Hormones and their mechanism Questions in English

(C) The diagram typically illustrates the 'Lock and Key' hypothesis or the 'Induced Fit' model,which explains the mechanism of enzyme action.
In this process,the substrate binds to the active site of the enzyme to form an enzyme-substrate complex,which then converts into products.
Therefore,the diagram represents the mechanism of enzyme action.

(D) The correct answer is $D$.
Steroid hormones,such as $Cortisol$,$Testosterone$,$Estradiol$,and $Progesterone$,are lipid-soluble.
Because they are lipid-soluble,they can easily pass through the lipid bilayer of the target cell membrane.
Once inside the cell,they bind to intracellular receptors,which are often located in the nucleus.
This hormone-receptor complex then interacts with the genome to regulate gene expression or chromosome function.
In contrast,peptide hormones like $Insulin$,$Glucagon$,$Somatostatin$,and $Oxytocin$ are water-soluble and bind to membrane-bound receptors on the cell surface.

(C) The correct statement is $(c)$.
Hormone action involves their reception by target cells.
Specific proteins called hormone receptors,which are located in target tissues,bind with these hormones.
$FSH$ (Follicle Stimulating Hormone) is a peptide hormone that cannot pass through the cell membrane.
Therefore,it binds to specific membrane-bound receptors located on the surface of ovarian cells to initiate its action.
Glucagon is secreted by $\alpha$-cells,not $\beta$-cells.
Thymosin secretion decreases with aging.
$FSH$ primarily stimulates follicular development and estrogen secretion,but progesterone is mainly stimulated by $LH$.

(D) The correct answer is $D$.
Secondary messengers are low-molecular-weight,diffusible molecules used to relay signals within a cell.
They are synthesized or released by specific enzymatic reactions,usually as a result of an external signal received by a transmembrane receptor.
$cAMP$,$cGMP$,and $Ca^{2+}$ act as secondary messengers and are located within the cytoplasm.
Sodium $(Na^+)$ is an essential mineral ion involved in maintaining membrane potential and nerve impulse conduction,but it does not function as a secondary messenger in hormone signaling pathways.

(B) Hormones are classified based on their chemical nature:
$1$. Peptide,polypeptide,protein hormones include insulin,glucagon,and pituitary hormones.
$2$. Steroids include cortisol,testosterone,estradiol,and progesterone. Hypothalamic hormones are primarily peptide hormones (e.g.,$GnRH$,$TRH$).
$3$. Iodothyronines include thyroid hormones ($T_3$ and $T_4$).
$4$. Amino acid derivatives include epinephrine and norepinephrine.
Therefore,the pair 'Steroids: Hypothalamic hormones' is incorrect because hypothalamic hormones are peptide-based,not steroids.

(D) Secondary messengers are molecules that relay signals received at receptors on the cell surface to target molecules in the cytosol and/or nucleus.
Common examples of secondary messengers include cyclic $AMP$ $(cAMP)$,cyclic $GMP$ $(cGMP)$,inositol triphosphate $(IP_3)$,diacylglycerol $(DAG)$,and calcium ions $(Ca^{++})$.
Iodothyronines (thyroid hormones like $T_3$ and $T_4$) are lipid-soluble hormones that pass directly through the plasma membrane to bind with intracellular receptors.
Therefore,iodothyronines are not secondary messengers.

(A) Hormones are defined as non-nutrient chemicals that act as intercellular messengers and are produced in trace amounts.
They are secreted by endocrine glands and travel through the blood to target organs to regulate physiological processes.
Therefore,the correct term to fill in the blank is 'Intercellular'.

(D) Hormones are classified based on their chemical nature:
$1$. Peptide,polypeptide,protein hormones: Insulin,Glucagon,Pituitary hormones,Hypothalamic hormones.
$2$. Steroids: Cortisol,Testosterone,Estradiol,Progesterone.
$3$. Iodothyronines: Thyroid hormones.
$4$. Amino acid derivatives: Epinephrine (adrenaline) and Norepinephrine.
Among the given list:
- Insulin $(I)$ and Glucagon $(VI)$ are peptide hormones.
- Estradiol $(III)$,Progesterone $(IV)$,and Testosterone $(V)$ are steroid hormones.
- Epinephrine $(II)$ is an amino acid derivative (derived from tyrosine).
Therefore,only $II$ is an amino acid derivative.

(D) Hormones are chemical messengers that regulate physiological processes in the body.
They exert their biological effects by binding to specific proteins known as hormone receptors.
These receptors are located either on the cell membrane (for peptide hormones) or inside the cell (for steroid hormones).
Upon binding,the hormone-receptor complex initiates a series of biochemical reactions within the target cell,leading to the desired physiological response.

(D) Hormones are classified based on their chemical nature into peptide,steroid,iodothyronines,and amino-acid derivatives.
$1$. Epinephrine is an amino-acid derivative.
$2$. Glucagon is a peptide hormone.
$3$. Thyroid hormones are iodothyronines.
$4$. Cortisol is a glucocorticoid,which is a type of steroid hormone derived from cholesterol.

(C) Statement $A$ is correct because hormones are defined as non-nutrient chemicals which act as intercellular messengers.
Statement $B$ is incorrect because hormones are produced in trace amounts (very small quantities),not in large amounts.

(C) Hormones are classified based on their chemical nature into several groups:
$1$. Peptide,polypeptide,protein hormones (e.g.,insulin,glucagon,pituitary hormones).
$2$. Steroids (e.g.,cortisol,testosterone,estradiol,progesterone).
$3$. Iodothyronines (thyroid hormones,e.g.,$T_3$ and $T_4$).
$4$. Amino acid derivatives (e.g.,epinephrine and norepinephrine).
Both $A$ (Iodothyronines) and $C$ (Epinephrine) are amino acid derivatives. However,in the context of standard biology curricula,epinephrine is the classic example of an amino acid derivative (derived from tyrosine),while iodothyronines are often classified as a separate category due to their unique structure. Given the options,$C$ is the most direct answer for an amino acid derivative.

(B) Hormones are classified based on their chemical nature into two groups regarding their mechanism of action:
$1$. Peptide, polypeptide, and protein hormones (e.g., $Insulin, Glucagon, TSH, FSH, LH, ACTH, STH, TCT, RH$) interact with membrane-bound receptors because they are not lipid-soluble and cannot enter the cell.
$2$. Steroid hormones (e.g., $Cortisol, Testosterone, Estrogen, Progesterone, Aldosterone$) and thyroid hormones $(T_3, T_4)$ are lipid-soluble and interact with intracellular receptors.
In option $B$, $RH$ (Releasing Hormones), $STH$ (Somatotropic Hormone), $TSH$ (Thyroid Stimulating Hormone), $FSH$ (Follicle Stimulating Hormone), and $Insulin$ are all peptide/protein hormones that interact with membrane-bound receptors.

(C) Epinephrine,also known as adrenaline,is a hormone secreted by the adrenal medulla.
Chemically,it is derived from the amino acid tyrosine.
Therefore,it is classified as an amino-acid derivative.
Steroid hormones include cortisol and testosterone,while iodothyronines include thyroid hormones like $T_3$ and $T_4$.

(A) Negative feedback is a regulatory mechanism in which a stimulus causes an opposite output in order to maintain homeostasis.
$A$ is an example of negative feedback because when the body temperature drops (stimulus),the body responds by constricting blood vessels and shivering (response) to increase heat production and conserve body temperature.
$B$ and $C$ are examples of reflex actions or conditioned responses,not homeostatic negative feedback.
$D$ is incorrect because dilation of blood vessels (not constriction) occurs during heat to release heat.

(A) Hormones exert their physiological effects by binding to specific proteins called hormone receptors located in the target tissues.
These receptors are either present on the cell membrane (for peptide hormones) or inside the cell (for steroid hormones).
The hormone-receptor complex formation is essential for triggering the biochemical changes within the target cell that lead to the physiological response.
If the receptor molecule is removed or absent,the hormone cannot bind to the target cell,and consequently,the target organ will not be able to recognize or respond to the hormone.

(A) Hormones are classified based on their chemical nature.
$1$. Epinephrine (also known as Adrenaline) is derived from the amino acid Tyrosine.
$2$. Progesterone and Estrogen are steroid hormones derived from cholesterol.
$3$. Prostaglandins are lipid derivatives (fatty acids).
Therefore,Epinephrine is the correct answer.

(B) Hormones are chemical messengers that regulate various physiological processes in the body. Based on their chemical nature,hormones are classified into three main categories:
$1$. Peptide,polypeptide,and protein hormones (e.g.,insulin,glucagon,pituitary hormones).
$2$. Steroid hormones (e.g.,cortisol,testosterone,estrogen,progesterone).
$3$. Iodothyronines (thyroid hormones) and amino acid derivatives (biogenic amines like epinephrine and norepinephrine).
Therefore,hormones are chemically composed of proteins,steroids,and biogenic amines.

(D) The correct statement is $D$. Hormones are defined as non-nutrient chemicals that act as intercellular messengers and are produced in trace amounts.
Option $A$ is incorrect because stimulating and inhibiting hormones are primarily produced by the hypothalamus,not the pituitary gland.
Option $B$ is incorrect because the adenohypophysis (anterior pituitary) is regulated by the hypothalamus through hypophyseal portal blood vessels,whereas the neurohypophysis (posterior pituitary) is under direct neural control.
Option $C$ is incorrect because organs like the gastrointestinal tract,heart,kidney,and liver are known to produce specific hormones (e.g.,$ANF$ from the heart,erythropoietin from the kidney).

(B) Hormones are classified based on their chemical nature into peptide,steroid,iodothyronines,and amino acid derivatives.
$1$. $Estriol$ and $Estradiol$ are steroid hormones derived from cholesterol.
$2$. $Ecdysone$ is a steroid hormone found in insects.
$3$. $Epinephrine$ (also known as adrenaline) is an amino acid derivative,specifically synthesized from the amino acid $Tyrosine$.
Therefore,the correct option is $B$.

(B) Steroid hormones are lipid-soluble and can easily pass through the plasma membrane of target cells.
Once inside the cytoplasm,they bind to specific intracellular receptors (usually present in the cytoplasm or nucleus) to form a hormone-receptor complex.
This hormone-receptor complex then enters the nucleus and binds to specific sequences of $DNA$ (hormone response elements).
This binding regulates gene expression by promoting or inhibiting the transcription of specific genes into $mRNA$,which subsequently leads to the synthesis of specific proteins that alter cellular activities.

$(C)$ Endocrine glands are ductless glands that secrete their chemical messengers, known as hormones, directly into the blood.
The circulatory system (blood) then transports these hormones to their target organs or tissues to exert their physiological effects.
In contrast, digestive glands produce enzymes, which are typically transported through ducts to the site of action in the digestive tract, not primarily by the circulatory system.
Therefore, the correct sequence is: $(I)$ Endocrine glands, $(II)$ Hormones, $(III)$ Circulatory system. This corresponds to row $C$.

(B) The diagram illustrates the mechanism of action of protein hormones.
$1$. Protein hormones are water-soluble and cannot cross the lipid bilayer of the plasma membrane.
$2$. Therefore,they bind to specific receptors $(B)$ located on the outer surface of the plasma membrane.
$3$. The hormone $(A)$ binds to the receptor to form a hormone-receptor complex.
$4$. This binding triggers the generation of second messengers like cyclic $AMP$ $(C)$ inside the cell,which then carry out the physiological responses.
Thus,$A$ is a Protein Hormone,$B$ is a Receptor,and $C$ is a Second Messenger (like cyclic $AMP$). Option $B$ correctly identifies these components.

(N/A) $FSH$ (Follicle Stimulating Hormone),being a glycoprotein,is insoluble in lipids and therefore cannot enter the target cells.
It binds to specific receptor molecules located on the surface of the cell membrane to form a hormone-receptor complex.
This complex triggers the release of the enzyme adenylate cyclase from the receptor site.
This enzyme catalyzes the conversion of $ATP$ into cyclic adenosine monophosphate $(cAMP)$ within the cell.
The $cAMP$ then activates the existing enzyme system of the cell,which accelerates metabolic reactions.
The hormone is referred to as the first messenger,while $cAMP$ is termed the second messenger.
Additionally,the hormone-receptor complex alters the permeability of the cell membrane to facilitate the transport of materials,thereby increasing cellular activity.

(D) On the basis of their chemical nature,hormones can be divided into the following groups:
$(i)$ Peptide,polypeptide,protein hormones (e.g.,insulin,glucagon,pituitary hormones,hypothalamic hormones,etc.)
$(ii)$ Steroids (e.g.,cortisol,testosterone,estradiol,and progesterone)
$(iii)$ Iodothyronines (thyroid hormones)
$(iv)$ Amino-acid derivatives (e.g.,epinephrine)
Therefore,all the mentioned groups are correct categories for the chemical classification of hormones.

(N/A) Hormones produce their effects on target tissues by binding to specific proteins called hormone receptors located in the target tissues only.
Hormone receptors present on the cell membrane of the target cells are called membrane-bound receptors,and the receptors present inside the target cell are called intracellular receptors,mostly nuclear receptors. Binding of a hormone to its receptor leads to the formation of a hormone-receptor complex.
Each receptor is specific to one hormone only and hence receptors are specific.
Hormone-receptor complex formation leads to certain biochemical changes in the target tissue.
$\Rightarrow$ Target tissue metabolism and hence physiological functions are regulated by hormones.
On the basis of their chemical nature,hormones can be divided into:
$(i)$ Peptide,polypeptide,protein hormones (e.g.,insulin,glucagon,pituitary hormones,hypothalamic hormones,etc.)
$(ii)$ Steroids (e.g.,cortisol,testosterone,estradiol,and progesterone)
$(iii)$ Iodothyronines (thyroid hormones)
$(iv)$ Amino-acid derivatives (e.g.,epinephrine).
Hormones which interact with membrane-bound receptors normally do not enter the target cell but generate second messengers (e.g.,cyclic $AMP$,$IP_3$,$Ca^{++}$,etc.) which in turn regulate cellular metabolism.
Hormones which interact with intracellular receptors (steroid,iodothyronines,etc.) mostly regulate gene expression or chromosome function by the interaction of the hormone-receptor complex with the genome.
$\Rightarrow$ Cumulative biochemical actions result in physiological and developmental effects.

(C) On the basis of their chemical nature,hormones are classified into $4$ main groups:
$(i)$ Peptide,polypeptide,and protein hormones (e.g.,insulin,glucagon,pituitary hormones,hypothalamic hormones,etc.).
$(ii)$ Steroids (e.g.,cortisol,testosterone,estradiol,and progesterone).
$(iii)$ Iodothyronines (thyroid hormones).
$(iv)$ Amino-acid derivatives (e.g.,epinephrine).

(N/A) Protein hormones cannot enter the target cell because they are not lipid-soluble. Instead,they act by binding to specific receptors located on the outer surface of the plasma membrane,forming a hormone-receptor complex.
This complex stimulates the enzyme adenylate cyclase located on the inner surface of the plasma membrane. The activated adenylate cyclase enzyme converts $ATP$ into cyclic $AMP$ $(cAMP)$.
$cAMP$ acts as a second messenger,which carries the hormonal signal into the target cell. It then induces a specific enzyme system through a cascade effect,leading to the desired physiological or biochemical response within the cell.

(A) The chemical nature of hormones is as follows:
$1$. Oxytocin is a peptide hormone.
$2$. Epinephrine is an amino acid derivative (derived from tyrosine).
$3$. Progesterone is a steroid hormone.
$4$. Growth hormone is a protein hormone.
Therefore, the correct matching is $(A-4), (B-1), (C-2), (D-3)$.

(C) Hormones that are water-soluble,such as peptide and amine hormones,cannot cross the lipid bilayer of the plasma membrane.
They bind to specific receptors located on the surface of the target cell membrane.
This binding triggers the generation of a second messenger (e.g.,$cAMP$,$IP_3$,or $Ca^{2+}$) inside the cell.
The role of the second messenger is to relay the signal from the cell surface to the intracellular metabolic machinery,thereby triggering the appropriate physiological response within the cell.

(N/A) The differences between the mechanism of action of protein hormones and steroid hormones are as follows:

Protein Hormone Mechanism	Steroid Hormone Mechanism
$(1)$ These hormones bind to specific receptors located on the surface of the plasma membrane.	$(1)$ These hormones are lipid-soluble and pass through the plasma membrane to bind with intracellular receptors.
$(2)$ They generate secondary messengers such as $cAMP$ or $Ca^{2+}$ to trigger cellular responses.	$(2)$ The hormone-receptor complex directly interacts with the genome to regulate gene expression.
$(3)$ They typically regulate cellular metabolism and physiological activities through a cascade of biochemical reactions.	$(3)$ They primarily regulate physiological processes like growth and development by controlling protein synthesis.

(N/A) The current scientific definition is as follows: Hormones are non-nutrient chemicals which act as intercellular messengers and are produced in trace amounts.

(C) The correct matching is as follows:
$(a)$ Pituitary hormones are primarily peptide or protein-based hormones,so $(a)$ matches with $(iii)$.
$(b)$ Epinephrine is a catecholamine derived from tyrosine,classified as a biogenic amine,so $(b)$ matches with $(iv)$.
$(c)$ Endorphins are endogenous opioid neuropeptides,so $(c)$ matches with $(ii)$.
$(d)$ Cortisol is a glucocorticoid hormone synthesized from cholesterol,which is a steroid,so $(d)$ matches with $(i)$.
Therefore,the correct sequence is $(a)-(iii), (b)-(iv), (c)-(ii), (d)-(i)$.

(B) Prostaglandin is a non-steroidal hormone. It is derived from fatty acids,specifically arachidonic acid. In contrast,Estradiol,Progesterone,and Estrone are all steroid hormones derived from cholesterol.

(A) Second messengers are signaling molecules that relay signals from receptors on the cell surface to target molecules inside the cell,thereby amplifying the effect of the first messenger (hormone).
$cAMP$ (Cyclic adenosine $3',5'$-monophosphate) is synthesized from $ATP$ by the enzyme adenylate cyclase. It acts as a second messenger for various physiological processes,including adrenaline-mediated glycogenolysis and the acceleration of heart muscle cell contraction.

(B) The endocrine system is responsible for chemical coordination in the body. It achieves this by secreting hormones directly into the bloodstream,which act as chemical messengers to regulate various physiological processes. Unlike the nervous system,which provides point-to-point rapid neural coordination,the endocrine system provides chemical integration.

(A) The nervous system and the endocrine system work together to coordinate and regulate the physiological functions of the body. Neurons (nervous system) regulate the activity of endocrine glands (e.g.,the hypothalamus controls the pituitary gland). However,the endocrine system does not directly regulate the functioning of individual neurons in the same manner. Therefore,the statement that neurons regulate endocrine activity but not vice-versa is the most accurate description of this specific regulatory relationship.

(B) hormone is a non-nutrient chemical that acts as an intercellular messenger and is produced in trace amounts.

(D) Hormones produce their effects on target tissues by binding to specific proteins called hormone receptors,which are located in the target tissue only.
Membrane-bound receptors are present on the cell membrane of the target cells.
Intracellular receptors are present inside the target cell,which are mostly nuclear receptors (present in the nucleus).
Therefore,hormone receptors can be present either on the cell membrane or inside the target cell.

(B) Hormones produce their effects on target tissues by binding to specific proteins called hormone receptors located in the target tissues only.
Each receptor is specific to one hormone only and hence,receptors are specific.
Hormone-receptor complex formation leads to certain biochemical changes in the target tissue,which results in the regulation of metabolism and physiological functions.

(A) Hormones that interact with intracellular receptors, such as steroid hormones and iodothyronines, primarily regulate gene expression or chromosome function through the interaction of the hormone-receptor complex with the genome.
These hormones are lipid-soluble and can easily cross the plasma membrane to bind with receptors located inside the cell (cytoplasm or nucleus).
In contrast, peptide hormones like $ACTH$ and $MSH$ are water-soluble and interact with membrane-bound receptors on the cell surface.
Therefore, the correct combination is $I$ and $III$.

(B) The chemical nature of hormones is classified as follows:
$1$. Peptide,polypeptide,or protein hormones: These include $ACTH$,$GH$,$MSH$,$ADH$ (vasopressin),$Oxytocin$,insulin,glucagon,etc.
$2$. Glycoprotein hormones: These include $FSH$,$LH$,and $TSH$.
$3$. Steroid hormones: These include cortisol,testosterone,progesterone,and estrogen.
$4$. Iodothyronines: These include thyroid hormones $(T_3, T_4)$.
Based on this classification,$ACTH$ $(I)$,$GH$ $(II)$,$MSH$ $(III)$,and $Oxytocin$ $(VI)$ are polypeptide in nature. Therefore,the correct set is $I, II, III$ and $VI$.

(A) The mechanism of action of steroid hormones involves the hormone entering the cell and binding to an intracellular receptor to form a $Hormone-receptor\, complex$.
This complex then enters the $Nucleus$ and binds to the $DNA$ to regulate gene expression, leading to the synthesis of $mRNA$ and subsequently $Protein$.
In the standard diagram for this process:
$A$ represents $DNA$,
$B$ represents the $Nucleus$,
$C$ represents the $Hormone-receptor\, complex$,
$D$ represents the $Hormone$ (steroid hormone).
Therefore, the correct combination is $A-DNA, B-Nucleus, C-Hormone\, receptor\, complex, D-Hormone$.

(D) In cell signaling,molecules that bind to specific receptors and activate them to initiate a biological response are known as agonists.
Conversely,molecules that bind to the same receptors but block or inhibit the biological response are known as antagonists.
Therefore,the molecule that induces post-receptor events is an agonist $(A)$,and the molecule that inhibits these events is an antagonist $(B)$.

(D) Hormones are classified based on their chemical nature into several groups:
$1$. Amino acid derivatives: These are derived from the amino acid tyrosine. Examples include Epinephrine (Adrenaline) and Norepinephrine (Noradrenaline).
$2$. Peptide/Protein hormones: These consist of chains of amino acids. Examples include Insulin,Glucagon,$ACTH$,$GH$,$ADH$,$PTH$,$TCT$,and $MSH$.
$3$. Steroid hormones: These are derived from cholesterol. Examples include Oestradiol (an estrogen) and Testosterone (an androgen).
Based on this classification,Epinephrine $(II)$ and Norepinephrine $(IV)$ are amino acid derivatives.
Therefore,the correct option is $D$.

(A) The binding of a hormone to its specific receptor leads to the formation of a hormone-receptor complex.
Each receptor is specific to only one hormone,which ensures the specificity of the hormonal action.
Therefore,the correct condition for the formation of a receptor-hormone complex is the binding of a hormone to its respective receptor.

(B) Steroid hormones are secreted by the cells of the adrenal cortex and the endocrine cells of the gonads. All steroid hormones are lipids that are derived from cholesterol.

(D) Second messengers are molecules that relay signals received at receptors on the cell surface to target molecules in the cytosol and/or nucleus.
$I.$ Cyclic $AMP$ $(cAMP)$ is a well-known second messenger involved in various signaling pathways.
$II.$ $IP_3$ (Inositol triphosphate) is generated from the hydrolysis of membrane phospholipids and acts as a second messenger to release calcium ions.
$III.$ $Ca^{2+}$ (Calcium ions) act as important second messengers in many cellular processes,including muscle contraction and hormone secretion.
Therefore,all three ($I, II,$ and $III$) are recognized as second messengers.

(C) Steroid hormones are lipid-soluble hormones,also categorized as hydrophobic hormones.
Because they are lipid-soluble,they can easily pass through the lipid bilayer of the cell membrane.
Once inside the cell,they interact with intracellular receptors,which are typically located in the cytoplasm or the nucleus.
This hormone-receptor complex then binds to specific $DNA$ sequences to regulate gene expression.
Generally,steroid hormones are derived from the cholesterol ring structure.

(A) Steroid hormones are lipid-soluble. Therefore,they can pass freely across the lipid bilayer of the plasma membrane.
After entering the cytoplasm,molecules of steroid hormones bind to receptor molecules located within the cytoplasm or nucleus of the target cell,forming a hormone-receptor complex.
This complex then moves into the nucleus of the cell and interacts with the genome to activate specific genes.
These activated genes ultimately lead to the transcription of $mRNA$ and the synthesis of specific proteins.