DNA and RNA Class XII Biology Based on NCERT

1. MOLECULAR BASIS OF
INHERITANCE
DR. RAMA KANT UPADHYAY
PART- I
DNA and RNA

2. Inheritance
Transfer of genetic information from parents to their offspring.
Possible genetic materials
Protein, DNA, RNA
What is a genetic material?

3.  Mostly double stranded
 Double helical structure
 Can duplicate/replicate
 Form RNA
 Have deoxy-ribose sugar
 Less reactive and more stable due
to the presence of only one free–
OH grp
 Thymine is present
 Mostly single stranded
 X
 X
 Formed by DNA
 Have ribose sugar
 More reactive and less stable due
to Prescence of 2 free– OH grp
 Uracil is present
DNA vs RNA

4. NUCLEUS
CHROMOSOME
GENE
DNA

5. DNA
Found in all cells
Same amount in
all somatic cells
Infinite variety
Replicate
(S- phase )
Distributed to
daughter cell
equally
Genetic
information as
codon
Express genetic
information by
transcription as
RNA
Can repair itself Ablity to mutate

6. Bacteriophage
x174= 5386
bp
Bacteriophage
Lambda =
48502 bp
Escherichia
coli =
4.6 X 10 6 bp
Human =
3.3 X 10 9 bp
DNA- SIZE

7. DNA: STRUCTURE
• Polynucleotide
• Nucleotide
• Nucleoside + phosphoric acid
• Nitrogenous bases
1- purine (adenine, guanine)
2- pyrimidine (thymine, cytosine, uracil)
Sugar: Ribose/ deoxyribose
Phosphate group
Nucleotide: Nitrogenous base + sugar + phosphate group
Nucleoside: Nitrogenous base + sugar

8. PURINES
PYRIMIDINES
Nitrogenous bases

9. The Sugars

10. RNA only DNA only
Purines:
Pyrimidines:
Bases of DNA (and RNA)

11. BASE NUCLEOSIDE NUCLEOTIDES
A Adenosine Adenylate
G Guanosine Guanylate
C Cytodine Cytidilate
U Uridine uridylate
T Thymidine Thymidylate
Nucleotides and Nucleosides

12.  Franklin and Wilkins
used x-ray to discover
that DNA was a double
helix.
Rosalind Franklin & Maurice Wilkins

13. Watson and Crick
• The two strands of DNA double helix two polynucleotide chains, where the backbone is
constituted by sugar-phosphate, and the bases project inside.
• Nucleotides are composed of sugar, phosphate group, and nitrogenous base.
• Chains are anti-parallel (i.e in opposite directions)- if one chain has the polarity 5’ 3',
the other has 3’ 5’.
• The bases in two strands are paired through hydrogen bond (H-bonds) forming base
pairs (bp).
• Adenine forms two hydrogen bonds with Thymine and , Guanine is bonded with
Cytosine with three H-bonds.
• It has a diameter of 20 A
• The total helix runs to a length of 34A
• The axial rise per base pair is 3.4 A
• Base pair per turn is 10A
• The plane of one base pair stacks over the other in double helix. This,
• in addition to H-bonds, confers stability of the helical structure
Chargaff discovered that DNA has the same amount of adenosine as thymine and the
same amount of cytosine as guanine.
A = T and G = C
Adenine and thymine are paired with two hydrogen bonds while guanine and
cytosine with three hydrogen bonds.

14. Double helical model of DNA
toppr.com

15. https://byjus.com/cbse-notes/cbse-class-12-biology-notes-chapter-6-molecular-basis-of-inheritance/
Phosphodiester bonds: The bond
formed between 3’ OH of one
nucleotide and the 5’Phosphate
group of another nucleotide.
Phosphodiester bonds
Source: Pinterest

16. Bonding between A/ T and G/C

17. POLYNUCLEOTIDE CHAIN
https://www.geeksforgeeks.org

18. RNA (Ribonucleic Acid)
First genetic material
Formed during the transcription process with the help of the enzyme RNA
polymerase.
Types- m RNA, t RNA, r RNA

19. • Transfer genetic information to form a polypeptide.
• Eucaryotic m RNA need processing after transcription, while prokaryotes can
synthesize protein production immediately, and it does not need to be
processed or matured.
M- RNA

20. r RNA
• The rRNA is the component of the ribosome
• Ribosome id composed of r RNA and ribophorin protein
• Provide binding site for mRNA
• Helps is the translation process.
• Most predominant RNA within the cells of all living beings.
A ribosome consists of an exit (E), an acceptor (A) site, and a peptidyl (P) to
combine the aminoacyl-tRNAs, and it connects the amino acids to form
polypeptides. r RNA
ribophorin
protein

21. • Transfer correct amino acids to the site of protein synthesis (ribosome) based
on codons of m RNA.
• Very small, therefore called soluble rRNA.
• Looks like clover leaf.
tRNA

22. tRNA- the Adapter Molecule
• tRNA has an anticodon loop that has bases complementary to the code, and it also
• has an amino acid acceptor end to which it binds to amino acids.
• tRNAs are specific for each amino acid
• For initiation, there is another specific tRNA that is referred to as initiator tRNA.
• There are no tRNAs for stop codons.
• Activation: when an amino acid is attached to the tRNA, it is known as the aminoacylation of tRNA.
• Aminoacyl-tRNA synthetases enzyme helps in this process.

23. • Facilitate the translation of DNA into proteins
• Functions as an adapter molecule in protein synthesis
• Serves as a messenger between the DNA and the ribosomes.
• They are the carriers of genetic information in all living cells
• Promotes the ribosomes to choose the right amino acid which is
required in the building up of new proteins in the body.
Functions of RNA

24. Packaging of DNA Helix (In eukaryotes)
• DNA is negatively charged.
• Histone protein is a positively charged protein.
• Histones are rich in the basic amino acid residues lysine and arginine.
• Histones are organized to form a unit of eight molecules called histone octamer.
• The negatively charged DNA is wrapped around the positively charged histone
octamer to form a structure called nucleosome.
• A typical nucleosome contains 200 bp of DNA helix.
• The nucleosomes in
• chromatin is seen as ‘beads-on-string’ structure
The beads-on-string structure in chromatin is packaged to form chromatin fibers that are further coiled and condensed at the
metaphase stage of cell division to form chromosomes.
The packaging of chromatin at higher level requires additional set of proteins called as NHC (Non-histone Chromosomal proteins).
Euchromatin: loosely packed (and stains light). Transcriptionally active
Heterochromatin: densely packed and stains dark. Transcriptionally inactive.