7. 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.
7
18. 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
18
20. 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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21. • 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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22. • 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
22
23. • 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
23
24. • 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
24
25. • 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
25
26. • 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
26
27. 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
27
15.
30. RNA
Three major classes of RNA:
Difference between RNA & DNA
RNA 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 30
31. 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.
3118
34. 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.
34
21
35. 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.
35
22
38. • Chromosome –
– double stranded DNA
molecule packaged by histone
& scaffold proteins
DNA double helix
nucleosome
30nm fiber
condensed chromosome
38
25
39. 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).
39
26
44. References
• Biochemistry by S C Rastogi
• Genes XI by Krebs, Goldstein and Kilpatrick
• Biotechnology by H K Das
• Biotechnology by John E. Smith (5th Ed.)
• http://www.genomicglossaries.com/
• http://biology-pages.info
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Hinweis der Redaktion
Nucleosides consist of a base (pyrimidine or purine) attached to a sugar (ribose or deoxyribose).
Nucleotides are nucleoside phosphates
Nucleotides may be nucleoside monophosphates, diphosphates or triphosphates or NMPs, NDPs, and NTPs, respectively
The vast majority of the DNA molecules present in the aqueous protoplasms of living cells almost certainly exist in the Watson-Crick double helix form described above. This is called the B-form of DNA and shows right-handed coiling. It contains 10.4 base pairs per turn (instead of the 10 mentioned above). Dehydrated DNA occurs in the A-form which is also a right handed helix, but it has 11 base pairs per turn.
Certain DNA sequences occur in Z-form, which shows left-handed coiling, contains 12 base pairs per turn. In Z-DNA, the sugar-phosphate backbone follows a zig-zagged path giving it the name Z-DNA or Z-form.
Specific segments of a DNA molecule can undergo conformational changes from B-form to Z-form and vice-versa; these changes may be brought about by some specific regulatory proteins. The Z-form DNA is postulated to play a role in gene regulation.
A nucleosome is composed of DNA & histones
A nucleosome wraps approx. 200bp DNA