Transcript nucleic acid,nursing2015 ppt

CHEM 203
Biochemistry
Unit 
Nucleic acids
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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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Nucleic acid can be easily separated from nucleoprotein by
addition of acids or alkalis .
Nucleoprotein
hydrolysis
Protein
Nucleic acids
Histone or protamin
(one or more molecules)
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
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Deoxyribonucleic acid (DNA)
Ribonucleic acid (RNA)
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Nucleoproteins
Protein
Nucleic acid
Histone or protamin
(Polynucleotide)
Large number of mononucleotides
Nucleoside
Nitrogenous base
Purin base
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Pyrimidine base
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Phosphoric
acid
Sugar
Ribose
Deoxyribose
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NUCLEIC ACID STRUCTURE
• Nucleic acids are polynucleotides
• Their building blocks are nucleotides
Nucleotides
 Nucleic acids consist of nucleotides that have a
nitrogen base, Pentose sugar , and phosphate
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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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 Nucleosides
A nucleoside:
 Has a nitrogen base
linked by a glycosidic
bond to C1’ of a ribose
or deoxyribose.
HO
 Is named by changing
the the nitrogen base
ending to -osine for
purines and –idine for
pyrimidines
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Nucleotides
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
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Nitrogenous bases + ribose = Nucleosides
Nucleoside + Phosphate group = Nuclotides
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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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Structure of Nucleic Acids
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’.
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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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Types of RNA
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DNA
 In DNA, A, C,
G, and T are
linked by 3’-5’
ester bonds
between
deoxyribose
and
phosphate.
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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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The negatively charged phosphate group
and the sugar units expose themselves to
the outside of the chain.
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DNA Double Helix Structure
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The antiparallel nature of the DNA double helix.
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The DNA Double Helix
Watson and Crick were Proposed a
structure of DNA double helix
The double helix is stabilized by hydrogen bonds and hydrophobic interactions
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1.Two helical polynucleotide chains are coiled around a
common axis. The chains run in opposite directions, (anti
parallel).
2. The two antiparallel polynucleotide chains are not
identical, but they are complimentary.
3. The purine, pyrimidine bases are on the inside of the
helix, the phosphate and deoxyribose groups are on the
outside.
4. The two chains are held together by hydrogen bonds
between pairs of bases. Adenine is two hydrogen bonds
(A= T), Guanine is bonded to cytosine by three hydrogen
bonds (G=C)
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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
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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
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.
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 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
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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Base Pairing & Double
Helix
DNA Replication - General considerations
Replicating
DNA
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).
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Information Transfer in Cells
Figure 10.1
The fundamental
process of
information transfer
in cells.
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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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Transcription: Synthesis of mRNA
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.
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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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Translation
 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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DNA
- General
considerations
TheReplication
flow of genetic
information
in the cell.
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).
DNA  RNA  protein
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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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