Unit Nucleic acids CHEM 203 Biochemistry 9/15/20141Ola Fouad Talkhan.

Unit Nucleic acids

CHEM 203 Biochemistry

9/15/2014 1Ola Fouad Talkhan

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.


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 .


Nucleoproteins

ProteinHistone or protamin

Nucleic acid(Polynucleotide)

Large number of mononucleotides

Phosphoric acid

Sugar

Ribose Deoxyribose

Nitrogenous base

Nucleoside

Purin base Pyrimidine base


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


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.


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


The antiparallel nature of the DNA double helix.


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


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


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


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


Information Transfer in Cells

Figure 10.1 The fundamental process of information transfer in cells.


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.


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


Translation


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 protein9/15/2014 34Ola Fouad Talkhan

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.


Unit Nucleic acids CHEM 203 Biochemistry 9/15/20141Ola Fouad Talkhan.

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