Nucleic Acids

Prepared by;Farah Shireen

Contents Introduction Occurrence Composition Nomenclature Molecular size Topology Sequences Types Sturucture Methods of study FAQs

Introduction

Complex organic substances present in living cells.

Discovered by Friedrick Miescher in 1870 in the nuclei Human WBC’s and named it ‘ nuclein’.

Function in encoding, transmitting and expression of genetic information.

A major foundation in the feild of forensic sciences, biotechnology and pharmaceutical industries etc.

Examples are DNA & RNA.

Occurrence

Found in all living forms and some non-living entities.

RNA and DNA are present together in all living entities but virus consists of either DNA or RNA.

Composition Elemental analysis showed that nucleic acids

contains C, H, O, P and N elements. Unlike proteins, sulphur is absent in nucleic

acids. Complete hydrolysis revealed that, nucleic acids

contains sugar component, inorganic phosphate and heterocyclic bases that are adenine, guanine, cytosine and thymine or uracil.

The sugar component in DNA is deoxyribose while its ribose in RNA.

The heterocyclic bases are same except for thymine is replaced by uracil in RNA.

And acidic nature of nucleic acid is by phosphoric acid moiety.

Sugar Component Heterocyclic Base Inorganic Phosphate

(Ribose or Deoxyribose) (Adenine, Guanine, Cytosine (Phosphoric acid moiety)

Thymine or Uracil)

Nucleic Acids (DNA or RNA)

Heterocyclic bases are classified into;i. Purines :

The bicyclic bases are known as purines e.g; adenine & guanine.

ii. Pyramidines : The monocyclic bases are known as

pyramidines e.g; cytosine, thymine and uracil. Polyfunctional May present in tautameric forms.

Composition in Labs

Nucleic acids can be generated in labs using DNA or RNA polymerase enzyme.

Chemically it is produced by solid phase chemical synthesis or by altering nucleic acids conformation e.g; polynucleic acids.

Nomenclature

The name ‘Nucleic Acids’ was suggested on the basis of their initial discovery within the nucleus.

DNA is abbreviated for Deoxyribo-nucleic-acid as it contains deoxyribose sugar.

RNA is abbreviated for Ribo-nucleic-acid as it contains ribose sugar.

Molecular size Vary in size. DNA is the largest molecule. Well studied biological molecules range from

small interferring RNA’s (21 nucleotides) to large Human chromosome # 1 (274 million bp).

Mostly DNA are double stranded while RNA are single stranded exception is present in some viruses.

Nucleic acids may have three or four strands too forming triplex or quadraduplex.

topology DNA are unbranched , linear and circular

molecules. Examples of Circular DNA are;

Mitochondrial and chloroplast DNA, plasmids and bacterial chromosomes are in circular form.

Examples of Linear DNA are; Eukaryotic chromosomes are linear. Watson and Crick model shows highly uniform

double – helical- 3D structure. RNA are mostly linear and single stranded

molecules but circularize due to RNA splicing.

Single stranded DNA/ RNA are not compelled to form double helical 3D structure but can form highly complex 3D structure.

sequences

DNA or RNA differs from eachother on the basis of their nucleotide sequences.

They carry all set of information that encodes behaviour, subcellular and cellular structures, organ and organism etc.

Many methods are established to determine sequences of nucleic acids. Various methods for sequencing nucleic acids used world-wide.

Types

Three types of nucleic acids;i. DNAii. RNAiii. Artificial nucleic acid analogues

DNA: Stands for Deoxyribonucleic acid. Macromolecule that contains genetic info.

that are required for development and function of living organisms.

Genetic info. are in form of segments called genes.

Consists of ; Two long chain polymer of nucleobase. Backbones of phosphate and sugar joined by

ester bonds. The two stands run in an anti-parallel direction to

each other.

Within cells DNA are organized into chromosomes ( long structures).

During cell division the cell recieves complete set of chromosomes by DNA replication.

DNA is also required to produce mRNA transcript during transcription.

Presence of DNA in eukaryotic cells are nucleus, mitochondria and chloroplasts. In contrast , prokaryotic cells store DNA in cytoplasm.

DNA are oganized and compact due to chromatin proteins e.g histones.

Rna: Stands for Ribonucleic acid. Genetic information from genes are converted to

amino acids to form proteins. Three types of RNA.

Messenger rna: Carries genetic info. from DNA and directs it to

protein synthesis. Ribosomal RNA:

Component of ribosomes. Catalyzes protein synthesis.

tRna:• Carry amino acids during protein synthesis.• Decoding of mRNA.

Artificial nucleic acid analogues: Artificially prepared. Prepared by altering structure of naturally

occurring DNA or RNA. Examples: Peptide nucleic acids Locked nucleic acids Glycol nucleic acids etc.

StructureStructure of nucleic acids are divided into 4

levels that are;PrimarySecondary TertiaryQuaternary

Primary structure: Linear nucleotide sequence. Glycosidic bonds are formed between

nitrogeneous base & sugar molecule. Ester bonds are formed between phosphorus

and sugar molecule.

Secondary structure: Includes interaction of bases i.e; strands are

bound to eachother. For DNA:

Purine always pairs with pyramidine. Guanine always pairs with cytosine, and adenine

always pairs with thymine or uracil. The strands wraps around eachother and forms

double helix structure. Examples are A-DNA, B-DNA, Z-DNA

For rna: Normally as single polynucleotide chain. Base pairing occurs when RNA folds in the

complementary regions. Both single stranded and double stranded are

found on RNA molecule.

Tertiary structure: Higher level of folding than secondary structure. Folding occurrs in linear polynucleotide to form

complex 3D- structure. Quaternary structure:

Chromatin is quaternary structure of DNA. Interaction of RNA to ribosome or splisosome

is quaternary structure of RNA.

Methods of study Many techniques are required to study RNA and

DNA. Some of them are; Purification

Phenol- chloroform extraction Minicolumn purification etc.

Quantification Spectroscopic quantification Q-PCR Microarray Gel electrophorosis

Synthesis Oligonucleotide synthesis PCR

Others Southern blothing Northern blothing Floresence insitu hybridization DNA sequencing etc

Faqsdifference b/w DNA and rna?

DNA Contains genetic info.

required for development & function of living body.

Consists of deoxyribose sugar.

Nucleobases are adenine, guanine, thymine and cytosine.

Damaged by UV– rays.

RNA Involved in protein

synthesis and sometimes genetic info. transmission.

Consists of ribose sugar.

Nucleobases are adenine, guanine, cytosine and uracil.

Resistant than DNA to UV-rays.

DNA

Long chain molecule. Less reactive due to C-

H bonds.

RNA

Relatively shorter than DNA.

Reactive due to presence of C-OH bonds.

Why deoxyribose is sugar moiety in DNA? Deoxyribose is more stable as ribose has OH-

group on carbon no.2 , and thus it forms a reactive structure. As deoxyribose doesn’t have free OH- group at carbon no.2. Hence it forms a stabilbized DNA structure.

Thymine VS. Uracil issue? Our body thymine is synthesized by methylation

of uracil . Cytosine occasionally converts into uracil by

deamination.

Thank you

Manana…