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Tuesday, 30 June 2015

BIOMOLECULES


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The various types of compounds which are found to be essential for animal for animal life:-

Carbohydrates: e.g. starch and sugar

Lipids: e.g. ghee and butter

Proteins: e.g. complex molecules present in meat and pulses

Vitamins: e.g. present in food in traces

Hormones: present in food or synthesised by the body

The molecules of the above listed compounds form the basis of the life. Such molecules of organic compounds which build up life system and required for the growth and the maintenance are called BIOMLECULES.


CELLULAR ENERGETICS: FREE ENERGY CHANGES IN BIOLOGICAL REACTIONS-

Cellular reactions follow the basic principles of thermodynamics. Only those reactions should be spontaneous for which ΔG negative. All the carbolic reactions proceed with decrease of energy(ΔG<0)but some important cellular reactions proceed even ΔG is positive.e.g. Photosynthesis in plants for which ΔG>0. Many anabolism reactions proceed with increase of free energy i.e. ΔG>0.

A very common reaction which provides energy in many cellular reactions is the hydrolysis of adenosine tri phosphate (ATP). The biochemical unit of energy is ATP. The cell obtains energy for the synthesis of ATP through photosynthesis / catabolism of nutrients such as carbohydrates and lipids, this all occurs through coupled reaction.

WHY ATP MOLECULE IS ENERGY RICH MOLECULE?

The ATP molecule is consists of four negatively charged oxygen atoms which are close to each other; the repulsive forces between them are very high. 
These forces makes them high energy molecules, actually this energy is stored in oxygen-phosphorous bonds. 
The oxygen bonds between the two phosphoric acid residues are high energy phosphate bonds. 
During hydrolysis these bond break, this reduces the number of oxygen atoms in the molecules and the repulsive forces between o-atoms decreases, and as a result large amount of energy is released. 
The energy released during this process depends upon the products formed and the Ph of the solution. AMP and ADP molecules get converted to ATP molecules during this process.

CARBOHYDRATES:

The polyhydroxy aldehydes, polyhydroxy ketones, or large polymeric molecules which on hydrolysis produce polyhydroxy aldehydes, polyhydroxy ketones, are called CARBOHYDRATES.

STARCH AND THE SUGARS ARE THE MOST COMMON CARBOHYDRATES.

The sugar is stored in the body as glycogen (C6H1005)

CALSSIFICATION OF CARBOHYDRATES:

Carbohydrates can be classified on the basis of I) Behaviour on hydrolysis ii) taste
ON BEHAVIOUR they are classified into Monosaccharide, Oligosaccharides, and Polysaccharides.


MONOSACCHRIDES
These are simple carbohydrate molecules which can not be hydrolysed into many simpler molecules. Each molecule represents a complete carbohydrate molecule unit. They contain 3 to 7 carbon atoms therefore their general formula (CH20) n.
Examples: - glucose, fructose, galactose, and ribose.

OLIGOSACCHRIDES:- The carbohydrates whose molecules on hydrolysis give 2 to 9 molecules of monosaccharides either same or different are called oligosaccharides. They are divided into di, tri, tetra and polysaccharides further.
Examples: Disaccharides ( C12H22011) such as Sucrose, maltose, Lactose, they produce two molecules of monosaccharides on hydrolysis.

Trisaccharides: - Carbohydrates which upon hydrolysis produce three molecules of monosaccharides. The gen. formula is (C18H32016). Example:- Raffinose which on hydrolysis give one molecule of each glucose, fructose and galactose.

Tetrasaccharides: - They give four molecules of mono saccharides on hydrolysis having gen. formula (C24H42021).
Example: - Stachyrose which upon hydrolysis give each of glucose, fructose and two molecules of galactose.

Polysaccharides :- Carbohydrates which upon hydrolysis produce large number of monosaccharides having gen. formula (C6H1005) n. where n = 100 – 3000. such as Starch, Cellulose, and glycogens.

CALSSIFICATION OF CARBOHYDRATES ON THE BASIS OF TASTE:- They are classified as Sugars and non-Sugars
Sugars: - which are sweet in taste and dissolve in water are called sugars. All mono and disaccharides are sweet in taste.
Examples: - Glucose, fructose, Sucrose, Lactose are sugars.

Non-Sugars:- Tasteless polysaccharides which are insoluble in water. They are generally amorphous in nature.
Examples: - Cellulose and Starch.

ADDITIONAL INFORMATION --- MONOSACCHARIDES

In addition to hydroxyl group they either contain aldehydic or ketonic group. The aldehydic being monovalent is either present at the end of the carbon chain. Hence such monosaccharides are called ALDOSE. On the other hand ketonic group being divalent can be present anywhere on the carbon chain. In natural monosaccharides this group is present normally at the second carbon atom. Hence they are also termed as KETOSE. Depending upon the no. of c-atoms these molecules are termed as trios, tetrose, pentose, and hexose. Ketose and aldose are added to the prefixes to the no. of c- atoms.

CHARACTERISTICS: - They are sweet and water soluble and when heated they get charred. Due to the presence of 0H-group they can be easily acetylated. They can be reduced to sugar alcohols. They can be oxidized at the aldehydic carbon to aldonic acid. Two molecules of monosaccharides combine with an elimination of water (H20) molecule to give a disaccharide.
They undergo oxidation, reduction, acetylation, react with hydroxylamine, phenyl hydrazine and fermentation.


ADDITIONAL INFORMATION ------ DISACCHARIDES.

Its main source is sugarcane and beet. These include Sucrose, Maltose, and Lactose. Sucrose is hydrolysed by both enzymes maltase and invertase.Sucrose is both a α-glucoside and β-fructoside. Hence it can be concluded that Sucrose consists of α-glucose and β-fructose. They are held together by α, β-glycosidic linkage.

INVERT SUGAR: - Cane sugar is dextrorotatory. On hydrolysis it gives dextrorotatory glucose and laevorotatory fructose. Therefore a equimolar mixture of glucose and fructose with opposite signs are called inversion of sugar or invert Sugar.



POLYSACCHARIDES: - There can be linear or branched chain polysaccharides. Polysaccharides are amorphous, tasteless and mostly insoluble in water. These include starch, dextrin, cellulose, and glycogens. Their main functions are storage of food.
They can further be classified as Homopolysaccharides and Hetropolysaccharides.
Homopolysaccharides contain same type of monosaccharides. Example: - glycogen, starch, and cellulose are polymers of glucose.
Hetropolysaccharides: - they contain two or more different mono saccharides. Example: - Gums.

STARCH: - It is odourless, tasteless, and insoluble in water. It is amorphous and white substance. When boiled it’s granules swells and burst to form a colloidal solution called starch paste. It is a polymer of α-glucose and composed of two components amylase(20%) and amylopectin(80%). Amylose is water soluble whereas amylopectin is water insoluble. The structure of glucose is similar as that of amylopectin. 
Amylose is linear polymer whereas amylopectin is a branched one.

AMINO – ACIDS: - The carboxylic acids containing amino (-NH2) group attached to any carbon atoms other than carboxylic carbon are called amino acids. An amino acid always contains one H-atom, one R group, one C00H group and one NH2 group and they are attached to single carbon atom. In aqueous solution the C00H group looses a proton to form carboxalate ion and the NH2 group gains this proton to form +NH3 ion. Hence in aqueous solution amino and carboxyl groups are in the ionized form and amino acid molecule exists as a dipolar ion. This dipolar ion is called Zwitter-ion. Amino acids in dipolar form are amphoteric in nature.
Therefore in acidic solution, an amino acid exists as a positive ion, and therefore it migrates to the negative electrode (cathode) when placed in an electrical field.
In a basic solution, an amino acid it exists negative ion and therefore it migrates towards the positive electrode when placed in electrical field.

The pH at which the amino acid molecule does not migrate to either of the electrodes is called the ISO-ELECTRIC POINT.


D- L- CONFIGURATIONS OF AMINO ACIDS: - The α- carbon atom in all the amino acids (except glycine) is asymmetric (chiral). Therefore amino acids can exist in two stereo isomeric forms, i.e. D and L forms. These two forms are the mirror images of each other but are non-superimposable on each other. Thy are drawn with the reference of glyceraldehydes, in which the NH2-group lies on the left hand side of the c- atom in L- configuration and the NH2- group lies on the right side of the c- atom in D- configuration. All natural occurring amino acids are L-isomers. Proteins consist of only L-amino acids.

The essential amino acids which must be present in our food are: - Isoleucine, Leucine, Lysine, Methionine, Phenylalanine Threonine, Tryptophan, Valine, Arginine and Histidine.

PEPTIDES: - The compounds formed by the condensation of two or more, or same or different amino acids are called peptides. During the formation of peptide, the amino (NH2) - group of one of the α-amino acid and the carboxylic (C00H) – group of another molecule of the same or the different α-amino acid get condensed with the elimination of the water molecule. During this process a bond of the type – C0NH- is formed between the two amino acids. This amide linkage is called peptide – linkage.
The peptide formed due to the condensation of only two, three or four molecules of the same or different amino acids is called dipeptide; tripeptide and tetrapeptide bonds respectively.
All the peptides contain a free amino (NH2) - group at one end and a free carboxylic (C00H) - group at the other end. These are called end-groups or the terminal groups.
Some important biological peptides are Oxytocin-nanopeptide, Vasopressin- nanopeptide, Angiotensin-octapeptide.

PROTIENS: - Proteins are complex nitrogenous organic compounds and are essential for the growth and development of the body. Proteins are macro molecules in which large numbers of amino acids are linked with peptide-bonds. On hydrolysis they give amino-acids, in other words they are polypeptides of very high molecular mass, (104 – 106g/mol).
Egg, meat, fish, pulses, and milk are the good source of proteins. Normally there are 20 amino-acids are present in proteins, and another six are found in the special tissues. The amino- acids differ in the side chain groups (R). the properties of amino-acids depend upon the nature of side chain. The human can synthesise 10 out of 20 amino-acids found in proteins. The other 10 must be supplied in the diet. Therefore they are called essential amino-acids. Lack of proteins can cause a disease called Kwashiorkar. The elements present in most of the proteins are carbon, hydrogen, oxygen, nitrogen and sulphur, iron, magnesium, phosphorous, etc.

CLASSIFICATION OF PROTIENS: - They are classified on the basis of chemical composition. Therefore there are mainly three classes of proteins. 
A) Simple proteins 
B ) Conjugated proteins 
 C) Derived proteins.

Simple proteins------ these are made up of only α-amino-acids and they upon hydrolysis give α-amino-acids.
Example ---------- Albumin,(in white of egg) Glutinin, (in wheat) Keratin, (in hairs & nails) are simple proteins.

Conjugated proteins: ------- the proteins which contain organic and inorganic compounds along with amino-acids are called Conjugated proteins. The non-amino-acid group of the protein is called prothestic group. This group controls the biological functions of the proteins. Conjugated proteins are further classified into -----------------------------------------------------
Lipoproteins ------these contain lipids and amino-acids. The prothestic group in them is lipids.
Nucleoproteins ----- these contain nucleic acids and amino-acids. The prothestic groups in them are nucleic acids.
Glycoprotein ------- these contain carbohydrates and an amino-acids.The prothestic group in them is carbohydrates/sugar.
Chromoproteins ------ they contain amino-acids and colored pigments.Haemoglobin, Myoglobin, Haemocynin, Cytochrome, and Riboflavin.
Phosphoproteins------- they contain amino-acids and phosphate group.

Derived-Proteins: - The degradation products obtained from the partial hydrolysis of simple and conjugated proteins are called Derived proteins.

CLASSIFICATION ON THE BASIS OF MOLECULAR STRUCTURE.

On the basis of structure they are classified as Fibrous Proteins and Globular Proteins:-


Fibrous Proteins:- They are consists of linear, thread-like polypeptide chain which are arranged and twisted to form long strands (fibres) and they are held together by hydrogen bonds therefore the inter molecular forces of attractions are very strong. They are insoluble in water and quite stable.
Example: - collagen of tendons, Keratin in skin, hairs and nails, Fibroin in silk, Myosin in muscles are Fibrous Proteins.


Globular Proteins:- The proteins in which polypeptides are tightly folded into a compact form are called Globular Proteins. In these proteins the hydrocarbon (lipohillic) ends are pushed inwards while the polar hydrophilic part is oriented outwards therefore these proteins are water soluble and very sensitive towards temperature and pH.
Examples: - All the enzymes, many hormones such as insulin, thryoglobins, antibodies, Haemoglobin, fibrinogen, albumin, and venoms of snakes, scorpion, wasp, and bees are globular proteins.

CLASSIFICATION ON THE BASIS OF FUNCTION: -

On the basis of their function these are classified into the following types: -
1 Structural Proteins
2 Contractile Proteins
3 Hormones
4 Enzymes
5 Blood proteins

ROLE OF PROTEINS:-

Enzymes: - All the enzymes found in the cells are proteins which catalyse large number of biological reactions in the body.

Hormones: - Many hormones are proteins in our body. Hormones are chemical regulators therefore regulate blood pressure. Glycoprotein and thryoglobins help in the synthesis of hormone thyroxin whereas nucleoproteins carry the genetic information from the parents to off-springs.

Haemoglobin: - It contains the protein called globin and is present in the blood, transfer the oxygen from lungs to tissues.

Blood proteins: - thrombin and fibrinogen are involved in blood clotting

DENATURATION OF PROTEINS:-

Energetically the most stable state of a protein is called as its native state or native form. The native state of a protein is dictated by the amino acid sequence in the protein. Proteins are very sensitive to heat, acids, alkalies and even to the electrolytes. Properties of globular proteins change altogether on heating or on treatment with acids/alkalies or electrolytes. On heating, water-soluble globular proteins precipitate out due to formation of water-insoluble fibrous proteins.The coagulated protein is called as denatured protein.

The process which leads to change in physical and biological properties of proteins without affecting its chemical composition is called as denaturation of proteins
Denaturation causes changes only in secondary, and tertiary structures of proteins. The primary structure of any protein does not change due to denaturation. 
Denaturation may be reversible in some cases. 
Denaturation is caused by following factors

Change in the pH
Increase in temperature
Presence of acids, alkalies, or salts
Exposure to ultraviolet rays or x- rays

The most common examples are
Boiling of egg
Preparation of cheese from milk.

CHARACTERISTICS OF ENZYMES:-

EFFECT OF TEMPERATURE 
The activity of enzymes is highest at near point temperatures. Above this temperature the enzymes get denatured and lose their activity. At lower temperature, the rates of enzyme catalyst reactions are slow because of kinetic effects. In general, the rate of all chemical reactions increase on increasing the temperature. But the rate of enzyme-catalyst reaction first increases shows a maximum at about 35- 37oC and then decreases at high temperature.

EFFECT OF pH 
The rate of pH on enzyme reaction is complex. The rate of an enzyme-catalyst reaction usually passes through the maximum at an optimum pH. At higher or lower pH than this optimum pH, the enzymes tend to get denatured and therefore lose their activity.

PRESENCE OF ELECTROLYTES AND ULTRAVIOLET RAYS- Enzymes lose their activity in the presence of electrolytes or when exposed to ultraviolet radiations. This is because enzymes get denatures in the presence of electrolytes or when exposed to ultraviolet rays.

ENZYME INHIBITORS Enzymes are very sensitive to catalytic poisons. Some typical poisons are HCN, H2S, CS2. Enzymes lose their activity in the presence of these substances because these molecules tend to get absorb on the surface of enzyme strongly.

EFFECT OF METAL IONS AND SIMPLE ORGANIC MOLECULES- most enzymes are associated with some non-protein compounds required for their activity. These non-protein compounds are called as prosthetic groups. Prosthetic groups may be metal ions or smaller organic molecules called coenzymes. Some of the metal ions involved are those of Zn, Mg, Mn, Fe, Cu, K and Na.Many of the coenzymes are derived from vitamins, such as thiamine, niacin, riboflavin, etc.

NUCLEIC ACID-

Nucleic acids are another important macromolecules present in the cells of all living organisms.Nucleic acids are long thread like macromolecules of high molecular masses. Nucleic acids are responsible for transmission of hereditary characters and for the bio-synthesis of proteins. Therefore they govern the metabolic activities in living organisms. They are present in the form of nucleoproteins.

CONSTITUENTS OF NUCLEIC ACIDS
Nucleic acid contains following three contents
A pentose sugar ( ribose or deoxyribose)
A nitrogen containing heterocyclic base; a purine or pyridimine base
A phosphate group

Nucleosides – The base sugar unit in any nucleic acid chain is called as nucleoside.The nucleosides are named after the names of the base, attached at the carbon atom number 1 of the sugar unit.
Eg. Ribose ribonucleoside, deoxyribose deoxyribonucleosides

Nucleotides – The base- sugar- phosphate is called as a nucleotide. Nucleotides are the phosphate esters of nucleosides.
For eg. Ribose- ribonucleotide, deoxyribose- deoxyribonucleotides

TYPES OF NUCLEIC ACIDS-
Deoxyribonucleic acid (DNA)- DNA is the genetic material and is responsible for heredity character of the cell. DNA is present in the nucleus of the cell. DNA is the most stable molecule of the biological world. DNA molecule may be consider immortal.

COMPOSITION OF DNA-

DNA contains the following four nitrogen bases- 

PURINES- adenine and guanine, 

 PYRIDAMINES- thymine and cytosine

Each unit of DNA strand has only four bases.
  • the number of purine nucleotides is equal to the number of pyridimine nucleotides.
  • the ratio of adenine(A) to thymine (T) . and guanine (G) to cytosine(C) is one

BIOLOGICAL SIGNIFICANCE OF DNA-
  • DNA acts as a carrier of genetic information from parents to their offsprings
  • DNA guides the process of protein synthesis in cells
  • DNA is involved in the synthesis of RNA.

RIBONUCLEIC ACID (RNA)
The RNA is found to be genetic material in some plants and animal viruses.RNA is found in nucleolus, cytoplasm and on the membrane in ribosomes. Each ribonucleotide contains
A pentose sugar-ribose
Purines- adenine and guanine
Pyridimines- cytosine and Uracyl
And phosphate groups.

Structure of RNA
Nucleotide of RNA consist of pentose sugar ribose. 
These ribonucleotides are linked to each other by 3’-5’ phosphodiester bonds. 
In this respect RNA resembles DNA. The polymeric chain of ribonucleotides forms RNA polynucleotide strands.
RNA is single stranded except in certain viruses.RNA doesn’t form helix. The primary structure of RNA differs from DNA in the following ways:
In RNA, the sugar residue is ribose, whine in DNA it is 2’deoxyribose
RNA consists of pyridimine base Uracyl(U) in the place of Thymine (T) in DNA.

Classification of RNA
The organisms which have RNA only as nucleic acid use this RNA in genetic mechanism. Such type of RNA is called as genetic RNA.
The organisms which have RNA along with some DNA , use their RNA in carrying out the orders of DNA.Such type of RNA is called as non genetic RNA.
The non genetic RNA is heterogeneous and is classified by cellular location

MESSENGER RNA- Messenger RNA (m-RNA) is short-lived molecule that carries genetic information from DNA to ribosomes where protein synthesis occurs.

RIBOSOMAL RNA- Ribosomal RNA(R-RNA) is an integral part of ribosome that also takes part in protein synthesis.
About 75% of cellular component of RNA is ribosomal RNA ts molecular mass varies from 40,000 to 1.5 million.

TRANSFER RNA- Transfer RNA (T-RNA) acts as a carrier of amino acids. Its molecules contains 75-78 nucleotide and their molecular mass varies from 23000 to 25000.
Near the middle of its molecule there is a sequence of three bases called anticodon
These three bases are hydrogen bonded to a complimentary sequence in m-RNA during protein synthesis.All t-RNA molecules have a L- shaped tertiary structure. 
The hydrophobic interactions are a major stabilising force in the tertiary structure of t-RNA.

FUNCTION OF NUCLEIC ACIDS: - They have two important functions to perform----

Replication The genetic information for the cell is contained in the sequence of the bases A, T, G, and C in the DNA molecule.
When the cell divides, DNA molecule replicates and makes exact copies of themselves so that daughter cell will have DNA identical to that of the parent cell, in this process the two strands of DNA helix- unwinds and each strands serves as a template for the synthesis for a new stand.

Synthesis of proteins. This process involves Transcription and Translation

Translation :- In this step the double helix of DNA opens up and two strands of DNA acts as template for the synthesis of complementary DNA molecule called messenger RNA (m-RNA)
The following sequences of bases in m-RNA formed and that of uncoiled strand of DNA takes place

Uncoiled strand of DNA : C G A C T T A C C G T A A
Tanscripted m-RNA : G C U G A A U G G C A U U

Translation:- During translation, m-RNA directs the protein synthesis in the cytoplasm of cell with the involvement of another type of RNA molecule namely , transfer-RNA (t-RNA) and the ribosomal particle.

LIPIDS:- Lipids are waxy or oily substances which are present in all living organisms.
 Lipids are the constituents of all cell membranes. Lipids are esters of long chain fatty acids and alcohols. Lipids show some common characteristics

Lipids are soluble in the organic solvents but insoluble in water

All lipids on hydrolysis give mono carboxylic acids ( saturated or unsaturated)

Lipids may be broadly classified as

SIMPLE LIPIDS( triglicerides)- Fats and oils Waxes

COMPLEX (compound) lipids-Phospholipids Glycolipids

Functions of lipids
To form a part of structure of biological membranes. Phospholipids serve as structural component of cell membrane
To store energy for the cell. Simple lipids serve as energy reservoirs for animals
Simple lipids act as shock absorbers and heat insulators for the bodies of many organisms including humans.

HARMONES- chemical compounds secreted by ductless glands which meditate communication between the cells and control various cellular activities are called as hormones.
Hormones may be called as chemical messengers or chemical regulators.Hormones are produced in ductless glands and transported by blood circulation to the target tissues for producing inhibitory or stimulatory effect.

Classification of hormones-Based on chemical structures hormones fall in three categories-
Steroid hormones, Polypeptide hormones, Amine hormones

VITAMINES- A group of bio molecules which are not produced by the body but required in very small quantities for normal metabolic activities and healthy growth of human beings and animals are called as Vitamins.

On the basis of their solubility they can be classified into-

WATER SOLUBLE VITAMINES- Vitamines which dissolve in water are called as water soluble vitamins. Eg. Vitamin B and C

OIL OR FAT SOLUBLE VITAMINS- Vitamins which dissolve in oil or fat are called as fat or oil soluble vitamins.
Eg. A, D, E and K.

IMPORTANT NCERT QUESTIONS

Q1 What are reducing and non-reducing sugars? What is a structural feature characterizing reducing sugar?

Q2 Draw simple fischer projections of D and L glucose. Are these enantiomers?

Q3 Write down the structures and the names of the products obtained when D glucose is treated with (a) acetic anhydride (b) hydrocynic acid, (c) bromine (d) concentrated HNO3, (e) HI.

Q4 Explain mutarotation. Explain its mechanism in D glucose.

Q5 What are essential and non essential amino acids? Give 2 eg. Of each. Give reasons for the following-
  1. amino acids have relatively higher melting point as compared to corresponding halo acids.
  2. On electrolysis in acidic solutions amino acids migrate toward cathode whereas in alkaline solution these migrate towards anode.

Q6 What type of linkages are responsible for the formation of these
  1. α- Helix formation
  2. β- sheet structure

Q7 What forces are responsible for the stability of α- helix? Why is it named as 3.613 helix?

Q8 What is denaturation and renaturation of proteins?

Q9 What products are obtained on complete hydrolysis of DNA? Write down the structures of purines and pyridimine bases present in DNA.

Q10 What are complementary bases? Draw structure to show hydrogen bonding between adenine and thymine bases present in DNA.

Q11 How does DNA replicate? Give the mechanism of replication. How is the process responsible for preservation of heredity?

Q12 Answer the following about protein synthesis-
  1. How do 64 codons code for only 20 amino acids
  2. During translation which one of the two-end functional groups of the polypeptide is formed first?

Q13 How are lipids classified? Give an example of each class.

Q14 Hormones are chemical messengers . Explain.

Q15 Name the deficiency diseases caused due to lack of Vitamin A , C, E , B1, B12, B6, and K.


REDUCING ANS NON-REDUCING SUGARS :-

Those carbohydrates which contain a free aldehydic or a ketonic group and reduce Tollen’s reagent are called Reducing sugars. E.g. Glucose, fructose, galactose. On the other hand which do not reduce Tollen’s reagent and do not contain free aldehydic or a ketonic group are called non-reducing sugars. E.g. Maltose, Lactose, Sucrose.






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