The document discusses the structure of DNA. It notes that DNA contains two chains that are related by a dyad perpendicular to the fiber axis. The two chains follow right-handed helices in opposite directions. DNA takes the form of a double helix, with the bases on the inside of the helix paired together through hydrogen bonds between complementary base pairs (A-T and G-C). This double-helical structure suggested a mechanism for DNA replication.
FEATURING THE SUMMARY OF SCIENCE 10 UNIT 3 MODULE 2.
INCLUDING RNA AND DNA
GENETIC ENGINEERING
HUMAN KARYOTYPING
DOWNS SYNDROME
CRI DU CHAT
EDWARDS SYNDROME
CHROMOSOME ABNORMALITIES
TRAITS INHERITED
DNA is a molecule composed of two chains that coil around each other to form a double helix carrying genetic instructions for the development, functioning, growth and reproduction of all known organism. DNA are nucleic acids;. The two DNA strands are also known as polynucleotides as they are composed of simpler monomeric units called nucleotides. Each nucleotide is composed of one of four nitrogen-containing nucleo bases (cytosine[C], guanine[G], adenine[A] or thymine[T]), a sugar called deoxyribose, and a phosphate group.
Nucleotide :- nitrogenous base,sugar,phosphate
Nucleoside :- :- nitrogenous base,sugar
FEATURING THE SUMMARY OF SCIENCE 10 UNIT 3 MODULE 2.
INCLUDING RNA AND DNA
GENETIC ENGINEERING
HUMAN KARYOTYPING
DOWNS SYNDROME
CRI DU CHAT
EDWARDS SYNDROME
CHROMOSOME ABNORMALITIES
TRAITS INHERITED
DNA is a molecule composed of two chains that coil around each other to form a double helix carrying genetic instructions for the development, functioning, growth and reproduction of all known organism. DNA are nucleic acids;. The two DNA strands are also known as polynucleotides as they are composed of simpler monomeric units called nucleotides. Each nucleotide is composed of one of four nitrogen-containing nucleo bases (cytosine[C], guanine[G], adenine[A] or thymine[T]), a sugar called deoxyribose, and a phosphate group.
Nucleotide :- nitrogenous base,sugar,phosphate
Nucleoside :- :- nitrogenous base,sugar
DNA = deoxyribonucleic acid.
DNA carries the genetic information in the cell – i.e. it carries the instructions for making all the structures and materials the body needs to function.
DNA is capable of self-replication.
Most of the cell’s DNA is carried in the nucleus – a small amount is contained in the mitochondria.
DNA = deoxyribonucleic acid.
DNA carries the genetic information in the cell – i.e. it carries the instructions for making all the structures and materials the body needs to function.
DNA is capable of self-replication.
Most of the cell’s DNA is carried in the nucleus – a small amount is contained in the mitochondria.
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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.
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The three-dimensional structure of DNA proposed by Watson and Crick, as well as recent advances in this field, are summarised below:
DNA is made up of two helical chains that are coiled around the same axis to form a right-handed double helix.
The two chains in the helix are antiparallel, meaning that the 5′ end of one polynucleotide chain and the 3′ end of the other polynucleotide chain are on the same side and close together.
Each turn is separated by 3.6 nm (formerly 3.4 nm).
Each turn contains 10.5 nucleotides (formerly 10 nucleotides).
Major and minor grooves are formed between the two strands due to their spatial relationship. Some proteins interact in these grooves.
The outside of the double helix has hydrophilic backbones made up of alternating deoxyribose and negatively charged phosphate groups.
The hydrophobic pyrimidine and purine bases are located inside the double helix, which helps to stabilize the DNA double helix.
An inter-chain hydrogen bond formed between a purine and pyrimidine base also helps to stabilise the double helix.
A particular purine base forms hydrogen bonds with only one pyrimidine base, i.e Adenine (A) pairs with Thymine (T) and Guanine (G) with Cytosine (C).
Adenine and Thymine (A = T) form two hydrogen bond pairs, while Guanine and Cytosine (G ≡ C) form three hydrogen bond pairs.
Complementary base pairs are A = T and G ≡ C.
The two chains of the DNA double helix are complementary to each other due to the presence of complementary base pairing.
One strand of the double helix is known as the sense strand, which codes for RNA/proteins, and the other is known as the antisense strand.
DNA structure, the bonds involved and it seperationMohit Adhikary
DNA structure, and the bonds that stabilizes it. The structural components, units and the proteins involved. Types of DNA and its separation methods. Chargaffs rule and its application
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Students, digital devices and success - Andreas Schleicher - 27 May 2024..pptxEduSkills OECD
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This is a presentation by Dada Robert in a Your Skill Boost masterclass organised by the Excellence Foundation for South Sudan (EFSS) on Saturday, the 25th and Sunday, the 26th of May 2024.
He discussed the concept of quality improvement, emphasizing its applicability to various aspects of life, including personal, project, and program improvements. He defined quality as doing the right thing at the right time in the right way to achieve the best possible results and discussed the concept of the "gap" between what we know and what we do, and how this gap represents the areas we need to improve. He explained the scientific approach to quality improvement, which involves systematic performance analysis, testing and learning, and implementing change ideas. He also highlighted the importance of client focus and a team approach to quality improvement.
8. La struttura del DNA (B)
•Il DNA ha una forma ad elica regolare,
diametro 20Å, passo 34Å
•Legami idrogeno tra le basi
•L’impilamento delle basi è determinato da
interazioni idrofobiche
•Ogni coppia è ruotata di 36°
•Solchi maggiore (22Å) e minore (12Å)
•Avvolgimento in senso orario (elica
destrorsa)
9. Nature, Vol. 171, p.737, April 25, 1953
MOLECULAR STRUCTURE OF
NUCLEIC ACIDS
A Structure for Deoxyribose Nucleic Acid
We wish to s uggest a structure for the salt of
deoxyribose nucleic acid (D.N.A.). This structure has
novel features which are of considerable biological
interest.
A structure for nucleic acid has already been
proposed by Pauling and Corey (1). They kindly made
their manuscript available to us in advance of
publication. Their model consists of three intertwined
chains, with the phosphates near the fibre axis, and the
bases on the outside. In our opinion, this structure is
unsatisfactory for two reasons: (1) We believe that the
material which gives the X-ray diagrams is the salt, not
the free acid. Without the acidic hydrogen atoms it is
not clear what forces would hold the structure together,
especially as the negatively charged phosphates near
the axis will repel each other. (2) Some of the van der
Waals distances appear to be too small.
Another three-chain structure has also been
suggested by F raser (in the press). In his model the
phosphates are on the outside and the bases on the
inside, linked together by hyd rogen bonds. This
structure as described is rather ill-defined, and for this
reason we shall not comment on it.
We wish to put forward a ra dically different
structure for the salt of deoxyribose nucleic acid. This
structure has two helical chains each coiled round the
same axis (see diagram). We have made the usual
chemical assumptions, namely, that each chain consists
of phosphate diester groups joining ß-D-
deoxyribofuranose residues with 3',5' linkages. The two
chains (but not their bases) are related by a dyad
perpendicular to the fibre axis. Both chains follow
right- handed helices, but owing to the dyad the
sequences of the atoms in t he two chains run in
opposite directions. Each chain loosely resembles
Furberg's2 model No. 1; that is, the bases are on the
inside of the helix and the phosphates on the outside.
The configuration of the sugar and the atoms near it is
close to Furberg's 'standard configuration', the sugar
being roughly perpendicular to the attached base. There
is a residue on each every 3.4 A. in the z-direction. We
have assumed an angle of 36° between adjacent
residues in the same chain, so that the structure repeats
after 10 residues on each chain, that is, after 34 A. The
distance of a phosphorus atom from the fibre axis is 10
A. A s the phosphates are on the outside, cations have
easy access to them.
The structure is an open one, and its water content
is rather high. At lower water contents we would expect
the bases to tilt so that the structure could become more
compact.
The novel feature of the structure is the manner in
which the two chains are held together by the purine
and pyrimidine bases. The planes of the bases are
perpendicular to the fibre axis. The are joined together
in pairs, a single base from the other chain, so that the
two lie side by side with identical z-co-ordinates. One
of the pair must be a purine and the other a pyrimidine
for bonding to occur. The hydrogen bonds are made as
follows : purine position 1 t o pyrimidine position 1 ;
purine position 6 to pyrimidine position 6.
If it is assumed that the bases only occur in the
structure in the most plausible tautomeric forms (that is,
with the keto rather than the enol configurations) it is
found that only specific pairs of bases can bond
together. These pairs are : adenine (purine) with
thymine (pyrimidine), and guanine (purine) with
cytosine (pyrimidine).
In other words, if an adenine forms one member of
a pair, on either chain, then on these assumptions the
other member must be thymine ; similarly for guanine
and cytosine. The sequence of bases on a single chain
does not appear to be restricted in any way. However, if
only specific pairs of bases can be formed, it follows
that if the sequence of bases on one chain is given, then
the sequence on t he other chain is automatically
determined.
It has been found experimentally (3,4) that the ratio
of the amounts of adenine to thymine, and the ration of
guanine to cytosine, are always bery close to unity for
deoxyribose nucleic acid.
It is probably impossible to build this structure
with a ribose sugar in place of the deoxyribose, as the
extra oxygen atom would make too close a van der
Waals contact. The previously published X-ray data
(5,6) on deoxyribose nucleic acid are insufficient for a
rigorous test of our structure. So far as we can tell, it is
roughly compatible with the experimental data, but it
must be regarded as unproved until it has been checked
against more exact results. Some of these are given in
the following communications. We were not aware of
the details of the results presented there when we
devised our structure, which rests mainly though not
entirely on published experimental data and
stereochemical arguments.
It has not escaped our notice that the specific
pairing we have postulated immediately suggests a
possible copying mechanism for the genetic material.
Full details of the structure, including the
conditions assumed in building it, together with a set of
co-ordinates for the atoms, will be published elsewhere.
We are much indebted to Dr. Jerry Donohue for
constant advice and criticism, especially on interatomic
distances. We have also been stimulated by a
knowledge of the general nature of the unpublished
experimental results and ideas of Dr. M. H. F. Wilkins,
Dr. R. E . Franklin and their co-workers at King's
College, London. One of us (J. D. W.) has been aided
by a fellowship from the National Foundation for
Infantile Paralysis.
J. D. WATSON
F. H. C. CRICK
Medical Research Council Unit for the Study of
Molecular Structure of Biological Systems, Cavendish
Laboratory, Cambridge.
1. Pauling, L., and Corey, R. B., Nature, 171, 346
(1953); Proc. U.S. Nat. Acad. Sci., 39, 84 (1953).
2. Furberg, S., Acta Chem. Scand., 6, 634 (1952).
3. Ch argaff, E., for references see Zamenhof, S.,
Brawerman, G., and Chargaff, E., Biochim. et Biophys.
Acta, 9, 402 (1952).
4. Wyatt, G. R., J. Gen. Physiol., 36, 201 (1952).
5. A stbury, W. T., Symp. Soc. Exp. Biol. 1, Nucleic
Acid, 66 (Camb. Univ. Press, 1947).
6. W ilkins, M. H . F., and Randall, J. T., Biochim. et
Biophys. Acta, 10, 192 (1953).
10. It has not escaped our notice that the specific
pairing we have postulated immediately suggests a
possible copying mechanism for the genetic material.
11. Il modello a doppia elica di Crick e Watson
suggerisce un meccanismo di replicazione
OLD NEW OLD NEW
NEW NEW
OLD OLD
18. Gli acidi nucleici possono formare
vari tipi di doppia elica
Elica
Coppie di basi
per giro
Rotazione tra
due basi
Diametro
B 10 (10,4) 36 (34,6) 20 (19)
A 11 32,7 23
Z 12 -30 18
25. separazione dei filamenti
(denaturazione di
regioni ricche in A+T)
strutture cruciformi
(in corrispondenza
di palindromi)
struttura Z
(in corrispondenza di
regioni di alternanza Pu/Py)