NUCLEIC ACIDS RNA and DNA. Nucleic Acids A nucleic acid is a macromolecule composed of chains of...

NUCLEIC ACIDS RNA and DNA

Nucleic Acids

A nucleic acid is a macromolecule composed of chains of monomeric nucleotides. In biochemistry

these molecules carry genetic information or form structures within cells.

The most common nucleic acids are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).

Nucleic acids are universal in living things, as they are found in all cells and viruses. Nucleic acids were first discovered by Friedrich Miescher.

Nucleotide

Nucleic acids consist of nucleotides that have a sugar, nitrogen base, and phosphate

Nitrogen-Containing Bases

Pentose (5 –Carbon) Sugars

Deoxyribonucleotide

Ribonucleotide

ATP (Adensosine triphosphate)

NAD+ + ATP -> NADP+ + ADP catalyzed by NAD+ kinase

Polynucleotides

DNA and RNA Structures

Difference between DNA and RNA structures

Characters DNA RNA

1. Molecule Double stranded, helical Single stranded, straight or variously folded and twisted.

2. Pentose sugar Deoxyribose Ribose

3. Pyrimidine base Thymine Uracil

4. Complementary base pairing

Always present and exists between A = T and G = C

Normally absent, but may be present in twisted segments of a molecule. If present, pairing is between A = U and G = C

5. Ratio of Purines: Pyrimidines

Always 1:1 Not necessarily 1:1

Double-helical structure of DNA

Double-helical structure of DNA

DNA Replication

Semiconservative Replication

DNA Polymerization

PlasmidsA plasmid is an extra-chromosomal DNA molecule separate from the chromosomal DNA which is capable of replicating independently of the chromosomal DNA.

In many cases, it is circular and double-stranded. Plasmids usually occur naturally in bacteria, but are sometimes found in eukaryotic organisms.

Classification of RNA

m- RNA

Messenger or mRNA

is a copy of the

information carried by

a gene on the DNA.

The role of mRNA is to

move the information

contained in DNA to

the translation

machinery.

t –RNA

tRNA is the information

adapter molecule.

It is the direct interface

between amino-acid

sequence of a protein and

the information in DNA.

Therefore it decodes the

information in DNA.

There are > 20 different

tRNA molecules.

r-RNA Ribosomal RNA (rRNA) is the central component of the

ribosome, the protein manufacturing machinery of all living cells.

The function of the

rRNA is to provide

a mechanism for

decoding mRNA

into amino acids

and to interact with

the tRNAs during

translation by

providing peptidyl

transferase activity.

REFERENCES

Michael L. Shuler and Fikret Kargı, Bioprocess Engineering: Basic Concepts (2 nd Edition),Prentice Hall, New York, 2002.

1. James E. Bailey and David F. Ollis, Biochemical Engineering Fundementals (2 nd Edition), McGraw-Hill, New York, 1986.

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http://207.207.4.198/pub/flash/26/

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