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Basic concepts of Genes, DNA & RNA
Course: BSc Biotech Sem-ISubject : Fundamentals of Biotechnology
Unit - 2
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BREAKTHROUGH DISCOVERY
• In 1953, James Watson and Francis Crick discovered the double helical structure of the DNA molecule
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DNA
A purine always links with a pyrimidine base to maintain the structure of DNA.Adenine ( A ) binds to Thymine ( T ), with two hydrogen bonds between them.Guanine ( G ) binds to Cytosine ( C ), with three hydrogen bonds between them.
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Nucleoside & Nucleotide, the fundamental building block of DNA
glycosidic bond
phosphoester bond
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Chargaff's rule
• Chargaff's rules state that DNA from any cell of all organisms should have a 1:1 ratio (base Pair Rule) of pyrimidine and purine bases and, more specifically, that the amount of guanine is equal to cytosine and the amount of adenine is equal to thymine.
• They were discovered by Austrian chemist Erwin Chargaff
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Relative proportions (%) of bases in DNA
Organism %A %G %C %T A/T G/C %GC %AT
φX174 24 23.3 21.5 31.2 0.77 1.08 44.8 55.2
Maize 26.8 22.8 23.2 27.2 0.99 0.98 46.1 54
Octopus 33.2 17.6 17.6 31.6 1.05 1 35.2 64.8
Chicken 28 22 21.6 28.4 0.99 1.02 43.7 56.4
Rat 28.6 21.4 20.5 28.4 1.01 1 42.9 57
Human 29.3 20.7 20 30 0.98 1.04 40.7 59.3
Grasshopper
29.3 20.5 20.7 29.3 1 0.99 41.2 58.6
Sea Urchin 32.8 17.7 17.3 32.1 1.02 1.02 35 64.9
Wheat 27.3 22.7 22.8 27.1 1.01 1 45.5 54.4
Yeast 31.3 18.7 17.1 32.9 0.95 1.09 35.8 64.4
E. coli 24.7 26 25.7 23.6 1.05 1.01 51.7 48.3
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CHEMICAL AND PHYSICAL PROPERTIES OF DNA
• ABSORPTION• The bases in DNA absorb ultraviolet
light at the wavelength of 260 nm• This absorption can be monitored using
a spectrophotometer• This is one method used to figure the
concentration of DNA in solution• The more DNA present, the higher the
absorption
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• DENSITY• Density can be measured by CsCl-
density ultracentrifugation• can be used to estimate G+C content• GC base pairs are more dense than AT
base pairs• Density studies show the existence of
satellite DNA
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• DENATURATION• DNA is considered denatured when the
double stranded DNA molecule is converted into two single stranded molecules
• As thermal energy increases, the frequency of hydrogen bonds breaking between the molecules increases
• G-C base pairs are held together by three hydrogen bonds (A-Ts by two) and it therefore takes more energy (higher temperatures) to separate molecules with high GC contents
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• Hydrophobicity of solvent• Hydrophobic substances will allow the
bases in DNA to dissolve into the solvent
• Whereas hydrophilic substances will keep the bases of DNA stacked upon one another in the orientation that most favors hydrogen bonding between DNA strands
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• pH• Acidic pH cause breakage of
phosphodiester bonds between nucleotides and breakage of the N-glycosidic bond between the sugar and purine bases
• Alkali - Above pH 11.3, all hydrogen bonds are disrupted and the DNA is totally denatured
• Salts will stabilize the DNA double helix
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• Electrophoresis• DNA has a negative charge that is proportional
to its size• This is due to the negatively charged
phosphates in the sugar-phosphate backbone• If DNA is placed in an electrical field it will
migrate towards the positive electrode (the cathode)
• smaller pieces will migrate faster than larger pieces
• Larger pieces have trouble squeezing through the gel matrix and are hence retarded while smaller pieces migrate easier
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• Type of gels• Agarose is used to separate fairly large
DNA molecules– 5 million to a few thousands base pairs
• Polyacrylamide is used to separate small pieces of DNA– 2 to several hundred base pairs
• The size of DNA is estimated by comparing its migration through the gel to DNA molecules of known size
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A, B and Z DNA• A form – favored by
RNA• B form – Standard
DNA double helix under physiological conditions
• Z form – laboratory anomaly, – Left Handed– Requires Alt. GC– High Salt/ Charge
neutralization 15.
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RNA
Three major classes of RNA:
Difference between RNA & DNARNA DNA
RNA nucleotides contain ribose sugar
DNA contains deoxyribose
RNA has the base uracil DNA has the base thymine
presence of a hydroxyl group at the 2' position of the ribose sugar.
Lacks of a hydroxyl group at the 2' position of the ribose sugar.
RNA is usually single-stranded
DNA is usually double-stranded
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mRNA
• Transcripts of structural genes.
• Encode all the information
necessary for the synthesis of a
polypeptide of protein.
• Intermediate carrier of genetic
information; deliver genetic
information to the cytoplasm.
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tRNA
RNA molecules 70- 100
nucleotide long.
The secondary structure of the
tRNA resembles a D loop,
anticodon loop, and T loop and
the acceptor stem.
Carry correct amino acids to
their position along the mRNA
template to be added to the
growing polypeptide chain.
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rRNA
• The central component of
the ribosome.
• Ribosome; factory for
protein synthesis;
composed of ribosomal RNA
and ribosomal proteins.
• rRNA provides a
mechanism for decoding
mRNA into amino acids.
• rRNA interact with the tRNAs during translation by providing peptidyl transferase activity. 22
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• Chromosome – – double stranded DNA
molecule packaged by histone & scaffold proteins
DNA double helix
nucleosome
30nm fiber
condensed chromosome
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Genome
Gene• Is the basic units of
inheritance; it is a segment within a very long strand of DNA with specific instruction for the production of one specific protein.
• Genes located on chromosome on it's place or locus.
Genome and Gene
• Totality of genetic information of an organism.• Encoded in the DNA (for some viruses, RNA).
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Image refrences
1.http://www.bbc.co.uk/history/historic_figures/crick_and_watson.shtml
2. http://m.harunyahya.com/tr/works/4159/Once-Upon-A-Time-There-Was-Darwinism/chapter/4732/Once-there-was-no-knowledge-of-biological-information
3. http://arabian-explorers.com/james-watson-francis-crick
4.https://www.bcps.org/offices/science/secondary/forensic/DNA.pdf
5.http://www.timerime.com/en/event/209438/Nobel+Prize+for+Literature/
6. http://pixgood.com/dna-model-labeled-structure.html
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Image refrences7.http://www.yourarticlelibrary.com/dna/
deoxyribonucleic-acid-dna-model-chemical-composition-and-transformation-experiments/22676/
8.http://ircamera.as.arizona.edu/NatSci102/NatSci/text/nucleicacid.html
9. http://quizlet.com/11685525/chapter-8-slides-flash-cards/
10.http://biology200.gsu.edu/houghton%2704/4564%20%2714/lecture6.html
11. http://www.slideshare.net/oreonixha/dna-11921134
12. http://www.bvgh.org/Current-Programs/Neglected-Disease-Product-Pipelines/Global-Health-Primer/Targets/cid/ViewDetails/ItemID/18.aspx
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Image refrences13. http://smarttechno.net/tag/purine-bases14. http://en.wikipedia.org/wiki/Nucleotide15.http://biomedical.youngdong.ac.kr/sgkim/
files/2013/06/POB_5e_ch08-SGKim.pdf16.
https://lh3.ggpht.com/b7SCiLAza-c_D_wbjzOP86F4AnXyKu_wrviHfbF3GFqCWJXzuqHQvIG7P51jXvJcNJnNfQ=s144
17.https://lh5.ggpht.com/uE2KYozDJ302Z1ScuRJwtmqjjthxvILPxYnYyxog8q75VSahpvcMgtztJl8qGrXKhgsugA=s136
18. https://lh4.ggpht.com/1cWohlnifUAe4-WcqCCzkt3_GjfAmlbW1Tc7D0rcQXm9j5qW6Ns_xRv11VPwLy1aOsRkaQ=s170
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Image refrences19.https://lh4.ggpht.com/
u0_RqejooRi2Vz7xOVJ7UkYuzUZquHOQnm4hSncWyNEOF0nAvJcM4WQlkYPuWaf2JiFN=s101
20. https://lh3.ggpht.com/ma2QHNXrMmoFjD-RtySlsVEPZjKqVEh7dv2oytsVIXO570HJZUXABdFoleQeALL8wy1fbg=s85
21.https://lh4.ggpht.com/rp027AgQNGhK99zk9t5qoLYRJgES8MDj0tnom_OYqQbMbTepfE1UttFktW5mSDBKuzUQ=s85
22.https://lh4.ggpht.com/iFsbqDCWZz_IqdhnffJBMcOFPvy60NzdBMG9V8SF4hIzzPYpgOJj4uhhnOct-vCGCB1k=s85
23. http://people.csail.mit.edu/donglai/24.
http://www.jeansforgenesday.org/disorders/basicterms
25. http://carolguze.com/text/442-1-humangenome.shtml
26. http://science.howstuffworks.com/life/cellular-microscopic/cell7.htm