DNA contains the genetic instructions used in the development and functioning of all known living organisms. It is a long polymer made from repeating units called nucleotides, with each nucleotide containing a sugar, phosphate, and one of four nitrogenous bases. DNA exists as a double helix held together through base pairing between adenine and thymine and between cytosine and guanine. DNA stores and transmits genetic information from one generation of cells to the next through the process of replication. It also controls the production of proteins through transcription of DNA into RNA and the translation of RNA into proteins, which are essential for the structure, function, and regulation of the body.

1. GPB-121
Department of Agriculture Botany
“Fundamentals of Genetics”
DNA and RNA , Structure, Functions, Types, difference,
Similarities, Protein Synthesis

2. Gene - The basic physical and functional unit of heredity.
 Gene are Segment of DNA.
 Each gene contains information about a
certain traits.
 Genes are transcribed and translated by
the cell to make proteins.
 Proteins creates Visible Phenotype.
E.g. One gene might code for eye colour.

3. Cell
Nucleus
Chromosome
DNA

4. DNA - Chemical in the cells of an plant that controls what
characteristics that plant will have.
 Deoxyribonucleic acid (Organic compound).
 Found in all Prokaryotic and Eukaryotic Cells.
 1st recognized and identified by J. F. Miescher (1869) -
research on white blood cells.
 Double helix structure of a DNA – J.Watson and F.Crick
(1953)- Proved that DNA is responsible for storing genetic
information in living organisms.
 DNA is a group of molecules that is responsible for
carrying and transmitting the hereditary materials or the
genetic instructions from parents to offsprings
 A molecule that contains the genetic code that is unique to
every individual.
 The molecule that carries genetic information for the
development and functioning of an organism.

5. DNA Structure representing the different parts of the DNA.
DNA comprises a sugar-phosphate
backbone and the nucleotide bases
(guanine, cytosine, adenine and thymine).

6. (a) Nucleotides: DNA is composed of repeating units called nucleotides. Each
nucleotide consists of three components:
1. A deoxyribose sugar molecule.
2. A phosphate group.
3. One of four nitrogenous bases: Adenine (A), Thymine (T), Cytosine (C), or
Guanine (G).
(b) Base Pairing: The two DNA strands are held together by hydrogen bonds
between the nitrogenous bases.
Adenine (A) always pairs with Thymine (T), and Cytosine (C) always pairs with
Guanine (G). This is known as complementary base pairing.
(c) Double Helix: The two nucleotide chains twist around each other to form a
spiral structure, creating a double helix. The sugar-phosphate backbones of the
two strands run in opposite directions, which is referred to as an antiparallel.
(d) Base Sequence: The sequence of nitrogenous bases along each strand of
DNA carries the instructions for the building and functioning of living
organisms.

7. 1. Nucleotide – Double stand helix made-up.
2. Nucleoside – Consist Deoxyribose sugar + P.
group.

8. o Nucleic acids are made up of nucleotides.
o DNA molecule composed units called nucleotides, and each nucleotide is composed of three
different components such as sugar, phosphate groups and nitrogen bases.
o The basic building blocks of DNA are nucleotides, which are composed of a sugar group, a
phosphate group, and a nitrogen base.
o The sugar and phosphate groups link the nucleotides together
to form each strand of DNA. Adenine (A), Thymine (T),
Guanine (G) and Cytosine (C) are four types of nitrogen
bases.
o These 4 Nitrogenous bases pair together in the following way:
 A with T, and C with G. These base pairs are essential for the
DNA’s double helix structure, which resembles a twisted
ladder.
o The order of the nitrogenous bases determines the genetic
code or the DNA’s instructions.
o The A and G are purines, and the C and T are pyrimidines.
o Bases form pairs with A and T forming hydrogen double bonds and G and C forming triple
bonds.
1. A = G (double bond)
2. C = T (triple bond)
Nucleic acids - large biomolecules.
Function - Storage and expression of genomic information.

9.  TypesofDNA(3):-
1. A-DNA:- Right-handed double helix similar to the B-DNA
form.
 Dehydrated DNA takes an A form that protects the DNA
during extreme conditions such as desiccation.
 Protein binding also removes the solvent from DNA, and the
DNA takes an A form.
2. B-DNA:- Most common DNA and is a right-handed helix.
 Majority of DNA has a B type conformation under normal
physiological conditions.
3. Z-DNA: Left-handed DNA where the double helix winds to
the left in a zig-zag pattern.
 Discovered by- Andres Wang and Alexander Rich.
 Found ahead of the start site of a gene and hence, is believed
to play some role in gene regulation.

10.  Watson and Crick Model of DNA (1953)
1. Two strands of DNA run in opposite directions.
2. These strands join together by - hydrogen bond that is present between
the two complementary bases.
3. Each strand forms a right-handed coil, and 10 nucleotides make up a
single turn.
4. Hence, the distance between two consecutive base pairs (i.e., hydrogen-
bonded bases of the opposite strands) is 0.34 nm.
5. Stands – Two Polynucleotide strand ( They are antiparallel to each
other nucleotide = nucleoside + Phosphate group).
 Diameter of DNA molecule ---- 2nm.
 Diameter of Helix (Distance between 2 stands of DNA) --- 200 A.
 Single Helix of length - 340 A.
 Peach Angle – 3600 .
 Two successive base pair angle - 360
 The pitch of each helix is 3.4 nm. (Distance bet, 2 successive base pairs).
 Each base pair – 10 nucleotides.
 Ends – 3/, 5/ and 5/ , 3/.

12. Chargaff’s Rule
 Erwin Chargaff, a biochemist, discovered that the number
of nitrogenous bases in the DNA was present in equal quantities.
 The amount of A is equal to T, whereas the amount of C is equal to G.
A=T; C=G
 In other words, the DNA of any cell from any organism should have a
1:1 ratio of purine and pyrimidine bases.
 Purine and Pyrimidine ratio – 1:1

13. DNA Replication
 The process by which DNA makes a copy of itself during cell division.
 The separation of the two single strands of DNA creates a 'Y' shape called a replication
'fork’.
 The two separated strands will act as templates for making the new strands of DNA. (leading
and lagging stands).
 DNA Synthesis at – Okazaki fragment.

14.  DNAreplicationtakesplaceinthreestages:
Step 1: Initiation
 At a point of DNA origin of replication.
 The two DNA strands are separated by the DNA helicase.
 This forms the replication fork.
Step 2: Elongation
 DNA polymerase III reads the nucleotides on the template strand and makes a new
strand by adding complementary nucleotides one after the other.
 E.g. if it reads an Adenine on the template strand, it will add a Thymine on the
complementary strand.
 While adding nucleotides to the lagging strand, gaps are formed between the
strands.
 These gaps are known as Okazaki fragments. These gaps or nicks are sealed by
ligase.
Step 3: Termination
 The termination sequence present opposite to the origin of replication terminates the
replication process.
 The TUS protein (terminus utilization substance) binds to terminator sequence and
halts DNA polymerase movement.
 It induces termination.

16.  Functions of DNA
1. Storage of Genetic Information: necessary for the development,
growth, functioning, and Reproduction of an organism. DNA encodes
the genetic code that determines an organism’s traits.
2. Replication: DNA can make identical copies of itself through a
process called DNA replication. It is essential for cell division and the
transmission of genetic information from one generation of cells or
organisms to the next.
3. Gene Expressing: Involves the process of transcribing DNA into
RNA and then translating RNA into proteins. Proteins play a wide
range of roles in the body, including enzyme activity, structural
support, and regulation of cellular processes.
4. Genetic Variation: DNA is subject to mutations, which are changes
in the DNA sequence. These mutations can lead to genetic diversity
within populations and can be a source of evolutionary change over
time.
5. Inheritance: DNA is the basis of inheritance. Offspring inherit their
DNA from their parents, and the combination of genetic information
from both parents determines an individual’s unique genetic makeup.
6. Evolution: DNA is central to the process of evolution by natural
selection. Mutations in DNA can lead to variations in traits within a
population, and advantageous traits may become more prevalent over
time through the process of natural selection.

17. RNA (Ribonucleic acid)
 A nucleic acid present in all living cells.
 Single stand.
 Act as a messenger carrying instructions from DNA for controlling the synthesis of proteins,
although in some viruses RNA rather than DNA carries the genetic information.
 RNA molecule composed of four types
Adenine (A), Cytosine (C), Guanine (G), and Uracil (U).
 Role of RNA is to convert the information stored in DNA into proteins.
 Raymond Jeener (1950) 1st suggestion that small RNA molecules move from the nucleus to
the cytoplasm and associate with ribosomes where they drive protein synthesis.
 The first reports of what we would now identify as mRNA were made by Al Hershey's group
in 1953 and by Volkin and Astrachan in 1956.

18.  RNA is typically single stranded and is made of ribonucleotides that are linked
by phosphodiester bonds.
Types of RNA -
1.m-RNA
(messenger)
2.r-RNA
(ribosomal)
3.t-RNA
(transfer)

19. 1.m-RNA
(messenger)
1. Long polymeric molecule made up of nucleotides.
2. It is a long, single-stranded molecule.
3. It consisting of nucleotides attached by phosphodiester bonds.
4. It contains four nitrogenous bases, adenine, guanine, cytosine and uracil.
5. Short lived.
6. It carries message from DNA for protein synthesis.
7. End - 5/ , 3/.
8. About – 5-10 % present
 Role of mRNA is to carry protein information from the DNA in a cell's
nucleus to the cell's cytoplasm.

20. 2.r-RNA
(ribosomal)
 Three-dimensional structure of rRNA, which has internal helices and loops.
 Secondary structure of SSU rRNA contains 4 distinct domains—the 5', central, 3' major and 3'
minor domains.
 About – 5-10 % present.
 Single stand.
 Ribosomes are responsible for translation, use to make proteins.
 rRNA are responsible for reading the order of amino acids and linking amino acids together.

21. 3.t-RNA
(transfer)
1. It has a distinctive folded structure with three hairpin
loops that form the shape of a three-leafed clover.
2. One of these hairpin loops contains a sequence called
the anticodon, which can recognize and decode an
mRNA codon.
3. Each tRNA has its corresponding amino acid attached
to its end.
4. 10-20% RNA present.
5. Short life/ Soluble.

23.  Difference, Similarities in between DNA and RNA

24. Protein Synthesis
 The process in which the DNA
(deoxyribonucleic acid) codes for the
production of essential proteins, such as
enzymes and hormones.
 Proteins are long chains of molecules
called amino acids.
 Two-part process because it allows for
more precise control.
1. It starts with Transcription in the
nucleus, where DNA is copied to mRNA.
2. Then Translation, the mRNA is processed
and exported to the cytoplasm, where
ribosomes and proteins can read and assemble
them.