Nucleic acid, chemical composition and structure of nucleic acid.ppt

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1. Unit 
Nucleic acids

CHEM 203 Biochemistry
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2. Nucleoproteins : are conjugated proteins formed of:
a) basic protein (histone or protamine)
and
b) nucleic acid as prothetic group.

They are very complex high molecular weight proteins
present in every cell.
Functions of nucleic acids
1-In cell nuclei they form the chromosomes which are
responsible for cell division and carries of hereditary
factors known as (genes).
2-In cytoplasm are associated with ribosome, the center
of protein biosynthesis in every cell.
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3. Nucleoprotein
hydrolysis
Protein
Histone or protamin
(one or more molecules)
Nucleic acids
Nucleic acids

Nucleic acids is composed of large number of nucleotides,
which considered as basal structural component of nucleic acids.
 There are two types of nucleic acid
Deoxyribonucleic acid (DNA)
Ribonucleic acid (RNA)
Nucleic acid can be easily separated from nucleoprotein by
addition of acids or alkalis .
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4. Nucleoproteins
Protein
Histone or protamin
Nucleic acid
(Polynucleotide)
Large number of mononucleotides
Phosphoric
acid
Sugar
Ribose Deoxyribose
Nitrogenous base
Nucleoside
Purin base Pyrimidine base
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5. Nucleotides
Nucleic acids consist of nucleotides that have a
nitrogen base, Pentose sugar , and phosphate
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NUCLEIC ACID STRUCTURE
• Nucleic acids are polynucleotides
• Their building blocks are nucleotides
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6. 6
Nitrogenous Bases
The nitrogen bases in nucleic acids are:

Pyrimidine bases:
Cytosine
Thymine
Uracil
 purine bases:
Adenine
Guanine
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Pentose Sugars
The pentose (five-carbon) sugar:
In RNA is ribose.
In DNA is deoxyribose.
Has carbon atoms numbered with primes to
distinguish them from the nitrogen bases.
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8. 8
HO
A nucleoside:
Has a nitrogen base
linked by a glycosidic
bond to C1’ of a ribose
or deoxyribose.
Is named by changing
the the nitrogen base
ending to -osine for
purines and –idine for
pyrimidines
 Nucleosides
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A nucleotide:
Is a nucleoside that forms a
phosphate ester with the C5’ OH
group of ribose or deoxyribose.
Is named using the name of the
nucleoside followed
by 5’-monophosphate.
In a nucleoside ,the glycosidic C-1
atom of the pentose bonded to
N-1 of the pyrimidine
or N-9 of the purine base
Nucleotides
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10. Nitrogenous bases + ribose = Nucleosides

Nucleoside + Phosphate group = Nuclotides
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11. 11
Names of Nucleosides and Nucleotides

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Primary Structure of Nucleic Acids
In the primary structure of nucleic acids:
Nucleotides are joined by phosphodiester
bonds.
The 3’-OH group of the sugar in one
nucleotide forms an ester bond to the
phosphate group on the 5’-carbon of the
sugar of the next nucleotide.
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Primary Structure of Nucleic Acids

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A nucleic acid polymer:
Has a free 5’-phosphate
group at one end and a free
3’-OH group at the other end.
Is read from the free 5’-end
using the letters of the bases.


This example reads
5’—A—C—G—T—3’.

Structure of Nucleic Acids
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RNA
In RNA, A, C, G,
and U are linked
by 3’-5’ ester
bonds between
ribose and
phosphate.
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17. 17
DNA
In DNA, A, C,
G, and T are
linked by 3’-5’
ester bonds
between
deoxyribose
and
phosphate.
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18. 18
DNA Double Helix: A Secondary Structure
In DNA:
There are two strands of nucleotides that wind
together in a double helix.
Two hydrogen bonds form between the
complementary base pairs A-T.
Three hydrogen bonds form between the
complementary base pairs G-C.
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19. The negatively charged phosphate group
and the sugar units expose themselves to
the outside of the chain.
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20. 20
DNA Double Helix Structure
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21. The antiparallel nature of the DNA double
helix.
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22. The DNA Double Helix
The double helix is stabilized by hydrogen bonds and hydrophobic
interactions
Watson and Crick were Proposed
a structure of DNA double helix
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24. Comparison between DNA and RNA
DNA RNA
Nitrogen bases
a-Purines
b- Pyrimidines
Adenine &Guanine
Cytosine& Thymine
Adenine &Guanine
Cytosine& Uracil
Sugar 2-Deoxy ribose Ribose
Shape of strand Double helix Single strand
Site Nucleus and Mitochondria Mainly in cytosol, less commonly in
nucleus and mitochondria
Functions Genetic information and synthesis of
mRNA
Protein synthesis
Reaction with dil. acids depurinated by dilute acid. resistant to dilute acid
Reaction with dil. base not susceptible to base hydrolyzed by dilute base.
•DNA - one type, one purpose .
•RNA - Several types, several purposes:
•ribosomal RNA - the basis of structure and function of ribosomes
(largest amount).
•messenger RNA - carries the message for protein synthesis (fewest and
unique).
•transfer RNA - carries the amino acids for protein synthesis (smallest
molecules).
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DNA replication involves:
Unwinding the DNA
Pairing the bases in each strand
with new bases to form new
complementary strands.
Producing two new DNA
strands that exactly duplicate
the original DNA.
DNA Replication
The duplication of DNA to give two DNA molecules identical to the
original one.
DNA in the chromosomes replicates itself every cell division
•Maintains correct genetic information
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26. Before new DNA strands can form, there must be RNA
primers present to start the addition of new nucleotides.
Primase is the enzyme that synthesizes the RNA Primer.
DNA polymerase can then add the new nucleotides
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DNA polymerase can only add nucleotides to the
3’ end of the DNA.
•This causes the NEW strand to be built in a 5’ to
3’ direction
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27. DNA Replication - General
considerations
A. Function of replication.
1.Proteins must have the correct shape.
2.The shape is determined by the primary structure (amino acid
sequence.
3.The amino acid sequence is determined by the gene (the sequence
of bases in the DNA).
B
a
s
e

P
a
i
r
i
n
g

&

D
o
u
b
l
e

H
e
l
i
x
Replicating
DNA
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28. Information Transfer in Cells
Figure 10.1
The fundamental
process of
information
transfer in cells.
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29. Transcription
Process of copying DNA to mRNA
Differs from DNA synthesis in that only one strand of
DNA, the template strand, is used to make mRNA
Does not need a primer to start as RNA polymerases
have ability to initiate synthesis de novo
Can involve multiple RNA polymerases
Divided into 3 stages
Initiation
Elongation
Termination
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In transcription:
A section of DNA containing the gene unwinds.
One strand of DNA is copied starting at the initiation
point, which has the sequence TATAAA.
An mRNA is synthesized using complementary base
pairing with uracil (U) replacing thymine (T).
The newly formed mRNA moves out of the nucleus to
ribosomes in the cytoplasm.
Transcription: Synthesis of mRNA
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RNA Polymerase
During transcription, RNA polymerase moves
along the DNA template in the 3’-5’direction to
synthesize the corresponding mRNA.
The mRNA is released at the termination point.
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32. Interpreting the information coded
in the mRNA into proteins
The nucleotides are read in triplets
(set of three) called codons
Each triplet code for a specific
amino acid, and sometimes more
than one codon exist for an amino
acid
mRNA are read by the translational
machinery including ribosomes,
tRNAs and rRNAs
Like transcription, it also includes
initiation, elongation and
termination
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Translation
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33. Translation
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34. DNA Replication - General
considerations
A. Function of replication.
1.Proteins must have the correct shape.
2.The shape is determined by the primary structure (amino acid
sequence.
3.The amino acid sequence is determined by the gene (the sequence
of bases in the DNA).
The flow of genetic information in the
cell.
DNA  RNA  protein
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35. Mutation
•
A change or alteration that occurs in the DNA.
Mutations can be caused by the environment (sun,
radiation, or chemicals), aging, or chance. Some
mutations do not affect the information contained
in the DNA. Other mutations have serious
consequences on how that gene functions.
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