Meiosis and Mitosis

Mitosis:- Mitosis is also called somatic cell division and equational division.
· chromosome number is kept constant in daughter cells.
·Two daughter cells are formed from parent cell.
It consists of following phase
 Interphase:- It consist of period of growth and development between cell division. it is further divided into three phase.
G1 phase:- First gap phase / first growth phase: It involve synthesis of protein and RNA chromatin is fully extended during the phase.
S-phase:- synthetic phase: Replication of DNA and synthesis of histone occur.
G2 Phase:- second gap / growth phase:
Synthesis of RNA and protein continues which is required for cell growth.
M-phase:- Mitotic phase for the consist of two parts
1:- karyokinesis ( nuclear division).
2:- cytokinesis (division of cytoplasm)
 1. karyokinesis:- It is further divided into four phase:
(A) Prophase:- Nuclear membrane disintegrate -nucleolus disappear
- chromatin fibre condenses to form chromosomes
-spindle Apparatus forms.
(B) Metaphase:- Chromosome arrange themselves at the equator of the spindle apparatus.
(C) Anaphase:- Each centromerc split so that two sister chromatid have their own centromerc.
- sister chromatid move towards opposite pole and maybe V-shaped or J- shaped.
(D) Telophase:- sister chromatid reach the opposite poles.
-At each pole, chromosome get surrounded by new nuclear membrane.
- Nucleolus is reformed.
- Chromosome decondense to form chromatin.
 significance of mitosis
Mitosis has the following significance of a living organism:
 1. The mitosis helps the cell in maintaining power size.
2. It help in the maintenance of an equilibrium in the amount of a DNA and RNA in the cell.
3. The mitosis provide the opportunity for the growth and development to organs and the body of the organisms.
4. The old decaying and dead cells of body are replaced by the help of mitosis.
5. In certain organism, The mitosis is involved in asexual Reproduction.
6. The gonads and the sex cells depend on the mitosis for the increase in their number.

DIAGRAM

                          MEIOSIS

Meiosis:- Meiosis is a special type of a division in which chromosome duplicate only once, but cell divides twice.So one parent cell produce four daughter cell,each having half the chromosome number and DNA amount.
 so meiosis is called the reductional division. it comprises of two divisions meiosis 1  and meiosis 2
Meiosis-1:- It also called reductional division because it involve formation of two daughter cells which have chromosome number half to those in parents cell. It is divided into two parts:
Karyokinesis:- It involves division of nucleus and is further divided into four phase:
Prophase-1:- It is of longest duration and again divisible into 5 subspace:
(A) leptotene: thin-thread stage chromosome appear thin, uncoiled and elongated and formation of aster occur.
(B) zygotene:- pairing of homologous chromosome ie synapsis occur to form bivalent (one paternal and one meternal chromosome)
- synapsis occur with the help of synaptonemol complex (formed nucleoprotein)
(C) Pachytene :- Crossing over occur ie two non-sister chromatid exchange their parts. the point where crossing over occur are called chiasmata.
(D) Diplotene:- Synaptonanal Complex dissolve.
- Desynapsis of homologous chromosome begin.
- Terminal occurs ie chismata start moving towards the end of chromosomes.
(E). Diakinesis:- Terminalisation is completed      - nuclear membrane and nucleolus disappear.  -formation of a spindle occur.
 Metaphase-1:- bivalent arrange themselves into parallel equatorial/metaphase plates.
- centromercs of homologous chromosome lie equidistant from equator.
 Anaphase-1:- Homologous chromosome start moving towards opposite poles. disjunction of chromosome occur.
 Telophase-1
-Nuclear membrane and nucleolus form at each pole.
-spindle fibre disappear.
2. cytokinesis-1:- May or may not occur.
-Occur by cell furrow formation in animal cells. -cell plate formation in plant cells.

Meiosis-2

 It is also called the equational division number of chromosome remains same after meiosis-1
 further divided into two parts
1. Karyokinesis-2:- It involve separation of two chromatid X1/2 of each chromosome and their movements to separate cells divide into four phases:
(A) Prophase-2:- Nuclear membrane disintegrates, nucleolus disappears.     chromatin fibre condense from chromosome.  -formation of Aster.
(B) Metaphase-2:- Arrangement of chromosome at the equator of spindle apparatus. Centromercs lie at the equator while arms are directed towards poles.
(C) Anaphase-2:-
Splitting of centromerc of each chromosome and movement of a chromatid toward opposite pole.
(D) Telophase-2:- Formation of a Daughter nucleus at each pole, nucleolus appear in each nucleus.
- spindle fibre disappear.

 significance of meiosis

 1:- Produce haploid gametes for reproduction. 2:- Maintain constant chromosome number generation after generation.
3:- Crossing over in a source of variation.
4:- Non-disjunction is also a source of variatiae.

Transformer

 It is a device used to change the voltage of alternating current. A transformer, which increase the voltage is called Step Up transformer, will other transformer which decrease the voltage is called step down Transformer.
Principle
 It is based upon is mutual induction i.e when current is one coil change, an EMF induced in neighbouring coil.
construction
It consists of a laminates soft iron core C. Two points P1 P2 and S1 S2 of insulated copper wire are wound on it but they are well insulated from each. the coil P1 P2 is connected to the source of alternating current. It is called primary coil other coil S1 S2 is called secondary coil. current is drawn from it. If Np and Ns be the number of turns in primary coil and secondary coil, then for Step Up transformer Ns>Np and for  step down Transformer. Ns<Np

 Theory and working
 when the primary coil is connected to the source of alternating current, magnetic flux linked with a primary coil Core and secondary coil change so EMF induced in both coil.
 If is the rate of change of magnetic flux linked with each turn of the primary coil, then
 Induced EMF is  primary coil Ep= -Np dø/dt
 If the resistance of a primary coil is small, then this induced EMF must be equal to the applied EMF.
 If there is no lenkage of magnetic flux, then the rate of change of magnetic flux through each turn of secondary coil =dø/dt
Induced EMF in secondary coil Es=-Nsdø/dt
 For open circuit,  this induced EMF is equal to the output EMF
Divide equation 2 and 1
Es/Ep=Ns/Np=K (Transformer ratio)
For step Up Transformer K>1 and 4 step down Transformer K <1. if Ip and Is are the current in primary and secondary coil and there is no loss of energy then
 output Power is equal to input power.
Or Es/Ep=Ip/Is___3
Thus when voltage is in secondary coil increase, the strength of a current decrease in the same ratio and vice versa.
Loss of energy 
In practice, the output power is less than input power due to a flowing loss of energy.
copper loss:-The copper wire of primary coil and secondary coil has same resistance so some electric energy change into heat energ [P=I²R]. which is a loss of energy.
 it can be reduced by using a thick copper wire.
2:- Eddy current:- As the magnetic flux linked with and iron core changes the eddy current are set up in it, which changed into heat. Which is a loss of energy.
It can be reduced by using a laminated iron core.
3:- when alternating current flow in the coil and the iron core is magnetized in one direction and demagnetize. it again magnetise in opposite direction and demagnetises. In this process of magnetization and demagnetization, some energy is wasted. it can be reduced by using a soft iron core.
4. leakage of magnetic flux:- The whole magnetic flux starting from primary coil does not pass through secondary coil. but some magnetic flux leak out into air. it can be reduced by winding both coil on same core on our other.
 5. humming loss:- Due to alternating current the core vibrates and produce humming noise. thus some electrical energy is wasted in the form of a humming noise.

 Uses of transformers
1. A step down Transformer is used for obtaining large current electric welding.
2. A step down Transformer is used to induction furnace for melting the metal.
3. A step up Transformer is used for the production of X rays.
4. Transformers are used in voltage regulator and stabilize power supply.
5. Small Transformer are used in radio sets, telephones, loudspeakers, sodium vapour lamps etc.
 6. They are used in transmission of electric energy from generating station to consumers.
Use of Transformer for long distance transmission of electric power
The electric power is transmitted at high voltage from generating station to consumers. In doing so, the loss of energy is small.
let we want to transmit 22,000 watt.
(i) If it is transmitted at 220 volt.
I=P/V 
22000/220=100A
 if R is the resistance of cable then heat produce.
I²RT
Fall of potential V=IR =100R
Thus at low voltage transmission
1:- A large amount of heat is produced, which loss of energy.
2:- large fall of potential takes place. so voltage at receiving station is much smaller than generating station.
3:- The cables must be thick to carry strong current. so the cables will be e expensive and strong poles are required to support thick cable.
4:- if the electric power is transmitted at 11000 volt, then I=22000/11000=2A, which is very smaller.
The above all problem are solved because heat produced and fall of potential are very small. and thin cables are can be used. Hence the electric power at transmitting station is stepped up to High Voltage. it is done by step up Transformer. now it is the transmitted. At receiving station it is stepped down by using step down Transformer. now it is distributed to consumer.
Advantage of AC over DC
1:- The generation of AC is more economical than DC.
2:- The voltage of alternating current can be easily change by using Transformer. while other voltage of DC cannot be changed by Transformer.
3:- Alternating current can be controlled by Choke coil with a very small loss of energy. while DC cannot be controlled by choke coil. it can be controlled only by resistance with a high loss of energy.
4:- AC can be transmitted at high voltage from generation station to any other place.In this process cost of transmission is low and loss of energy is also reduce. As the voltage of DC cannot be changed by Transformer.So it transmission is costly and loss of energy is heavy.
5:- AC can be converted into DC easily by using rectifier.
6:- AC equipment such as electric more are more durable and convenient as compared to DC equipments.
Disadvantage of AC or DC
1:- The peak value of AC is high. so it is more dangerous than DC of same voltage.
2:-The shock of AC is attractive, while that DC is repulsive.
3:- In phenomena like electrolysis, electroplating etc.  AC cannot be used.
4:- AC is transmitted more from the surface of conductor than inside it is called Skin effect. therefore the serverl fine wires are used to transmit high current instead of a single thick wire.

Photoelectric effect

 It is the phenomena of emission of electron from a metal surface when the radiation of suitable frequency fall on them. The emitted electron are called Photo electron . And the current so produced is called Photoelectric effect.
For example:- alkali metal EMIT the photoelectron when visible light fall on them. while other metal like zinc, emit Photon electrons, when ultraviolet radiation fall on them.

Work function:- It is minimum amount of energy required by an  electron to just escape from the metal surface.
Its value depend upon 1. nature of metal  2. condition of its surface generally is measured in electron volt.

Laws of Photoelectric effect

1:- For a given metal &  frequency of incident radiation, the number of photoelectrons emitted per second is directly proportional to the intensity of incident radiation.
2:- For a given metal, if the frequency of incident radiation is less than a particular frequency then no photoelectrons emitted this frequency is called Threshold frequency. for a given metal, its value is constant but for different metal its value is different.
3:- Above the threshold frequency. Then maximum kinetic energy of emitted photoelectrons depend upon frequency of incident radiation it does not depend upon their intensity.
4:- It is an instantaneous process. the time lag between incidence of radiation and emission of photoelectron is very small and less than 10 raise to power -9.

Einstein equation of Photoelectric effect

 when a photon of energy fall on a metal surface, its energy is absorbed by free electron of the metal surface one part of this energy is used in liberting the electron from metal surface which is equal to the work function of the metal and remaining part of the energy appear in the form of kinetic energy of photoelectrons. thus
 energy of photon = work function + kinetic energy of photoelectron.
Where m and v be the  mass and velocity of the photo electron.
 Now we consider a photon of frequency v*. Where v* = threshold frequency. this photon can only eject the photoelectron.
                  hv-hv*=1/2mv2
       or h(v-v*)=1/2mv2

Explanation of laws of photoelectric emission 

1:- When a photon fall on a metal surface, energy is absorbed by the free electron of metal surface. one part of this energy is used in librating the electron from the metal surface and remaining part appear in the form of kinetic energy of photoelectron. Thus as the number of a photon or intensity of incident radiation increases, the number of a photoelectron emitted per second also increase.

2:- If v<v* then kinetic energy of photoelectron become negative. which is not possible no photo electron is emitted. In this way if the frequency of incident radiation is less than threshold frequency. then no photoelectrons emitted.
3:- As h is  constant. for a given metal v* is constant. So maximum kinetic energy of photoelectron depend upon frequency of incident radiation.
 As the intensity of incident radiation increase the number of incident Photon falling per second increases. but the energy hv of the a photon remains same, so the kinetic energy of photoelectron remain same.
4:-  As the photoelectron are emitted due to the collision between photon and electron so it is an instantaneous process.

Experimental study of Photoelectric effect-

 The experiment arrangement of to study the laws of photo electric effect is shown in figure. It consists of a glass tube in which vacuum is created. A quartz window is fitted with it. Two electrodes C and A are sealed in it. C is a photo sensitive cathode and A is a collecting anode. the anode A can be kept at desired positive or negative potential with respect to cathode. the current is measured by milliameter and potential difference is measured by voltmeter.

                Circuit of photoelectric effect

1:-Effect of intensity

 The anode A is kept at positive potential with respect to cathode. now that radiation of  fixed frequency (greater than threshold frequency) are allowed to fall on the cathode. The cathode emitts the electron which reach at anode and current start to flow. we increase the intensity of incident radiation in steps and corresponding current is noted. A graph is plotted between intensity and current as shown in figure. from figure it is clear that the current is directly proportional to intensity of the incident radiation or we can say that the number of photoelectron emitted per second is directly proportional to the intensity.

2:- Effect of potential of anode on photoelectric current

 We allowed to fall the radiation of constant frequency and intensity on the cathode the positive potential of anode is increased in steps and not the corresponding current. Initially the current increase and finally become maximum called the saturation current. At this state all photoelectron emitted by cathode reach at anode directly. if the anode potential is further increase the value of a current remains same is maximum
 Now we give negative potential to the anode we see that the value of a photoelectric current  decrease because the photoelectron emitted by cathode are repelled by anode and only energetic photoelectrons reach at anode. As we increase the negative potential of anode the value of a current is decreases. at a certain negative potential it becomes zero. This potential is called stopping potential or cutoff potential. It is defined as the minimum negative potential given to anode with respect to the cathode at which photoelectric current becomes zero is called stopping potential.
 It is clear that ev*=half mVsquaremax the Vmax =maximum velocity of electron.
Now we allowed the fall the radiation of a high intensity i1 and i3 but same frequency v. we see that the saturation current is more and more but stopping potential is same. Thus it is clear that
1:- All photoelectrons does not have same kinetic energy.
2:-  For a given frequency the stopping potential for maximum kinetic energy of photoelectron does not depend upon the intensity of incident radiation.

Effect of frequency of incident radiations

 Now we allowed to fall the radiation intensity and frequency. we see that the saturation current is same for stopping potential are more negative. It is clear that the saturation current does not depend upon the frequency, while stopping potential depend upon the frequency of incident radiation as stopping potential is the measurement of a maximum kinetic energy of photoelectron.so maximum Kinetic energy of photoelectron depend upon frequency of incident radiation.
 If we draw a graph between frequency of incident radiation and stopping potential we get a straight line it is clear that for a particular frequency , the stopping potential is zero or we can say that the kinetic energy of photoelectron is zero. the frequency is called Threshold frequency.
If the frequency of incident radiation is less than a particular frequency then no photoelectrons emitted.
 From Einstein equation Photoelectric effect

What are lipids & Classification of lipids

Fats (or lipids) are fatty acid Ester of alcohols and related substance, which are insoluble in water but get dissolved in a number of non- polar organic solvent such as benzene, Ether, Acetone, chloroform etc.
There are three types of lipids
 1:-simple lipids
2:- compound lipids
3:-derived lipids

Simple lipids:- simple lipids are the Ester of fatty acids and alcohols which no additional groups,such as true fats, waxes, cutin and suberin.

Compound lipids:- compound lipids or fats have additional group beside fatty acid and alcohol,such as phospholipids, glyco-lipids and sulpho-lipids etc.
True fats:- They are triglycerides which are formed by esterification of 3 molecule of fatty acid which one molecule of trihydric alcohol glycerol.
·The three fatty acids may be similar (example:- Tripalmitin) or disimilar (example:- butter).
· Where R-CO- is derived from the fatty acid at each esterification a molecule of water is given out.
· If a true fat is hydrolysed, Ester linkage breakdown and the two components of the fat are regenerated.
· Hydrolysis by mean of alkalis is called 'Saponification' as it yield salts of fatty acid or soaps.
·  The soap action of the fatty acid is due to the presence of extremely polar water soluble end of an otherwise extremely non-polar water insoluble substance.
· True fats  chiefly serve as reserve food. they are stored in the cell inside sphaerosomes or oil bodies.
Waxes
1:- Wax is a soft hydrophobic mixture of long chain carbon compound including alcoholic Ester of fatty acid which are poor in oxygen and having a melting point between 36 to 200 degree Celsius.
2:- Waxes differ from true facts in having fatty acid ester of long chain monohydric alcohols Free alcohol, free hydroxy fatty acid, sterols and other fat-like substance may also occur in waxes.
3:- Waxes found on the the upper surface of floating leaves prevent wetting and submergence of the leaves. wax found on the surface of aerial part in useful in reducing insulation and transcription.
Cutin
1:-It is a complex produced by cross- esterification and polymerization of hydroxy fatty acid and having simple fatty acid with or without esterification by alcohols other than glycerol.
2:- It occur in the aerial epidermal cell walls and as a separate layer of a cutin on the outside of this epidermal cells.cutin reduce the rate of a transpiration and binds epidermal cell.
Suberin
It is a mixture of a fatty material having condensation product of a glycerol and phellonic acid or its related substance.suberin makes the cell wall strong and impermeable. it occur in the Wall of cork and endodrmal cells.
Compound lipids
Phospholipids
They are the triglycerides where on fatty acid is replaced by phosphoric acid linked to choline (in lecithin), ethanolamine (in cephalin) or inositol(in ionoside) etc
Glycolipids
They are those fats and lipids in which the terminal hydroxyl group of a glycerol is attached to a sugar instead of fatty acids. they occur especially in the chloroplast membranes.

Derived lipids
Steroids and sterols
The complex lipids which are unsponifiable include the biochemically important class, the steroids they fall in the category of isoprenoid lipids along with carotenes & bile acids.
· They are the tetracyclic Crystalisable alcohols of high molecular weight example:- cholestrol, cortisone, testosterone, ergasterol.
 · Cholesterol is important metabolically in human beings and plants where it occur.

Cholesterol

Function of lipids & fats
1:-They serve as food reserve in both plants and animals. their oxidation yield energy for growth.
2:- They function as a concentrated food because as compared to carbohydrates they yield more than twice as much energy per unit weight.
3:- In seeds and spores, they help in a thermal insulation protection from ultraviolet radiation.
4:- vitamin A, D, E and K are soluble in fats. therefore the functions as the transportable energy supply.
5:- In animals fat from an insulating layer below the skin for protection against low temperature.
6:- Several plants fats are edible. so are animals fats present in milk.
7:-  Soap is a manufactured from plant fats.(previously from animal fat).
8:- Steroids act as hormones example:- Testosterone.

DNA INFORMATION IN DETAIL

Watson and crick in 1950 determined the structure of DNA using X Ray crystallography in 1953 describe the structure of DNA
The important feature of watson crick model or double helix model of DNA are as follows
1· The DNA molecule consists of two polynucleotide chains or stands spirally twisted around each other and cold around a common Axis to form a right handed double helix.
2· The two strands are antiparallel they run in opposite directions so that the third end of one chain facing v end of the other.
3·The sugar phosphate backbone remain on the outside while the core of helix contain the purine and pyrimidine bases.
4·The two strands are held Together by hydrogen bond between the purine and pyrimidine base of the opposite stands.
5·The diameter of DNA is 2.0nm or 20 Å.
6·Adjacent bases are seperated 0.34nm or by 3.4Å along axis.
7·The length of complete turn of helix is 34Å .
8· There are 10 BP per turns
9· Adenine(A) always pair with thymine(T) by  to hydrogen bond & guanine(G) always pair with cytosins(c) by three hydrogen bond. This complimentary is know as the base pairing rule.
10· They are two types of groove in DNA- major groove and minor groove.

Function of DNA

1:-DNA is a genetic material which carries all the the hereditary information the genetic information is coded in the sequence of nitrogenous base.
2:-DNA has a unique property of replication production of carbon copies this is essential for transfer of genetic information from one cell to its daughter and from one generation to Next generation
3:-DNA occur inside chromosomes during meiosis crossing over gives rise to the new combination of gene called recombination
4:- change in the sequence of nitrogenous base due to the addition,deletion /wrong. Replication is called Mertation, which the fountain head of variations and evolution.
5:-DNA form RNA true process of replication.
6:- It controls metabolic reaction of the cell through synthesis of enzyme.
7:- Due to the  differential function of specific region of DNA cell are differentiated to perform specific function.
Forms of DNA.

There are various forms of DNA

A-form of DNA 
The a form of DNA is found at 75% relative humidity in a presence of NA+,K+ & Cs+ ions. it contain 11 base pair as compared to the 10 base pair of B DNA which tilt form the  axis of helix by 20 degree.
B form of DNA
 The structure of B form of DNA has been produced bi patsan and Crick it is present in every cell at a very high relative humidity 92% and low concentration of ions it is antiparallel double helix rotating clockwise (right hand) & made up of sugar phosphate backbone combined with base pair of purine pyrimidine.
C form of DNA
 C form of DNA is found at 66% relative humidity in the presence of Lithium ion as compared to A and B DNA in C DNA the numbers of base pair per turn is less.
D form of DNA 
The D-form of DNA is found rarely as extreme variants total number of base pairs per turn of helix is 8 therefore it shows 8 fold symmetry this form is also called Poly (DA-DT) & poly (DA-DC) form.
 Z form of DNA
 In 1979 rich and co-workers at MIT in USA obtained Z DNA by artificially synthesizing d(C-G) 3 molecules in the form of crystals they proposed a left handed double helix model with zigzag sugar phosphate backbone running in antiparallel direction

PROTEIN

The substance that's found in food like egg, meals. which help people for growth and  healthy is called protein.

Classification of protein

On the basis of constitution protein are three types.
1. Simple protein.
2. Conjugate protein.
3. Derived protein
·Simple protein:- Simple protein are built of one or more complete polypeptides without any additional group. They are composed solely of amino acid. They are further divided into two categories.
A. Structural protein.:- They are constituents of active protoplasm. Depending upon their function. The structural protein or 'enzymatic' & non-enzymatic.

B. Reserve or storage protein:- These protein are present as food reserve. They are globular and soluble in water. Some of them are heat sensitive also.

· Conjugated protein:- These protein contains in addition to amino acids other organic and inorganic material called prosthetic group of proteins.

Eg- HAEMOGLOBIN:- It contain iron as additional component.
GLYCOPROTEIN:- It contain carbohydrates as additional component.
LIPOPROTEIN:- It contain lipids as additional component.

· Derived protein:- They include met proteins, albuminoses, peptones, polypeptides and other products of partial hydrolysis of protein. They are intermediate products which do not accumulate.

Classification of protein.

On the basis of shape.
Fibrous protein:- They are thread-like proteins which may occur single in group s to form sheets. When they occur in groups, the polypeptide chains run parallel along a single axis. F·P are tough & insoluble in aquatic solution. They are non-enzymatic but structural proteins.

fibrous protein

Globular protein:-They are proteins in which the tightly packed polypeptide chains are coiled and abundantly folded to form sphere or globes. They may be enzymatic or non-enzymatic. They are generally soluble in aqueous solution and are capable of rapid fusion.

Function of protein.

1. They are the major constituents of protoplasm.
2. They are essential for cell division, growth,repair and reproduction.
3. Connective tissue of animals is two types of protein fibres- collagen & elastin.
4. Nucleoproteins performs an important function in controlling the working of DNA.
5. Some protein take part in the transport of substance. Example:- oxygen by haemoglobin.
6. Reserve protein provide amino acid for growth and repair eg. Albumin.
7. Some protein function as antibodies.
8. They act as buffers, since they resist the change in PH of the cells.
9. Toxin protein are used as defense by organisms eg snake venom.
10. Some protein act as hormones & regulate various activities in living organism eg Growth hormones.

Various levels of structure of protein

primary structure:-It consists of the sequence of amino acid residues joint through peptide bonds in the polypeptide of a protein the number of amino acid residues in a chain and the arrangement of amino acid are usually specific as each polypeptide is synthesized under construction from a cistron of DNA through mRNA.
Secondary structure:- It refers to the manner of extension or helical coiling of the polypeptide chain (particularly in fibrous protein). Which results mainly from hydrogen bonding between oxygen of carboxylic group of one amino acid residues and 'NH' group of next 4th amino acid residue. It is various types but  two main categories
1. Alpha helix
2. Beta-pleated sheet

Alpha helix:- Alpha helix is a secondary structure of proteins that consists of a peptide chain folded into right-handed spiral conformation & stabilized by H-bonds between C=O of one amino acid & N-H of fourth amino acid from that postion.

Beta-pleated sheet:- Beta-pleated sheet are made of Beta strands connected laterally by 2 more hydrogen bond forming a backbone twisted, pleated sheet. this structure occur when two or more segments of polypeptide chain overlap one another & and form hydrogen bond with each other.
Tertiary structure:- It refers to the folding and bending of polypeptide chain to form globular protein include buy covalent disulphide bonds (-S-S),hydrogen & Salt bonds & hydrophobic/hydrophilic interaction.
Quarternary structure:- It is found only those proteins which have two or more polypeptides. it refers to the manner in which the individual polypeptide chains fit together in a multimeric or oligomeric protein example:- in haemoglobin.