Types of DNA sequences

Types of DNA

sequences

INTRODUCTION

• Complex organisms- Cell- Protein.

Proteins specified for a particular

function is controlled by a set of

molecules called nucleic acids.

• Nucleic acids are very large

molecules made up of a sugar-

backbone, phosphate molecule and

nucleotide base.

• The genetic information of every

living organism is stored inside these

nucleic acid moleculesAn illustration showing an example of the structure and organization of DNA in the nucleus of a

human cell. (Image couresty of the National Institute on Aging/National Institutes of Health.)

There are two types of nucleic acids namely:

•DNA- Deoxyribonucleic acid

•RNA - Ribonucleic acid

http://www.classhelp.info/Biology/AUnit6Heredity.htm

TYPES

→ In most living organisms (except for viruses), genetic information is stored in the form

of DNA.

→ DNA is present in the nucleus of every cell.

→ The nucleotide bases present in the DNA are adenine (A), cytosine (C), guanine (G),

and thymine (T).

→ The original structure of the DNA molecule is a double helix. DNA is a double

stranded structure.

Types of DNA

There are two major types of DNA: Genomic DNA and Mitochondrial DNA

Genomic DNA / Nuclear DNA:

• This comprises the genome of an organism. This genomic DNA is spread across 46

chromosomes leading to an expression of genetic traits.

• The genomic DNA controls expression of the various traits in an organism. The

genomic DNA was sequenced as part of the Human Genome Project to study the

various functions of the different regions of the genome.

• Usually, during DNA replication there is a recombination of genes bringing about a

change in sequence leading to individual specific characteristics.

• This way the difference in sequence could be studied from individual to individual.

Mitochondrial DNA:

• The DNA located in Mitochondria is called

Mitochondrial DNA.

• mtDNA being derived from the circular

bacterial genomes-hence mtDNA is a double

stranded circular molecule.

• mtDNA is always Maternally

inherited.Mutations in the mtDNA can lead

to maternally inherited diseases.

• Each Mitochodrion contains about 2-10

mtDNA molecules.

• Nuclear DNA which during the process of

inheritance undergoes recombination,

mtDNA does not change from parent to

offspring.

cDNA

cDNA is a DNA copy synthesized from

mRNA.

The enzyme used is reverse transcriptase

an RNA-dependent DNA polymerase

isolated from a retrovirus

Complementary DNA is often used in

gene cloning or as gene probes or in the

creation of a cDNA library

STS

Sequence-Tagged Site (STS):

A short (200 to 500 base pair) DNA sequence that occurs but once in the genome and

whose location and base sequence are known.

STSs are detectable by polymerase chain reaction (PCR), are useful for localizing and

orienting the mapping and sequence data, and serve as landmarks on the physical map of

a genome.

The DNA sequence of an STS may contain repetitive elements, sequences that appear

elsewhere in the genome, but as long as the sequences at both ends of the site are unique

and conserved, researches can uniquely identify this portion of genome using tools

usually present in any laboratory.

ESTs Expressed sequence tags (ESTs) are fragments

of mRNA sequences derived through single

sequencing reactions performed on randomly

selected clones from cDNA libraries.

300-700bp

Fast & Cheap

Sequences of multiple ESTs can reconstitute a

full-length cDNA

SNP data mining

To date, over 45 million ESTs have been

generated from over 1400 different species of

eukaryotes

Expressed sequence tags (ESTs) are STSs

derived from cDNAs (complementary DNAs).

http://www.maizegdb.org/documentation/mgdp/education/finding.php

GSS

Genome Survey Sequences (GSS):

GSS are nucleotide sequences similar to EST's that the only difference is that most of them are genomic in origin, rather than cDNA (mRNA, RNA transcript).

Current genome sequencing approaches are mostly high-throughput shotgun methods, and GSS is often used on the first step of sequencing.

It has coding and non-coding DNA and contain repetitive section of the genome unlike ESTs

http://www.tutorvista.com/biology/types-of-dna-and-rna

http://dwb4.unl.edu/Chem/CHEM869N/CHEM869NLinks/www.dur.ac.uk/~dbl0w

ww/Staff/Croy/cDNAfigs.htm

http://en.wikipedia.org/wiki/Complementary_DNA

http://www.ncbi.nlm.nih.gov/pubmed/19277571

http://www.ch.embnet.org/CoursEMBnet/Zurich04/slides/EST.pdf

http://www.medicinenet.com/script/main/art.asp?articlekey=5464

THANK