormones; different amino acid derivative hormones share different features with these other hormone classes
• common examples: epinephrine, norepinephrine, triiodothyronine, and thyroxine

Question 12

Hormones are classified by their

Answer 12

target tissue

Question 13

Direct hormones

Answer 13

major effects in non - endocrine tissues
act directly on a target tissue

• secreted into the bloodstream and travel to a target tissue, where they have direct effects

Question 14

Tropic hormones

Answer 14

major effects in other endocrine tissues
require an intermediate to act

• secretion of another hormone that then travels to the tissue to cause an effect