The document provides an overview of DNA and RNA. It discusses the key structures and functions of DNA and the various types of RNA. Some key points: - DNA is made up of nucleotides containing deoxyribose, phosphate groups, and the nitrogen bases adenine, guanine, cytosine, and thymine. It exists as a double helix with the bases pairing together (A-T and C-G). - There are different forms of DNA structure including bent, kinked, triple-stranded, and four-stranded structures. Melting temperature refers to the temperature at which half of the DNA helix dissociates. - The three main types of RNA are mRNA,

1. Lecture notes on dna and rna
Department Of Medical Biochemistry, Faculty Of Basic
Medical Sciences.
By Oweh, O.T.
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2. OUTLINE
INTRODUCTION
OBJECTIVES
DEOXYRIBONUCLEIC ACID
RIBONUCLEIC ACID
CLINICAL CORRELATION
SUMMARY
ASSIGNMENT
REFERENCES
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3. INTRODUCTION
 Genetic information is coded in the polynucleotide called
DNA.
 DNA is the basis of hereditary, organized into genes.
 These genes regulate RNA synthesis.
 Genes are DNA length that code for specific proteins.
 A knowledge of the structure and function of DNA and
RNA is vital in understanding the genetic bases of diseases.
 DNA regulates the synthesis of RNA, and RNA in turn
regulates protein synthesis.
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4. OBJECTIVES
The following are the objectives of the class.
1. To be able to identify the bases in DNA and RNA
2. To identify the features of the double helical DNA
structure.
3. To understand the conformational difference
between the various structural forms of DNA.
4. To understand the differences between DNA and
RNA.
5. To identify the various form of RNA and their
functions.
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5. DEOXYRIBONUCLEIC ACID (DNA)
 DNA is a polymer of deoxyribonucleotides also known as
deoxynucleotides.
 The basic units of DNA are deoxyadenylate,
deoxyguanylate, deoxycytidylate and deoxythymidylate.
 DNA is made of two polynucleotide strands running in
opposite directions.
 They are held by hydrogen bonds between the bases.
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6. The bases in DNA are A, G, C and T
A links with T using a double bond =. A = T
G links with C using a triple bond Ξ G Ξ C
This is the Chargaff’s rule of DNA composition
A=T and G Ξ C
 purines = pyrimidines
CHARGAFF’S RULE of molar equivalence
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7.  The double strands are arranged in a way that gives allows
for the pairing of only one purine and one pyrimidine base
between the two polynucleotide strands.
 In the DNA structure, the nucleotides are all orientated in
the same direction.
 The phosphate group joins the 3rd Carbon of one sugar to
the 5th Carbon of the next in line.
 The attachment of the bases are to the Carbon1 of the
sugar.
 This order is important as it determines the genetic
information of the molecule
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8.  Structure showing the bond pattern in DNA
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9. The DNA Double Helix Features
It is comparable to a twisted ladder.
The right handed double helix structure contains
two Polydeoxyribonucleotide chains that are
twisted around each other.
Both strands are anti-parallel (5’-3’ and 3’-5’)
direction.
Genetic information is stored in only one strand
(template strand).
The opposite strand is called the coding strand.
It matches RNA transcript that encodes protein.
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10. Hydrophilic deoxyribosephosphate backbone(3’-
5’-phosphodiester bond)outside.
These strands Complements each as a result of the
base pairing.
Two strands with hydrogen bonds formed by
complementary base pairs.
hydrogen bonds are formed between the bases of
opposite strands.
There are major and minor grooves in the DNA
structure that allows for protein interaction using
hydrogen bonding.
Regulatory proteins through this interactions
controls the expression of specific genes.
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12. 12

13. Forms of DNA helical structure
There are 6 different forms of DNA helical structure:
A,B,C,D,E and Z.
However, A, B and Z are most important.
The transition between these different helical forms of
DNA is vital in regulating gene expression.
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14. Comparing the features between the A,B and Z forms of
the DNA helical structure.
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15. Other types of DNA structure
There exist other forms of DNA structure outside the
helical structure.
These structures aids molecular recognition of DNA by
proteins and enzymes.
There are:
1.Bent DNA
2.Kinked DNA
3.Triple stranded DNA
4.Four stranded DNA
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16. Bent DNA& KinkedDNA
Bent conformation is due to a replacement in the
Adenosine tracts (composed of adenine base). I e:
adenine is replaced by other bases.
This bent conformation can also be as a result of :
damage caused by a light catalyzed reaction or wrong
pairing of bases.
Certain antitumor drugs like (CISPLASTIN)
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17. Triple strandedDNA
DNA becomes triple stranded when extra hydrogen
bonds are added.
Hence, thymine can selectively form two hydrogen
bonds to adenine ‘’HOOGSTEENHYDROGEN
BONDS”TO THE ADENINE OF A=T pair to form T-A-
T or C-G-C
Also called as HOOGSTEENTRIPLE HELIX.
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19. Four strandedDNA
This is very common with Polynucleotides having high
Guanine contents such that they form a tetrameric
structure G-Quartets
These structures are planar and are connected by
Hoogsteen-hydrogen bonds.
When these four stranded DNA structure are
antiparallel, they form G-tetraplexes seen at the ends
of eukaryotic chromosomes called telomers.
Telomeres are special structures occuring at the ends
of chromosomes with the same short DNA sequence
repeated.
Telomeres are targets site for anticancer
chemotherapies.
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20. G-tetraplexes :
1. They are implicated in the recombination of
immunoglobulin genes.
2. They also help in the formation of dimers of double-
stranded genomic RNA of the Human
Immunodeficiency Virus (HIV).
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21. Denaturation of DNA strands
The concept explaining the loss of DNA helical
structure of is known as Denaturation.
This occurs when there is a disruption of the hydrogen
bonds between the strands.
It leads to separation of the strands.The
phosphodiester bonds are however not broken.
RENATURATION: This occurs when the separated
DNA strands forms back double helix
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23. Melting temperature(Tm) :The temperature at which the
DNA loses half of its helical structure.
The higher the bond, the greater the temperature required
to break the bond. Hence, G Ξ C > A=T
DNA in association with various proteins forms chromatin
which is arranged into a compact structure called
chromosomes.
DNA double helix is wrapped around the major proteins
called HISTONES.
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24. STRUCTURE OF RNA
 RNA is a ribonucleotide polymer held together by 3’,5’-
phosphodiester bridges.
 RNA is much more abundant than DNA and are Single
stranded.
 RNA contains ribose (DNA 2’-deoxy ribose).
 RNA also contains uracil base in place of thymine in DNA
 RNA does not obey Chargaff ’s rule.
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25. RNA can be easily hydrolysized by alkaline.
 RNA retains all information of DNA
 There are specific RNA for specific functions
 Structure similar to A-form DNA
3 major types OF RNA
 mRNA : 5-10%
tRNA: 10-20 %
rRNA: 50-80 %
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26. TYPES OF RNA AND THEIR FUNCTIONS
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27. Messenger RNA(mRNA)
 It has a high molecular weight with short half life.
 It is synthesized in the nucleus(in eukaryotes) as
heterogeneous nuclear RNA(hnRNA).
It functions as messenger, transporting the
information from the gene in DNA to synthesize
proteins.
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28. Transfer RNA(tRNA)/soluble RNAmolecule
 It contains about 71-80 nucleotides with a Molecular
Weight of 25,000.
At least 20species of tRNAs, corresponding to
20 amino acids present in protein structure.
 They transfer amino acids from cytoplasm to the
ribosome for protein synthesis.
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29. Structure of tRNA
The Primary structure contains nucleotide sequence that
folds extensively into a secondary structure.
The secondary structure resembles a clover leaf with 4
major arms which are
1] Acceptor arm (6bp)
2] Anticodon arm (5bp)
3] DHU arm or D arm (4 bp)
4] Pseudouridine arm (5 bp)
5] Variable (Extra) arm
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31. Ribosomal RNA(rRNA)
They are known as machinery of protein synthesis.
 The eukaryotic (mammalian) ribosomes are
composed of two major nucleoprotein complex:
1. 60s units that contains a 28s rRNA, 5s rRNA and 5.8s
rRNA and over 50 polypeptide chain.
2. A 40s units that is smaller and contains a single 18s
rRNA and about 30 polypeptide chain.
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32. Catalytic RNAs - Ribozymes
 Ribozymes are RNA component of a
ribonucleoprotein which are catalytically active.
RNAase P(ribonuclease P) is a ribozymes that
Contains a protein and RNA component.
RNAase P helps in Cleaving tRNA precursors to
generate mature tRNA molecules.
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33. Recombinant Ribozymes (rRibozymes)
these ribozymes are used as therapeautic agents to
cure disease.
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34. Clinical Correlation
 The therapeutic use of recombinant ribozymes in various disease
management.
 Histones when modified through acetylation are important in post-
translational functioning usually in gene expression where they help to
change the structure of chomatin.
 Tumor formation and a progression in cancer could arise when there is
an error with histone acetylation.
 The enzyme telomerase helps to add the TTAGGG telomere sequence
at the end of the chromosomes.
 When telomerase activity is inhibited, it could result in the destruction
of cancer cells; affect fertility, hinder wound healing and the ability to
fight infections amongst others.
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35. SUMMARY
The bases in DNA are adenine, guanine, cytosine and
thymine. They bind to each other in the form of; A = T,
G Ξ C.
They are various forms of DNA structure which
includes bent, kinked, triple and four stranded DNA.
The bases in RNA are adenine, guanine, cytosine and
uracil.
There are three major types of RNA mRNA, tRNA and
rRNA and they all function together to aid protein
synthesis.
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36. PRACTICE QUESTIONS
1. What two parts of a nucleotide do not change throughout the structure of DNA?.
a). Five-Carbon Sugar and Nitrogen Base
b). Phosphate Group and Nitrogen Base
c). Five-Carbon Sugar and Phosphate Group
d). All components remain the same throughout the DNA structure?
2. Which shows the correct complementary base pairing for DNA?
a). C-A, T-G
b). A-G, C-T
C). C-G, U-A
d). T-A, G-C
3. A monomer of DNA is called a(n)
a). Monosaccharide
b). Amino Acid
c). Triglyceride
d). Nucleotide
4. Which of the following best describes a DNA molecule?
a). double helix
b). contains ribose
c). made of amino acids
d). contains Uracil
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37. 5. Which of the following units are repeatedly joined together to form a strand of DNA?
a). amino acids
b). nucleotides
c). fatty acids
d). polysaccharides
6. In a molecule of double-stranded DNA, the amount of Adenine present is always equal to
the amount of
a). cytosine
b), guanine
c). thymine
d). uracil
6. Adenine bonds with ______________.
a). Guanine
b). Thymine
c). Cytosine
d). Adenine
7. Guanine bonds with ______________.
a). Adenine
b). Guanine
c). Cytosine
d). Thymine
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38. REFERENCES
Harper’s Biochemistry (28th Edition). Murray, R. K. et al.,
2009.
Medical Biochemistry at a glance (3rd Edition). Salway, G.
J. (2012).
Fundamentals of Biochemistry (5th Edition). Voet et al.
(2016).
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