Biomolecules Test - 14

The furanose ring is found in the fructose unit of cane sugar. In cane sugar, the fructose molecule has a five-membered ring structure (furanose ring).

Fructose also exists in a cyclic form which is known as furanose with an analogy to the compound furan which is a five-membered cyclic compound with one oxygen and four carbon atoms. It is called furanose because of its structural similarity to furan. The structure of furanose can be drawn as:

Hence, the correct option is (C).

The monomers of the nucleic acids are linked by a 'link'(as shown in the below diagram) is also know as N-glycosidic linkage or just the glycosidic linkage. 

A glycosidic bond or glycosidic linkage is a type of covalent bond that joins a carbohydrate molecule to another group, which may or may not be another carbohydrate.

Hence, the correct option is (C).

The most common types of secondary structures are the α helix and the β pleated sheet. 

Helix structure: In this structure, the -NH group of an amino acid residue forms an H-bond with the group of the adjacent turn of the righthanded screw (-helix).

\(\beta\)-pleated sheet structure: This structure is called so because it looks like the pleated folds of drapery. In this structure, all the peptide chains are stretched out to nearly the maximum extension and then laid side by side. These peptide chains are held together by intermolecular hydrogen bonds.

Hence, the correct option is (B).

Acetylation is a type of reaction in which a hydrogen atom is substituted by an acetyl (CH₃C=O) group in a compound. 

Glucose is the most common monosaccharide. It is known as Dextrose because it occurs in nature principally as the optically active dextrorotatory isomers.

When glucose is acylated with acid halide or acetic anhydride gives pentaacetate which confirms the presence of five –OH groups. You have seen above in the structure of glucose that there are five hydrogens that are attached to oxygen and they can be replaced by an acetyl group. So, there is a need of 5 moles of acetic anhydride in the acetylation of glucose.

Hence, the correct option is (B).

Alanine (symbol Ala or A) is an α-amino acid that is used in the biosynthesis of proteins. It contains an amine group and a carboxylic acid group, both attached to the central carbon atom which also carries a methyl group side chain. 

Alanine can be synthesized from pyruvate and branched-chain amino acids such as valine, leucine, and isoleucine. Alanine is produced by reductive amination of pyruvate, a two-step process. In the first step, α-ketoglutarate, ammonia and NADH are converted by glutamate dehydrogenase to glutamate, NAD+ and water. In the second step, the amino group of the newly-formed glutamate is transferred to pyruvate by an aminotransferase enzyme, regenerating the α-ketoglutarate, and converting the pyruvate to alanine. The net result is that pyruvate and ammonia are converted to alanine, consuming one reducing equivalent.

\(CH _{3}-\overset{O}{\overset{||}{ \underset{Pyruvate}{C} }}- COO^-\ce{->[aminotransferase]}CH _{3}-\overset{NH_3^+}{\overset{|}{\underset{\text { Alanine }}{ CH }}}- COO ^{-}\)

Hence, the correct option is (A).

The functional groups which are found in amino acids are COOH (carboxyl group) and NH₃ (amine group). 

Every amino acid is formed in such a way that it has a central carbon with hydrogen and an R group (varies for each amino acid), a carboxylic group and an amine group.  It varies for every amino acid. A single (aliphatic) carbon binds all of these groups. The carbon which gets attached directly to the carboxyl group is the alpha position, so all the amino acids in proteins are referred to as alpha-amino acids.

The general structure of amino acid is given as:

Hence, the correct option is (D).

Glucose can be tested by both tollens and benedicts reagent.

Tollens' test, also known as the silver-mirror test, is a qualitative laboratory test used to distinguish between an aldehyde and a ketone. It exploits the fact that aldehydes are readily oxidized (see oxidation), whereas ketones are not. Tollens' test uses a reagent known as Tollens' reagent, which is a colorless, basic, aqueous solution containing silver ions coordinated to ammonia \(\left[ Ag \left( NH _{3}\right)^{2+}\right]\).

Benedict's test is used to test for simple carbohydrates. Benedict's test identifies reducing sugars (monosaccharide's and some disaccharides), which have free ketone or aldehyde functional groups. Benedict's solution can be used to test for the presence of glucose in urine.

Hence, the correct option is (D).

Enzymes are globular proteins and catalyze metabolic reactions in living organisms. They have a specific tertiary structure with an active site complementary to the substrate. They can speed up a reaction but do not get used up. Their activity can be affected by temperature and pH.

Hence, the correct option is (C).

An invert sugar is carbohydrate that on inversion gets converted from one optical rotatory form to another, that is, dextro (+) to laevo (-) or laevo (-) to dextro (+) form. Sucrose is a sugar that is made up of equimolar quantities of glucose and fructose. Sucrose on hydrolysis gives glucose and fructose in the same number of moles. Sucrose during the process of hydrolysis brings about a change in optical rotation and that's why the products are known as invert sugar.

Therefore, an invert sugar is a mixture of glucose and fructose in equimolar quantities.

Hence, the correct option is (D).

Pyranose is a collective term for saccharides that have a chemical structure that includes a 6-membered ring consisting of 5 carbon atoms and 1 oxygen atom. There may be other carbons external to the ring. The name derives from its similarity to the oxygen heterocycle pyran, but the pyranose ring does not have double bonds. A pyranose in which the anomeric OH at C(l) has been converted into an OR group is called a pyranoside.

Hence, the correct option is (B).

The glycosidic linkage involved in linking the glucose units in the amylose part of the starch is \(C _{1}- C _{4}- \alpha-\) linkage.

Amylases starch is a polymer of glucose molecule linked with glycosidic linkage. It comes in two forms, i.e.,  amylose and amylopectin. Here amylose shows a linear structure of glucose units linked together by glycosidic bonds to form a helical structure.

Amylose is a long unbranched chain with 200-100 \(\alpha\)-D-(+) glucose units held by \(C _{1}- C _{4}\) glycosidic linkage.

Hence, the correct option is (D).

Anomeric carbon is carbon whose stereochemistry determines the type of anomer that the compound is. It is used to refer to only the cyclized forms of sugars. In the open-chain form of sugar, the anomeric carbon is known to be the carbonyl carbon that is involved in the aldehydic or the ketonic group. After cyclization, the anomeric carbon is found near the oxygen atom in the pyranose or furanose ring.

The cyclic hemiacetal forms of glucose differ only in the configuration of the hydroxyl group at C−1, called anomeric carbon. Such isomers, i.e., α & β form are called anomers.

When the hydroxyl group on the \(C -1\) atom is pointing downwards, it is called the \(\alpha\)-anomer and when it is pointing upwards, it is called the \(\beta\) - anomer. The structures are:

Hence, the correct option is (A).

Maltose is made up of two α-D-glucose.

Maltose is also known as maltobiose or malt sugar. It is also soluble in water. Maltose is the basic molecule of starch. It is white crystalline sugar. Maltose is formed from two molecules of glucose. When the two molecules bond together, the water molecule is removed. It is prepared from starch by diastase. Maltose is a disaccharide formed from two units of glucose joined with an αbond. So maltose is made up of two α-D-glucose.

Hence, the correct option is (A).

Vitamins A and D are absorbed from the intestines along with fats. These are fat-soluble vitamins, which are absorbed in fat globules (called chylomicrons) that travel through the lymphatic system of the small intestines, and into the general blood circulation within the body.

Hence, the correct option is (A).

On oxidation with a mild oxidising agent like \(Br _{2} / H _{2} O\), the glucose is oxidised to six carbon carboxylic acid (gluconic acid). This indicates that the carbonyl group is present as an aldehydic group.

\(CHO -( CHOH )_{4} CH _{2} OH \stackrel{ Br _{2} \text { water }}{\longrightarrow} COOH -\underset{\text { Gluconic acid }}{( CHOH )_{4}}- CH _{2} OH\)

Hence, the correct option is (C).

Carbohydrates are stored in the human body as glycogen.

The carbohydrates act as the primary supply of energy in the body. It breaks down into smaller units of sugar such as glucose and fructose. This glucose (source of energy) is absorbed by the small intestine and into the bloodstream to the liver, where it breaks the bonds between carbon atoms present. This energy is utilised for basic body functioning and physical activities. When the energy to support various functions is enough, excess of it is stored as glycogen in the muscles and liver. The glycogen is a multibranched polysaccharide of glucose, allowing its rapid dissemination and serving as the main storage form of glucose in the body. Therefore, the carbohydrates are stored as glycogen in the body.

Hence, the correct option is (C).

Commercially glucose is obtained by hydrolysis of starch by heating it with dilute \(H _{2} SO _{4}\) at \(393 K\) under pressure.

\(\underset{\text { Starch }}{\left( C _{6} H _{10} O _{5}\right)_{ n }}+ nH _{2} O\ce{->[H+][393K;2-3atm]}\underset{\text { Glucose }}{ nC _{6} H _{12} O _{6}}\)

Hence, the correct option is (A).

Sucrose is a non-reducing sugar. 

Reducing sugar is any sugar that either has an aldehyde group or is capable of forming one in solution through isomerism. The aldehyde functional group allows the sugar to act as a reducing agent. 

Sucrose is a disaccharide that is a combination of the monosaccharides glucose and fructose with the formula \(C _{12} H _{22} O _{11}\). It is a non-reducing sugar as the molecule does not have the characteristics of reducing sugars. Non-reducing sugars does have a group attached to any of the anomeric carbon. Therefore, they are unable to reduce other compounds.

Hence, the correct option is (B).

Each polypeptide is a protein that has amino acids linked with each other in a specific sequence. This sequence of amino acids is said to be the primary structure of proteins.

Polypeptides are long chains of amino acids linked with peptide bonds and these long chains are called proteins. The primary structure of a protein refers to the linear sequence of amino acids in the polypeptide chain. The primary structure is held together by covalent bonds such as peptide bonds, which are made during the process of protein biosynthesis or translation. The primary structure of proteins tells us about the sequence of amino acids in which they are linked.

Hence, the correct option is (A).

A diabetic person carries a packet of glucose with him always because glucose increases the blood sugar level almost instantaneously.

When the amount of glucose travels into the cells via the bloodstream is termed blood sugar. There is a hormone called insulin, which helps in the travel of glucose from the blood. For a diabetic patient, it is necessary to maintain the level of glucose in the blood. He or she always needs energy. As when they perform a lot of physical work, and they might have a lot of sweating, and the sugar level decreases in the body. At that time the energy is required, so instead of any drink, intake of glucose is a better option. Thus, intake of glucose increases the blood sugar level instantaneously. 

Hence, the correct option is (C).

α-amino acids are the building blocks of protein. 

• They are constituents of all proteins. Chemically proteins are condensation polymers (actual polyamides) in which the monomeric units are the α-amino acids. All the proteins contain the elements carbon, nitrogen, oxygen, sulfur, iron, copper, etc, on partial hydrolysis gives peptides and complete hydrolysis gives α-amino acids. So, option (A) is true.
• Alanine having one amino and one carboxyl group. α-amino acids can be classified into three classes- neutral, acidic, and basic amino acids. Neutral are those which have one amino and one carboxyl group. Alanine comes under this group. So, option (B) is true.
• All naturally occurring proteins from all living organisms consist of L amino acids. A protein exclusively consists of L-amino acids. In contrast, all the sugar belongs to D-series. So, option (C) is not true.
• Glycine is the only naturally occurring amino acid that is optically inactive. All the amino acids are optically active because they have chiral carbon atoms i.e., a carbon atom that has all four substituents different. But in glycine, the carbon atom has one amino, one carboxyl, and two hydrogen groups. So, option (D) is true.

Hence, the correct option is (C).

Amides are different from amino acids as they contain more nitrogen. Amides are a sort of functional group that can't be skipped because of the presence of a nitrogen atom in the compounds. An amide is a functional group that consists of a group and nitrogen atom and may be derived from the varied functional group referred to as carboxylic acid.

Hence, the correct option is (C).

Cellulose is found in abundance in nature.

Cellulose is a type of carbohydrate, containing chains of glucose rings. The cell walls, which are responsible for providing support and rigidity to the plants are made of cellulose. It is also the primary constituent of wood, making it the most abundant organic compound found in nature.

Hence, the correct option is (D).

In fibrous proteins, polypeptide chains are held together by hydrogen bonds and disulphide bonds.

Fibrous proteins are long narrow in shape and they are insoluble in water. The proteins which consist of linear, thread-like polypeptide chains arranged or twisted to form fibers are called fibrous proteins.

Fibrous and globular shapes of proteins are found in the tertiary structure of the protein, the tertiary structure of the protein is stabilized by hydrogen, disulphide, and van der Waals forces. Therefore, we can say that when the polypeptide chain runs parallel and is held together by hydrogen and disulphide bonds then the proteins formed are known as fibrous proteins.

Hence, the correct option is (C).

Starch is a polysaccharide consisting of glucose monomers that are joined by α-1,4 glycosidic linkages. Glucose is stored as a polymer, in plants as starch and in animals as glycogen. It is a polymeric carbohydrate. The basic chemical formula of the starch molecule is (C₆H₁₀O₅)_n.

Hence, the correct option is (B).

D-Glucose and D-Fructose are the hydrolysis products of sucrose.

Sucrose is a saccharose, also known by names such as table sugar, cane sugar, beet sugar, etc. It is a carbohydrate, more specifically, a disaccharide made up of two monosaccharides, namely, glucose and fructose.

Glucose is an aldehyde, which forms a six-carbon ring. Whereas, fructose is a ketone, which forms a five-membered ring (so, a furan). Therefore, on hydrolysis sucrose will break into its monomeric sugars. The reaction can be represented as:

Sucrose is made by linking C1 of alpha-glucose and C2 of beta-fructose. The bond formed between glucose and fructose is known as the 1,2-glycosidic bond. Also, sucrose is a dextrorotatory sugar, which changes to levorotatory, due to the dominant levorotatory nature of fructose.

Therefore, hydrolysis products of sucrose are D-glucose and D-fructose.

Hence, the correct option is (D).

The secondary structure of a protein refers to the helical backbone. Secondary structure refers to the spatial arrangement of amino acid residues that are nearby in the sequence. Some of these arrangements are of a regular kind, giving rise to a periodic structure. The α helix and β strand are elements of secondary structure. The secondary structure arises due to the regular folding of the backbone of the polypeptide chain due to intramolecular hydrogen bonding between the carboxyl and amino groups.

Hence, the correct option is (A).

To convert glucose to saccharic acid, the reagent used is nitric acid.

Dilute nitric acid oxidises glucose to saccharic acid. Primary - OH group and - CHO group of glucose are oxidised to - COOH group.

Dilute nitric acid also oxidises gluconic acid to saccharic acid.

Primary - OH group of gluconic acid is oxidised to - COOH group.

Hence, the correct option is (C).

D and L just tell us the configuration of carbohydrates relative to (+) glyceraldehyde. 

The letters D and L represent the position of the second last hydroxyl group in a carbohydrate. If the carbohydrate has the hydroxyl group at the last chiral carbon towards the right side (when the chain is properly oriented), it is denoted by the letter D and if the hydroxyl group at the last chiral carbon lies towards the left side, it is denoted by the letter L. Proper orientation means that the chain is vertical and the principal functional group is at the top. 

D and L have no relation with dextrorotatory and laevorotatory nature.

Hence, the correct option is (C).

A sulphur-containing amino acid is a cysteine. 

Cysteine is an α-amino acid with the chemical formula \(C _{3} H _{7} NO _{2} S\). It is a semi-essential amino acid, which means that it can be biosynthesized in humans. When taken as a supplement, it is usually in the form of N-acetyl-L-cysteine (NAC). The body makes this into cysteine and then into glutathione, a powerful antioxidant.

Hence, the correct option is (B).