Dna chips

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DNA MICROAARRAY(DNA CHIP)

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• Introduction

• Principle

Steps involved in DNA microarray

•Types of DNA Chips

cDNA - based chips

Oligonucleotide - based chips

• Applications

• Advantages and disadvantages

• Conclusion

• Reference

CONTENTS

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Introduction:

Definition: DNA microarrays are solid supports, usually of

glass or silicon, upon which DNA is attached in an organized grid

fashion. Each spot of DNA, called a probe, represents a single

gene.

There are several synonyms of DNA microarrays such as DNA

chips, gene chips, DNA arrays, gene arrays and biochips.

History: Microarray technology evolved from Southern

blotting, where fragmented DNA is attached to a substrate and

then probed with a known DNA sequence.

The use of miniaturized microarrays for gene expression profiling

was first reported in 1995, and a complete eukaryotic genome

(Saccharomyces cerevisiae) on a microarray was published in 1997.

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a) A DNA chip can be

manufactured to contain

hundreds of thousands of

synthetic single-stranded DNA

sequences.

b) Unknown DNA from a patient is

separated into single strands,

enzymatically cut and labeled with

a fluorescent dye.

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c) The unknown DNA is inserted into

the chip and allowed to hybridize

with the DNA on the chip.

d) The tagged DNA will bind only to

the complementary DNA on the chip.

The bound DNA will be detected by

its fluorescent dye and analyzed by a

computer. The red light is a gene

expressed in normal cells; green is a

mutated gene expressed in tumor

cells; and yellow, in both cells.

Fig: DNA Chip Technology

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Principle

The principle of DNA microarrays lies on the

hybridization between the nucleotide. Using this

technology the presence of one genomic or cDNA

sequence in 1,00,000 or more sequences can be

screened in a single hybridization.

The property of complementary nucleic

acid sequences is to specifically pair with each other

by forming hydrogen bonds between complementary

nucleotide base pairs.

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i. DNA Chip

ii. Target sample (Fluorescently labelled)

ii. Enzymes

iii. Fluorescent dyes

iv. Probes

v. Scanner

Requirements:

There are certain requirements for designing a DNA

microarray system and they are:

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Design of a

DNA

Microarray

System

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1. Sample

preparation

2. Purification

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3. Reverse

Transcriptio

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4. Labelling

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5.Hibridization

6. Scanning

7.Normalization

and analysis

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There are 2 types of DNA Chips/Microarrays:

Types of DNA chips

1. cDNA based microarray

2. Oligonucleotide based microaaray

cDNA CHIPS

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This type of chips are prepared by using cDNA, it is called

cDNA chips or cDNA microarray or probe DNA. The cDNAs

are amplified by using PCR. Then these immobilized on a

solid support made up of nylon filtre of glass slide (1 x 3

inches).

The probe DNA are loaded into a spotting

spin by capillary action. Small volume of this DNA

preparation is spotted on solid surface making physical

contact between these two. DNA is delivered mechanically or

in a robotic manner.

When one DNA spotting is done, the pin is

washed and loaded with fresh DNA to Start the second cycle.

cDNA – based chips:

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Oligonucleotide-based chips

Fig: Construction of a DNA chip with attached

oligonucleotide sequences (two cycles are shown)

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The DNA chips are used in many areas as given

below:

• Gene expression profiling

• Discovery of drugs

• Diagnostics and genetic engineering

• Alternative splicing detection

• Proteomics

• Functional genomics

• DNA sequencing

• Toxicological research (Toxicogenomics)

Applications

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Provides data for thousands of genes.

One experiment instead of many.

Fast and easy to obtain results.

Huge step closer to discovering cures for diseases and cancer.

Different parts of DNA can be used to study gene expression.

ADVANTAGES

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Disadvantages:

The biggest disadvantage of DNA chips is that

they are expensive to create.

The production of too many results at a time

requires long time for analysis, which is quite

complex in nature.

The DNA chips do not have very long shelf life,

which proves to be another major disadvantage

of the technology.

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DNA Microarrays are one of the most effective

invention ever developed. A DNA Microarray is a test that allows for the

comparison of thousands of genes at once. Microarray technology uses

chips with attached DNA sequences as probes for gene expression. Any

DNA in the sample that is complementary to a probe sequence will

become bound to the chip. Microarray technology is most powerful

when it used on species with a sequenced genome. The microarray chip

can hold sequences from every gene in the entire genome and the

expression of every gene can be studied simultaneously. Gene expression

data can provide information on the function of previously

uncharacterized genes.

Conclusion

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Source:

•Lehninger, 2005, DNA Chips, Principle of Biochemistry, W.H. Freeman and Company,

Newyork, forth Edition, Pg. 326- 328.

• Presscot M. Lansing, 2002, DNA Chips, Microbiology, Athenaeum Press Ltd,

Gateshead, Tyne and Wear, Britain, Fifth Edition, 353 – 354.

• Dubey C. R, 2008, DNA Chips, A textbook for Biotechnology, S. Chand and Company

Ltd., New Delhi, 13th Edition, Pg. 194 – 197.

•Tortora J. Gerard, DNA Chips, Book for Microbiology, Pearson Education, Inc., San

Francisco, CA, tenth edition, Pg. 292 – 293.

Net Source:

• www.wikipedia.org

• www.gene-chips.com

• www.biotechnology4u.com

• www.biotechnologyforums.com

• www.ehow.com

Reference

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