Biochemistry of Hormones 1

7/31/2019 Biochemistry of Hormones 1

1/21

BIOCHEMISTRY OF

HORMONESPART 1


2/21

How do hormones work?

Initial Signal Perception

Signal Transduction and Amplification

Final Response


3/21


Reaction of hormone with receptor site

target cell- cell that respond to the hormone

Formation of hormone-receptor complex


4/21


Importance of Receptors

1. Presence or absence of particular receptor

determine which cells are able to respond to

that hormone

2. Different cell types possesses different

receptors that may elicit different responses

to the same hormone


5/21

Signal Transduction andAmplification

Activated hormone-receptor complex sets into

motion a cascade of biochemical events that

leads to final response

The hormone-receptor complex activates the gprotein which also binds and activates

adenylate cyclase that in turn stimulates the

formation of cyclic adenosine monophosphate

(cAMP)


6/21

Signal Transduction andAmplification

Alternative pathway: G protein may interact

with an ion channel which controls the flow of

calcium to the cell. The calcium binds with

calmodulin. Both pathway results into activation of specific

protein kinases.


7/21

Hormone Binding Proteins inPlants

Binding must be specific

The receptor should exhibit high affinity for the

hormone

Receptors can be saturated with hormone

molecules

The hormone must bind reversibly with

putative receptor


8/21

Final Response

Activated protein kinase enzymes phosphorylateother proteins, giving rise to hormone response.

2 classes of messengers

first messenger- hormone

second messenger- cAMP and calcium

Amplification- a single hormone will onlyactivate one molecule of adenylate cyclase

but each molecule will produce hundreads of

cAMP molecules that will stimulate theresponse


9/21


10/21


11/21

Auxin Binding Proteins

Two Tissues that Respond to Auxin by Cell

Enlargement

Callus cultures of tobacco pith tissue

Maize coleoptiles


12/21


Callus Cultures of Tobacco Pith Tissues

Associated with membrane fractions One has relatively low affinity for auxin but high affinity

for napthylphthalmic acid (NPA), an auxin transport

inhibitor One has moderate binding affinity for IAA but does not

bind NPA

Distributed with cytoplasmic and nuclear fractions Has high affinity for IAA

Functions the same as steroid hormones in animalcell


13/21


Maize Coleoptile

Only one membrane-associated auxin binding protein

designated as ABP1, a 43kDa glycoprotein dimer with

22 kD units with high affinity for IAA

Localized at endoplasmic reticulum but also found to

be associated with the plasma membrane and the cell

Antibodies (designated as IgG) raised against the

auxin binding protein (designated as IgG-antiABP)inihibit both auxin-induced coleoptile elongation and

auxin induced hyperpolarization


14/21

Cytokinin Binding Proteins

CBF-1 protein from wheat germ- loosely

associated with ribosomes after washing

ribosomal fraction with salt; might have a role

in regulation the protein translation process


15/21

Gibberlin and Abscisic Acid-Binding Proteins

GA has little attention; no confirmed reports of

high affinity binding proteins

There is a strong evidence for a high affinity

ABA-binding site on guard cell protoplasts


16/21

Second Messengers in Plants

1. Calcium- controls physiological process in

plants which includes cell elongation and

division, cytoplasmic streaming, the secretion

and activity of various enzymes, hormoneaction and tactic and tropic responses

Calmodulin- calcium binding protein; many

many of its properties are similar withbovine calmodulin


17/21

Second Messengers

How Calcium Functions Effectively?

Cystosolic Ca2+ concentration must be low

and under metabolic control through the action

of membrane bound calcium-dependentATPases

Concentration of cystosolic Ca2+ is also under

control of light and hormones


18/21

Second Messengers

Calcium as Second Messengers

Ca2+ reacts with calmodulin that results CaM-

Ca2+

This complex activates certain enzymes.

There are two classes of enzymes, the NAD

kinases and protein kinases


19/21

Second Messengers

2. Phosphoinositides- inositol triphosphate

system

The hormone receptor complex activates the

enzyme phospholipase C

Phospholipase C catalyzes the breakdown of

phosphotidylinositol biphosphate to inositol

triphosphate and diacyglycerol Inositol triphosphate moves to cytoplsam

where it stimulates the release of calcium


20/21

Second Messengers

Inositol Triphosphate System cont.

Ca2+ binds with calmodulin, the complex may

stimulate a response or through activation of

protein kinase


21/21

Hormones and Gene Action

The gene may be turned on or off by a

hormone

The hormone may increase (upregulated ) or

decreased (downregulated) its output

Biochemistry of Hormones 1

Documents

Transcript of Biochemistry of Hormones 1