Post on 18-Dec-2015
Unit Nucleic acids
CHEM 203 Biochemistry
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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 acids1-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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Nucleoprotein hydrolysis
ProteinHistone or protamin(one or more molecules)
Nucleic acids
Nucleic acidsNucleic 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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Nucleoproteins
ProteinHistone 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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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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Nitrogenous BasesThe nitrogen bases in nucleic acids are:
Pyrimidine bases: Cytosine Thymine Uracil
purine bases: Adenine Guanine
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Pentose SugarsThe 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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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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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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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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RNAIn RNA, A, C, G,
and U are linked by 3’-5’ ester bonds between ribose and phosphate.
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DNAIn 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
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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Comparison between DNA and RNADNA RNA
Nitrogen basesa-Purines
b- Pyrimidines
Adenine &GuanineCytosine& Thymine
Adenine &GuanineCytosine& 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 ReplicationThe 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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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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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).
Base
Pair
ing
&
Dou
ble
Heli
xReplicating DNA
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Information Transfer in Cells
Figure 10.1 The fundamental process of information transfer in cells.
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TranscriptionProcess 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 stagesInitiationElongationTermination
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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 PolymeraseDuring 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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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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Translation
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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.
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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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