Definition - Rolling circle replication is a process of unidirectional nucleic acid replication.
* can rapidly synthesize multiple copies of circular molecules of DNA or RNA, such as plasmids.
* Eucaryotic also replicate.
* widely used in molecular biology & biomedical
nanotechnology, especially in the field of
biosensing (as a method of signal Amplification).
Steps:
Circular ds DNA will be “nicked”
3` end is elongated →Leading strand
5` end displaced → Lagging strand
made up of double stranded by OKAZAKI fragments.
4) Replication of both “ unnicked” and displaced ss DNA
5) Displaced DNA circulates and synthesis its own complementary strand.
Initation-- phosphate ends, by the action of:
a) Helicase
b) Topoisomerases
c) Single stranded binding proteins(SSBPs)
Elongation-OH group of broken strand, using the unbroken strand as a template. The polymerase will start to move in a circle for elongation, due to which it is named as Rolling Circle Model.
end will be displaced and will grow out like a waving thread.
Termination-* At the point of termination, the linear DNA molecule is cleaved from the circle resulting in a double stranded circular DNA molecule and a single- stranded linear DNA molecule.
* The linear single stranded molecule is circularized by the action of ligase and then replication to double stranded circular plasmid molecule.
Example- Conjugation of F+ and F- bacteria
Diagrammatic representation of Rolling circle
some Examples-Viral DNA
* Human herpes virus
* Human papilloma virus
* Geminivirus
Viral RNA
* pospiviridiae
* Avsunviridiae
Reference:- https://en. m. wikipedia.org
what- when- how.com
https//www.sciencedirect.com
www.slideshare.com
Genetics-notes.wikispace.com
you tube
Prescott 5th edition page.no: 236, 237
Brock biology of microorganism , page.no: 253,616
It is the DNA located in the mitochondria.Mitochondrial DNA (mtDNA or mDNA) is the DNA located in the mitochondria.
They are double stranded circular DNA molecule.
It is only 16 kb in length – contains 16,600 bp.
It is haploid in nature.
It codes for 37 genes.
13 genes provide instructions for making enzymes involved in oxidative phosphorylation.
It is a process that uses oxygen and simple sugars to create ATP, the cells main energy source.
Definition - Rolling circle replication is a process of unidirectional nucleic acid replication.
* can rapidly synthesize multiple copies of circular molecules of DNA or RNA, such as plasmids.
* Eucaryotic also replicate.
* widely used in molecular biology & biomedical
nanotechnology, especially in the field of
biosensing (as a method of signal Amplification).
Steps:
Circular ds DNA will be “nicked”
3` end is elongated →Leading strand
5` end displaced → Lagging strand
made up of double stranded by OKAZAKI fragments.
4) Replication of both “ unnicked” and displaced ss DNA
5) Displaced DNA circulates and synthesis its own complementary strand.
Initation-- phosphate ends, by the action of:
a) Helicase
b) Topoisomerases
c) Single stranded binding proteins(SSBPs)
Elongation-OH group of broken strand, using the unbroken strand as a template. The polymerase will start to move in a circle for elongation, due to which it is named as Rolling Circle Model.
end will be displaced and will grow out like a waving thread.
Termination-* At the point of termination, the linear DNA molecule is cleaved from the circle resulting in a double stranded circular DNA molecule and a single- stranded linear DNA molecule.
* The linear single stranded molecule is circularized by the action of ligase and then replication to double stranded circular plasmid molecule.
Example- Conjugation of F+ and F- bacteria
Diagrammatic representation of Rolling circle
some Examples-Viral DNA
* Human herpes virus
* Human papilloma virus
* Geminivirus
Viral RNA
* pospiviridiae
* Avsunviridiae
Reference:- https://en. m. wikipedia.org
what- when- how.com
https//www.sciencedirect.com
www.slideshare.com
Genetics-notes.wikispace.com
you tube
Prescott 5th edition page.no: 236, 237
Brock biology of microorganism , page.no: 253,616
It is the DNA located in the mitochondria.Mitochondrial DNA (mtDNA or mDNA) is the DNA located in the mitochondria.
They are double stranded circular DNA molecule.
It is only 16 kb in length – contains 16,600 bp.
It is haploid in nature.
It codes for 37 genes.
13 genes provide instructions for making enzymes involved in oxidative phosphorylation.
It is a process that uses oxygen and simple sugars to create ATP, the cells main energy source.
This power point presentation explains double helical structure of DNA as proposed by Watson and Crick (1953).Attempts have also been made to high light the valuable contributions made by Rosalind Franklin and Wilkins. Brief details of different types of DNA have also been included.
Nucleic acids are naturally occurring chemical compounds that serve as the primary information-carrying molecules in cells. They play an especially important role in directing protein synthesis. The two main classes of nucleic acids are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). The information/images in this study material have been adapted from various sources including but not limited to books, journals, websites, and related materials openly available on the internet. This will be purely utilized for academic purposes only, by college students. The author has no intention of using this information/images/other materials that may be copyrighted and included in this study material for commercial benefit.
Nucleic acid-DNA and RNA
Gene-part of DNA
Functions of DNA
RNA-Functions, different types of RNA-Ribosomal RNAs (rRNAs), Messenger RNAs (mRNAs), Transfer RNAs (tRNAs)-Other RNA-Small nuclear RNA (snRNA), Micro RNA (miRNA), Small interfering RNA (siRNA), Heterogenous RNA (hnRNA).
Nucleic acid-nucleotides-nucleoside
Components of nucleotide-a nitrogenous (nitrogen-containing) base (pyrimidine and purine), (2) a pentose, and (3) a phosphate
Structure of pentose sugar, and 5 major bases (cytosine, thymine, uracil-pyrimidine bases and adenine, guanine-purine bases).
Deoxyribonucleotides and Ribo nucleotides-Molecular structure of deoxyadenosine monophosphate (dAMP), deoxyguanosine monophosphate (dGMP), deoxythymidine monophosphate (dTMP), deoxycytidine monophosphate (dCMP) and Adenosine monophosphate (AMP), Guanosine monophosphate (GMP), Cytosine monophosphate (CMP) and Uridine monophosphate (UMP), Watson crick base pairing, Hoogsteen base pairing,
Helical structure-Heterocylic N -Glycosides, Syn and Anti Conformers, detailed structure of single strand and double stranded DNA.
DNA Nucleotides and Tautomeric Form-Tautomers of Adenine, Cytosine, Guanine, and Thymine
Template strand, non coding strand and coding strand
Hydrogen bonds, phosphodiester linkage, hydrolysis of DNA and RNA.
Different forms of DNA-A, B, and Z forms.
Palindrome sequence, Linear DNA, Cruciform DNA, H DNA (Triplex DNA), Denaturation of DNA, Hyperchromicity, Tm, Renaturation of DNA, Tertiary structure of DNA, Difference of DNA and RNA, RNA structural elements, primary. secondary and tertiary structure of RNA. Detailed structure and functions of tRNA, mRNA, rRNA, miRNA, siRNA, hn RNA, snRNA.
Nucleic acid hybridization, C0t analysis, Buoyant density of DNA, Isopycnic centrifugation.
Dna chemistry structure,fuctions and its orgainizationneha sheth
DNA, Nucleotides, Structure of DNA, Features of DNA, watson-crick Model of DNA,base pairing rule, Denaturation of DNA,Higher organization of DNA, Histones, chromosomes, nucleosomes, introns, extrons, repeat sequences of DNA
EIA for Major development projects - Mining projectsJenson Samraj
EIA is a decision making tool for developmental projects (Mining, construction of dams).
It will have environmental implication in changing the variables such as quality of air, ground water, soil in that area.
The purpose of assessment is to ensure that decision makers consider the environmental impacts to implement the project
EIA helps us to measure or predict the impact of any developmental projects on the environment. Mining refers to Extraction of valuable minerals or other geological materials from the Earth, usually from an ore body, lode, vein, seam, reef, or placer deposit.
Metals, coal, oil shale, gemstones, limestone, chalk, dimension stone, rock salt, potash, gravel, and clay. Large scale mining pollution contaminates all living organisms within the body of water
Affects environment adversely
Results in deforestation
New Educational Policy 2020 and its ImplicationJenson Samraj
New Education Policy and its Implementation replaces the old educational policy 1986. New education policy 2020 approved by the Union Cabinet of India on 29 July 2020, outlines the vision of India’s new education system. This policy is a comprehensive framework for elementary education to higher education. It aims to increase state expenditure on education from around 4-6% as soon as policy.
Rainwater harvesting is the collection and storage of rain, rather than allowing it to run off. Rainwater is collected from a roof-like surface and redirected to a tank, cistern, deep pit, aquifer, or a reservoir with percolation, so that it seeps down and restores the ground water.
Rainwater harvesting is one of the simplest and oldest methods of self-supply of water for households, and residential and household-scale projects, usually financed by the user.[5] However, larger systems for schools, hospitals, and other facilities can run up costs only able to be financed by owners, organizations, and governmental units.
This slide brings us to know about the Amendments of 2006 and 2009 in Environmental Impact Assessment. The draft EIA notification issued by the ministry and forests for amendment 2009. The process of amendment 2006 was well sketched in the presentation. Hope everyone would like this.
Baseline data is a significant part of EIA. As the proverb says "Look before you leap". Every environmental aspect should be considered before initiating each and everything. The baseline should be well-known about an environment.
This is my presentation for the World Wetlands Day celebration. Testified wetland's significance, awareness, and ways to conserve. Finally, conducted a quiz for more interactions.
Here you will find about the antibody' structure and functions. Because, it is very important for us to know about the immunity responses against the antigen. Immunoglobulin (Ig) is very important for us that are present in the plasma (fluid of the blood)
PAPER PRESENTATION ON REMOVAL OF LEAD IONSJenson Samraj
This presentation describes the removal of lead contents from the waste stream using Water hyacinth. In this way, the elimination of water hyacinth occurs corresponding to the removal of Lead ions.
This is the certificate designed for conducting an awareness program at SPKCEES, Alwarkurichi. If you want in presentation format, I am ready to provide you soon.
It is an unforgettable thing and it is the first conference paper which I have presented in my university. This describes how the Nanotechnology alters the world to advance. It also has lots of applications due to it's large surface area.
CHEMICALLY DERIVED NANO-PIGMENT FOR ANTIBACTERIAL ACTIVITY, SURFACE COATING A...Jenson Samraj
This dissertation describes the properties of Nanopigment. The work which was furnished with lots of information about the antibacterial effects of the nanopigment.
COMPARATIVE ANALYSIS OF WATER QUALITY IN TAMIRABARANI RIVER ENCROACHED BY WAT...Jenson Samraj
This dissertation explains the analysis of water quality in which the Eichhornia crassipes lives further from many different samples the water was analyzed by my friend Mr. Esakki Raja
It is our Mini-project report which we will submit at the end of B.Sc completion. I browsed many things for obtaining the articles and it is my hard work to complete this for my friend Mr. SENTHIL KUMAR. Hope that it will be very useful for those who write Mini-project report.
A MINI PROJECT REPORT ON MANIMUTHAR RIVER, DAM AND CANALJenson Samraj
It is our Mini-project report which we will submit at the end of B.Sc completion. I browsed many things for obtaining the articles and it is my hard work to complete this for my friend Mr. AJAY KALLAPIRAN. Hope that it will be very useful for those who write Mini-project report.
It is our Mini-project report which we will submit at the end of B.Sc completion. I browsed many things for obtaining the articles and it is my hard work to complete this for my friend Mr. VETRI. Hope that it will be very useful for those who write Mini-project report.
"Understanding the Carbon Cycle: Processes, Human Impacts, and Strategies for...MMariSelvam4
The carbon cycle is a critical component of Earth's environmental system, governing the movement and transformation of carbon through various reservoirs, including the atmosphere, oceans, soil, and living organisms. This complex cycle involves several key processes such as photosynthesis, respiration, decomposition, and carbon sequestration, each contributing to the regulation of carbon levels on the planet.
Human activities, particularly fossil fuel combustion and deforestation, have significantly altered the natural carbon cycle, leading to increased atmospheric carbon dioxide concentrations and driving climate change. Understanding the intricacies of the carbon cycle is essential for assessing the impacts of these changes and developing effective mitigation strategies.
By studying the carbon cycle, scientists can identify carbon sources and sinks, measure carbon fluxes, and predict future trends. This knowledge is crucial for crafting policies aimed at reducing carbon emissions, enhancing carbon storage, and promoting sustainable practices. The carbon cycle's interplay with climate systems, ecosystems, and human activities underscores its importance in maintaining a stable and healthy planet.
In-depth exploration of the carbon cycle reveals the delicate balance required to sustain life and the urgent need to address anthropogenic influences. Through research, education, and policy, we can work towards restoring equilibrium in the carbon cycle and ensuring a sustainable future for generations to come.
WRI’s brand new “Food Service Playbook for Promoting Sustainable Food Choices” gives food service operators the very latest strategies for creating dining environments that empower consumers to choose sustainable, plant-rich dishes. This research builds off our first guide for food service, now with industry experience and insights from nearly 350 academic trials.
Willie Nelson Net Worth: A Journey Through Music, Movies, and Business Venturesgreendigital
Willie Nelson is a name that resonates within the world of music and entertainment. Known for his unique voice, and masterful guitar skills. and an extraordinary career spanning several decades. Nelson has become a legend in the country music scene. But, his influence extends far beyond the realm of music. with ventures in acting, writing, activism, and business. This comprehensive article delves into Willie Nelson net worth. exploring the various facets of his career that have contributed to his large fortune.
Follow us on: Pinterest
Introduction
Willie Nelson net worth is a testament to his enduring influence and success in many fields. Born on April 29, 1933, in Abbott, Texas. Nelson's journey from a humble beginning to becoming one of the most iconic figures in American music is nothing short of inspirational. His net worth, which estimated to be around $25 million as of 2024. reflects a career that is as diverse as it is prolific.
Early Life and Musical Beginnings
Humble Origins
Willie Hugh Nelson was born during the Great Depression. a time of significant economic hardship in the United States. Raised by his grandparents. Nelson found solace and inspiration in music from an early age. His grandmother taught him to play the guitar. setting the stage for what would become an illustrious career.
First Steps in Music
Nelson's initial foray into the music industry was fraught with challenges. He moved to Nashville, Tennessee, to pursue his dreams, but success did not come . Working as a songwriter, Nelson penned hits for other artists. which helped him gain a foothold in the competitive music scene. His songwriting skills contributed to his early earnings. laying the foundation for his net worth.
Rise to Stardom
Breakthrough Albums
The 1970s marked a turning point in Willie Nelson's career. His albums "Shotgun Willie" (1973), "Red Headed Stranger" (1975). and "Stardust" (1978) received critical acclaim and commercial success. These albums not only solidified his position in the country music genre. but also introduced his music to a broader audience. The success of these albums played a crucial role in boosting Willie Nelson net worth.
Iconic Songs
Willie Nelson net worth is also attributed to his extensive catalog of hit songs. Tracks like "Blue Eyes Crying in the Rain," "On the Road Again," and "Always on My Mind" have become timeless classics. These songs have not only earned Nelson large royalties but have also ensured his continued relevance in the music industry.
Acting and Film Career
Hollywood Ventures
In addition to his music career, Willie Nelson has also made a mark in Hollywood. His distinctive personality and on-screen presence have landed him roles in several films and television shows. Notable appearances include roles in "The Electric Horseman" (1979), "Honeysuckle Rose" (1980), and "Barbarosa" (1982). These acting gigs have added a significant amount to Willie Nelson net worth.
Television Appearances
Nelson's char
Natural farming @ Dr. Siddhartha S. Jena.pptxsidjena70
A brief about organic farming/ Natural farming/ Zero budget natural farming/ Subash Palekar Natural farming which keeps us and environment safe and healthy. Next gen Agricultural practices of chemical free farming.
UNDERSTANDING WHAT GREEN WASHING IS!.pdfJulietMogola
Many companies today use green washing to lure the public into thinking they are conserving the environment but in real sense they are doing more harm. There have been such several cases from very big companies here in Kenya and also globally. This ranges from various sectors from manufacturing and goes to consumer products. Educating people on greenwashing will enable people to make better choices based on their analysis and not on what they see on marketing sites.
Artificial Reefs by Kuddle Life Foundation - May 2024punit537210
Situated in Pondicherry, India, Kuddle Life Foundation is a charitable, non-profit and non-governmental organization (NGO) dedicated to improving the living standards of coastal communities and simultaneously placing a strong emphasis on the protection of marine ecosystems.
One of the key areas we work in is Artificial Reefs. This presentation captures our journey so far and our learnings. We hope you get as excited about marine conservation and artificial reefs as we are.
Please visit our website: https://kuddlelife.org
Our Instagram channel:
@kuddlelifefoundation
Our Linkedin Page:
https://www.linkedin.com/company/kuddlelifefoundation/
and write to us if you have any questions:
info@kuddlelife.org
2. ✓ Although the name nucleic acid suggests their location
in the nuclei of cells, certain of them are, however, also
present in the cytoplasm.
✓ The nucleic acids are the hereditary determinants of
living organisms.
✓ They are the macromolecules present in most living
cells either in the free state or bound to proteins as
nucleoproteins.
✓ Like the proteins, the nucleic acids are biopolymers of
high molecular weight with mononucleotide as their
repeating units, just as amino acids are the repeating
units of proteins.
3. ✓ There are two kinds of nucleic acids, deoxyribonucleic
acid (DNA) and ribonucleic acid (RNA).
✓ Both types of nucleic acids are present in all plants and
animals.
✓ DNA is found mainly in the chromatin of the cell
nucleus whereas most of the RNA (90%) is present in
the cell cytoplasm and a little (10%) in the nucleous.
✓ It may be added that extranuclear DNA also exists; it
occurs, for example, in mitochondria and chloroplasts.
6. Phosphoric Acid
✓ The molecular formula of phosphoric acid is H3PO4.
✓ It contains 3 monovalent hydroxyl groups and a
divalent oxygen atom, all linked to the pentavalent
phosphorus atom
7. Pentose Sugar
✓ The two types of nucleic acids are distinguished primarily
on the basis of the 5-carbon keto sugar or pentose which
they possess.
✓ One possesses D-2-deoxyribose, hence the name
deoxyribose nucleic acid or deoxyribonucleic acid, while
the other contains D-ribose, hence the name ribose nucleic
acid or ribonucleic acid.
8. ✓ An important property of the pentoses is their capacity
to form esters with phosphoric acid.
✓ In this reaction the OH groups of the pentose, especially
those at C3 and C5, are involved forming a 3′, 5′-
phosphodiester bond between adjacent pentose residues.
✓ This bond, in fact, is an integral part of the structure of
nucleic acids.
9.
10. Nitrogenous Bases
✓ Two types of nitrogenous bases are found in all nucleic
acids.
✓ The nitrogenous bases are derivatives of pyrimidine and
purine.
✓ Pyrimidine bases – Uracil, Thymine and Cytosine
✓ Purine bases – Adenine and guanine
11. Pyrimidine Derivatives
✓ These are all derived from their parent heterocyclic
compound pyrimidine, which contains a six membered
ring with two-nitrogen atoms and three double bonds.
✓ It has a melting point of 22°C and a boiling point of
123.5°C.
12. Uracil (C4H4O2N2), found in RNA only, MW = 112.10
daltons, M.P - 338°C.
Thymine (C5H6O2N2), found in DNA only, MW = 126.13
daltons, M.P - 335°C.
Cytosine (C5H4ON3), found in both DNA and RNA, MW =
111.12 daltons, M.P – 320-325°C
13. Purine Derivatives
✓ These are all derived from their parent compound
purine, which contains a six-membered pyrimidine ring
fused to the five-membered imidazole ring and is
related to uric acid.
✓ It has a melting point of 216°C.
14. Adenine (C5H5N5), found in both RNA and DNA, with MW
= 135.15 daltons and M.P. 360-365°C.
Guanine (C5H5ON5), also found in both RNA and DNA,
with MW = 151.15 daltons and M.P. 360°C
15. ✓ The nucleosides are compounds in which nitrogenous
bases (purines and pyrimidines) are conjugated to the
pentose sugars (ribose or deoxyribose) by a β-
glycosidic linkage.
✓ The β-glycosidic linkage involves the C-1′ of sugar and
the hydrogen atom of N-9 (in the case of purines) or N-
1 (in the case of pyrimidines), thus eliminating a
molecule of water.
Nucleosides
18. ✓ Nucleotides are the phosphoric acid esters of
nucleosides.
✓ These occur either in the free form or as subunits in
nucleic acids.
✓ In the ribose moiety of a ribonucleoside,
phosphorylation is possible only at three positions (C2′,
C3′, C5′) since C1′ and C4′ are involved in the furanose
ring formation.
✓ In the deoxyribose component of a 2′-
deoxyribonucleoside, only two positions (C3′, C5′) are
available for phosphorylation, since in this sugar C1′
and C4′ are involved in the furanose ring and C2′ does
not bear a hydroxyl group.
Nucleotides
20. Deoxyribonucleic Acid
✓ A nucleic acid may be visualized as a polymer of a
nucleotide monomer.
✓ In other words, it may be considered as a
polynucleotide.
✓ DNA as .... (base-deoxyribose-phosphate)n
✓ RNA as .... (base-ribose-phosphate)n
21. Base Composition of DNA-Chargaff Rule
✓ The sum of purines (Pu) is equal to the sum of
pyrimidines (Py), i.e., Pu/Py = 1. In other words, A + G
= T + C
✓ The ratio of adenine to thymine is also one, i.e., A/T =
1.
✓ The ratio of guanine to cytosine is also one, i.e., G/C=
1.
✓ Bases with 6-amino groups are equal to bases with 6-
keto (hydroxyl) groups, i.e., A + C = G + T.
✓ The ratio of A + T/G + C, known as dissymmetry ratio,
varies greatly from one species of DNA to the other
and is characteristic of that species.
✓ Chargaff’s data suggest that A is always paired with T
and G is always paired with C.
22. Primary structure
✓ Primary structure of DNA refers to the phosphodiester
bond backbone.
✓ In nucleic acid strands, nucleotides are linked by
phosphodiester bond.
✓ The bond is formed between the 5’-phosphate group of
one nucleotide and 3—hydroxyl group of adjacent
nucleotide.
✓ A single nucleic acid strand formed by phosphodiester
bond has two termini namely 5’ end with phosphate group
and 3’ end with hydroxyl group.
23.
24. Secondary Structure
✓ Double helical DNA model was proposed by Watson
and Crick.
✓ This model is also called as B-form.
✓ DNA double helix is made up of two DNA strands
running in opposite directions along a common axis.
✓ A pairs with T via two hydrogen bonds and G pairs with
C via three hydrogen bonds.
✓ DNA will have 1:1 ratio of purine and pyrimidine bases
(Chargaff’s rule).
25.
26. Tertiary structure
✓ Supercoiled, DNA, chromosomes and chromatin are the
three types of tertiary structures of DNA
✓ DNA can be twisted, coiled into compact structure which
resembles a coiled telephone wire
✓ Supercoiling may be right handed or left handed.
27.
28. Double Helical Structure of DNA
(Watson-Crick Model)
✓ DNA molecule consists of two helical polynucleotide
chains which are coiled around (or wrapped about) a
common axis in the form of a right-handed double helix.
✓ The two helices are wound in such a way so as to
produce 2 interchain spacing or grooves, a major or wide
groove (width 12 Å, depth 8.5 Å) and a minor or narrow
groove (width 6 Å, depth 7.5 Å).
29.
30. ✓ The phosphate and deoxyribose units are found on the
periphery of the helix, whereas the purine and
pyrimidine bases occur in the centre.
✓ The planes of the bases are perpendicular to the helix
axis.
✓ The planes of the sugars are almost at right angles to
those of the bases.
31. ✓ The diameter of the helix is 20 Å.
✓ The bases are 3.4 Å apart along the helix axis.
✓ Therefore, the helical structure repeats after 10
residues on each chain, i.e., at intervals of 34 Å.
✓ In other words, each turn of the helix contains 10
nucleotide residues.
32. ✓ The two chains are held together by hydrogen bonds
between pairs of bases.
✓ Adenine always pairs with thymine by 2 hydrogen bonds
and guanine with cytosine with 3 hydrogen bonds.
✓ The individual hydrogen bonds are weak in nature but, as
in the case of proteins, a large number of them involved
in the DNA molecule confer stability to it.
✓ It is now thought that the stability of the DNA molecule
is primarily a consequence of van der Waals forces
between the planes of stacked bases.
33. ✓ The sequence of bases along a polynucleotide chain is
not restricted in any way.
✓ The precise sequence of bases carries the genetic
information.
✓ As a corollary, the entire structure of a DNA molecule
resembles a winding staircase, with the sugar and
phosphate molecules of the nucleotides forming the
railings and the linked nitrogen base pairs (A-T and G-
C) forming the steps.
34. A-DNA
✓ A-DNA appears when the DNA fibre (B-DNA) is
dehydrated, i.e., relative humidity is reduced from 92 to
75% and Na+, K+ and Cs+ ions are present in the
medium. In other words, in solution, DNA assumes the
B form and after dehydration it assusmes the A form.
✓ This is because the phosphate groups in the A-DNA
bind fewer water molecules than the phosphates in B-
DNA.
35.
36. C-DNA
✓ C-DNA is formed at 66% relative humidity in the
presence of Li+ ions.
✓ This form of DNA is also right-handed, with an axial
rise of 3.32 Å per base pair.
✓ There are 9.33 base pair per turn of the helix ; the value
of helix pitch is, therefore, 3.32 × 9.33 Å or 30.97 Å.
✓ The rotation per base pair in C-DNA is 360/9.33 or
38.58°.
✓ The C-helix has a diameter of 19 Å, smaller than that
of both B- and A-helix.
37.
38. D-DNA
✓ D-DNA is an extremely rare variant with only 8 base
pairs per helical turn.
✓ This form of DNA is found in some DNA molecules
devoid of guanine.
✓ By contrast, A-, B- and C forms of DNA are found in all
DNA molecules, irrespective of their base sequence.
39.
40. Z-DNA
✓ Z-DNA is the more radical departure from B-DNA and
is characterized by a lefthanded helical rotation.
✓ It was discovered by Rich, Nordheim and Wang in
1984.
✓ They found that a hexanucleotide, CGCGCG, forms a
duplex of antiparallel strands held together by Watson-
Crick base pairing, as expected.
✓ Surprisingly, they found that this double helix was left-
handed and the phosphates in the DNA backbone were
in a zigzag manner ; hence, they termed this new form
as Z-DNA.
41.
42. Palindromic DNA
✓ It has sequences with twofold symmetry.
✓ In order to superimpose one repeat (shaded sequence) on
the other (unshaded sequence), it must be rotated 180°
around the horizontal axis and then again about the
vertical axis, as shown by arrows.
43. Mirror repeat
✓ It has a symmetric sequence on each strand.
Superimposing one repeat on the other requires only a
single 180º rotation about the vertical axis.
44. Bent DNA
✓ Some sequences cause bends in the DNA helix.
✓ Bends are produced whenever 4 or more adenine
residues appear sequentially in one of the two strands.
✓ Six adenines in a row produce a bend of about 18°.
✓ Bending may be important in the binding of some
proteins to DNA.
Hairpin
✓ When only a single strand of palindromic DNA (or
RNA) is involved, a hairpin is formed.
Cruciform
✓ When both the strands of a double helical DNA are
involved, a cruciform is formed.
45.
46. H-DNA
✓ H-DNA is usually found in polypyrimidine or
polypurine segments that contain within themselves a
mirror repeat.
✓ One simple example is a long stretch of alternating T
and C residues.
✓ A striking feature of H-DNA is the pairing and
interwinding of 3 strands of DNA to form a triple helix.
✓ Triple-helical DNA is produced spontaneously only
within long sequences containing only pyrimidines (or
purines) in one strand.
✓ Two of the three strands in the H-DNA triple helix
contain pyrimidines and the third contains purines.