1. CHAPTER 6
CHROMOSOMES AND DNA

2. REPLICATION OF DNA
Before the start of cell
division, the DNA material
in the original cell must be
duplicated so that after cell
division, each new cell
contains the full amount of
DNA material. The process
of DNA duplication is
usually called replication.

3. STRUCTURE OF DNA
• DNA, or
deoxyribonucleic acid,
is the hereditary
material in humans and
almost all other
organisms. Nearly every
cell in a person’s body
has the same DNA.
Most DNA is located in
the cell nucleus.

4. STRUCTURE OF NUCLEOTIDE
• DNA is a double helix having two
anti-parallel poly nucleotide
chains whose basic unit is a
nucleotide .
• A Nucleotide consists of a
nitrogenous base, pentose sugar,
and a phosphate.
• DNA contains four different types
of nitrogenous bases, two with
purine bases, adenine(A) and
guanine (G) which have a double
ring, and two with pyrimidine
bases, thymine (T) and cytosine
(C) which have a single ring.

5. REPLICATION OF DNA

6. MODELS OF DNA REPLICATION
There are three models of DNA replication.
Semi
Conservative
conservative
model
model
Dispersive model

7. REPLICATION OF DNA
• DNA replication requires the concerted action of a
number of proteins.
• The proteins involved are clustered together in the
cell.
• The DNA to be copied is fed through the proteins of the
replication factory.
• The duplex DNA to be copied is unzipped into single
strand.
• Each of the two template strand is copied and becomes
half of a new DNA double helix.
• DNA replication is semi conservative.

8. REPLICATION OF DNA
Steps of DNA replication
Formation of
replication fork
(unzipping)
Ligation of
Formation of
okazaki
RNA primer
fragments
Formation of
Removal of
new DNA
RNA primer
strands

9. REPLICATION OF DNA
• Helicase
Enzymes • Single strand binding proteins
• Primase
Of • DNA polymerase III
• DNA polymerase I
Replication • DNA ligase

10. REPLICATION OF DNA

11. GENE EXPRESSION

12. TRANSCRIPTION AND TRANSLATION

13. TRANSCRIPTION
• The production of mRNA
from DNA is called
Transcription.
• There are three types of
RNA
1. Ribosomal RNA (r RNA)
2. Transfer RNA (t RNA)
3. Messenger RNA (m RNA)

14. MESSENGER RNA
• It is formed from DNA
inside the nucleus.
• It carries the coded
information (codons)
from DNA to
ribosomes in the
cytoplasm to be
translated into
protein.

15. TRANSFER RNA
• It is present in cytoplasm and
consists of two ends and a central
loop portion.
• The loop has specific base sequence
called Anticodon which is the site of
attachment to m RNA.
• There are more than 40 different
kinds of t RNA.
• Each t RNA picks up specific amino
acid at its one end according to its
anticodon and transfer it to
ribosomes during protein synthesis.

16. RIBOSOMAL RNA
• It is found in
ribosomes.
• It provides site for
lining up the amino
acids in the sequence
dictated by m RNA
fop the formation of
polypeptide chain.

17. PROCESS OF TRANSCRIPTION
• Transcription is initiated when a special
enzyme called RNA Polymerase binds to a
particular sequence of nucleotides on
one of the DNA strand which is present at
the edge of a gene.
• The RNA Polymerase proceed to assemble
a single strand of RNA with a nucleotide
sequence complementary to the DNA
strand it has bound.
• Assembly of bases occur according to
base pairing rules i.e.
• Adenine to Uracil
• Thymine to Adenine
• Cytosine to Guanine
• Guanine to Cytosine

18. TRANSLATION
• The process of m RNA directed poly
peptide synthesis by ribosomes is
called Translation.
• Translation begins when a newly
formed and processed m RNA
enters the cytoplasm via nuclear
pore, where many free amino acids,
t RNA and ribosomes are present.
• Translation proceeds in three steps:
1. Initiation
2. Elongation
3. Termination

19. PROCESS OF TRANSLATION
Initiation
A t RNA binds to the one end of m RNA
transcript having start codon i.e. AUG
Elongation
Amino acids brought by t RNA assemble
according to the sequence of codons on
m RNA which is passing between two
ribosomal subunits.
Termination
It occurs when stop codon comes on m
RNA (UAA,UAG,UGA) and newly formed
polypeptide chain is released from
ribosome.

20. GENETIC CODE
• The information present in the sequence of
nucleotides on DNA carried by RNA for the
synthesis of proteins is called genetic code.
• A series of three adjacent bases in DNA or RNA
which codes for a specific amino acid is called
codon or triplet code.
• The m RNA codons are recognized by t RNA
having anticodons, carrying a particular amino
acid and binding to m RNA. This is called
Decoding.

21. CODONS OF m RNA