Introduction,Components, and Structure of DNA and RNA

1. DNA and RNA
[Introduction, Components,
and Structure]
M A Y A N N R O G O N
Prepared by:

2. DNA[Introduction, Components,
and Structure]

3. DNA [Deoxyribonucleic acid]
 a polymer of deoxyribo-nucleotides.
 Usually double stranded.
 And have double-helix structure.
 found in chromosomes, mitochondria and
chloroplasts.
 It acts as the genetic material in most of the
organisms.
 Carries the genetic information

4. A Few Key Events Led to the Discovery
of the Structure of DNA
Friedrich Meischer
 DNA as an acidic substance
present in nucleus was first
identified by Friedrich
Meischer in 1868.
 He named it as ‘Nuclein’.

5. James Watson and Francis Crick worked
out the three-dimensional structure of
DNA, based on work by Rosalind Franklin
In 1953 , James Watson and
Francis Crick, described a very
simple but famous Double
Helix model for the structure of
DNA.

6. X-Ray Evidence
Rosalind Franklin
British Scientist
Used a technique called
X-Ray diffraction
Provided important clues
about the structure of
DNA

7. X-Ray Evidence
There were 2 strands
Strands were twisted
around each other
(helix)
The nitrogen bases
are in the middle

8. The Double Helix
• Francis Crick & James Watson
• Trying to understand the structure of DNA by
building models.
• Unsuccessful until early 1953, Watson was shown a
copy of Franklin’s X-ray pattern.
• “The instant I saw the picture my mouth fell open
and my pulse began to race.”
– James Watson
• Within weeks Watson and Crick had figured out the
structure of DNA
• Published their results in a historic one page paper
in April of 1953

9. • Watson and Crick later discovered what held the
two strands together.
• Hydrogen bonds could form between certain
nitrogen bases and provide enough force to hold
the two strands together.
• Hydrogen bonds could only form between certain
base pairs adenine and thymine and guanine and
cytosine.
• This principal is called Base pairing.
• This explains Chargaff’s Rule.

10. Components of DNA
Deoxyribose
[a pentose
sugar]
Nitrogen Base
(there are four
different ones)
Phosphate

11. H
OH
O
CH2
Base
Phosphate
Ribose
OHH
5′
4′
1′
3′
2′
H
A, G, C or U
HH
H
O
CH2
Base
Phosphate
Deoxyribose
5′
OHH
4′ 1′
3′ 2′
OO
O
P
O–
HH
DNA Nucleotide RNA Nucleotide
A, G, C or T

12. CCytosine
G
Guanine
A
Adenosine
T
Thymine
4 Kinds
of
Nitrogen
Bases
Purines
Pyrimidines

13. Nitrogenous Bases of DNA & RNA

14. Nucleotide Structure
Nucleotides are formed by the condensation of
a sugar, phosphate and one of the 4 bases
The following illustration represents one
nucleotide
Phosphate
Deoxyribose
Nitrogenous
Bases

15. HH
H
O
CH2
Base
DNA nucleotide
Phosphate
Deoxyribose
5′
OH
4′ 1′
3′ 2′
OO
O
P
O–
HH

16.  Base + sugar  nucleoside
 Example
 Adenine + ribose = Adenosine
 Adenine + deoxyribose = Deoxyadenosine
 Base + sugar + phosphate(s)  nucleotide
 Example
 Deoxyadenosine monophosphate (dAMP)
 Deoxyadenosine diphosphate (dADP)
 Deoxyadenosine triphosphate (dATP)

17. Nomenclature of Nucleic Acid Components
Base Nucleoside Nucleotide Nucleic
acid
Purines
Adenine Adenosine Adenylate RNA
Deoxyadenosine Deoxyadenylate DNA
Guanine Guanosine Guanylate RNA
Deoxy guanosine Deoxyguanylate DNA
Pyrimidines
Cytosine Cytidine Cytidylate RNA
Deoxycytidine Deoxycytidylate DNA
Thymine Thymidine Thymidylate DNA
(deoxythymidine) (deoxythymidylate)
Uracil Uridine Uridylate RNA

18. Sugar
Base
P
Sugar
Base
P
Nucleotides are linked together by covalent bonds
called phosphodiester linkage.
1
23
4
5
1
23
4
5
A chemical bond that
involves sharing a pair of
electrons between atoms in
a molecule.

20. Antiparallel strands
 The strands run opposite of each
other.
 The 5’ end always has the phosphate
attached.
 It is made of two polynucleotide
chains, where the backbone
is constituted by sugar-phosphate,
and the bases project inside.
 The two chains have anti- parallel
polarity. It means, if one chain
has the polarity 5’-3’, the other has
3’-5’.
5’ 3’
3’ 5’
G C
T A
C G
A T
DNA Double Helix & Hydrogen bonding
Salient features of the Double-helix structure of DNA:

22. DNA Double Helix & Hydrogen bonding
3 Hydrogen bonds
2 Hydrogen bonds

23. The bases in two strands are paired through
hydrogen bond (H-bonds) forming base pairs (bp).
Adenine forms two hydrogen bonds with Thymine
from opposite strand and vice-versa. Similarly,
Guanine is bonded with Cytosine with three H-
bonds.
Based on the observation of Erwin Chargaff that for
a double stranded DNA, the ratios between Adenine
and Thymine; and Guanine and Cytosine are
constant and equals one.

24. Hydrogen bond
a chemical bond in
which a hydrogen atom
of one molecule is
attracted to an
electronegative atom,
especially a nitrogen,
oxygen, or fluorine
atom, usually of
another molecule.
24

26. DNA Double Helix
There are two asymmetrical grooves on the outside of the helix:
a)Major groove
b)Minor groove
Groove any furrow(slight depression in the smoothness of a surface)
or channel on a bodily structure or part.
Certain proteins can bind within these groove
They can thus interact with a particular sequence of bases.

27. (b) Space-filling model of DNA(a) Ball-and-stick model of DNA
Minor
groove
Major
groove
Minor
groove
Major
groove

28. Structure of Double-helix
B- DNA
A- DNA
Z- DNA

29. Biologically THE MOST COMMON
It is a -helix meaning that it has
a Right handed, or clockwise,
spiral.
Complementary base pairing
• A-T
• G-C
Minor Groove is Narrow, Shallow.
Major Groove is Wide, Deep.
B- DNA
This structure exists when
plenty of water surrounds
molecule and there is no
unusual base sequence
in DNA-Condition that are
likely tobe present in the cells.
B-DNA structure is most stable
configuration for a random
sequence of nucleotides under
physiological condition.

30. A- DNA
Right-handed helix
Wider and flatter than B-DNA
Its bases are tilted away from
main axis of molecule
Narrow Deep major Groove and
Broad, Shallow minor Groove.
Observed when less water is
present. i.e.Dehydrating
condition.
A-DNA has been observed in
two context:
• Active site of DNA polymerase
(~3bp)
• Gram (+) bacteria undergoing
sporulation

31. Z- DNA
A left-handed helix
Seen in Condition of High salt
concentration.
In this form sugar-phosphate
backbones zigzag back and
forth, giving rise to the name
Z-DNA(for zigzag).
12 base pairs per turn.
A deep Minor Groove.
No Discernible Major Groove.
Part of some active genes form
Z-DNA, suggesting that Z-DNA
may play a role in regulating
gene transcription.

34. RNA[Introduction, Components,
and Structure]

35. RNA [Ribonucleic acid]
 RNA is a polymer of ribonucleotides linked
together by phosphodiester linkage.
 RNA was first genetic material.
 In 1967 Carl Woese found the catalytic
properties of RNA and speculated that the
earliest forms of life relied on RNA both
to carry genetic information and to catalyse
biochemical reactions.
 Their theories were not validated until the work of
Nobel Prize laureate Thomas R. Cech. In the
1970s, Cech was studying the splicing of RNA in a
single-celled organism, Tetrahymena thermophila,
when he discovered that an unprocessed RNA
molecule could splice itself. He announced his
discovery in 1982 and became the first to show
that RNA has catalytic functions.

36. RNA [Ribonucleic acid]
 RNA exists in several different single-stranded
structures, most of which are directly or indirectly
involved in protein synthesis or its regulation.
 It also acts as the genetic material in some
viruses.
 It function as messenger(mRNA), adapter(tRNA),
structural(rRNA) and in some cases as a catalytic
molecule(Ribozyme).
 RNA strands are typically several hundred to
several thousand nucleotides in length.

37. Components of DNA
Ribose
[a pentose
sugar]
Nitrogen Base
(there are four
different ones)
Phosphate

38. CCytosine
G
Guanine
A
Adenosine
U
Uracil
4 Kinds
of
Nitrogen
Bases
Purines
Pyrimidines

39. Nucleotide Structure
Nucleotides are formed by the condensation of
a sugar, phosphate and one of the 4 bases
The following illustration represents one
nucleotide
Phosphate
Ribose
Nitrogenous
Bases

40. HH
OH
O
CH2
Base
RNA nucleotide
Phosphate
Ribose
5′
OH
4′ 1′
3′ 2′
OO
O
P
O–
HH

41.  Base + sugar  nucleoside
 Example
 Adenine + ribose = Adenosine
 Base + sugar + phosphate(s)  nucleotide
 Example
 Adenosine monophosphate (AMP)
 Adenosine diphosphate (ADP)
 Adenosine triphosphate (ATP)

42. Sugar
Base
P
Sugar
Base
P
Nucleotides are linked together by covalent bonds
called phosphodiester linkage.
1
23
4
5
1
23
4
5
A chemical bond that
involves sharing a pair of
electrons between atoms in
a molecule.

43. Adenine (A)
Guanine
(G)
Uracil (U)
BasesBackbone
Cytosine (C)
O
HH
HH
O
OO
O–
P CH2
O–
HH
HH
O
OO
O
P CH2
O–
NH2
H
N
HH
HH
O
OO
O
P CH2
O–
H
H
HH
OH
HH
O
OO
O
P CH2
O–
Sugar (ribose)
Phosphate
5′
4′ 1′
2′3′
5′
4′ 1′
2′3′
5′
4′ 1′
2′3′
5′
4′ 1′
2′3′
OH
OH
OH
OH
RNA
nucleotide
Phosphodiester
linkage
3′
5′
NH2
OH
H
H
O
NH O
N
N
N
N
N
N
N
N N
N
NH2
H
H

44. Structure of RNA

45. Types of RNA
In all prokaryotic and eukaryotic
organisms, three main classes of
RNA molecules exist
1) Messenger RNA(m RNA)
2) Transfer RNA (t RNA)
3) Ribosomal RNA (r RNA)

46. Messenger RNA (mRNA)
 Messenger RNA (mRNA) carries
information about a protein
sequence to the ribosomes, the
protein synthesis factories in the
cell.
 It is coded so that every three
nucleotides (a codon) correspond
to one amino acid.
 In eukaryotic cells, once
precursor mRNA (pre-mRNA)
has been transcribed from DNA,
it is processed to mature mRNA
 This removes its introns—non-
coding sections of the pre-
mRNA
 The mRNA is then exported
from the nucleus to the
cytoplasm, where it is bound to
ribosomes and translated into its
corresponding protein form with
the help of tRNA

47. Transfer RNA (tRNA)
 Transfer RNA (tRNA) is a small
RNA chain of about
80 nucleotides
 It transfers a specific amino
acid to a
growing polypeptide chain at the
ribosomal site of protein
synthesis during translation
 It has sites for amino acid
attachment and
an anticodon region
for codon recognition that binds
to a specific sequence on the
messenger RNA chain through
hydrogen bonding

48. Ribosomal RNA (rRNA)
 Ribosomal RNA (rRNA) is the
catalytic component of the
ribosomes
 Three of the rRNA molecules
are synthesized in
the nucleolus, and one is
synthesized elsewher
 In the cytoplasm, ribosomal
RNA and protein combine to
form a nucleoprotein called a
ribosome
 The ribosome binds mRNA
and carries out protein
synthesis
 Several ribosomes may be
attached to a single mRNA at
any time.
 Nearly all the RNA found in a
typical eukaryotic cell is rRNA.

50. RNA vs. DNA
Structurally ,DNA and RNA are nearly identical
.However there are three fundametal
differences that account for the very different
functions of two molecules.

51. Differences between RNA and DNA

52. REFERENCES:
• J. D. Watson and F. H. C. Crick. Molecular structure of nucleic acids: a
structure for deoxyribose nucleic acids. Nature 171:737–738 (1953).
• J. D. Watson and F. H. C. Crick. Genetical implications of the structure
of deoxyribonucleic acid.Nature 171:964–967 (1953).
• U.satyanarayana. Structure of DNA and RNA. Biochemistry. Retrieved
from: http://www. Slideshare.com./ph
• Lehninger, Micheal M. Cox and David l. Nelson .Principle of
biochemistry. Retrieved from: www. Slideshare.com.ph
• Tazeen Anwaar and Uzma Imtiyaz. Presentation on DNA and RNA
Structure. Retrieved from: http://www. Slideshare.com./ph

53. fin
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