Structure of RNA

 Structure of RNA 

1. The acceptor arm : This arm is capped with a sequence CCA (5′to 3′). The

amino acid is attached to the acceptor arm.

2. The anticodon arm : This arm, with the three specific nucleotide bases

(anticodon), is responsible for the recognition of triplet codon of mRNA. The

codon and anticodon are complementary to each other.

3. The D arm : It is so named due to the presence of dihydrouridine.

4. The TψC arm : This arm contains a sequence of T, pseudouridine

(represented by psi, ψ) and C.

5. The variable arm : This arm is the most variable in tRNA. Based on this

variability, tRNAs are classified into 2 categories :

(a) Class I tRNAs : The most predominant (about 75%) form with 3–5 base

pairs length.

(b) Class II tRNAs : They contain 13–20 base pair long arm.

Classification of proteins on the basis of functional and chemical nature

A Functional classification of proteins:-

Based on the functions they perform, proteins are classified into the following

groups (with examples)

1. Structural proteins : Keratin of hair and nails, collagen of bone.

2. Enzymes or catalytic proteins : Hexokinase, pepsin.

3. Transport proteins : Hemoglobin, serum albumin.

4. Hormonal proteins : Insulin, growth hormone.

5. Contractile proteins : Actin, myosin.

6. Storage proteins : Ovalbumin, glutelin.

7. Genetic proteins : Nucleoproteins.

8. Defense proteins : Snake venoms, Immunoglobulins.

9. Receptor proteins for hormones, viruses.

B Protein classification based on chemical nature and

solubility:-

This is a more comprehensive and popular classification of proteins. It is based

on the amino acid composition, structure, shape and solubility properties.

Proteins are broadly classified into 3 major groups

1. Simple proteins : They are composed of only amino acid residues.

2. Conjugated proteins : Besides the amino acids, these proteins contain a non-

protein moiety known as prosthetic group or conjugating group.

3. Derived proteins : These are the denatured or degraded products of simple

and conjugated proteins.

Modern Classification of protein:-

1. Simple proteins

(a) Globular proteins : These are spherical or oval in shape, soluble in

water or other solvents and digestible.

(i) Albumins : Soluble in water and dilute salt solutions and

coagulated by heat. e.g. serum albumin, ovalbumin (egg),

lactalbumin (milk).

(ii) Globulins : Soluble in neutral and dilute salt solutions e.g. serum

globulins, vitelline (egg yolk).

(iii) Glutelins : Soluble in dilute acids and alkalies and mostly found

in plants e.g. glutelin (wheat), oryzenin (rice).

(iv) Prolamines : Soluble in 70% alcohol e.g. gliadin (wheat), zein

(maize).

(v) Histones : Strongly basic proteins, soluble in water and dilute

acids but insoluble in dilute ammonium hydroxide e.g. thymus

histones.

(vi) Globins : These are generally considered along with histones.

However, globins are not basic proteins and are not

precipitated by NH4OH.

(vii) Protamines : They are strongly basic and resemble histones but

smaller in size and soluble in NH4OH. Protamines are also

found in association with nucleic acids e.g. sperm proteins.

(viii) Lectins are carbohydrate-binding proteins, and are involved in

the interaction between cells and proteins. They help to

maintain tissue and organ structures. In the laboratory, lectins

are useful for the purification of carbohydrates by affinity

chromatography e.g. concanavalin A, agglutinin.

(b) Fibrous proteins : These are fiber like in shape, insoluble in water and

resistant to digestion. Albuminoids or scleroproteins are predominant

group of fibrous proteins.

(i) Collagens are connective tissue proteins lacking tryptophan.

Collagens, on boiling with water or dilute acids, yield gelatin

which is soluble and digestible.

(ii) Elastins : These proteins are found in elastic tissues such as

tendons and arteries.

(iii) Keratins : These are present in exoskeletal structures e.g. hair,

nails, horns. Human hair keratin contains as much as 14%

cysteine.

2. Conjugated proteins

(a) Nucleoproteins : Nucleic acid (DNA or RNA) is the prosthetic group

e.g. nucleohistones, nucleoprotamines.

(b) Glycoproteins : The prosthetic group is carbohydrate, which is less than

4% of protein. The term mucoprotein is used if the carbohydrate

content is more than 4%. e.g. mucin (saliva), ovomucoid (egg white).

(c) Lipoproteins : Protein found in combination with lipids as the prosthetic

group e.g. serum lipoproteins.

(d) Phosphoproteins : Phosphoric acid is the prosthetic group e.g. casein

(milk), vitelline (egg yolk).

(e) Chromoproteins : The prosthetic group is coloured in nature e.g.

hemoglobins, cytochromes.

(f) Metalloproteins : These proteins contain metal ions such as Fe, Co, Zn,

Cu, Mg etc., e.g. ceruloplasmin (Cu), carbonic anhydrase (Zn).

3. Derived proteins : The derived proteins are of two types. The primary

derived are the denatured or coagulated or first hydrolysed products of

proteins. The secondary derived are the degraded (due to breakdown of

peptide bonds) products of proteins.

(a) Primary derived proteins

(i) Coagulated proteins : These are the denatured proteins produced

by agents such as heat, acids, alkalies etc. e.g. cooked proteins,

coagulated albumin (egg white).

(ii) Proteans : These are the earliest products of protein hydrolysis by

enzymes, dilute acids, alkalies etc. which are insoluble in

water. e.g. fibrin formed from fibrinogen.

(iii) Metaproteins : These are the second stage products of protein

hydrolysis obtained by treatment with slightly stronger acids

and alkalies e.g. acid and alkali metaproteins.

(b) Secondary derived proteins : These are the progressive hydrolytic

products of protein hydrolysis. These include proteoses, peptones,

polypeptides and peptides.

Elemental composition of proteins

 Elemental composition of proteins

Proteins are predominantly constituted by five major elements in the following

proportion.

Carbon(C):👉       50 – 55%

Hydrogen(H):👉    06 – 7.3%

Oxygen(O): 👉       19 – 24%

Nitrogen(N):👉       13 – 19%

Sulfur(S):    👉          0 – 4%

Besides the above, proteins may also contain other elements such as P, Fe, Cu,

I, Mg, Mn, Zn etc.

Function of lipids

Functions of lipids:-

Lipids perform several important functions

1. They are the concentrated fuel reserve of the body.

2. Lipids are the constituents of membrane structure and regulate the membrane

permeability (phospholipids and cholesterol).

3. They serve as a source of fat soluble vitamins (A, D, E and K).

4. Lipids are important as cellular metabolic regulators (steroid hormones and

prostaglandins).

5. Lipids protect the internal organs, serve as insulating materials and give shape

and smooth appearance to the body

Classification of lipids

 Classification of lipids:-

Lipids are broadly classified (modified from Bloor) into simple, complex,

derived and miscellaneous lipids, which are further subdivided into different

groups

1. Simple lipids : Esters of fatty acids with alcohols. These are mainly of two

types

(a) Fats and oils (triacylglycerols) : These are esters of fatty acids with

glycerol. The difference between fat and oil is only physical. Thus, oil

is a liquid while fat is a solid at room temperature.

(b) Waxes : Esters of fatty acids (usually long chain) with alcohols other

than glycerol. These alcohols may be aliphatic or alicyclic. Cetyl

alcohol is most commonly found in waxes. Waxes are used in the

preparation of candles, lubricants, cosmotics, ointments, polishes etc.

2. Complex (or compound) lipids : These are esters of fatty acids with alcohols

containing additional groups such as phosphate, nitrogenous base,

carbohydrate, protein etc. They are further divided as follows

(a) Phospholipids : They contain phosphoric acid and frequently a

nitrogenous base. This is in addition to alcohol and fatty acids.

(i) Glycerophospholipids : These phospholipids contain glycerol as

the alcohol e.g., lecithin, cephalin.

(ii) Sphingophospholipids : Sphingosine is the alcohol in this

group of phospholipids e.g., sphingomyelin.

(b) Glycolipids : These lipids contain a fatty acid, carbohydrate and

nitrogenous base. The alcohol is sphingosine, hence they are also

called as glycosphingolipids. Glycerol and phosphate are absent e.g.,

cerebrosides, gangliosides.

(c) Lipoproteins : Macromolecular complexes of lipids with proteins.

(d) Other complex lipids : Sulfolipids, aminolipids and lipopolysaccharides

are among the other complex lipids.

3. Derived lipids : These are the derivatives obtained on the hydrolysis of group

1 and group 2 lipids which possess the characteristics of lipids. These include

glycerol and other alcohols, fatty acids, mono-and diacylglycerols, lipid (fat)soluble vitamins, steroid hormones, hydrocarbons and ketone bodies.

4. Miscellaneous lipids : These include a large number of compounds

possessing the characteristics of lipids e.g., carotenoids, squalene,

hydrocarbons such as pentacosane (in bees wax), terpenes etc.

Functions of carbohydrates

Functions of carbohydrates:-

1. They are the most abundant dietary source of energy (4Cal/g) for all

organisms.

2. Carbohydrates are precursors for many organic compounds (fats, amino

acids).

3. Carbohydrates (as glycoproteins and glycolipids) participate in the structure of

cell membrane and cellular functions such as cell growth, adhesion and

fertilization.

4. They are structural components of many organisms. These include the fiber

(cellulose) of plants, exoskeleton of some insects and the cell wall of

microorganisms.

5. Carbohydrates also serve as the storage form of energy (glycogen) to meet the

immediate energy demands of the body.

cryopreservation

 Cryopreservation

Why Preservation is important?

• Until tow decades ago the genetic resources were getting depleted owing to the continuous depredation by man.
• It was imperative therefore that many of the elite Economically important and endangered species are preserved to make them available when needed.
• The conventional methods of storage of storage failed to prevent losses caused to various reason.
• A new methodology had to be devised for long term preservation of material.

There are various methods of storage

1. Cryopreservation:- Generally involves storage in liquid Nitrogen.
2. Cold storage:- It involve storage in low and non freezing temperature.
3. Low pressure:- It involves partially reducing the atmospheric pressure of surrounding.
4. Low oxygen storage:- It involves reducing the oxygen level but maintaining the pressure.

Cryopreservation;-

• Cryo is greek word, (Kroyes -frost)
• It literally means preservation in "frozen state"

The principle:- to bring plant cells or tissue to a zero metabolism and non dividing state by reducing the temperature in the presence of cryoprotectant.

It can be done:-

• Over solid carbon dioxide (at-79°C)
• Low temperature deep freezer (at-80°C)
• In vapor phase nitrogen (at-150°C)
• In liquid nitrogen (at-196°C)

Major advantages are:-

• Once the material is successfully conserved. Particular temperature it can be preserved indefinitely.
• Once in storage no chance of new contamination of fungus or Bacteria.
•  Minimal space required.
• Minimal labor required.

Mechanism of Cryopreservation:-

 

                             There cryopreservation technique followed by the regeneration of plants involves following steps:-

1. Selection of of material.
2. Addition of Cryoprotectant.
3. Freezing
4. Storage in liquid nitrogen.
5. Thawing.
6. Washing and reculturing.
7. Measurement of viability
8. Regeneration of plants.

1. Selection of plant material:-

             Two important factors depends on it such as 

                          a. Nature and

                          b. Density

      Any tissue can be selected for this purpose e.g., meristem, embryo, ovules, seeds, etc.

The density should be high.

2.Addition of Cryoprotectant:-

• They are chemical which prevent cryodestruction.
• These are sucrose, alcohol's, glycols, Some amino acid (proline), DMSO (dimethyl sulfoxide)
• Generally tow cryoprotectant should be used together instead of single one as they are more effective.

3. Freezing:-

      

               The sensitivity of cells to low temperature depends on the plant species.

  There are four different types of Freezing:-

• Slow freezing method:- The tissue or plant material is slowly frozen at slow cooling rate. The advantage is the plant cells are partially dehydrated and survive better.
• Rapid freezing method:- It involves pluming the vials in liquid nitrogen. The temperature decreases from -300°C to -1000°C  rapidly.
• Rapid freezing method:- This is combination of both slow and rapid freezing method. The process is carried out in step wise like manner.
• Dry freezing method:- In this method dehydrated cells and seeds are stored.

4.Storage:-

• The maintenance of the frozen cells or material at specific temperature is kept -70°C to -196°C
• Prolong storage is done at temperature of -196°C in liquid nitrogen.
• To prevent damage, continuous supply of Nitrogen is done.

 

5.Thawing:-

• Usually carried out by plunging the vials. into warm water bath with vigorous swirling.
• As thawing occurs the vials are transferred to another bath at 0°C degree.

6.Washing and reculturing:-

• The preserved material is washed few times to remove the cryoprotectant.
• This material is then recultured in a fresh medium.

7.Measurement of viability

• There is possibility of death of cells due to storage stress.
• Thus viability can be found at any stage.
• It is calculated by formula:-

  No. of cells growing/no of cells thawed ✖100

8.Plant regeneration:-

• The viable seeds are cultured on non specific growth medium.
• Suitable Environment Conditions are maintained. 

                                                        Application

• It is ideal method for long term conservation of material.
• DISEASE FREE PLANT CAN BE CONSERVED AND PROPAGATE.
• Peculcitrant seeds can be maintained for long time.
• Endangered species can be maintained.
• Pollens can be maintained to increase longitivity.
• Rare germplasm and other genetic manipulations can be stored.

Micro propagation

 MICROPROPAGATION:-

                                    It has been demonstrated that a variety of plant can be conveniently propagated through the techniques of cell, tissue organ culture. This is popularly described as micro propagation.

Technique of Micro propagation:-

                          In most of cases, clone propagation is achieved by placing sterilized short tips or axillary buds on to a culture medium that is sufficient to induce formation of multiple buds. 

Following stage are involved in the method of micro propagation 

  1. Stage I involves establishment of tissue in vitro.

  2. Stage II involve multiplication of shoots.

  3. Stage III concerned root formation and conditioning of propagules prior to transfer to the greenhouse. This stage requires high intensity and alteration of media for promotion of  root formation. 

   4. Stage IV involves growth in pots followed by field trials.

Advantages of Micro propagation:-   

• Rapid multiplication of superior clones and maintenance of uniformity.                                                                                                
• Multiplication of disease free plant.                                                         
• Multiplication of sexually derived sterile hybrids.                                                      
• A wide range of plants have now been regenerated through technique of tissue culture. This technique is very useful in the    commercial production of some plants like banana, potato, orchids and Chrysanthemum etc.