AMAZING FACTS ABOUT HUMAN DNA AND …

1 Published on September 20 2011 AMAZING FACTS ABOUT HUMAN DNA AND GENOMEDr. Shishir Kumar Gangwar and Mr. Birhanu WoraboBiotechnology is founded upon an ever increasingunderstanding of the mechanisms that maintain livingorganisms andallow them to reproduce from generation the heart of life is deoxyribonucleic acid,DNA, the long, double helix molecule that carries thehereditary genetic instructions necessary to produceorganisms. The genetic composition of an organism itsgenotype in conjunction with environmental influencesdetermines its appearance and physical characteristics itsphenotype. One only has to remember how a HUMAN beingchanges in size, shape and behavior during a 70-80 yearlifetime to knowthat thecorrelation is not acid (DNA) and the basic proteincalledhistoneare present in the genetic instructions for a HUMAN being its genome are contained on DNA that is around meters long butonly one fifth of a millionth of a centimeter wide.

2 Every cellof our bodies contains a copy of this DNA divided into 46parts of discrete length the chromosomes. These are sohighly condensed that they can fit into the cell s nucleuswhich measures 3-4 millionthsof a meter in them, HUMAN chromosomes carry some threethousand million units of chemical coding. The units areknown as bases and come in four types adenine, thymine,cytosine and guanine, or A, T, C, and is the sequence ofthesebases in the DNA molecules which determines thebiochemistry of cells and physiology of (bacterial artificial chromosome)clonesseem torepresent HUMAN DNA far more faithfully than their YAC orcosmid counterparts and appear to be excellent substrates forshotgun sequence analysisresulting in accurate contiguoussequence data(Principles ofgene manipulation andgenomics,pp 81)Minisatellites also called variable number of tandemrepeats (VNRT) have been used to carry out the first humanDNA fingerprinting (Jeffreyset al.)

3 ,1985). Itisthemostcommonly used fingerprint also helps in regulation of gene expressionbyselective import of proteins into the nucleus. Proteinsresponsible for genome structure and organisation are allimported into the nucleus selectively. They include histones,DNA polymerases, RNA Polymerases, transcription factorsand splicing proteins are targeted to thenucleus by specific amino acid sequences called nuclearlocalisation signals. These signals direct their transportthrough the nuclear pore complex.(Biotechnology part one,pp 41)The sequence of the HUMAN genomeis 109basepairs ( Gbp or gigabase pairs) in length. If the sequencewere typed onto paper, at ABOUT 3000 letters per page, itwould fill 1 million pages of text. This extraordinary amountof information is encoded by the sequence of just four bases,cytosine, adenosine, guanine, and thymine.

4 Most peopleexpected the HUMAN genome sequence to reveal the actualnumber of genes found in HUMAN beings. In reality themassive amount of sequence needs sophisticatedinterpretation in order to determine how many genes itcontains. The best estimates so far predict only 25,000genes, but the number may be more or less. Of the identifiedgenes, we only know the function of around 50%. More than40% of the predicted HUMAN proteins are similar in structureto proteins in organisms such as fruit flies or worm ( ,2009 Biotechnology applying the genetic revolution)Using antisense to regulate gene expression is sowidespread in nature that scientists became curious howmany potential antisense/sense partners exist in variousgenomes. Computer algorithms have been devised to searchfor sequences that could function asantisense.

5 In the humangenome, there are a predicted 1600 different partners. Themost interesting finding in the antisense field is therealization that small noncoding regulatory RNAs calledmicroRNAs (miRNAs) inhibit gene expression through anantisense mechanism. Using computer searches, anadditional 250 potential microRNAs have been identified inhumans, but because these are only ABOUT 20 nucleotideslong, identifying them conclusively by computer is verydifficult.(David ,2009 Biotechnology applying thegenetic revolution pp. 129)The HUMAN genome contains only a few percent ofcoding DNA; thus, using real genes does not produceenough points on the map. A sparse map makes it difficult toorder the sequences obtained in the genomesequencingproject. Therefore, other markers, including physicalmarkers, are also used on genomic maps.

6 ( ,2009 Biotechnology applying the genetic revolutionpp. 232)The entire HUMAN genome could be represented in10000 YAC clones. In a BAC, HUMAN DNA is inserted into aplasmid in anE. colicell. (A plasmid is a small piece ofdouble-stranded DNA found in addition to the main genome,usually but not always circular.) A BAC can carry ABOUT 250000 bp. Despite their smaller capacities, BACsare preferredto YACs because of their greater stability and ease a YAC, HUMAN DNA is stably integrated into asmall extra chromosome in a yeast cell. A YAC can containup to 106 base pairs.(Arthur m. Lusk,2002 Introduction tobioinformatics ,pp 74)Most of the HUMAN genome is not involved in coding the HUMAN genome, only about3%of the totalamount of DNA is actually coding sequence. Even when theintrons andcontrol sequences are added, the majority of theDNA hasno obvious function.

7 This is sometimes termed junk DNA, although this is perhaps the wrong way to thinkabout this apparently redundant DNA.(Dismond T. nicoll,2008 an introduction to genetic engineering ,pp 29)Early analysis of HUMAN DNA indicated that the average size of a coding region is around 1500 base pairs,and the average size of a gene is 10--15 density isabout one gene per 40--45 kbp, and the intergenic distance isaround 25--30 kbp. However, gene structure in eukaryotescan be very complex, and thus using average estimates is alittle misleading..(Dismond T. nicoll ,2008 an introductionto genetic engineering ,pp 29)Inthe humanDNA, ABOUT 40% of the total is eitherhighly or moderatelyrepetitive sequence DNA, which canoften causeproblems in the cloning and analysis of the remaining 60%, whichrepresents unique sequenceand low-copy-number sequence elements,only around 3%constitutes the actual coding sequence.

8 Thisimmediatelyposes a problem in the analysis of the humangenome, inthataround 97% of the DNA could perhaps be avoided if thegenesthemselves could be identified for further (Dismond T. nicoll ,2008 an introduction to geneticengineering ,pp 179)SOME INTERESTING FACTS ABOUTOUR GENOME The information would fill two hundred 500-pagetelephonedirectories. Between humans, our DNA differs by only , or 1in 500 bases (letters). (This takes into account thathuman cells have two copies of thegenome.) If we recited the genome at one letter per second for 24hours a day it would take a century to recite the book oflife. If two different people started reciting their individualbooks at a rate of one letter per second, it would takenearly eightand a half minutes (500 seconds) beforethey reached a difference A typist typing at 60 words per minute (around 360letters) for 8 hours a day would take around 50 years totype the book of life.

9 Our DNA is 98% identical to that of chimpanzees. The vastmajority of DNA in the HUMAN genome 97% has no known function The first chromosome to be completely decoded waschromosome 22 at the Sanger Centre Cambridge shire,in December 1999. There are 6 feet of DNA in each ofour cells packed into a structure only inchesacross (it would easily fit on the head of a pin). There are 3 billion (3000000000) letters in the DNAcode in every cell in your body. If the entire DNA in the HUMAN body was put end to endit would reach to the sun and back over 600 times (100trillion 6 feet divided by 93 million miles=1200)..(Dismond T. nicoll ,2008 an introduction to geneticengineering ,pp187 ) Ninety per cent of HUMAN DNA is non-coding and theminisatellites which contain the repeating units arescattered throughout these areas.

10 Within any particularminisatellite there is a repeating sequence ofnucleotides. The sequence that is repeatedisrelativelyin variant with in the minisatellite and consists ofapproximately 7-30 nucleotides In HUMAN DNA, at Least 30% of the Genome Consistsof Repetitive Sequences On average,Single nucleotide polymorphisms(SNPs)occur every500 1,000 nucleotides in HUMAN DNA 10 percent of HUMAN DNA consists of sequences presentin hundreds of thousands to millions of copies. Much ofthishighly repetitive DNAconsists ofSINEs, orShortInterspersed Elements (David , 2005, molecularbiology understanding thegenetic revolution ) ABOUT 7% of HUMAN DNA consists of repeats of the300bp Aluelement (An example of a SINE, a particularshort DNA sequence found in many copies on thechromosomes of humans and other primates.)