METABOLISM OF NITROGEN Questions in English

(D) $Mo$ (Molybdenum) is an essential micronutrient for plants. It acts as a vital component of the enzyme $Nitrate$ $reductase$. This enzyme is responsible for the reduction of nitrate to nitrite during the process of nitrogen assimilation. In this enzyme, $Mo$ functions as a prosthetic group, which is necessary for its catalytic activity.

(B) The enzyme nitrate reductase catalyzes the reduction of nitrate $(NO_3^-)$ to nitrite $(NO_2^-)$.
This is the first step in the process of nitrate assimilation in plants,where nitrogen is converted into a form that can be incorporated into organic compounds.

(A) In plants, the process of nitrogen assimilation begins with the reduction of nitrate $(NO_3^-)$ to nitrite $(NO_2^-)$.
This reaction is catalyzed by the enzyme $Nitrate \text{ } reductase$.
Subsequently, the nitrite is reduced to ammonia $(NH_3)$ by the enzyme $Nitrite \text{ } reductase$.
Therefore, the first enzyme involved in this pathway is $Nitrate \text{ } reductase$.

(C) Nitrogen balance is a measure of nitrogen input versus nitrogen output.
Negative nitrogen balance occurs when the amount of nitrogen excreted from the body (primarily through urine in the form of urea) exceeds the amount of nitrogen ingested through dietary proteins.
This state typically indicates that the body is breaking down more tissue protein than it is synthesizing,which can occur during starvation,malnutrition,or severe illness.

(C) Deamination is the biochemical process in which an amino group $(-NH_2)$ is removed from an amino acid molecule.
This process results in the formation of a keto acid and ammonia $(NH_3)$.
Transamination involves the transfer of an amino group from one amino acid to a keto acid,whereas deamination specifically refers to the removal of the amino group.

(A) Transamination is a chemical reaction that transfers an amino group to a ketoacid to form new amino acids.
In this process,glutamic acid acts as the main donor of the amino group.
The amino group is transferred from glutamic acid to the keto group of a keto acid (such as $α$-ketoglutaric acid) to form the corresponding amino acid.
Therefore,the correct answer is glutamic acid.

(B) In the process of reductive amination,$\alpha$-ketoglutaric acid reacts with ammonia in the presence of the enzyme glutamate dehydrogenase and $NADPH$ to form glutamic acid.
The reaction is represented as: $\alpha$-ketoglutaric acid + $NH_4^+$ + $NADPH \xrightarrow{\text{glutamate dehydrogenase}}$ Glutamic acid + $H_2O$ + $NADP^+$.
Therefore,the correct option is $B$.

(C) Reductive amination is a key process in nitrogen assimilation in plants.
In this reaction,ammonia $(NH_3)$ reacts with $\alpha$-ketoglutaric acid and $NADPH$ in the presence of the enzyme $Glutamate \ dehydrogenase$ to form glutamic acid.
The reaction is: $\alpha$-ketoglutaric acid + $NH_4^+$ + $NADPH \xrightarrow{Glutamate \ dehydrogenase} \text{Glutamate} + H_2O + NADP^+$.
Therefore,the enzyme $Glutamate \ dehydrogenase$ is involved in this process.

(C) Molybdenum $(Mo)$ is an essential micronutrient that plays a critical role in nitrogen metabolism.
It is a key component of the enzyme nitrogenase,which is responsible for biological nitrogen fixation in plants.
Additionally,it is a component of nitrate reductase,an enzyme that catalyzes the reduction of nitrate to nitrite,which is the first step in the assimilation of nitrogen by plants.

(B) Transamination is a process involving the transfer of an amino group from one amino acid to the keto group of a keto acid.
This reaction is catalyzed by enzymes known as transaminases.
Through this process,the amino group from glutamic acid is transferred to other keto acids to synthesize various other amino acids required by the plant.
Therefore,transaminase is responsible for the synthesis of amino acids other than glutamic acid.

(B) In plants,ammonia is converted into amino acids through two main processes: reductive amination and transamination.
$1$. In reductive amination,ammonia reacts with $\alpha$-ketoglutaric acid and $NADPH$ to form glutamic acid.
$2$. In transamination,the amino group $(NH_2)$ is transferred from one amino acid (usually glutamic acid) to a keto acid to form a new amino acid.
$3$. Aspartic acid is formed from oxaloacetic acid via transamination,and asparagine is formed from aspartic acid by the addition of another amino group. Thus,the sequence Glutamic acid $\rightarrow$ Aspartic acid $\rightarrow$ Asparagine represents a logical pathway for amino acid synthesis and interconversion.

(D) Amino acids are primarily synthesized from $\alpha -$ ketoglutaric acid through the process of reductive amination and transamination.
In plants,ammonia $(NH_3)$ reacts with $\alpha -$ ketoglutaric acid in the presence of the enzyme glutamate dehydrogenase to form glutamic acid (glutamate).
This glutamic acid then serves as the main amino group donor for the synthesis of other amino acids via transamination,where the amino group is transferred to other keto acids.

(C) The reaction provided is the reductive amination process, which is a key mechanism for the assimilation of ammonia in plants.
In this reaction, $\alpha -$ Ketoglutaric acid reacts with ammonia $(NH_4^+)$ and a reducing agent, $NADPH$, in the presence of the enzyme glutamate dehydrogenase.
The products formed are glutamate, water $(H_2O)$, and $NADP^+$.
The balanced equation is:
$\alpha -$ Ketoglutaric acid $+ NH_4^+ + NADPH \xrightarrow[\text{Dehydrogenase}]{\text{glutamate}} \text{Glutamate} + H_2O + NADP^+$.
Comparing this with the given equation:
$A = NADPH$
$B = \text{Glutamate}$
Therefore, the correct option is $C$.

(N/A)

Reductive Amination	Transamination
$1$. In this process,ammonia reacts with $\alpha$-ketoglutaric acid to form glutamic acid.	$1$. It involves the transfer of an amino group from one amino acid to the keto group of a keto acid.
$2$. The main substrate is $\alpha$-ketoglutaric acid.	$2$. The main donor of the amino group is glutamic acid.
$3$. The enzyme responsible for this is glutamate dehydrogenase.	$3$. The enzyme responsible for this is transaminase.
$4$. Only glutamic acid is formed in this process.	$4$. Other $17$ types of amino acids are produced through this process.

(C) The analysis of xylem exudates reveals that nitrogen is primarily transported in plants in organic forms. These organic forms mainly consist of amino acids and amides,which are synthesized from the nitrogen absorbed by the roots. While some nitrogen is absorbed as inorganic ions (nitrates and nitrites),it is converted into organic compounds before being translocated through the xylem to other parts of the plant.

(D) The correct answer is $D$.
Plants primarily absorb nitrogen from the soil in the form of nitrate $(NO_3^-)$,which is an oxidised form of nitrogen.
Although some plants can also absorb ammonium $(NH_4^+)$,nitrate is the most common and preferred source for most terrestrial plants.

$(A)$ The organic acid, $\alpha$-ketoglutaric acid, plays a key role in the synthesis of amino acids.
In this process, ammonia $(NH_{4}^{+})$ formed by nitrogen assimilation reacts with $\alpha$-ketoglutaric acid to form an amino acid, i.e., glutamic acid (glutamate).
This reaction is catalyzed by the enzyme glutamate dehydrogenase.
Since the reaction involves the addition of an amino group and the reduction of the substrate using $NADPH$, it is known as reductive amination.

(C) In chemistry,oxidation states indicate the degree of oxidation of an atom in a chemical compound.
Nitrogen in $NH_{3}$ (ammonia) has an oxidation state of $-3$,which is its most reduced form.
In contrast,nitrogen in $NO_{3}^{-}$ (nitrate) has an oxidation state of $+5$,which is its most oxidized form.
Therefore,nitrogen in $NH_{3}$ is the correct example of a nutrient in its reduced form.

(C) The given reaction represents the transfer of an amino group $(-NH_3^+)$ from an amino donor to the carbonyl position $(C=O)$ of an amino acceptor. This process is known as transamination.
In this reaction,the amino group is transferred from one amino acid to a keto acid,resulting in the formation of a new amino acid and a new keto acid. This is a key mechanism in nitrogen metabolism in plants.

(B) Molybdenum $(Mo)$ is an essential micronutrient for nitrogen metabolism. It is a key component of the enzyme nitrogenase,which catalyzes the biological nitrogen fixation process. Nitrogenase consists of two subunits: the $Fe$-protein and the $Mo-Fe$ protein.

(D) Asparagine and glutamine are the two most important amides found in plants. These are structural parts of proteins and are formed from two amino acids,namely aspartic acid and glutamic acid,respectively,by the addition of another amino group to each. Since amides contain more nitrogen than amino acids,they are transported to other parts of the plant via xylem vessels.

(A) Nitrification is the process of converting ammonia $(NH_3)$ into nitrate $(NO_3^-)$. This involves the loss of electrons,which is an oxidation process.
Nitrate assimilation is the process by which plants take up nitrate $(NO_3^-)$ and convert it back into ammonia $(NH_3)$ to be incorporated into amino acids. This involves the gain of electrons,which is a reduction process.
Therefore,nitrification is an oxidation process and nitrate assimilation is a reduction process.

(A) The process of converting nitrate $(NO_{3}^{-})$ into ammonia $(NH_{3})$ in plants is known as nitrate assimilation.
This process occurs in two steps:
$1$. Nitrate $(NO_{3}^{-})$ is reduced to nitrite $(NO_{2}^{-})$ by the enzyme nitrate reductase.
$2$. Nitrite $(NO_{2}^{-})$ is further reduced to ammonia $(NH_{3})$ by the enzyme nitrite reductase.
Therefore,the correct answer is nitrate assimilation,catalysed by nitrate and nitrite reductase.

(B) Plants primarily absorb nitrogen from the soil in the form of nitrates $(NO_{3}^{-})$,although some nitrogen is also absorbed as nitrites $(NO_{2}^{-})$ or ammonium ions $(NH_{4}^{+})$.
Once absorbed,nitrogen is assimilated into organic compounds,and the most usable form for the synthesis of amino acids and other nitrogenous compounds within the plant is ammonia $(NH_{3})$.
Therefore,the most common form of uptake is $NO_{3}^{-}$ and the usable form is $NH_{3}$.

(A) Glutamic acid plays a central role in nitrogen metabolism. It acts as the primary amino acid from which other amino acids are synthesized through the process of transamination. In this process,the amino group $(NH_2)$ is transferred from glutamic acid to other keto acids to form different amino acids.

(A) The process of reductive amination involves the reaction of ammonia with an $\alpha$-keto acid to form an amino acid,facilitated by the enzyme glutamate dehydrogenase and the coenzyme $NAD(P)H$.
The primary reaction is:
$\alpha$-ketoglutaric acid + $NH_4^+$ + $NAD(P)H \xrightarrow{\text{Glutamate dehydrogenase}}$ Glutamate + $H_2O$ + $NAD(P)$
In this reaction,$\alpha$-ketoglutaric acid acts as the substrate that accepts the ammonium ion to synthesize glutamate.

(A) The given reaction is: $\alpha$-Ketoglutaric acid + $NH_4^+ + NADPH \rightarrow$ Glutamate + $H_2O + NADP$.
This process is known as reductive amination.
In this reaction,ammonia $(NH_4^+)$ reacts with $\alpha$-ketoglutaric acid in the presence of the enzyme glutamate dehydrogenase to form glutamic acid (glutamate).
This is a key step in the assimilation of ammonia in plants.

(B) The given chemical reaction shows the transfer of an amino group $(-NH_3^+)$ from one amino acid to the keto group of a keto acid.
This process is known as transamination.
The enzyme that catalyzes this transfer of the amino group is called transaminase.
Therefore,the correct reaction is transamination and the enzyme is transaminase.