IIII

1. Molecular Biology
Unit -1
• Introduction to nucleic acids
• Types of DNA
• Central dogma of life
• Hydrolysis of nucleic acids

2. Structure and Function
NUCLEIC ACIDS
Nucleic acids are long-chain polymeric molecules, the monomer (the repeating unit) is known as the nucleotides and
hence sometimes nucleic acids are referred to as polynucleotides.
Chemically, DNA is composed of a pentose sugar, phosphoric acid and some cyclic bases containing nitrogen.
The sugar moiety present in DNA molecules is β-D-2-deoxyribose.
The cyclic bases that have nitrogen in them are :
Adenine (A)
Guanine (G)
Cytosine(C)
Thymine (T)
These bases and their arrangement in the molecules of DNA play an important role in the storage of information from one
generation to the next one.
DNA has a double-strand helical structure in which the strands are complementary to each other.
Deoxyribonucleic Acid (DNA)
Ribonucleic Acid (RNA)
The RNA molecule is also composed of phosphoric acid, a pentose sugar and some cyclic bases
containing nitrogen. RNA has β-D-ribose in it as the sugar moiety. The heterocyclic bases present in RNA are
adenine (A), guanine (G), cytosine(C) and uracil (U)
In RNA the fourth base is different from that of DNA.
The RNA generally consists of a single strand which sometimes folds back; that results in a double helix
structure.
There are three types of RNA molecules, each having a specific function:
1. messenger RNA (m-RNA)
2. ribosomal RNA (r-RNA)
3. transfer RNA (t-RNA)

4. DIFFERENCE BETWEEN DNAAND RNA
Nucleic acids: are responsible for the transmission of inherent characters from parent to offspring.
1. They are responsible for the synthesis of protein in our body
2. DNA fingerprinting is a method used by forensic experts to determine paternity.
3. It is also used for the identification of criminals.
4. It has also played a major role in studies regarding biological evolution and genetics.

5. Types of DNA molecule
The three major types of DNA are double stranded and linked together by interactions between complementary base
pairs. The terms A-form, B-form, and Z-form DNA are used interchangeably.
Table 1: Comparisons of B-form, A-form and Z-DNA
B-Form A-Form Z-Form
helix sense Right Handed Right Handed Left Handed
base pairs per turn 10 11 12
vertical rise per bp 3.4 Å 2.56 Å 19 Å
rotation per bp +36° +33° -30°
helical diameter 19 Å 19 Å 19 Å
Source: shorturl.at/doqw1
A-DNA
1. A-DNA is DNA that is right-handed. It is made up of two helices.
2. The A form of this DNA type is formed primarily to protect the DNA in the event of extreme conditions,
such as desiccation.
3. Dehydrated DNA is commonly used to obtain this type.
4. The protein binding around it aids in the removal of the solvent from the DNA. As a result, it takes the shape
of an A.
B-DNA
1. The most common form of DNA conformation is B-type DNA.
2. It has a right-handed helix structure.
3. Furthermore, it is very common to see that much DNA has a B-type conformation under normal
psychological conditions.

6. Z-DNA
1. This DNA type is known as left-handed DNA.
2. A double helix is present here, with the wind zigzagging to the left.
3. The Z-DNA was created by Alexander Rich and Andres Wang.
4. According to multiple reports, the Z-type DNA was discovered at the beginning of the gene.
5. As a result, one can speculate that it may play important roles in gene regulation.
The Chargaff Rule
Erwin Chargaff, a biochemist, discovered that the number of nitrogenous bases in DNA was equal.
The amount of C is equal to G's, while the amount of A is equal to T. A = T;C triple bond with G
Simply put, the DNA in any cell of any living creature should have a 1:1 ratio of pyrimidine and purine bases.
Definition of Central Dogma
The central dogma is the process by which genetic information flows from DNA to RNA to produce a functional
protein."
Source:
https://www.nist.gov/image/geneticsdogmajpg

7. Hydrolysis of nucleic acid
1. The two strands of DNA helix are held together by hydrogen bonds.
2. Disruption of hydrogen bonds (by change in pH or increase in temperature) results in the separation of polynucleotide strands.
3. This phenomenon of loss of helical structure of DNA is known as denaturation .
4. The phosphodiester bonds are not broken by denaturation. Loss of helical structure can be measured by increase in absorbance at 260
nm (in a spectrophotometer).
5. Melting temperature (Tm) is defined as the temperature at which half of the helical structure of DNA is lost. Since G-C base pairs are
more stable (due to 3 hydrogen bonds) than A-T base pairs (2 hydrogen bonds), the Tm is greater for DNAs with higher G-C content.
Thus, the Tm is 65°C for 35% G-C content while it is 70°C for 50% G-C content. Formamide destabilizes hydrogen bonds of base
pairs and, therefore, lowers Tm.
6. This chemical compound is effectively used in recombinant DNA experiments.
7. Renaturation (or reannealing) is the process in which the separated complementary DNA strands can form a double helix.

8. THANK YOU