17.5- Target cells interactions with hormones

Question 1

What are the steps for lipid soluble hormones creating an effect with a cell?

Answer 1

1) Unbound hormone diffuses readily though the plasma membrane and binds with an intracellular receptor in the cytosol or the nucleus to form a hormone receptor complex.
2) The hormone receptor complex binds with a specific DNA sequence called HRE (hormone response element).
3) Binding with the HRE stimulates mRNA synthesis.
4) mRNA exist the nucleus and is translated by a ribosome in the cytosol. A new protein is synthesized.

Question 2

What are some descriptors of lipid-soluble hormones?

Answer 2

Small, non-polar, and lipophilic

Question 3

What does the change in protein synthesis cause?

Answer 3

An alteration in cell structure

Or shift in the target cells metabolic activities if the newly synthesized proteins are enzymes.

Question 4

How do water soluble (proteins and biogenic amines except thyroid hormone) hormones effect cells?

Answer 4

Hormone binds to a plasma membrane receptor.

This initiates signal transduction pathway.

Question 5

Signal transduction pathway

Answer 5

In this pathway the hormone is the signaling molecule/ fist messenger.
This binding to the receptor on the plasma membrane results in the forming of a different molecule in the cell called a second messenger.
Second messenger modifies some cellular activity.

Question 6

What are the two most common Signaling Transduction Pathways?

Answer 6

Adenylate cyclase activity
Phospholipase C activity
Both these pathways use a intraplasma membrane complex called a G protein. (named based on its ability to bind base guanine nucleotide)
Guanine diphosphate- bound when G protein is in its inactive state.
Guanine triphosphate- bound to G protein when it is its active state.
When a hormone binds to a receptor on the outside of the plasma membrane, it moves G protein from guanine diphosphate to guanine triphosphate and makes it active.
The G protein then moves across the inside of the plasma membrane causing the formation or availability of a second messenger.

Question 7

What are the two enzymatic cascades that movement of the G protein causes?

Answer 7

Adenylate cyclase activity

Phospholipase C activity

Question 8

Describe the adenylate cyclase activity

Answer 8

Activated G protein moves along the inside of the plasma membrane where it binds to the plasma membrane protein adenylate cyclase.
Activated adenylate cyclase increases the formation of the second messenger cAMP from ATP.
cAMP activate protein kinase A (a phosphorylating enzyme)
Phosphorylation results in activation or inhibition of whatever molecule is phosphorylated.
Examples of hormones that cause this cascade are glucagon and thyroid stimulating hormone.

Question 9

Describe the phospholipase C activity

Answer 9

Activated G binds to and activates phospholipase C.
Phospholipase 2 splits PIP2 into two messenger- DAG and IP3.
DAG activates protein kinase C.
IP3 increase Ca2+ in the cytosol by stimulating Ca2+ release from the endoplasmic reticulum and entry of Ca2+ across the plasma membrane from the interstitial fluid.
Ca2+ acts as a third messenger to activate protein kinase enzymes. (Ca2+ does this directly or by first binding to calmodulin)
Ca2+ may also alter the activity of ion channels in the plasma membrane.
Examples of this are: oxytocin and antidiuretic hormone.

Question 10

What does DAG do?

Answer 10

This is a secondary messenger that remains in the plasma membrane.
It activates protein kinase C.
Protein kinoase C phosphorylates other molecules.

Question 11

What does IP3 do?

Answer 11

Leaves the plasma membrane and enters the cytosol.
It then causes the ER to release Ca2+ or opens Ca2+ channels in the plasma membrane allowing Ca2+ to defuse into the cell.
The Ca2+ acts as another messenger that activates protein kinase enzymes directly or binds to calmodulin to do so.,
Ca2+ can also alter membrane permeability by biding to plasma membrane ion channels which allows ions of that specific type to flow into or out of the cell.

Question 12

Overall, what is the net effect of water soluble hormones binding to plasma membranes?

Answer 12

Activation or inhibition of enzymatic pathways
Stimulation fo growth through cellular division
Release of cellular secretions
Changes in membrane permeability
Muscle contraction or relaxation