NUCLEIC ACID BY PRODUCTS : 1 NUCLEIC ACID BY PRODUCTS U.ARULRAJA,
TRICHY. Nucleic Acids : 2 Nucleic Acids Nucleic Acids
Structures of Nucleic Acids
RNA and Transcription Slide 3: 3 Nucleotides and nucleic acids 10/10/05 1 Fig. 8-1, 8-19, 8-25 Nucleotides are the building blocks of nucleic acids Nucleotides also play other important roles in the cell Nucleotide DNA RNA Nucleotides : 4 Nucleotides Nucleic acids consist of nucleotides that have a sugar, nitrogen base, and phosphate
nucleoside Sugar Base PO4 Nitrogen-Containing Bases : 5 Nitrogen-Containing Bases Sugars : 6 Sugars Nucleosides in DNA : 7 Nucleosides in DNA Base Sugar Nucleoside
Adenine (A) Deoxyribose Adenosine
Guanine (G) Deoxyribose Guanosine
Cytosine (C) Deoxyribose Cytidine
Thymine (T) Deoxyribose Thymidine Nucleosides in RNA : 8 Nucleosides in RNA Base Sugar Nucleoside
Adenine (A) ribose Adenosine
Guanine (G) ribose Guanosine
Cytosine (C) ribose Cytidine
Uracil (U) ribose Uridine Example of a Nucleoside : 9 Example of a Nucleoside Nucleotides in DNA and RNA : 10 Nucleotides in DNA and RNA DNA
dAMP Deoxyadenosine monophosphate
dGMP Deoxyguanosine monophosphate
dCMP Deoxycytidine monophosphate
dTMP Deoxythymidine monophosphate
AMP adenosine monophosphate
GMP guanosine monophosphate
CMP cytidine monophosphate
UMP uridine monophosphate Structure of Nucleic Acids : 11 Structure of Nucleic Acids Polymers of four nucleotides
Linked by alternating sugar-phosphate bonds
RNA: ribose and A, G, C, U
DNA: deoxyribose and A,G,C,T
nucleotide nucleotide nucleotide nucleotide P sugar base P sugar base P sugar base P sugar base Nucleic Acid Structure : 12 Nucleic Acid Structure 3,5-phosphodiester bond 3 5 Double Helix of DNA : 13 Double Helix of DNA DNA contains two strands of nucleotides
H bonds hold the two strands in a double-helix structure
A helix structure is like a spiral stair case
Bases are always paired as A–T and G-C
Thus the bases along one strand complement the bases along the other Complementary Base Pairs : 14 Complementary Base Pairs Two H bonds for A-T
Three H bonds for G-C Double Helix of DNA : 15 Double Helix of DNA Learning Check NA1 : 16 Learning Check NA1 Write the complementary base sequence for the matching strand in the following DNA section:
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• • • • • • • • • • Solution NA1 : 17 Solution NA1 Write the complementary base sequence for the matching strand in the following DNA section:
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-T-C-A-G-G-T-T-A-C-G- DNA Replication : 18 DNA Replication DNA in the chromosomes replicates itself every cell division
Maintains correct genetic information
Two strands of DNA unwind
Each strand acts like a template
New bases pair with their complementary base
Two double helixes form that are copies of original DNA DNA Unwinds : 19 DNA Unwinds G- -C
T- -A G-C
T-A DNA Copied with Base Pairs : 20 DNA Copied with Base Pairs Two copies of original DNA strand
T-A G-A Slide 21: 21 DNA structure determination 21 Franklin collected x-ray diffraction data (early 1950s) that indicated 2 periodicities for DNA: 3.4 Å and 34 Å.
Watson and Crick proposed a 3-D model accounting for the data. Slide 22: 22 DNA structure 22 Fig. 8-15 DNA consists of two helical chains wound around the same axis in a right-handed fashion aligned in an antiparallel fashion.
There are 10.5 base pairs, or 36 Å, per turn of the helix.
Alternating deoxyribose and phosphate groups on the backbone form the outside of the helix.
The planar purine and pyrimidine bases of both strands are stacked inside the helix. Slide 23: 23 DNA structure 23 Fig. 8-15 The furanose ring usually is puckered in a C-2' endo conformation in DNA.
The offset of the relationship of the base pairs to the strands gives a major and a minor groove.
In B-form DNA (most common) the depths of the major and minor grooves are similar to each other. Slide 24: 24 Base stacking in DNA 36 Berg Fig. 1.4; 5.13 C-G (red) and A-T (blue) base pairs are isosteric (same shape and size), allowing stacking along a helical axis for any sequence. Base pairs stack inside the helix. Slide 25: 25 DNA strands Fig. 8-16 The antiparallel strands of DNA are not identical, but are complementary.
This means that they are positioned to align complementary base pairs: C with G, and A with T.
So you can predict the sequence of one strand given the sequence of its complement.
Useful for information storage and transfer!
Note sequence conventionally is given from the 5' to 3' end Slide 26: 26 Nucleic acids 26 Fig. 8-19 Slide 27: 27 RNA has a rich and varied structure Fig. 8-26 Watson-
Crick base pairs
Usually A-form). Helix is secondary structure.
Note A-U pairs in RNA. DNA can form structures like this as well. Slide 28: 28 RNA displays interesting tertiary structure 28 Fig. 8-28 Fig. 8-25 Single-stranded RNA right-handed helix T. thermophila intron,
A ribozyme (RNA enzyme)
(1GRZ) Hammerhead ribozyme
(1MME) Yeast tRNAPhe
(1TRA) Slide 29: 29 The mother of all biomolecules 29 1ffk Large subunit of the ribosome (proteins at least) Slide 30: 30 THANK YOU