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Biology: The Dynamic Science (Mind...

4th Edition
Peter J. Russell + 2 others
ISBN: 9781305389892

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BuyFindarrow_forward

Biology: The Dynamic Science (Mind...

4th Edition
Peter J. Russell + 2 others
ISBN: 9781305389892
Textbook Problem

In the sequence that unfolds after molecules of a hormone such as ABA bind to receptors at the surface of a target plant cell:

a. first messenger molecules in the cytoplasm are mobilized, then G proteins carry the signal to second messengers such as protein kinases, which alter the activity of cell proteins such as IP3.

b. binding activates G proteins, which in turn activate second messengers such as IP3; subsequent steps are thought to involve activation of genes that encode protein kinases.

c. binding activates phospholipase C, which in turn activates G proteins, which then activate molecules of IP3, a step that leads to the synthesis of protein kinases.

d. binding stimulates G proteins to activate protein kinases, which then bind calcium channels in ER; the flux of calcium ions activates second messenger molecules that alter the activity of cell proteins or enter the cell nucleus and alter the expression of target genes.

e. binding activates G proteins, which in turn activate phospholipase C; this substance then stimulates the synthesis of second messenger molecules, the second messengers bind calcium channels in the cell’s ER, and finally protein kinases alter the activity of proteins by phosphorylating them.

Summary Introduction

Introduction:

Abscisic acid (ABA) is a plant hormone that is responsible for suppressing growth. This is brought about by changing the gene expression and inhibiting growth. It is also involved in presenting a response toward environmental stresses. These stresses include drought, cold, soil salinity, and others. The response presented by ABA is a part of evolutionary adaptation.

Explanation

Justification/explanation for the correct answer:

Option (e) is, ‘binding activates G proteins, which in turn activates phospholipase C; this substance then stimulates the synthesis of second messenger molecule, the second messengers bind to calcium channels in the cell’s ER (endoplasmic reticulum), and finally protein kinases alter the activity of proteins by phosphorylating them’.

The sequence mentioned in this option correctly states the steps followed when the ABA hormone binds with the receptors present on the target cell surface. The second messengers, like IP3 (inositol triphosphate) are synthesized in the second step. The release of calcium ions is responsible for activation of protein kinases. Hence, option (e) is correct.

Explanations for the incorrect answers:

Option (a) is, ‘first messenger molecules in the cytoplasm are mobilized, then G proteins carry the signal to second messenger such as protein kinases, which alter the activity of cell proteins such as IP3’. The G proteins do not carry signal to the second messengers. Protein kinases are not secondary messengers and IP3 is not a cell protein. So, it is an incorrect option...

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