The Endocrine System: Hormones and Gene Expression

Samuel YangHenok Daniel

4/3/13

Background: Hormone Receptors and Gene Expression

• In the 1970s, experiments suggested that estradiol and various other steroid affect gene transcription after they bind to their receptors.

• It was discovered that inside a steroid hormone receptor, there was a distinctive DNA-binding region known as a zinc finger.– It was also confirmed that steroid-hormone receptors bind to specific spots on

DNA called hormone-response elements.

• After binding to the hormone-response element, the hormone receptor complex binds to DNA, which induces transcription.

• mRNA transcripts are produced, amplifying hormone signal.• Each transcript is translated many times.

• Steroid hormones directly regulate gene expression.

Signal Transduction• Signal Transduction is the phenomenon that allows a message

from a hormone to be changed into a form that is active inside the cell.

• Signal Transduction is broken down into two stages:1. A specific receptor protein on the plasma membrane is activated by a hormone2. A second messenger relays the signal into the cell, which produced a physiological

response.

1. For cell-surface proteins -------->

cAMP: Second Messenger

• cAMP – Cyclic adenosine monophosphate– It is considered a second messenger (non-protein

signal) that increases in concentration inside the cell

– So as a hormone binds to receptor in the cell, the activation of a G protein occurs.

– Synthesis of cAMP from ATP occurs by adenylyl cyclase enzyme• cAMP transfers the signal from the cell surface to the

signaling cascade in the cell

Signaling Cascade: Amplification

• The signaling cascade consists of a series of steps that serve the purpose to amplify a signal from a hormone.

• cAMP bind to protein kinase A• The protein kinase A then activates molecules

of phosphorylase kinase• Phosphorylase kinase activates molecules of

phosphorylase

Presentation

Signaling Cascade: Amplification

• Alpha-1 receptors– Calcium ions and IP3 (inositol triphosphate) serve

as both messenger molecules

– Diacylglycerol (DAG) and cyclic GMP (cGMP) are also second messengers