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Chemistry 3 Marks Question

Biomolecules · Rajasthan Board (RBSE) STD 12 Science (Rajasthan - English Medium). 12 questions.

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Question 13 Marks
Explain by giving an equation how the presence of carbonyl group and five -OH groups in the structure of glucose is determined ### Write the equation reactions of glucose with NH, OH, HCN, and acetic anhydride and state what information is obtained about the structure of glucose through it.
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Question 23 Marks
What are the functions of hormones in body?
Answer
→Hormones have several functions in the body.
→They help to maintain the balance of biological activities in the body.
→The role of insulin in keeping the blood glucose level with in the narrow limit is a example of this function.
→Insulin is released in response to the rapid rise in blood glucose level.
On the other hand hormone glucagon tends to increase the glucose level in the blood.
→The two hormones together regulate the glucose level in the blood. →Epinephrine and norepinephrine mediate responses to external stimuli. →Growth hormone and sex hormones play role in growth and development.
→Thyroxine produced in the thyroid gland is an iodinated derivative of amino acid tyrosine.
→ Abnormally low level of thyroxine leads to hypothyroidism which is characterized by lethargyness and obesity.
→ Increased level of thyroxine causes hyperthyroidism.
→Low level of iodine in the diet may lead to hypothyroidism and enlargement of the thyroid gland. This condition is largely being controlled by adding sodium iodide to commercial table salt. ("Iodized" salt).
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Question 33 Marks
Write a note on chemical composition of nucleic acid compounds.
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Question 43 Marks
Explain the importance of carbohydrate compounds.
Answer
→Carbohydrates are essential for life in both plants and animals.
→They form a major portion of our food.
→Honey has been used for ayurvedic system of medicine.
→Carbohydrates are used as storage molecules as starch in plants and glycogen in animals.
→Cell wall of bacteria and plants is made up of cellulose.
→We build furniture etc. from cellulose in the form of wood and cloth ourselves in the form of cotton fibre.
→They provide raw materials for many important industries like textiles; paper; lacquers and breweries.
→Two aldopentoses viz. D-ribose and 2-deoxy D-ribose are present in nucleic acids.
→Carbohydrates are found in biosystem in combination with many proteins and lipids.
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Question 53 Marks
Why vitamin D, E and K compounds are essential for us? Describe their important sources.
Answer
→Deficiency of vitamin D leads to Rickets (bone deformities in children) and osteomalacia (soft bones and joint pain in adults), so it is essential for us. Important sources are exposure to sunlight, fish and egg yolk.
→Deficiency of vitamin E leads to increased fragility of RBCs and muscular weakness, so H is essential for us. Important sources are vegetable oils like wheat germoil, sunflower oil etc.
→Deficiency of vitamin K leads to increased blood clotting time so it is essential for us. Important sources are green leafy vegetables.
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Question 63 Marks
What are vitamin compounds? Give primary information about vitamin compounds.
Answer
→"It has been observed that certain organic compounds are required in small amounts in our diet but their deficiency causes specific diseases. These compounds are called vitamins."
→Most of the vitamins can not be synthesised in our body but plants can synthesise almost all of them.
→So, they are considered as essential food factors.
→However, the bacteria of the gut can produce some of the vitamins required by us.
→All the vitamins are generally available in our diet.
→Different vitamins belong to various chemical classes and it is difficult to define them on the basis of structure.
→They are generally regarded as organic compounds required in the diet in small amounts to perform specific biological functions for normal maintenance of optimum growth and health of the organism.
→Vitamins are designated by alphabets A, B, C, D, etc.
→Some of them are further named as sub-groups e.g. $B_1, B_2, B_6, B_{12}$ etc.
→The term "Vitamine" was coined from the word vital + amine since, the earlier identified compounds had amino groups. Later work showed that most of them did not contain amino groups, so the letter 'e' was dropped and the term 'vitamin' is used these days.
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Question 73 Marks
Short note on: Maltose
Answer
$\rightarrow$ Maltose is composed of two $a-D-$glucose.
$\rightarrow $ ​​​​​​​
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$\rightarrow$ In maltose $C_1$ of one glucose $(I)$ is linked to $C_4$ of another glucose unit $(II).$
$\rightarrow$ The free aldehyde group can be produced at $C_1$ of second glucose in solution and it shows reducing properties
​​​​​​​so, it is a reducing sugar.​​​​​​​
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Question 83 Marks
Give primary information about carbohydrate compounds?
Answer
→Carbohydrates are primarily produced by plants and form a very large group of naturally occurring organic compounds.
→Some common examples of carbohydrates are cane sugar, glucose, starch etc.
→Most of them have a general formula, $C _{ x }\left( H _2 O \right)_{ y }$and were considered as hydrates of carbon from where the name carbohydrate was derived.
→For example, the molecular formula of glucose $\left( C _6 H _{12} O _6\right)$ fits into this general formula, $C _6\left( H _2 O \right)_6$.
→But all the compounds which fit into this formula may not be classified as carbohydrates.For example acetic acid $\left( CH _3 COOH \right)$ fits into this general formula, $C _2\left( H _2 O \right)_2$ but is not a carbohydrate.
→Similarly rhamnose, $\left( C _6 H _{12} O _5\right)$is a carbohydrate but does not fit in this definition.
→"Chemically, the carbohydrates may be defined as optically active polyhydroxy aldehydes or ketones or the compounds which produce such units on hydrolysis."
→Some of the carbohydrates, which are sweet in taste, are also called sugar. The most common sugar, used in our homes is named as sucrose where as the sugar present in milk is known as lactose.
→Carbohydrates are also called saccharides.
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Question 93 Marks
What is a peptide bond or peptide chain? Elaborate on how protein compounds are formed from amino acid compounds.
Answer
$\rightarrow$ Proteins are the polymers of $a-$amino acids and they are connected to each other by peptide bond or peptide linkage.
$\rightarrow$ Chemically peptide linkage is an amide formed between $-COOH$ group and $-NH_2$ group
$\rightarrow$ "The reaction between two molecules of similar or different amino acids, proceeds through the combination of the amino group of one molecule with the carboxyl group of the other. This results in the elimination of water molecule and formation of a peptide bond$-CO-NH - ."$
$\rightarrow$ The product of the reaction is called a dipeptide because it is made up of two amino acids.
$\rightarrow$ For example when carboxyl group of glycine combines with the amino group of alanine we get a dipeptide glycylalanine.
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$\rightarrow$ The third amino acids combines to a dipeptide, the product is called a tripeptide.
$\rightarrow$ A tripeptide contains three amino acids linked by two peptide linkages.
$\rightarrow$ Similarly, when four, five or six amino acids are linked to the respective products are known as tetrapeptide, pentapeptide or hexapeptide, respectively.
$\rightarrow$ When the number of such amino acids is more than ten, then the products are called polypeptides.
$\rightarrow$ A polypeptide with more than hundred amino acid residues, having molecular mass higher than $10,000 u$ is called a protein.
$\rightarrow$ However, the distinction between a polypeptide and a protein is not very sharp. Polypeptides with fewer amino acids are likely to be called proteins if they ordinarily have a well defined conformation of a protein such as insulin which contains $51$ amino acids.
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Question 103 Marks
Note on: Cyclic structure of glucose.
Answer
→Limitations of open chain structure of glucose shows that free -CHO group is absent in glucose.
→It was proposed that one of the -OH groups may add to the -CHO group and form a cyclic hemiacetal structure.
→It was found that glucose forms a six membered ring in which-OH at C-5 is involved in ring formation.
→This explains the absence of -CHO group and also existence of glucose in two forms as shown below:
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→These two cyclic forms exist in equilibrium with open chain structure.
→The two cyclic hemiacetal forms of glucose differ only in the configuration of the hydroxyl group at $C_1$ called anomeric carbon. (the aldehyde carbon before cyclisation)
→Such isomer i.e. a-form and ẞ-form are called anomers.
→The six membered cyclic structure of glucose is called pyranose structure (a- or ẞ-) in analogy with pyran.
→Pyran is a cyclic organic compound with one oxygen atom and five carbon atoms in the ring.
→The cyclic structure of glucose is more correctly represented by haworth structure as given below.
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Question 113 Marks
Short note on: Sucrose.
Answer
One of the common disaccharides is sucrose which on hydrolysis gives equimolar mixture of D-(+)glucose and D-(-)fructose.
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These two monosaccharides are held together by a glycosidic linkage between $C _1$ of $\alpha- D$ Glucose and $C _2$ of $\beta-D$ fructose.
Since the reducing groups of glucose and fructose are involved in glycosidic bond formation, sucrose is a non reducing sugar.
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Sucrose is dextrorotatory but after hydrolysis gives dextrorotatory glucose and laevorotatory fructose.
Since the laevorotation of fructose (-92.4°) is more than dextrorotation of glucose (+52.5°) the mixture is laevorotatory.
Thus, hydrolysis of sucrose brings about a change in the sign of rotation, from dextro (+)
to laevo (-) and the product is named as invert sugar.
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Question 123 Marks
Give the function of steroid hormones.
Answer
→Steroid hormones are produced by adrenal cortex and gonads (testes in males and ovaries in female) Hormones released by the adrenal cortex play very important role in the function of the body.
For example, glucocorticoids control the carbohydrate metabolism, modulate inflammatory reactions and are involved in reactions to stress.
→The mineralocorticoid control the level of excretion of water and salt by the kidney. If adrenal cortex does not function properly then one of the results by addison's disease characterized by hypoglycemia, weakness and increased susceptibility to stress.
→The disease is fatal unless it is treated by glucocorticoids and mineralocorticoids.
→Hormones released by gonads are responsible for development of secondary sex characters.
→Testosterone is the major sex hormone produced in males. It is responsible for development of secondary male characteristics and estradiol is the main female sex hormones. It is responsible for development of secondary female characteristics and participates in the control of menstrual cycle.
→Progesterone is responsible for preparing the uterus for implantation of fertilized egg.
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