biological chemistry

Disaccharides: Properties, Structure, Formation and Examples (Short Lecture Notes)


Disaccharides Lecture Notes

DISACCHARIDES
(Carbohydrates Part 3: Properties, Structure and Examples of Disaccharides)

What are Disaccharides?

Disaccharides are carbohydrates which contain two covalently linked monosaccharide units. Sucrose, Maltose, Lactose, Trehalose and Cellobiose are naturally occurring disaccharides. The individual monosaccharide units in a disaccharide are called ‘residues’. All disaccharides are soluble in water

Glycosidic bonds links monosaccharide units

The monosaccharide units in disaccharides (and also in polysaccharides) are linked through a special type of covalent bond called Glycosidic bond (specifically O-glycosidic bond). O-glycosidic bond is formed by the reaction between the hydroxyl group of one monosaccharide with the anomeric carbon atom of the other. During the glycosidic bond formation, one molecule of water is eliminated as given in the diagram. Glycosidic bonds are strong covalent bonds and they can be hydrolyzed by treating with mild acids. The hydrolysis of the glycosidic bond of a disaccharide releases its corresponding monosaccharide units.

Structure of Glycosidic Bond

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biological chemistry

Monosaccharides: Definition, Structure, Characteristics, Classification, Examples and Functions


Biochemistry of Monosaccharides

Monosaccharides
Chemical Structure, Characteristics, Examples & Classification

Monosaccharides are Simplest Sugars

Monosaccharides are the simplest carbohydrates. They are polyhydroxy aldehydes or ketones with a carbon backbone. The carbon backbone in monosaccharides usually consists of 3 – 6 carbon atoms. The simplest monosaccharides are glyceraldehyde and dihydroxyacetone (with 3 carbons). The most abundant monosaccharide in nature is a 6 carbon sugar called glucose. Majority of the monosaccharides follow the empirical formula C(H2O)n.

Monosaccharide with five or more carbon can predominantly exist as cyclic structures in the aqueous condition. All monosaccharides are colourless, crystalline solids and that are readily soluble in water but insoluble in nonpolar solvents. Most of the monosaccharides are sweet in taste.

More in Biochemistry: Lecture Notes, MCQ, PPTs, Videos

Polyhydroxy aldehydesChemical Structure of Monosaccharides

Ø  All monosaccharides are polyhydroxy (contain many hydroxyl groups) aldehydes or ketones.

Ø  The hydroxyl groups are attached to the carbon backbone.

Ø  The number of carbon atoms in the backbone of monosaccharides varies from 3 to 6.

Ø  The carbon backbone of monosaccharides is unbranched and individual carbon atoms are connected by single bonds.

Ø  Monosaccharides are broadly classified into Aldoses and Ketoses.

Ø  In the open chain conformation of a monosaccharide, one of the carbon atoms of the backbone is double bonded to an oxygen atom to form the carbonyl group (C=O).

Ø  If the carbonyl group is at the end of the carbon chain it will be an aldehyde group (R – COH) and thus the sugar formed will be an Aldose sugar.

Ø  Similarly, if the carbonyl group is inner to the carbon chain, it will be a keto group (C=O) and the sugar formed will be a Ketose sugar.

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mcq biology

Biology MCQ-04 Biochemistry: Carbohydrates – Part 3 for JRF/NET Life Science Examination


Biochemistry Quizzes

Biology MCQ (Multiple Choice Questions in Life Science)
(Sample/Model/Practice Questions for JRF/NET Life Science Examination, ICMR JRF, DBT JRF, GATE, ICAR NET, PG Entrance)


Biochemistry: Carbohydrates Part 3 (MCQ 04)


1. Which of the following is an example for a trisaccharide?

a.       Verbascose
b.      Stachyose
c.       Raffinose
d.      Sucralose

2. Chrysolaminarin is ________.

a.       A storage polysaccharide of green algae
b.      A storage polysaccharide of brown algae
c.       A storage polysaccharide of red algae
d.      A storage polysaccharide of diatoms

3. Which of the following is an example for an artificial sweetener of saccharide origin?

a.       Sucralose
b.      Saccharin
c.       Stachyose
d.      All of these

4. In a chemical reaction ‘X’ is able to convert Cu2+ ions to Cu+ ions. If ‘X’ is a carbohydrate, which of the following best explains to be the ‘X’?

a.       ‘X’ is a reducing sugar
b.      ‘X’ is a non-reducing sugar
c.       ‘X’ is a monosaccharide
d.      Both (a) and (b)
e.       Both (a) and (c)

5. Which of the following is a reducing sugar?

a.       Glucose in closed ring form
b.      Glucose in open chain form
c.       Sucrose

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mcq biology

Biology MCQ-03 Biochemistry: Carbohydrates – Part 2 for JRF/NET Life Science Examination


Biochemistry Quizzes

Biology MCQ (Multiple Choice Questions in Life Science)
(Sample/Model/Practice Questions for JRF/NET Life Science Examination, ICMR JRF, DBT JRF, GATE, ICAR NET, PG Entrance)


Biochemistry: Carbohydrates Part 2 (MCQ-03)


1.  The vitreous humor of eye is composed of_______.

a.       Heparin
b.      Hyaluronic acid

c.       Keratan Sulfate
d.      Chondroitin sulfate

2. N-acetyl glucosamine (NAG) and N-acetyl muramic acid (NAM) in peptidoglycan is connected by ____glycosidic linkage.

a.       α 1 – 4
b.      β 1 – 4

c.       α 1 – 2
d.      β 1 – 2

3.  Sulbactam is a ____________.

a.       β-lactam antibiotic
b.      β lactamase

c.       β lactamase inhibitor
d.      A class of penicillin

4.  Which of the following is not a sugar molecule of the O-antigen of gram negative bacteria?

a.       Tyvelose
b.      Abequose

c.       2 keto-3-deoxyoctanoate
d.      Teichoic acid

5.  Glycosidic bond between galactose and glucose in lactose is____.

a.       α 1 – 4
b.      β 1 – 4

c.       α 1 – 2
d.      β 1 – 2

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mcq biology

Biology MCQ-02 Biochemistry: Carbohydrates – Part 1 for JRF/NET Life Science Examination


Biochemistry Quizzes

Biology MCQ (Multiple Choice Questions in Life Science)
(Sample/Model/Practice Questions for JRF/NET Life Science Examination, ICMR JRF, DBT JRF, GATE, ICAR NET, PG Entrance)


Biochemistry: Carbohydrates Part 1 (MCQ-02)


1. The general chemical formula of carbohydrate is

a.       (CH2O)n
b.      (CH2O)2n

c.       (CHO)n
d.      CnH2nO

2. Which of the following is an aldotriose?

a.       Dihydroxyacetone
b.      Glyceraldehyde

c.       Ribulose
d.      Erythrose

3. What is the molecular formula of sucrose?

a.      C12H22O11
b.      C10H20O10

c.       C6H12O6
d.      C12H20O11

4. The glycosidic linkage between glucose molecule in maltose is

a.      β 1 – 4
b.      α 1 – 2

c.       α 1 – 4
d.      β 1 – 2

5. A keto pentose will have _____ sterioisomers.

a.      4
b.      6

c.       8
d.      10

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