Plus Two Chemistry Notes Chapter 14 Biomolecules is part of Plus Two Chemistry Notes. Here we have given Plus Two Chemistry Notes Chapter 14 Biomolecules.
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Kerala Plus Two Chemistry Notes Chapter 14 Biomolecules
They are macromolecules which are naturally occuring in biological systems. They form the basis of life.
Carbohydrates: They are optically active poly-hydroxy aldehydes or ketones or the com¬pounds which produce such units on hydro-lysis. eg., sugar, glycogen, starch, cellulose, dextrins and gums.They can be classifieds as:
- Monosaccharides: They are simple carbo-hydrates that cannot be hydrolysed into simpler units, eg., glucose, fructose.
- Oligosaccharides: Those carbohydrates which yield 2 to 10 monosaccharide units on hydrolysis are called oligosaccharides, eg., su-crose, maltose.
- Polysaccharides: Those carbohydrates, which produce large number of monosaccha ride units are called polysaccharides, eg., sta¬rch, cellulose.
Reducing sugars: Those carbohydrates which contain free aldehydic or ketonic group and re-duce Fehling’s solution or Tollen’s reagent are called reducing sugars, eg., all monosaccha rides, maltose, lactose.
Non-reducing sugars: Those sugars which do not have free aldehydic or ketonic group and do not reduce Fehling’s solution or Tollen’s re¬agent are called non-reducing sugars, eg., sucrose.
Glucose: Glucose can be prepared from cane sugar (sucrose).
Structure of Glucose: It is an aldohexose because it has a aldehyde group and six carbon atoms. Glucose is currently named as D (+) – glucose ‘D’ stands for configuration.
Cyclic structure of Glucose
The following reactions could not be explained by the above structure.
- Glucose doesn’t give Schiff’s test.
- It doesn’t react with NaHSO3
- The pentaacetate of glucose doesn’t react with hydroxylamine indicating the absence of free -CFIO group. Thus the following cyclic structure of glucose was proposed.
Which of the following is incorrect for glucose?
a. It contains four > CHOH groups
b. It contains one ketone group
c. It contains one CH2OH group
d. It contains one -CHO group
It contains one ketone group
Reactions of Gulcose:
Structure of Fructose:
The cyclic structures of two anomers of fructose are represented by Haworth structures:
Disaccharides: The sugar which on hydrolysis gives two units of monosaccharides is called a disaccharide, eg., sucrose, maltose, lactose.
Glycosidic linkage: Two monosaccharide units are linked through oxygen atom accompanied by the loss of a water molecule. This linkage is called glycosidic linkage.
Inversion of Sugar:
- Sugar is dextrorotatory (+).
- After hydrolysis it gives leavorotatory (-) fruc-tose (92.4°) and dextrorotatory (+) glucose (+52.5°). This mixture is laevorotatory (-).
- As hydrolysis brings about a change in sign of rotation, the product is called invert sugar.
- The fundamental unit of starch is ∝ -D-glucose.
- It is a polymer of a-glucose and consist of two components amylose and amylopectin.
It is water soluble It is 15-20% of starch It is long straight chain
It is water insoluble It is 80-85% of starch It is long branched chain
- It is a linear polymer of β-glucose.
- It is a chief constsituent of cell walls in plants.
- It is polysaccharide of glucose.
- The carbohydrates are stored in animal body as glycogen.
- It has long branched chains.
- It is also called animal starch.
Amino Acids. The compounds, which contain carboxylic acid group and amino group, are called amino acids. Amino acids form proteins. Amino acids are classified:
- Neutral: contain one -NH2 and one -COOH group, eg., glycine, valine.
- Acidic: contain one -NH2 and two -COOH group, eg., aspartic acid, glutamic acid.
Basic:contain two and one -COOH group, eg., lysine, histidine.
Essential amino acids: Those amino acids which cannot be synthesised in body and must be obtained through diet, eg., valine, leucine.
Non-essential amino acids: Those amino acids which are synthesised in body, eg., Glycine, alanine.
The amino acids are the end product of the digestion of
Proteins :- Proteins’” are complex polyamides formed from amino acids. They are essential for proper growth and maintenance of body. Chemically, poteins are the polymers of a ∝ – amino acids which are linked by peptide bonds.
Peptide bond: When COOH group of first amino acid forms bond with NH2 group of second amino acid with loss of a water molecule, the so formed bond is called peptide bond (-CO-NH-).
Types of proteins based on molecular shape :
Fibrous Proteins:- The proteins, which have long and thread-like structures, are called fibrous proteins.
- They are water insoluble.
- They are chief structural materials of animal tissues.
- eg., firbroin, keratin, myosin.
Globular Proteins :- The proteins whose mol-ecules are folded forming compact units of nearly spherical shape (globules).
- They are water soluble.
- eg., insulin, albumin, haemoglobin.
Structure of Protein
1. Primary Structure of Protein :- The sequence in which the amino acids are arranged in a protein is called the primary structure of protein.
2. Secondary Structure of Protein :- This ex-plains the folding of the structure of protein.
- The ∝-helix structure results due to coiling of polypeptide chain which is stabilised by intramolecular hydrogen bonding.
- In β – pleated sheet structure, all peptide chains are stretched to maximum extension and arranged side by side and held together by intermolecular H-bonding.
3. Tertiary Structure of Protein :- It explains further folding of secondary structure.
4. Quaternary Structure of Protein :- Some of the proteins are composed of two or more polypeptide chains referred to as sub-units. This type of spatial arrangements is called quaternary structure of protein.
Denaturation of Proteins
When protein is subjected to change in pH or temperature, it uncoils and loses biological activity. This is called denaturation. eg., boiling of egg, conversion of milk into curd.
What changes occur in the nature of egg proteins on boiling?
On boiling, the globular proteins present in the egg undergo coagulation to form fibrous ; proteins. As a result, proteins lose their biological activity and thus get denatured. Chemistry, during denaturation, the secondary and tertiary structures of proteins are destroyed but primary structure remains intact.
They are essential biological catalysts which are needed to catalyse biochemical reactions, eg., maltase, lactase, amylase, invertase. Almost all enzymes are globular proteins.
Vitamins are group of organic compounds which are required in very small amounts for the healthy growth and functioning of animal organism.
Classification of Vitamins:
- Fat- soluble vitamins: Vitamins A, D, E, K are soluble in fat and oils but insoluble in water. They are stored in liver and adipose tissues.
- Water-soluble vitamins: Vitamins belonging to group B and Vitamin C are soluble in water.
Note: They cannot be stored (except B12) in our body as they are excreted in urine.
Which of the folio wing acids is a vitamin ?
a. Aspartic acid
b. Ascorbic acid
c. Adipic acid
d. Saccharic acid
Deoxyribonucleic Acid (DNA)
- Sugar is β -D-2-deoxyribose.
- Nitrogen containing bases are adenine, gua-nine, thymine, cytosine (AGTC).
- The two strands of DNA are said to be complementary to each other.
- They are responsible for transferring genetic charcteristics.
- Provides message for protein synthesis.
Ribonucleic Acid (RNA)
- Sugar is p -D-ribose.
- Nitrogen containing bases are adenine, guanine, cytosine, uracil (AGUC).
- It has single stranded structure.
- It carries out protein synthesis.
- There are 3 types of RNA. They are messenger RNA (m-RNA), Ribosomal RNA (r-RNA), Transfer RNA (t-RNA).
Constituents of Nucleic acids:
- Pentose sugar
- Phosphoric acid
- Nitrogeneous bases
Nucleoside: Pentose sugar + Nitrogeneous base.
Nucleotide: Nucleoside + Phosphoric acid unit.
Which base is present in RNA, but not in DNA?
Structure of Nucleic Acids
DNA has double strand structure. The two strands are complementary to each other because H-bonds are formed by specific pairs of bases, i.e., adenine (A) is attached with thymine (T) by two H-bonds and guanine (G) is attatched to cytosine (C) by three H-bonds. RNA has single strand in secondary structure.
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