Describes what are nucleic acids and structure of DNA and DNA organization

1. Prof.(Dr) Viyatprajna Acharya

2.  It takes about eight hours for one of
your cells to completely copy its DNA.
 The human DNA code is made up of
about thirty billion A,T, C, and Gs on
each side of the DNA strand.

3.  If the total DNA in one person were laid
in a straight line, it would stretch to
the sun and back over 600 times (it's 93
million miles from here to the sun).
 You could fit one million threads of
DNA across the period at the end of
this sentence.

4.  Our genes are remarkably similar to those
of other life forms. For example, we share
98% of our genes with chimpanzees, 90%
with mice, 85% with zebra fish, 21% with
worms, and 7% with a simple bacterium
such as E. coli.

5.  The highest point in Kings
Park, the DNATower
(pictured) is so named
because it resembles the DNA
double-helix molecule.The
15m high staircase has 101
steps and was inspired by a
double staircase in a chateau
at Blois in France.

6. James Watson & Francis Crick

7. Maurice Willkins

8. Rosalind Franklin
The unsung
heroine…..

9.  Meischer (1869)- discovered nuclein from leucocytes…but didn’t know
that it was nucleic acids
 Chargaff (1952)- Gave his findings toWatson & Crick
 Phoebus Levene (1905)- Russian scientist- Polynucleotide model,
tetranucleotide model
 Erwin Chargaff (1950)- Chargaff’s rule; Showed that different species
contain different DNA sequence
 Jerry Donohue (1952)- Suggested different cardboard cutouts to
Watson & Crick
Meischer 1869

10.  GENES – units of genetic material that
CODES FOR A SPECIFICTRAIT
 Called NUCLEIC ACIDS
 DNA is made up of repeating molecules
called NUCLEOTIDES

12. DNA- Deoxyribonucleic acid

13. O
O=P-O
O
Phosphate
Group
N
Nitrogenous base
(A, G, C, orT)
CH2
O
C1
C4
C3 C2
5
Sugar
(deoxyribose)

15.  Deoxyadenylate (A)
 Deoxyguanylate (G)
 Thymidylate (T)
 Deoxycytidylate (C)

16.  Units combine by 3’-5’ phosphodiester
bonds to polymerise
 3’- hydroxyl of one sugar is combined to 5’-
hydroxyl of another sugar through a
phosphate group
 Bases jot in
 Sugar phosphate skeleton
 Sequence of nucleotides are of paramount
importance- Genetic code
 5’-3’ polarity

17. Listen to the faintest sound, for opportunities knock only once

19. 
Nitrogenous
Base (A,T,G or C)
“Rungs of ladder”
“Legs of ladder”
Phosphate &
Sugar Backbone

20. 1. Right handed double helix
2. Base pairing rule- complementary strands
A-T & G-C
Chargaff’s rule
3. Hydrogen bonding-
A-T– 2 H bonds
G-C– 3 H bonds

21. 4. Antiparallel strands
5. Each strand acts as a template for the
synthesis of the opposite strand
during synthesis
6. Pitch- 3.4 nm
10 bp / turn
Adjacent bases- 0.34 nm apart
Width- 20 A0

22.  Major groove –
1.2nm
 Minor groove- 0.6
nm
 Tm- Melting
temperature of DNA
 Annealing

23.  Supercoils & negative
supercoils
 Euchromatin &
Heterochromatin

24.  Human diploid genome- 7109 bp-
distributed over 46 chromosomes
 When placed end to end- 2meters
 If one nucleotide added per second- 250
years to synthesize whole DNA of a
human cell
 Length of DNA is compressed 10,000 fold
to generate chromosomes
 Bacterial DNA- closed circular

25.  Each chromatid- one strand of DNA
 Hence 46 DNAs in 1 cell
 Each DNA-2 strands
 Hence total 92 strands of DNA

26. Human karyotype

29. Histone core of nucleosome Linker DNA

30.  Chromosome = 2 chromatins
 Chromatin= DNA + Histone proteins
+ Non- histone proteins + RNA
 Histone= basic proteins
 H1,H2A, H2B, H3 & H4
 Histone octamer=
(H3-H4)2 + 2 (H2A-H2B)
 H1- loosely bound

31.  ‘Beads on String
appearance’
 1.75 superhelical
turns- 146 bp
 Nucleosomes →
solenoids
→chromatins

32.  H2A & H2B- Lysine rich
 H3 & H4 – Arginine rich
 Histone synthesis stops when
DNA synthesis ceases
 Chemical modifications-
acetylation, methylation, ADP
ribosylation, phosphorylation
 Acetylation and methylation of
Lys residues- MC modification

33.  Acetylation- activation of transcription
 Deacetylation- depression of transcription
 Phosphorylation- condensation of
chromosomes
 ADP-ribosylation- DNA repair
 Methylation- gene is repressed
 Sumolytion of histones- repression of
transcription
(SUMO- Small ubiquitin related modifier)

34.  3 structural forms
 A-E & Z
 Change in structure helps in
different processes like
transcription, gene expression

36. Characteristi
c property
A- DNA B-DNA Z-DNA
Shape Broad Intermediate Narrowest
Type of helix Rt handed Rt handed Lt handed
Base pair per turn 11 10 12
Tilt of the base
pairs relative
200 10 90
Diameter of helix 25.5 A0 23.7A0 18.4A0
Pitch per turn 25.3A0 35.4A0 45.6A0
Major groove Narrow Wide Flat
Minor groove Very broad Narrow Very narrow
Occurrence High salt medium
(Na, K, Cs)
Physiological form
In 92% HUMIDITY
Unusual DNA

37.  A -form is meta-stable and quickly changes
to D form
 C-DNA- found in 66% humidity, Li+ ions are
found- 9.33bp
 D-form- 8bp/turn; 8-fold symmetry;
pronounced negative tilt
 Z-DNA- initially synthesised in the lab; a
transient form; may have some regulatory
function. Repeating unit is a dinucleotide as
compared to B-DNA

38.  ↑Temp or ↓salt concentration- splitting of 2
strands
 Along with H bonds, the N bases also fall off
 ↑optical absorbance- Hyperchromicity
 DNA loses viscosity after denaturation
 Tm- exactly half of DNA is denatured
 ↑cations- ↑Tm; 10-fold increase will increase
16.60 Tm.

39.  Separated strands tend to renature
 Need base pair matching
 Post-transcriptional joining- physiological
phenomenon

40.  1% of cellular DNA
 2-10 copies
 Circular double stranded
 Heavy & light chain strands
 16,569 bp
 Genes code for 13 proteins of respiratory
chain
(54 out of 67 are coded by nuclear genes)
 Genetic code different (UGA forTrp & AGA,
AGG of Arg as stop codons)

41.  2 r RNAs & 22 t-RNAs
 No introns
 High mutation rates
 Stays in a relaxed or super-
coiled state- preferable mode
 Maternal Mendelian
inheritance
 OXPHOS diseases

42.  Find out the OXPHOS diseases
 Compare and contrast cellular and
mitochondrial DNA

43. www.vpacharya.com