Types of DNA and RNA and their importance in genetics

1. A
Presentation on
Types of DNA and RNA and their
importance
Course title: Principle of Genetics (GP501)
Submitted to:
Dr. N.V.Soni,
Submitted by:
Gami Pankajkumar B.
M.Sc.(Agri.)GPB 1st sem,
1

2. Introduction:
Deoxyribonucleic acid (DNA)
J.D. Watson and F.H.C. Crick showed in 1953
that DNA has a double helical structure with two
polynucleotide chains connected by hydrogen
bonds and running in opposite directions.
When DNA samples are analysed from different organs
of body of the same individual or from different
individuals belonging to the same species, no
differences in the relative composition of different
bases were observed.

3. The following generalizations could also be made :
(1) Number of adenine molecules always
equal to number of thymine molecules.
(2) Number of cytosine molecules always
equal to number of guanine molecules.
(3) Number of adenine molecules did not necessarily
equal that of guanine and similar relationship was
observed between cytosine and thymine.
Although A = T and C ≡ G, there is no
restriction on the ratio (A + T)/(C + G); nor is there
any restriction on sequence of bases in one
polynucleotide chain.

4. But, since A is always linked to T and C to G as
determined from the above evidences, sequence of bases in
one polynucleotide should determine the sequence of bases
in the other polynucleotide of the double helix.
 Studied by X-ray crystallography by Frederick
demonstrated that DNA was a helical structure with a
diameter of 20 Å and a pitch (one round) of about 34 Å.
 On the basis of these studies of chemical analysis and
X-ray crystallography , following features of the DNA
molecule are now known :

7. (1) DNA consists of a double helix, in which two
polynucleotide chains are coiled about the same axis in
such a fashion that they can separate from one another
only by uncoiling and that lateral separation would not be
possible.
(2) Bases are set in a plane at right angle to the long axis.
(3) Two polynucleotide chains which run in opposite
directions have complementary base sequence.
(4) Distance between two base pairs is 3.4 Å and there
are 10 base pairs in each turn. Choice of base pairing is
understandable because of a constant diameter of 20 Å in
the molecule; two purines would need too much space
and two pyrimidines would occupy too little space to
pair. When a pyrimidine always pairs with a purine,
space could remain constant.

8. Alternative forms of DNA double helices:
 The well known structure of DNA described by Watson
and Crick (1953).
Helical coiling of this DNA assumed to be right handed
and this form of has been called B-form.
It has been shown that DNA may also exist in other
alternative forms of double helical structures.
 These alternative forms are differ in features like
I. number of residues per turn ('n') or
II. the spacing of residues along the helical axis ('h').
III. Diameter
IV. Sugar phosphate backborne
V. Major Groove
VI. Minor Groove

9. The various types of conformations that the
DNA can adopt depend on different factors
such as:
Hydration level
Salt concentration
Quantity and direction of super-coiling
Presence of chemically modified bases
Different types of metal ions and its
concentrations
Presence of polyamines in solution.

10. Why??
The existence of DNA as double helix has also been
confirmed by experiments used to measure the number of
base pairs per turn and it has been shown that this is 10.4
instead of 10.0 shown in classical B –form.
This will lead to modification of the twist angle
(rotation) between two pairs from 36 to 34.60 (360/10.4).
 This figure of 10.4 base pairs per turn is an average and
according to conditions, this may shift in either direction.
It is thus obvious that there may be several families of
structures of DNA, each of a characteristic type showing
variation in the values of 'n‘ and ‘h.
Three structural forms, namely A, B and C are known
for a long time and transitions between them can occur.

13. B-DNA:
This is the most common and predominant form of DNA.
It is observed when humidity is 92% and salt
concentration is high.
The coiling is in the right direction.
The number of base is 10 per turn of helix.
The pitch is 33.2 Å.
The sugar phosphate linkage is normal.
The helix is narrower and more elongated than A form.
The major groove is wide which is easily accessible to
proteins.
The minor groove is narrow.
The base pairing is nearly perpendicular to helix axis.
The sugar puckering is C2'-endo.

14. Z- Form:
The existance of this DNA was discovered by Andrews
wang and Alexander Rich.
The helix has left hand coiling pattern. Due to syn
position of the purine while the B DNA has a anti position.
The number of bases is 12 per turn of helix
The pitch is 45 Å
The sugar phosphate linkage is zig-zag.
The major "groove" is not really a groove.
The minor groove is narrow.
The helix is narrower and more elongated than A or B
form.

15. The base pairing is nearly perpendicular to helix
axis.
The conformaion is favored by high salt
concentrations.
Z-DNA is one of the biologically active forms of
DNA found in vivo in the cells.
The exact biological function of Z-DNA is not
clear but the Z-DNA is usually located upstream of
the start site of a gene and thus it may have some
role in the regulation of gene expression.

16. Differences between Z-DNA and B-
DNA
(1) Z-DNA has left-handed helical sense as
against right handed helical sense of B-DNA.
(2) Due to a different arrangement of molecules within
Z-DNA polymer, phosphate backbone follows a zig-zag
course, while in B-DNA it is regular.
(3) In Z-DNA, sugar residues have alternating
orientation so that repeating unit is a dinucleotide as
against B-DNA where repeating unit is a mononucleotide
and the orientation of sugar molecules is not alternating.

17. (4) In Z-DNA, one completc helix i.e. a twist through 3600,
has twelve base pairs or six repeating dinucliotidc units (12
base pairs), while in B-DNA, one complete helix has only
ten base pairs or ten repeating units.
(5) One complete helix is 45 Å in Z-DNA while it is 34 Å
in B-DNA.
(6) Since bases get more length to spread out in Z-DNA
and they are closer to the axis and hence the diameter of Z-
DNA molecule is 18 Å, whereas it is 20 Å in B-DNA.

18. A-form:
 A DNA conformation is rare in nature and it adopted under
dehydration condition.
This form is observed at the humidity of the sample is 75%.
The coiling is in the right direction.
The number of bases is 10.7 per turn of helix.
The pitch is 2.8 nm.
The sugar phosphate linkage is normal.
The major groove is deep and narrow which is not easily
accessible to proteins.
The minor groove is wide and shallow which is accessible to
proteins.
The helix is shorter and wider than B form.
The sugar puckering is C3'-endo.

20. C-DNA
C-DNA formed at 66% relative humidity
(low)in presence of Li+ or Mg2+.
Right handed ,with axial rise of 3.32A° per
base pair .
9.33 base pairs per turn.
Helical pitch 3.32A°×9.33°A=30.97A°.
Base pair rotation=38.58°.
Has diameter of 19A°,smaller than that of A-
&B- DNA.
The tilt of base is 7.8°

21. D-DNA
• Extremely rare variant with only 8base pairs per helical
turn .
• This forms of DNA found in some DNA
molecules devoid of guanine.
• Axial rise of 3.03A°per base pairs .Tilt is 16.7° from
axis of helix.
• Actually 2 different forms of D-DNA
1. D(A):Takes part in D-A-B transition.
2. D(B):Associated with D-B change of confirmation.
• 2 DNA structure have same helical parameters.

22. E-DNA
• Cytosine methylation or bromination of DNA
sequence d(GGCGCC)2 is to induce a novel
extended &eccentric double helix, which we call E-
DNA.
• E-DNA has a long helical axis rise and base
perpendicular to the helical axis.
• Deep major groove and shallow minor groove.
• E-DNA allowed to crystallize for a longer period
time, the methylated sequence forms standard A-
DNA.

23. • E-DNA is the intermediate in the transition to
A- DNA.

25. A B Z
HELIX RIGHT
HANDED
RIGHT
HANDED
LEFT HANDED
Base Pairs Per
Turn
11 10 12
Diameter 26A° 20A° 18A°
Sugar
phosphate
backborne
Regular Regular Zig-Zig
Major Groove Narrow&
Deep
Wide &Deep Flat
Minor Groove Wide
&
Shallow
Narrow&Deep Narrow&Deep

26. There are 3 basic types of DNA tested by ancestry DNA
tests now-a-days:
Paternal DNA (Y-DNA)
Maternal DNA (mtDNA) and,
Autosomal DNA (atDNA)
Y-DNA: paternal lineage
This is the test you go for if you want to research your father’s side
of the family. Since only males have the Y-chromosome which is
passed on almost unchanged from father to son, you can trace a direct
line between male members on your paternal side.
The Y-DNA test can only be taken by males. Women who want to
trace their paternal side have to ask their brother, father, paternal
uncle, paternal grandfather or paternal cousin to take the test for them.
With a Y-DNA test, it’s possible to go thousands of years back
through your ancestry timeline.

27. mtDNA: Maternal lineage
Mitochondria are small internal cellular structures that serve as the
body’s energy factories, and they have their own DNA called
mitochondrial DNA or mtDNA.
Only mothers can pass mtDNA to her children. mtDNA in sperm is
destroyed either in the male genital tract or by the fertilized egg. As a
result, only female mtDNA survives inheritance.
Because a mother passes mtDNA to both male and female children,
both men and women can get value from this test.
By comparing your mtDNA to that of other people, you have a chance
of finding a relative from your maternal side.
As with Y-DNA, mtDNA has several limitations. The biggest one is the
limited set of ancestors it can trace. You can only trace someone with a
direct maternal line to your mother. So it’ll go from your mother to your
mom’s mom to her mom’s mom and so on.

28. Autosomal DNA (atDNA): long-term ancestry and recent
lineage
An autosome refers to the remaining 22 numbered chromosomes
except for your 23rd, sex chromosome (X-Y).
Unlike Y-DNA and mtDNA, autosomal DNA is inherited from
both parents. So you can use it to trace either side of your family.
The major DNA testing providers rely mostly on autosomal DNA
testing.
But the timescale is limited with this test – you can use this test
to find relatives up to the second cousin level. Beyond that, you’ll
need to use a family tree or other types of DNA testing.
Autosomal DNA testing also tells you a lot about location and
migration patterns of your ancestors.

29. Types of
RNA
Genetic
RNA
Non genetic
RNA
m-RNA t-RNA r-RNA

30. TWO TYPES OF RNA:
1) GENETIC RNA:
 RNA which act as genetic material like DNA is
called Genetic RNA.
 Genetic RNA may be single stranded or double
stranded.
 Genetic RNA has self replication property .
 Example:RNA is found as genetic material in:
Plant viruses: TMV
Bacteriophages: MS2

31. 2)NON GENETIC RNA:
• RNA which does not act as genetic material is
known as non-genetic RNA.
• This is found in higher where DNA act as
genetic material.
• such RNA is usually single stranded.
• The organisms having DNA along with RNA.
• In such organisms ,RNA has no genetic role
,but carries the orders of DNA.
• All non genetic RNA have DNA Dependent
replication they does not have self replication
property.

32. TYPES OF NON GENETIC 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)
• The other are –
 small nuclear RNA (snRNA)
 micro RNA(mi RNA)
 small interfering RNA(Si RNA)
 heterogeneous nuclear RNA (hnRNA)
 Signal-recognition particle(SRP) RNA
 Monocistronic RNA & Polycistronic RNA

33. 1. Messenger RNA or mRNA
• Jacob and Monod (1961) proposed the name
messenger RNA for the RNA carrying information
for protein Synthesis from the DNA (genes) to the
sites of protein formation(ribosomes) cytoplasm.
• It consists of only 5 to 10% of the total cellular RNA.

34. Size of Messenger RNA
• The molecular weight of an average sized mRNA
molecule is varies from 20,00,000 to 5,00,000, and its
sedimentation coefficient is 8S.
• It should be noted however, that mRNA varies
greatly in length and molecular weight.

35. Stability of Messenger RNA
• The cell does not contain large quantities of mRNA.
This is because mRNA, unlike other RNAs is
constantly undergoing breakdown.
• It is broken down to its constituent ribonucleotides
by ribonucleases.

36. Structure of Messenger RNA
• It is a kind of single stand RNA molecule which is
complementary to sense strand of DNA molecule.
• Produced by transcription of structural genes in the
DNA Sequence.
• mRNA carries the genetic message from the
chromosome to the site of protein synthesis i.e.
Ribosome.
• mRNA molecule corresponds to each gene that is
expressed.
Function: The main function of mRNA is protein
synthesis in ribosomes in the cytoplasm.

37. 2. Transfer RNA or tRNA
• After rRNA the second most common RNA in the
cell is transfer RNA.
• It is also called soluble RNA because it is too small to
be precipitated by ultracentrifugation at 10,000 g. It
constitutes about 10-20% of the total RNA of the cell.
• Transfer RNA is a relatively small RNA having a
molecular weight of about 25,000Da to 30,000Da and
the sedimentation coefficient of mature eukaryote
tRNA is 3.8S.

38. • tRNAs are RNA molecules that provide the means of
translating the genetic code.
• One end of the tRNA contains a three nucleotide
sequence called the anticodon loop that is
complementary to the codon of the mRNA.
• The other end of the tRNA is covalently attached to a
specific amino acid.
• They carry the activated aminoacids to the ribosome
for protein synthesis.
• There is a specific tRNA for each of the twenty
aminoacids.
• Transfer RNAs (tRNAs), the smallest of the three
major species of RNA molecules .

39. • tRNAs species make up about 15% of the total RNA
in the cell.
• tRNA contains many unusual bases between 7 and 15
per molecule.
• The 5‘ end of tRNA have poly G and it is
phosphorilated.
• tRNA is folded into a clover leaf pattern. It has five
following special region as follows.

40. Structure of t- RNA
• The carboxyl group of amino acid is attached to
3’OH group of Adenine nucleotide of the acceptor
arm. The anticodon arm base pairs with the codon
present on the m- RNA

41. i. CCA end: The base sequence in 3’ end of all tRNA is
CCA. The activated amino acid is attached to 3’ hydroxyl
group of the terminal adenosine.The amino acid is
accepted this point only.
ii. TΨC arm: Involved in the binding of the tRNA to
ribosome
iii. Anticodon loop: It consists of sevenbases with following
sequences.
• Anticodon (codon Recognition site)
• Codon recognition site is complementary to codons of
mRNA.
iv. DHU arm: It is the site for the recognition of amino acid
activated enzymes

42. Function: The main function of tRNA is to carry
various types of amino acids and attach them to
mRNA template for protein synthesis.
*For further reading :Genetics by P.K.Gupta
( chepter:31 )

43. 3. Ribosomal RNA or rRNA
• It is a kind of RNA molecule serving as a major
component of ribosomes.
• rRNA is a type of RNA that is a component of
ribosomes and plays a role in the process of
translation (making protein from nucleic acid
sequence).
• E.Coli has three kind of rRNA i.e., 23s, 16s, 5s.
• Ribosomal RNA (rRNAs) are found in association
with several proteins as components of the
ribosomes-the complex structures that serve as the
sites for protein synthesis.

44. • rRNAs species make up 80% of the total RNA in
the cell.
Function: The function of ribosomal RNA binding
of mRNA and tRNA to ribosomes in the cytoplasm.

45. small nuclear RNA(sn RNA)
• Play structural and catalytic roles in spliceosomes,
the complexes of protein and RNA that splice pre-
mRNA in the eukaryotic nucleus.
small interfering RNA
• Affects gene expression; used by scientists to knock
out a gene being studied.
Micro RNA
• Affects gene expression; importance in growth and
development.

46. SRP RNA
• Is a component of the signal-recognition
particle(SRP),the protein-RNA complex that
recognizes the signal peptides of polypeptides
targeted to the ER.
Monocistronic RNA
• The mRNA which is coded by one cistron (gene).
Polycistronic RNA
• The mRNA which is coded by several cistrons
(genes).

47. SR NO. Particulars DNA RNA
1 Location Nuclear and cytoplasm Chromosomes & Ribosomes
2 Replication Self replication Self replication rare
3 Types Sevaral Three: mRNA, tRNA& rRNA
4 Strands Usually two, rarely one Usually one, rarely Two
5 Bases A,G,C&T A,G,C&U
6 Base
pairing
AT & GC AU & GC
7 Sugar Deoxyribose Ribosome
8 Size Upto 4.3 million
nucleotides
Upto 12,000 nucleotides
9 Function Genetic Role Protein synthesis; genetic in some
viruses.

48. REFERENCES:
1. Genetics by B. D. Singh
2. Biotechnology : Expanding horizons by B. D.
Singh
3. Genetics by P. K. Gupta
4. https://www.ncbi.nlm.nih.gov
5. https://www.medicinenet.com

49. Than
ks