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What is Biochemistry?

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The study of chemistry with in a living system is known as biochemistry.

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Living systems are made up of which Biomolecules?

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Living systems are made up of various complex biomolecules like carbohydrates, proteins, nucleic acids, lipids etc.

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What are monosaccharides?

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Monosaccharides are carbohydrates that can not be hydrolysed further to give simpler units of polyhydroxy aldehyde or ketone.

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Describe detailed information on classification of carbohydrates.

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Carbohydrates are classified on the basis of their behaviour on hydrolysis. They have been broadly divided into following 3 groups
(i) Monosaccharide compounds: A carbohydrate that can not be hydrolysed further to give simpler unit of polyhydroxy aldehyde or ketone is called a monosaccharide.
About 20 monosaccharides are known to occur in nature. Some common examples are glucose, fructose, ribose, etc.
(ii) Oligosaccharide compounds: Carbohydrates that yield two to ten monosaccharide units, on hydrolysis are called oligosaccharides.
They are further classified as disaccharides, trisaccharides, tetrasaccharides, etc., depending upon the number of monosaccharides they provide on hydrolysis.
Amongst these the most common are disaccharides. The two monosaccharide units obtained on hydrolysis of a disaccharide may be same or different.
For example, one molecule of sucrose on hydrolysis gives one molecule of glucose and one molecule of fructose where as maltose gives two molecules of only glucose.
(iii) Polysaccharide compounds: Carbohydrate which yield a large number of monosaccharide units on hydrolysis are called polysaccharides.
Some common examples are starch, cellulose, glycogen, gums etc. Polysaccharides are not sweet in taste. Hence, they are also called non-sugars.

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Give primary information about carbohydrate compounds?

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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(H 2 O)y and were considered as hydrates of carbon from where the name carbohydrate was derived.
For example, the molecular formula of glucose (C6H12O6) fits into this general formula, C 6(H 2 O)6.
But all the compounds which fit into this formula may not be classified as carbohydrates. For example acetic acid (CH 3 COOH) fits into this general formula, C 2(H 2 O)2 but is not a carbohydrate.
Similarly rhamnose, (C 6 H 12 O 5) 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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Note on preparation of glucoseOR Explain the preparation of glucose with it's

equations.

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Glucose occurs freely in nature as well as in the combined form. It is present in sweet fruits and honey. Ripe grapes also contain glucose in large amounts. It is prepared as follows:
(1) From sucrose (sugar cane): If sucrose is boiled with dilute HCl or H 2 SO 4 in alcoholic solution, glucose and fructose are obtained in equal amounts.
C 12 H 22 O 11 + H 2 O C 6 H 12 O 6 + C 6 H 12 O 6
Sucrose Glucose + Fructose
(2) From starch: Commercial glucose is obtained by hydrolysis of starch by boiling it with dilute H 2 SO 4 at 393 K under pressure.
(C 6 H 10 O 5)n + nH 2 O nC 6 H 12 O 6
Starch or cellulose Glucose

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Explain the classification of monosaccharide compounds.

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Monosaccharides are further classified on the basis of number of carbon atoms and the functional group present in them.
If a monosaccharide contains an aldehyde group it is known as an aldose and if it contains a keto group it is known as ketose.
Number of carbon atoms constituting the monosaccharide is also introduced in the name. e.g. 3 carbon containing monosaccharide is known as triose and 4 carbon containing monosaccharide is known as tetrose.
Different types of monosaccharide compounds are given below in table:

Carbon atoms | General term | Aldehyde | Ketone
3 | Triose | Aldotriose | Ketotriose
4 | Tetrose | Aldotetrose | Ketotetrose
5 | Pentose | Aldopentose | Ketopentose
6 | Hexose | Aldohexose | Ketohexose
7 | Heptose | Aldoheptose | Ketoheptose

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Explain by giving an equation how the presence of carbonyl group and five –OH groups in the structure of glucose is determined. OR Write the equation reactions of glucose with NH2OH, HCN, and acetic anhydride and state what information is obtained about the structure of glucose through it.OR Explain presence of Five –OH group in structure of glucose.

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Glucose reacts with hydroxylamine to form an oxime and adds a molecule of hydrogen cyanide to give cyanohydrin. These reactions confirm the presence of carbonyl group in glucose.
Acetylation of glucose with acetic anhydride gives glucose penta–acetate which confirms the presence of five –OH groups. Since, it exists as a stable compound, five –OH groups should be attached to different carbon atoms.

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Draw the stereo structure of glucose, gluconic acid and saccharic acid given by Fischer.

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The exact spatial arrangement of different –OH groups was given by Fischer after studying many other properties.
It's configuration is correctly represented as I. So gluconic acid is represented as II and saccharic acid III.
I II III

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Explain the D and L notation method of spatial arrangement with respect to glucose.

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The letters 'D' or 'L' before the name of any compound indicate the relative configuration of a particular stereoisomer of a compound with respect to configuration of some other compound, configuration of which is known.
In the case of carbohydrates, this refers to their relation with a particular isomer of glyceraldehyde.
Glyceraldehyde contains one asymmetric carbon atom and exists in two enantiomeric forms as shown below.
(+)–Glyceraldehyde (–)–Glyceraldehyde
(+) Isomer of glyceraldehyde has 'D' configuration it means that the –OH group lies on right hand side in the structure.
All those compounds which can be chemically correlated to D(+) isomer of glyceraldehyde are said to have D-configuration.
Where as those which can be correlated to L (–) isomer of glyceraldehyde are said to have L – configuration. In 'L(–)' isomer –OH group is on left hand side.
For assigning the configuration of monosaccharides it is the lowest asymmetric carbon atom (as shown below) which is compared. As in (+) glucose –OH on the lowest asymmetric carbon is on the right side which is compared to (+) glyceraldehyde. So, (+) glucose is assigned D-configuration.
D–(+)–Glyceraldehyde D–(+)–Glucose
Other asymmetric carbon atoms of glucose are not considered for this comparison. Also, the structure of glucose and glyceraldehyde is written in a way that most oxidised carbon (in this case -CHO) is at the top.

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Note on: Cyclic structure of glucose.

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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:
a–D(+)–Glucose b–D(+)–Glucose
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 b-form are called anomers.
The six membered cyclic structure of glucose is called pyranose structure (a- or b-) 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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What is fructose? Explain the structure of fructose.

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Fructose is an important ketohexose. It is obtained along with glucose by the hydrolysis of disaccharide sucrose.
It is natural monosaccharide found in fruits, honey and vegetables. In it's pure form it is used as a sweetner.
Structure of fructose:
Fructose has the molecular formula C 6 H 12 O 6.
On the basis of it's reactions it was found to contain a ketonic functional group at carbon number 2 and six carbons in straight chain as in the case of glucose.
It belongs to D-series and is a laevorotatory compound. It is appropriately written as
D(–) fructose.
Its open chain structure is as shown.
D–(–)–Fructose
It also exists in two cyclic forms which are obtained by the addition of –OH at C 5 to the group.
The ring, thus formed is a five membered ring and is named as furanose with analogy to the compound furan.
Furan is a five membered cyclic compound with one oxygen and four carbon atoms.
The cyclic structures of two anomers of fructose are represented by Haworth structures as given.
a–D-Fructofuranose b–D-Fructofuranose

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What do you understand by the term glycosidic linkage?

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The two monosaccharides are joined together by an oxide linkage formed by the loss of water molecule. Such a linkage between two monosaccharide units through oxygen atom is called glycosidic linkage. In maltose the glycosidic linkage is as shown below.

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What are reducing sugars?OR Explain the classification of carbohydrate compounds on the basis of their reducing nature.

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Carbohydrate compounds are classified as reducing sugars and non reducing sugars.
Reducing sugars are carbohydrates that reduce Fehling’s solution and Tollen’s reagent. All monosaccharides and disaccharides, excluding sucrose, are reducing sugars.

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Write short note on: Sucrose.OR Explain: Sucrose is a non reducing sugar (figure not essential).

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One of the common disaccharides is sucrose which on hydrolysis gives equimolar mixture of D–(+)glucose and D–(–)–fructose.
C 12 H 22 O 11 + H 2 O → C 6 H 12 O 6 + C 6 H 12 O 6
Sucrose D–(+)–Glucose D–(–)–Fructose
These two monosaccharides are held together by a glycosidic linkage between C 1 of a–D Glucose and C 2 of b–D fructose.
Since the reducing groups of glucose and fructose are involved in glycosidic bond formation, sucrose is a non-reducing sugar.
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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Short note on: Maltose

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Maltose is composed of two a-D-glucose.
C 12 H 22 O 11 + H 2 O → C 6 H 12 O 6 + C 6 H 12 O 6
Maltose a–D–Glucose a–D–Glucose
In maltose C 1 of one glucose (I) is linked to C 4 of another glucose unit (II).
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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Write Short note on: Lactose

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It is more commonly known a s milk sugar si nce this disaccharide is found in milk.
It is composed of b-D-galactose and b-D-Glucose
C 12 H 22 O 11 + H 2 O → C 6 H 12 O 6 + C 6 H 12 O 6
Lactose b-D-galactose b-D-glucose
The linkage is between C 1 of galactose and C 4 of glucose.
Free aldehyde group may be produced at C–1 of glucose unit, hence it is al so a reducing sugar.

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Write detailed note on: Starch

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Starch is the main storage polysaccharide of plants.
It is the most important dietary source for human beings.

- High content of starch is found in cereals, roots, tubers and some vegetables.
- It is a polymer of a-glucose and consists of two components amylose and amylopectin.
- Amylose is water soluble component which constitutes about 15–20% of starch.
- Chemically amylose is along unbranched chain with 200–1000 a-D-(+)-glucose units held together by C 1-C 4 glycosidic linkage.

Amylopectin is insoluble in water and constituents about 80–85% of starch.
It is a branched chain polymer of a–D–glucose units in which chain is formed by C 1–C 4 glycosidic linkage where as branching occurs by C 1–C 6 glycosidic linkage.

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Write Short note on: Cellulose.

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Cellulose occurs exclusively in plants and it is the most abundant organic substance in plant kingdom.
It is a predominant constituent of cell wall of plant cells.
Cellulose is a straight chain polysaccharide composed only of b–D–glucose units which are joined by glycosidic linkage between C 1 of one glucose unit and C 4 of the next glucose unit.

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What is the basic structural difference between starch and cellulose?

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Starch consists of two components – amylose and amylopectin.
Amylose is a long linear chain of a–D–(+)–glucose units joined by C 1–C 4 glycosidic linkage (a–link).
Amylopectin is a branched – chain polymer of a–D–glucose units, in which the chain is formed by glycosidic C 1–C 4 glycosidic linkage and the branching occurs by C 1–C 6 glycosidic linkage.
On the other hand cellulose is a straight – chain polysaccharide of b–D–glucose units joined by C 1–C 4 glycosidic linkage (b–link).

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Write short note on: Glycogen

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“The carbohydrates are stored in animal body as glycogen.”
It is also known as animal starch because its structure is similar to amylopectin and is rather more highly branched.
It is present in liver, muscles and brain.
When the body needs glucose, enzymes break down glycogen into glucose.

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What is glycogen? How is it different from starch?

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The carbohydrates are stored in animal body as glycogen.
It is also known as animal starch because it’s structure is similar to amylopectin and is highly branched.
A major difference between glycogen and starch is their chain length.
The amylopectin chain consists of 20–25 a–D– glucose units while glycogen has a chain of 10–14 a–D–glucose units.
Glycogen is more branched than amylopectin.
It is present in liver, muscle and brain.
When the body needs glucose, enzymes break down glycogen to form glucose.
Glycogen is also found in yeast and fungi.
Starch is the most important dietary source for human beings.
High content of starch is found in cereals, roots, tubers and some vegetables.

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Write the two main functions of carbohydrates in plants.

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The two main functions of carbohydrates are as follows:
(i) As a constitutive component of plant cell wall: Cellulose, a polysaccharide is used to build the cell wall.
(ii) As a storage of food: Polysaccharides such as starch as storage molecule.

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Explain the importance of carbohydrate compounds.

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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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Give primary information about the protein compounds.

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Protein are the most abundant biomolecules of the living system.
Chief sources of proteins are milk, cheese, pulses, peanuts, fish meat etc. They occur in every part of the body and form the fundamental basis of structure and functions of life.
They are also required for growth and maintenance of the body.
The word protein is derived from g reek word "Proteios" which means primary or of prime importance.
All proteins are polymers of a–amino acids.

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How do you explain the amphoteric behaviour of amino acids? OR Explain the Zwitter ion formation in an amino acid compounds.

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Amino acids are usually colourless, crystalline solids.
These are water-soluble, high melting solids and behaves like salts rather than simple amines or carboxylic acids.
This behaviour is due to the presence of both acidic (Carboxylic acid group) and basic (amino group) groups in the same molecule.
In aqueous solution the carboxyl group can lose a proton and amino group can accept a proton; giving rise to a dipolar ion known as zwitter ion.
This is neutral but contains both positive and negative charges.
In zwitter ionic form, amino acids show amphoteric behaviour as they react both with acids and bases.

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What are amino acid compounds? Explain the nomenclature of amino acid compounds.

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Amino acids contain amino (–NH 2) and carboxyl (–COOH) functional groups.
Depending upon the relative position of amino group with respect to carboxyl group, the amino acids can be classified as a, b, g, d, and so on.
Only a – amino acids are obtained on hydrolysis of proteins.
They may contain other functional groups also.
All a – amino acids have trivial names, which usually reflect the property of that compound or it's source.
Glycine is so named since it has sweet taste (in g reek glykos means sweet) and tyrosine was first obtained from cheese (in Greek, tyros means cheese).
Amino acids are generally represented by a three letter symbol, sometimes one letter symbol is also used.
e.g. glycine 3-letter symbol is 'Gly' and one letter symbol is "G".

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What are essential and non essential amino acids? Give 2 examples of each type.OR Write note on classification of amino acid compounds.

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Amino acid compounds can be classified on the basis of two things:
Relative number of amino and carboxyl group available in their molecule.
According to the need of them in our body.
(i) Amino acids are classified as acidic, basic or neutral depending upon the relative number of amino and carboxyl groups in their molecule.
Equal number of amino and carboxyl groups makes it neutral. e.g., Glycine, Alanine, Leucine etc.
More number of carboxyl than amino groups makes i t acidic e.g., Glutamic acid, Aspartic acid.
More number of amino than carboxyl groups makes it basic. e.g., Arginine, Lysine, Tryptophan and Histidine.
(ii) Based on need of amino acids can be classified in two types. Essential and non-essential.
The amino acids which can be synthesized in the body are known as non essential amino acids. e.g., Glycine, Alanine, Glutamine etc.
The amino acids which can not be synthesized by the body but must be obtained through diet are known as essential amino acid. e.g., Valine, Leucine, Isoleucine. etc...

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Give the names naturally occurring amino acid compounds along with their 3 letter and 1-letter symbol.

Amino Acids | Side Chain R | Symbol | Letter Code
1. Glycine | H | Gly | G
2. Alanine | – CH 3 | Ala | A
3. Valine* | (H 3 C)2 CH– | Val | V
4. Leucine* | (H 3 C)2 CH–CH 2– | Leu | L
5. Isoleucine* |  | Ile | I
6. Arginine* |  | Arg | R
7. Lysine* | H 2 N–(CH 2)4– | Lys | K
8. Glutamic acid | HOOC–CH 2–CH 2– | Glu | E
9. Aspartic acid | HOOC–CH 2– | Asp | D
10. Glutamine | H 2 N––CH 2–CH 2– | GIn | Q
11. Aspargine | H 2 N––CH 2– | Asn | N
12. Threonine* | H 3 C–CHOH– | Thr | T
13. Serine | HO–CH 2– | Ser | S
14. Cysteine | HS–CH 2– | Cys | C
15. Methionine* | H 3 C–S–CH 2–CH 2– | Met | M
16. Phenylalanine* | C 6 H 5–CH 2– | Phe | F
17. Tyrosine | (p) HO–C 6 H 4–CH 2– | Tyr | Y
18. Tryptophan* |  | Trp | W
19. Histidine* |  | His | H
20. Proline | a = Entire structure | Pro | P

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In the above table * means Essential Amino Acids.

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Explain the property of optical activity of an amino acids.

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Except glycine, all other naturally occurring a-amino acids are optically active since the a-carbon atom is asymmetric.
These exist both in "D" and "L" forms.
Most naturally occurring amino acids have
L – configuration.
L – amino acids are represented by writing the –NH 2 group on left hand side.

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What is a peptide bond or peptide chain? Elaborate on how protein compounds are formed from amino acid compounds.

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Proteins are the polymers of a-amino acids and they are connected to each other by peptide bond or peptide linkage.
Chemically peptide linkage is an amide formed between –COOH group and –NH 2 group.
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 –.
The product of the reaction is called a dipeptide because it is made up of two amino acids.
For example when carboxyl group of glycine combines with the amino group of alanine we get a dipeptide glycylalanine.
The third amino acids combines to a dipeptide, the product is called a tripeptide.
A tripeptide contains three amino acids linked by two peptide linkages.
Similarly, when four, five or six amino acids are linked to the respective products are known as tetrapeptide, pentapeptide or hexapeptide, respectively.
When the number of such amino acids is more than ten, then the products are called polypeptides.
A polypeptide with more than hundred amino acid residues, having molecular mass higher than 10,000 u is called a protein.
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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What are the common types of secondary structure of proteins?OR Write note on secondary structure of proteins.

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The secondary structure of protein refers to the shape in which a long polypeptide chain can exist.
They are found to exist in two different types of structures viz. a - helix and b - pleated sheet structure.
The structures arise due to the regular folding of the backbone of the polypeptide chain due to hydrogen bonding between and – NH – groups of the peptide bond.
α - Helix structure: a - Helix is one of the most common ways in which a polypeptide chain forms all possible hydrogen bonds by twisting into a right handed screw (helix) with the –NH group of each amino acid residue hydrogen bonded to the of an adjacent turn of the helix as shown diagram.
α-Helix structure of proteins
β-Pleated sheet structure: In b-structure all peptide chains are stretched out to nearly maximum extension and then laid side by side which are held together by intermolecular hydrogen bonds.
The structure resembles the pleated folds of drapery and therefore is k nown as b-pleated sheet.

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Write a note on primary structure of protein compounds.

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Proteins may have one or more polypeptide chains.
“Each polypeptide in a protein has amino acids linked with each other in a specific sequence and this sequence of amino acids is said to be the primary structure of that protein.”
Any change in the primary structure i.e., the sequence of amino acids creates a different protein.

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What type of bonding helps in stabilising the α-helix structure of proteins?

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H-bonding helps in stabilising the a-helix structure of proteins.
A polypeptide chains forms all possible hydrogen bonds in a-helix structure.
In this structure, polypeptide chain twists into a right handed screw (helix) with the –NH group of each amino acid residue hydrogen bonded to the of an adjacent turn of the helix.

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Write a note on tertiary structure of protein compound.

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“The tertiary structure of proteins represents overall folding of the polypeptide chains i.e., further folding of the secondary structure.”
It gives rise to two major molecular shapes viz. Fibrous and globular.
The main forces which stabilise the 2° and 3° structures of proteins are hydrogen bonds, disulphide linkages, van der Waals and electrostatic forces of attraction.
Tertiary structure

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What is quaternary structure of proteins?

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Some of the proteins are composed of two or more polypeptide chains referred to as sub-units. The spatial arrangement of these subunits with respect to each other is known as quaternary structure.
e.g. haemoglobin

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Differentiate between globular and fibrous proteins.

OR
Explain the classification of protein compound based on its molecular shape.

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Proteins can be classified into two types on the basis of their molecular shape.
(a) Fibrous protein compounds: When the polypeptide chains run parallel and are held together by hydrogen and disulphide bonds, then fibre-like structure is formed. Such proteins are generally insoluble in water. Some common example are keratin (present in hair, wool, silk) and myosin (present in muscles) etc.
(b) Globular protein compounds: This structures results when the chains of polypeptides coil around to give a spherical shape. These are usually soluble in water. Insulin and albumins are the common examples of globular proteins.

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What is the effect of denaturation of the structure of proteins?

OR Explain the denaturation of protein compounds.

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“Protein found in a biological system with a unique 3-D structure and biological activity is called a native protein.”
When a protein in its native form, is subjected to physical change like change in temperature or chemical change like change in pH, the hydrogen bonds are disturbed.
Due to this globules unfold and helix get uncoiled and protein loses its biological activity. This is called denaturation of protein.
During denaturation 2° and 3° structures are destroyed but 1° structure remains intact.
The coagulation of egg white on boiling is a common example of denaturation. Another example is curdling of milk is caused due to the formation of lactic acid by the bacteria present in milk.

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What are enzymes?

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Enzymes are proteins that catalyse biological reactions.
They are very specific in nature and catalyse only a particular substrate. Enzymes are usually named after the particular substrate or class of substrate and sometime after the particular reaction.

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Explain the mechanism of enzyme action.

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Enzymes are needed only in small quantities for the progress of a reaction.
Similar to the action of chemical catalysts enzymes are said to reduce the magnitude of activation energy.
For example activation energy for acid hydrolysis of sucrose is 6.22 KJ / mol, while the activation energy is only 2.15 KJ / mol. when hydrolysed by the enzyme sucrase.

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Explain the nomenclature of Enzymes.

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They are generally named after the compound or class of compounds upon which they work.
For example, the enzyme that catalyses hydrolysis of maltose into glucose is named as maltase.
C 12 H 22 O 11 + H 2 O 2C 6 H 12 O 6
Maltose Glucose
Sometimes enzymes are also named after the reaction, where they are used.
For example the enzymes which catalyse the oxidation of one substrate with simultaneous reduction of another substrate are named as oxidoreductase enzymes.
The ending of the name of an enzyme is ‘ase’.

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What are vitamin compounds? Give primary information about vitamin compounds.

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“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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How are vitamins classified? Name the vitamin responsible for the coagulation of blood.OR Explain the classification of vitamin compounds.

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Vitamins are classified into two groups depending upon their solubility in water or fat.
(i) Fat soluble vitamins: Vitamins which are soluble in fat and oils but insoluble in water are kept in this group. These are vitamins A, D, E and K. They are stored in liver and adipose (fat storing) tissues.
(ii) Water soluble vitamins: B group vitamins and vitamin C are soluble in water so they are grouped together. Water soluble vitamins must be supplied regularly in diet because they are readily excreted in urine and cannot be stored (except vitamin B 12) in our body.
Vitamin K increases blood clotting time.

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Why B complex vitamine compounds are essential for us? Describe their important sources.

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Deficiency of vitamin B 1 (thiamine) leads to the disease like Beriberi (loss of appetite, retarded growth). So, it is essential for us. Important sources are yeast, milk, green vegetables and cereals. etc....
Deficiency of vitamin B 2 (Riboflavin) leads to the cheilosis (fissuring at corners of mouth and lips), digestive disorders and burning sensation of the skin, so it is essential for us. Important sources are milk, egg white, liver and kidney.
Deficiency of vitamin B 6 (Pyridoxine) leads to convulsions so it is essential for us. Important sources are yeast, milk, egg yolk, cereals and grams.
Deficiency of vitamin B 12 leads to pernicious anaemia (RBC deficient in haemoglobin), so it is essential for us. Important sources are meat, fish, egg and curd.

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Why vitamin D, E and K compounds are essential for us? Describe their important sources.

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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 it is essential for us. Important sources are vegetable oils like wheat germ oil, 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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Write a note on chemical composition of nucleic acid compounds.

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Complete hydrolysis of DNA (or RNA) yields a pentose sugar, phosphoric acid and nitrogen containing hetero cyclic compounds (called bases).
In DNA molecules the sugar moiety is b-D-2 deoxy-ribose where as in RNA molecule it is b-D-ribose.
DNA contains four bases viz, adenine (A), guanine (G), cytosine (C) and thymine (T). RNA also contains four bases, the first three bases are same as in DNA but the fourth one is uracil (U).

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What are the different types of RNA found in the cell?OR Write a note on structure of RNA.

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In secondary structure of RNA, helices are present which are only single stranded.
Sometimes they fold back on themselves.
RNA molecules are of 3 types and they perform different functions.
They are named as messenger RNA (m-RNA), ribosomal RNA (r-RNA) and transfer RNA (t-RNA).

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Give primary information about nucleic acid compounds.

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Every generation of each and every species resembles its ancestors in many ways.
These characteristics transmitted from one generation to the next generation.
It has been observed that nucleus of a living cell is responsible for this transmission of inherent characters also called heredity.
The particles in nucleus of the cell, responsible for heredity are called chromosomes which are made up of proteins and another type of biomolecules called nucleic acids.
These are mainly of two types, the deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).
Nucleic acids are long chain polymers of nucleotides, so they are also called Polynucleotides.

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Explain the structure of nucleic acid compounds.

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A unit formed by the attachment of a base to 1' position of sugar is known as nucleoside.
In nucleosides the sugar carbons are number as 1', 2', 3' etc. In order to distinguish these from the bases - when nucleoside is linked to phosphoric acid at 5'-position of sugar moiety, we got a nucleotide.
Nucleotides are joined together by phosphodiester linkage between 5' and 3' carbon atoms of the pentose sugar. The formation of a typical dinucleotide is shown in figure.
A simplified version of nucleic acid chain is as shown below.

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What is the difference between a nucleoside and a nucleotide?

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A nucleoside is formed by the attachment of a base to 1’ position of sugar.
On the other hand all three basic component of nucleic acids (i.e. pentose sugar, phosphoric acid and base) are present in nucleotide.

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Write a note on: Double Helical structure of DNA.

5'
5'
T
G
C
G
A
T
C
C
A
C
G
T
T
G
C
A
A
G
A
T
C
A
T
3'
C
T
A
T
A
G
A
T
3'

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Information regarding the sequence of nucleotides in the chain of a nucleic acid is called its primary structure. Nucleic acids have a secondary structure too.
James Watson and Francis Crick gave a double strand helix structure for DNA. Two nucleic acid chains are wound about each other and held together by hydrogen bonds are formed between specific pairs of bases. Adenine forms hydrogen bonds with thymine where as cytosine forms hydrogen bonds with guanine.

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Describe the biological functions of nucleic acid compounds.

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DNA is the chemical basis of heredity and may be regarded as the reserve of genetic information.
DNA is exclusively responsible for maintaining the identity of different species of organisms over millions of years.
DNA molecule is capable of self duplication during cell division and identical DNA strands are transferred to daughter cells.
Actually, the proteins are synthesized by various RNA molecules in the cell but the message for the synthesis of a particular protein is present in DNA.

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What are hormones?

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Hormones are molecules that act as intracellular messengers. These are produced by endocrine glands in the body and are poured directly in the blood stream which transports them to the site of action.
In terms of chemical nature, some of these are steroids. e.g. estrogens and androgens, some are polypeptides for example insulin and endorphins and some others are amino acid derivatives such as epinephrine and norepinephrine.

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What are the functions of hormones in body ?

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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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Give the function of steroid hormones.

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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.