hormones/chemical coordination

Hormones/Chemical Coordination

2. HORMONES/CHEMICAL COORDINATION

2.1 Types of hormonal glands and functions.

Q : Complete the following table

Gland Hormone FunctionInhibitory and Releasing Hormone

Released from posterior pituitary

Regulate the anterior pituitary

Oxytocin,

ADH

GH

Prolactin,

FSH

LH

TSH

ACTH

Stimulates contraction of uterus

Promotes retention of water

Growth and metabolic function

Milk production

Stimulates production of ova and spermStimulates ovaries and testes

Stimulate thyroid gland

Stimulate adrenal cortex to secrete glucocorticoids

HMM/SCM 1424, CFS, IIUM1


T3 and T4

Calcitonin

Stimulate and maintain metabolic process

Lowers blood calcium level

PTH Raises blood calcium level

Insulin

Glucagon

Lowers blood glucose level

Raises blood glucose level

Epinephrine & Norepinephrine

Glucocorticoids

Mineralocorticoids

Raise blood glucose level,Increase metabolic activities, constrict certain blood vessels

Raise blood glucose level

Promote reabsorption of sodium ion and excretion of potassium ion in kidneys

2.1.1 Types of Hormones

Hormones Diffuse into capillaries and transported by the

blood to target cells. e.g: insulin, glucagons



Neurohormones Produced by neuroendocrine cells Diffuse into capillaries and transported by the

blood to the target cells. e.g: oxytocin and ADH

Local regulators signaling molecule that diffuses through the

interstitial fluid and acts on nearby cells

Q: Name the two types of local regulators regulation and explain with the aid of diagrams.

autocrine regulation hormone diffuses through the interstitial

fluid and acts on the very cells that produce it

e.g: female hormone estrogen

paracrine regulation hormone diffuses through interstitial fluid

and act on nearby target cells e.g: prostaglandin



Q : List the three major classes of molecules that function as hormones in vertebrates.

Protein (peptide) hormones : short chains such as oxytocin and ADH and longer chains such as growth hormone, TSH, and neuropeptides.

Amino acid derivatives : Thyroid hormones, epinephrine, and norepinephrine are amines

Steroid hormones : cortisol, testosterone, estrogens and progestone

Q: Compare and contrast the lipid soluble molecule and water soluble.

Lipid soluble Water soluble- hydrophobic - hydrophilic- enter target cell - do not enter target

cell, only bind to cell-surface receptors.

- E.g: steroid hormones - E.g: peptide hormones

2.2 Hormonal mechanisms

Signaling by all hormones involves : reception, signal transduction, and response.

Reception - the signal molecule binds to a specific receptor protein in or on the target cell.

Binding of a signal molecule to a receptor protein triggers signal transduction.

2.2.1 Non steroid hormones via activation of cyclic AMP

The receptors - embedded in the plasma membrane.



Cannot cross the plasma membrane G protein-linked receptors

Figure 45.3 (a)

The hormone serves as the first messenger and relays information to a second messenger. E.g of 2nd messenger: cAMP, DAG & IP3

Q: Discuss the water soluble hormone mechanism



G protein-linked receptors

G protein-linked receptors initiate signal transduction

G protein-linked receptors activate G proteins in the plasma membrane.

The activated G protein binds GTP; inactive G protein binds GDP.

The activated G protein activates adenylyl cyclase.

Adenylyl cyclase then catalyzes the conversion of ATP to Cyclic AMP-cAMP(common 2nd messenger).

cAMP activates protein kinases. Protein kinases catalyze the phosphorylation of

a specific protein cAMP is rapidly inactivated and converted to

AMP



2.2.2 Mechanism of hormone action via gene activation

Eg. steroids, thyroid hormones, and the hormonal form of vitamin D enter target cells

Bind to protein receptors in the cytoplasm or nucleus.

All these hormones are small, nonpolar molecules Transcription of specific genes mRNA produced in response to hormone

stimulation is translated into new protein

Figure 45.3 (b)



2.3 Invertebrate regulatory system

Invertebrates produce a variety of hormones in endocrine and neurosecretory cells.

Some invertebrate hormones have homeostatic functions, such as regulation of water balance.

Others function in reproduction and development.

Q: State the names of hormones involved in the invertebrate regulatory system and describe their functions.



Figure 45.15, pg : 960

Brain hormone stimulates the release of ecdysone from the prothoracic gland.

Ecdysone promotes molting and the development of adult characteristics.

Juvenile hormone promotes the retention of larval (juvenile) characteristics.

Q : What happens when the level of juvenile hormone : (i) increases?

(ii) declines?

HMM/SCM 1424, CFS, IIUM

Brainhormone (BH)

Brain

Neurosecretorycells

Corpuscardiacum

Corpusallatum

Prothoracicgland

Ecdysone

EARLYLARVA

LATERLARVA PUPA ADULT

Juvenilehormone(JH)

LowJH

9


(i) High level of juvenile hormone -ecdysone still stimulates molting, but the product is simply a larger larva.

(ii) When the level of juvenile hormone declines –ecdysone induced molting and produce a pupa.

-Within the pupa, metamorphosis produces the adult form.

Q : State the usage of synthetic juvenile hormone. Synthetic juvenile hormone is used as insecticide

to prevent insects from maturing to reproductive adults.

2.4 Plant Hormones

Plant hormones help coordinate growth, development, and responses to environmental stimuli.

Some of the major classes of plant hormones include auxin, cytokinins, gibberellins, brassinosteroids, abscisic acid, and ethylene.

2.4.1 Examples of plant hormones and functions



Figure 39.1, pg : 794

Auxin

The natural auxin occurring in plants is indoleacetic acid, or IAA.

Q : Discuss the role of auxin in cell elongation.



The Role of Auxin in Cell Elongation (Refer Figure 39.8, pg:795)

Figure 39.8

Lateral and Adventitious Root Formation Auxin is involved in root formation and

branching

Auxins as Herbicides An overdose of auxins can kill eudicots

(flowering plants/angiosperm)

Other Effects of Auxin Fruit growth and development

Synthetic auxin used commercially for development of fruit.

Normally fruit will not develop without fertilisation.

After fertilization: ovule develops into seeds, mature ovary becomes fruit.



In certain plants, ovary has enough auxin to promote partenocarpy (development of fruit without fertilization) e.g. grapes, pineapples.

Q: How does Auxin affects secondary growth ? (i) inducing cell division in the vascular

cambium (ii) influencing differentiation of secondary

xylem

Cytokinins

Cytokinins are so named because they stimulate cytokinesis (cell division)

Control of Cell Division and Differentiation Produced in actively growing tissues such as

roots, embryos, and fruits Works together with auxin

Q : Discuss the function of cytokinin in controlling of apical dominance. Cytokinins, auxin, and other factors interact in

the control of apical dominance (a terminal bud’s ability to suppress development of axillary buds)

(Refer Figure 39.9 (a) , (b), pg : 796) If the terminal bud is removed, plants become

bushier



Figure 39.9

Anti-Aging Effects Inhibiting protein breakdown Stimulating RNA and protein synthesis Mobilizing nutrients from surrounding tissues

Gibberellins

Gibberellins have a variety of effects : stem elongation, fruit growth, and seed germination

Stem Elongation Stimulate growth of leaves and stems In stems: stimulate cell elongation and cell

division


Intact plant Plant with apical bud removed

Lateral branches

“Stump” afterremoval ofapical bud

Axillary buds

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Fruit Growth In many plants, both auxin and gibberellins

must be present for fruit to set Spraying of gibberellin during fruit

development - make the individual grapes grow larger and the internodes of the grape bunch elongate. (Refer Figure 39.10, pg : 797, The effect of gibberellin treatment on Thompson seedless grapes) Enhances air circulation between the

grapes Harder for yeast/ other microorganisms to

infect the fruits.

Figure 39.10

Germination Signals the seed to break dormancy and

germinate.

Brassinosteroids

Chemically similar to cholesterol and the sex hormones of animals.



Induce cell elongation and cell division in stem segments/seedlings at concentrations as low as 10−12 M.

Retard leaf abscission and promote xylem differentiation.

Effects are quite similar to auxin

Abscisic Acid (ABA)

Among its many effects are: Seed dormancy Drought tolerance

Seed Dormancy Ensures that the seed will germinate only in

optimal conditions Precocious germination is observed in maize

mutants that whose effect of ABA is blocked

Drought Tolerance ABA - primary internal signal that enables

plants to withstand drought/accumulation causes stomatal closure

Ethylene

Plants produce ethylene in response to stresses such as drought, flooding, mechanical pressure, injury, and infection.



Q : With the aid of diagram in figure 39.13 below, briefly describe the triple response of ethylene to mechanical stress.

Figure 39.13

Ethylene induces the triple response, which allows a growing shoot to avoid obstacles

The triple response consists of a slowing of stem elongation, a thickening of the stem, and horizontal growth

Ethylene-insensitive mutants fail to undergo the triple response after exposure to ethylene

Fruit Ripening Burst of ethylene in a fruit triggers the ripening

process



Enzymatic breakdown of cell wall components softens the fruit/ conversion of starches and acids to sugars makes the fruit sweet.

Production of new scents and colors - advertise fruits’ ripeness to animals - eat the fruits - disperse the seeds.

Ethylene (gas) spreads from fruit to fruit. Fruits ripen quickly by storing the fruit in a

plastic bag- accumulating ethylene gas/ enhancing ethylene levels in commercial production.

Alternatively, to prevent premature ripening, apples are stored in bins flushed with carbon dioxide - prevents ethylene from accumulating, inhibits the synthesis of new ethylene.

Apoptosis: Programmed Cell Death A burst of ethylene is associated with

apoptosis- programmed destruction of cells, organs, or whole plants

Leaf Abscission(loss of leaves)A change in the balance of auxin and ethylene

controls leaf abscission, the process that occurs in autumn when a leaf falls

2.4.2 Interaction between hormones

For example, flooding of deepwater rice leads to a 50-fold increase in internal ethylene and a rapid increase in stem elongation.



Flooding also leads to an increase in sensitivity to GA (Gibbberellic acid) that is mediated by a decrease in ABA levels.

Q : Explain the terms synergism and antagonism in hormones interaction.Give examples of the hormones involved.

Interaction between different hormone: Synergism

Occurs when two or more plant hormones interact to give a greater effect than the sum of their individual actions.

E.g: Auxin and Cytokinin

Antagonism Two or more plant hormones may interact

to reduce each other’s effect E.g: ABA causes dormancy in bud,

Gibberellins breaks the dormancy

Effect depend on: its concentration on the tissue being acted on on the developmental stage of the plant

2.4.3 Phytochromes and effect of light on flowering

Phytochromes function as photoreceptors in many plant responses to light.

It consists of a protein covalently bonded to a nonprotein part that functions as a chromophore, the light-absorbing part of the molecule. (Refer Figure 39.19, pg : 804, structure of a phytochrome)



Figure 39.19

The chromophore is photoreversible and reverts back and forth between two isomeric forms with one (Pr) absorbing red light and becoming (Pfr), and the other (Pfr) absorbing far-red light and becoming (Pr). (Refer Figure 39.20,pg : 804, a molecular switching mechanism)

Figure 39.20 This interconversion between isomers acts as a

switching mechanism that controls various light-induced events in the life of the plant.


Synthesis

Pr Pfr

Red light

Far-red light

Slow conversionin darkness(some plants)

Enzymaticdestruction

Responses:seed germination,control offlowering, etc.

20


Q : Phytochrome has 2 forms; Pr and Pfr. Briefly explain the differences between these two phytochrome in terms of the light absorption capability.

Phytochrome has 2 forms; Pr = red light-absorbing phytochrome,

strongly absorbs light with a relatively short red wavelength (660 nm)

Pfr = far-red light phytochrome, absorbs light with a relatively long red wavelength (730 nm)

(Refer Figure 36-5 page: 691, Solomon)

The Pfr form triggers many of the plant’s developmental responses to light.

In darkness, the phytochrome ratio shifts gradually in favor of the Pr form, in part from synthesis of new Pr molecules and, in some species, by slow biochemical conversion of Pfr to Pr.

When the sun rises, the Pfr level suddenly increases by rapid photoconversion of Pr.

This sudden increase in Pfr each day at dawn resets the biological clock.

A physiological response to photoperiod, such as flowering, is called photoperiodism.

A short-day plant, requires a dark period longer than a critical period to flower.



Examples include chrysanthemums, poinsettias, and some soybean varieties.

Long-day plants will only flower when the dark period is shorter than a critical period.

Examples include spinach, iris, and many cereals.

Day-neutral plants will flower when they reach a certain stage of maturity, regardless of day length/night length

Examples include tomatoes, rice, and dandelions.

It is night length, not day length, that controls flowering and other responses to photoperiod.

Q : Figure 39.22 (a and b) shows the photoperiodic control of flowering in different plant types.



Figure 39.22, pg : 807

(i) Are plants in (a) and (b), a long day (short night) plant or a short day (long night) plant?

(a) : ___________________________

(b) : ___________________________

(ii) Explain your answers in (a) and (b).

Note : (a) – “Short-day” plants flowered only if a period of continuous darkness was longer than a critical dark period for that particular species (13


Light

“Short-day” plants “Long-day” plants

Darkness

Flash oflight

Criticaldarkperiod

24

ho

urs

23


hours in this example). A period of darkness can be ended by a brief exposure to light.

(b) – “Long-day” plants flowered only if a period of continuous darkness was shorter than a critical period for that particular species (13 hours in this example)

If a flash of red light during the dark period is followed immediately by a flash of far-red light, then the plant detects no interruption of night length, demonstrating red/far-red photoreversibility. (Refer Figure 39.23, pg : 807)

Figure 39.23

The flowering signal, not yet chemically identified, is called florigen, and it may be a hormone or some change in the relative concentrations of two or more hormones.



(Verily! In the creation of the heavens and the earth, and in the alternation of night and day, and the ships which sail through the sea with that which is of use to

mankind, and the water( rain( which Allah sends down from the sky and makes the earth alive therewith after its death, and the moving ( living( creatures of all kinds that

He has scattered therein, and in the veering of winds and clouds which are held between the sky and the earth, are indeed (Ayat(proofs( evidences, signs,etc for

people of understanding(


hormones/chemical coordination

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