Important Questions On Carbohydrate Chemistry

Explore important questions on carbohydrate chemistry, covering key topics like monosaccharides, disaccharides, polysaccharides, and their biological significance. These questions will help reinforce essential concepts for NEET PG preparation, providing a solid foundation in carbohydrate structure, classification, and metabolic functions critical for medical studies and exams.

Q. How to classify the simple carbohydrate where only carbohydrate units are present?

Ans. The classification of simple carbohydrates is based on the number of carbohydrate units—into three types:

• Monosaccharides— single carbohydrate unit in them
• Oligosaccharides — 2 to 10 units of carbohydrates. E.g., disaccharides
• Polysaccharides — these have more than 11 units of polysaccharides

Q. In glucose, how many functional groups do you find?

Ans. Only one functional group is present in glucose and that is monosaccharide. The functional group that presents in glucose is aldehyde. Therefore, glucose is an Aldose.

• Glucose is a hexose → glucose has 6 carbon atoms.
• Quick tips:
  • Based on the no. of carbon atoms – glucose is a hexose
  • Based on the functional group – glucose is an aldehyde

Q. In fructose, how many functional groups do you find?

Ans. In Fructose, only one functional group is present, that is monosaccharide because it  has only one sugar unit. The functional group that presents in fructose is the Ketone group – makes fructose ketose.

• Quick tips:
  • Based on the no. of carbon atoms – 6 carbon atoms – fructose is a hexose
  • Based on the functional group – one sugar unit makes it a ketose – ketone group.
• Glucose and fructose share the same molecular formula – C6 H12 O6 

Q. Why are glucose and fructose known as reducing sugars?

Ans.

• Because it has reduced sugar, both have free carbonyl groups.
• Glucose — free carbonyl group in first carbon atom
• Fructose — free carbonyl group in second carbon atom

Q. Why is sucrose non-reducing?

Ans. Because sucrose is obtained by linking the 1st carbon atom of glucose & 2nd carbon atom of fructose; linkage presents in sucrose alpha (1,2)

Q. Which one will be the branch among these two?

Ans.

• Storage will be branched – then only it will accommodate more molecules in limited space.
• Structural homopolysaccharides will be unbranched.

Q. Identify the Structure:

1. Sucrose
2. Lactose
3. Maltose
4. Isomaltose

Explanation:

How many carbon atoms in the ring?

• 4 carbon atoms - Fructose
• 5 carbon atoms - Glucose /Mannose /Galactose

How to know which out of the three it is?

• Check 2nd & 4th carbon atoms.
  • If in both 2nd & 4th carbon atoms, OH lies below the plane it is Glucose.
  • If in the 2nd carbon atom, if OH lies above the plane of the ring it is Mannose.
  • If in the 4th carbon atom, if OH lies above the plane of the ring it is Galactose.

Q. Which Mucopolysaccharides are present in the glomerular basement membrane?

Ans: Heparan Sulphate

MCQs on Carbohydrate Chemistry 

Q. All the following are trioses except

1. Maltotriose
2. Glycerose
3. Dihydroxyacetone
4. Glyceraldehyde

Q. The linkage present in lactose is:

1. ɑ (1,4)
2. β (1,4)
3. ɑ (1,2)
4. β (1,2)

Q. The linkage present in isomaltose is:

1. ɑ (1,4)
2. β (1,4)
3. ɑ (1,6)
4. β (1,6)

Q. All the following are aldoses except

1. Glucose
2. Galactose
3. Ribose
4. Ribulose

Q. All the following are components of mucopolysaccharides except?

1. Uronic acid
2. Amino sugar
3. Sulphate
4. NANA

• NANA (N-Acetylneuraminic acid) is a Component of Glycolipid, specifically ganglioside.

Q. The mucopolysaccharide with galactose is?

1. Hyaluronic acid
2. Heparin
3. Heparan sulphate
4. Keratan sulphate

Q. The mucopolysaccharide with glucuronic acid is?

1. Hyaluronic acid
2. Heparin
3. dermatan sulphate
4. Heparan sulphate

Q. The mucopolysaccharide present in the cornea is?

1. Keratan sulphate II
2. Heparan sulphate
3. Dermatan sulphate
4. Keratan sulphate I

Q. The mucopolysaccharide with glucosamine acid is?

1. Hyaluronic acid
2. Chondroitin sulphate
3. Dermatan sulphate
4. Keratan sulphate

Q. An 18-month-old female child presented with a flat nasal bridge, big lips, macroglossia, gingival hypertrophy, abdominal distension, short stature, and delayed milestones. On the examination, hepatosplenomegaly and an inguinal hernia were observed. Chest X-ray shows cardiomegaly, and Urinary MPS were elevated. WBC L-iduronidase activity was low. Which of the following would accumulate?

1. Heparan sulphate
2. Keratan sulphate
3. Hyaluronic acid
4. Chondroitin sulphate

Q. In O -linked glycoproteins, the carbohydrate side chains are attached to which amino acids of the core proteins?

1. Serine
2. Cysteine
3.  Asparagine
4.  Proline

Q. Which of the following is true about proteoglycans?

1. They are receptor proteins
2. They are uncharged
3. They hold excess water
4. They have lesser carbohydrate content than glycoproteins

Q. Which of the following is true about glycoproteins?

1. The side chains provide them with negative charges.
2. They are present in extracellular membranes.
3. They hold excess water.
4. Plasma proteins are glycoproteins.

Q. Glucose and fructose are examples of ?

A. Optical isomerism

B. Functional isomerism

C. Stereoisomerism

D. Epimerism

Q. Ribose and arabinose are examples of ?

1. Optical isomerism
2. Diastereoisomerism
3. Enantiomerism
4. Epimerism

Q. Ribose and Xylose are examples of ?

1. Optical isomerism
2. Diastereoisomerism
3. Enantiomerism
4. Epimerism

Q. D- Glucose and L- Glucose are examples of ?

1. Optical isomerism
2. Diastereoisomerism
3. Enantiomerism
4. Epimerism

Q. An intern lab technician prepared a fresh glucose solution (100mg/dL). She estimated the concentration of the same using the glucose oxidase peroxidase method and found the concentration to be 10mg/dL. The probable cause is:

1. The glucose oxidase used was ineffective.
2. The weighing balance is defective.
3. Glucose oxidase acts only on the beta form.
4. Glucose oxidase acts only on the alpha form.

Q. All the following answer Benedict's test positively except?

1. Ribose
2. Vitamin C
3. Homogentisic acid
4. Trehalose

Explanation: Ribose is a pentose, Vitamin C is an antioxidant, and Homogentisic acid is a reducing substance. All three answer Benedict's test, whereas Trehalose is a non-reducing disaccharide made of 2 residues of Glucose (a1-1 linkage).

Q. Barfoed's test is not answered by?

1. Maltose
2. Glucose
3. Fructose
4. Ribose

Explanation: Maltose is a disaccharide made of 2 glucose residues with a 1-4 linkage.

Q. Foulger's test is not answered by?

1. Erythrose
2. Ribulose
3. Fructose
4. Sedoheptulose

Explanation: Foulger's test is positive for ketose, whereas erythrose is an aldose.

Image Based MCQ

Q. Identify the structure.

1. Heparan sulphate
2. Chondroitin sulphate
3. Dermatan sulphate
4. Keratan sulphate

Q. Identify the Image

1. N-linked Glycoprotein
2. O -linked Glycoprotein
3. Proteoglycan
4. GPI anchored Glycoprotein

Q. Identify the structure.

A. Heparan sulphate

B. Chondroitin sulphate

C. Dermatan sulphate

D. Keratan sulphate

Q. A person gives her urine sample for the routine screening test. Benedict's test result is as follows. All of the following can be a cause except.

1. Multiple Myeloma
2. Pregnancy
3. Fanconi's syndrome
4. Galactosemia

Explanation: Multiple Myeloma is plasma cell neoplasia, the monoclonal proliferation of plasma cells and excess production of antibodies, a disproportionate product of light chains. In this case, light chains will be excreted through urine, called Bence Jones protein (non-reducing)

Q. A person's urine answers Benedict's test. The biochemist runs a battery of urine tests to detect the reducing sugar present in urine. Based on the images provided below find out the substance found in urine. Which of the following is the most probable cause?

1. Diabetes Mellitus
2. Fructosuria
3. Fanconi's syndrome
4. Galactosemia

Integrated Clinical Case-Based MCQS

Q. A 21-year-old man presents with diarrhea, bloating, flatulence, and frothy stools every time he consumes milk and ghee butter. The probable enzyme detects in this condition is:

1. Aldolase B
2. Fructokinase
3. Galactose-1-phosphate uridyl Transferase
4. Lactase

Q. Neonate presents with diarrhea, incessant cry, and frothy stools. Perianal rashes are prominent. The neonate responded well when the child was given rice porridge. What is the test that can be performed to diagnose this condition?

1. Schilling's test
2. Guthrie's test
3. Methane Breath test
4. Stool acidity

Q. A 45-year-old man presents with multiple joints pain, intervertebral disc bulges, and prolapses. On enquiry, he gives a history of urine turning dark on standing. Which of the following screening tests will be positive in the condition?

1. Ferric Chloride test
2. Guthrie's test
3. Cyanide nitroprusside test
4. Benedict's test

Explanation:

• Urine turning dark indicates alkaptonuria (alkapton means black)
• Ferric chloride test and Guthrie's test is a screening test for Phenylketonuria.
• Cyanide nitroprusside test is done to detect Homocystinuria.

One Liners

• Glucose and fructose are functional isomers.
• Inulin is a homopolysaccharide made up of fructose.
• Chitin is made up of N- Acetyl Glucosamine.
• Non-reducing disaccharides are sucrose and trehalose.
• In starch, amylose is unbranched, and amylopectin is branched.
• The Mucopolysaccharide with galactose is Keratan sulphate
• Mucopolysaccharide with Iduronic acid are Heparan sulphate and Dermatan sulphate.
• Mucopolysaccharides with galactosamine are Chondroitin sulphate and Dermatan sulphate.
• The Mucopolysaccharide present in the Glomerular Basement membrane is Heparan sulphate.
• The urine test to detect the presence of a reducing substance is Benedict's test.
• The test done to detect the presence of reducing monosaccharides is Barfoed's test.
• Galactose can be detected by the Mucic Acid test.
• Seliwanoff's test is answered by ketoses (urine sugar- fructose).
• Bial's test is answered by pentoses.

Also Read: Amino Acid Protein Chemistry

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