Cancer

CANCER
RISHABH GARG
First Degree Program (ECE)
Birla Institute of Technology & Science,
K.K. Birla Campus Goa 403 726 IN
A GENETIC MISHAP
RISHABH GARG (BE ECE) BITS GOA

 Growth and repair (replacement of dead cells) take
place as result of cell division (mitosis).
 Some cells end up their life by death and
degradation - Apoptosis.
 In growing animals, cell division is high so that cell
multiplication is greater than cell death.
 In adults, a steady state - the origin of new cells is
counter-balanced with the death of old cells.
Thus, cell division is a regulated process.
Cell Division
is a normal process in multicellular organism

Loss of Regulatory
Mechanism
 Cancer results from the
break down of regulatory
mechanism that governs
the division, differentiation
and survival of individual
cells.
 Cancer cell grows and
divide in an uncontrolled
manner.

Loss of Regulatory
Mechanism
 Uncontrolled proliferation
 Spread throughout the
body
 Interferes with the
functions of normal tissues
and organs.

Initiation & Promotion
of Tumors
Gene
altered by
Additional
mutations
Cell - Cell
Communications
Hyperplasia
Neoplasia
Base substitutions/ Frame shift mutations / Deletions /
Duplications / Error prone replication of normal DNA /
Unrepaired DNA damage / normal replication of damaged
cDNA / Structural or numerical changes in chromosomes
Mutated cells become dominant
Direct transfer of ions, metabolites, nucleotides and
other small regulatory molecules through gap
junctions
Cells acquire the capacity to undergo rapid,
abnormal and uncontrolled growth of animal cells.

of Tumors

of Tumors
Normal Cells Tumor invades nearby
cells and grow rapidly
Cancer breaks through the
membrane

 By infection of an oncogenic virus carrying an
oncogene
OR
 By introduction of DNA isolated from a tumor into a
marrow cell
Oncogene
Infection into marrow cells
Viral RNA DNA mRNA Proteins
REVERSE
TRANSCRIPTASE

 Cell possess a variety of genes called
PROTO-ONCOGENES.
 They encode protein for normal activities
of cell. Promote normal cell growth.
 Activation by point mutation, amplification
and dysregulation.
 ONCOGENES (Tumor causing genes).
Role of Oncogene

 Oncogenes encode protein that promote
loss of growth control.
(Oncoproteins include polypeptide growth factors, receptors
for growth factors, components of intracellular signalling
pathways and transcription factors)
 Transforms a normal cell into a malignant
or neoplastic cell.
(Elevated expression of oncogenees, defective differentiation
and failure to go apoptosis)
Role of Oncogene

Loss of DNA Repair
The DNA replication system has high fidelity with very
few errors :
Normal mutator gene typically protects the genetic material through
DNA repair
Mutator gene gets error prone and allows the mutation to
accumulate
Note : if these mutations involve oncogenes or tumor suppressor
genes, there is a greater possibility of developing malignancy.

Loss of DNA Repair
Mutators - their class and location

Tumor Suppressor Gene
Normal cells contain genes on their chromosomes that
suppress unregulated cell growth. These are called
Tumor Suppressor Gene.
• They encode protein that restraints cell growth and prevents cells
from becoming mutant.
• TSG products have an inhibitory role in cell growth and division.
• TSG is a recessive gene. It is necessary to have mutations in both
the alleles to result in tumor.
• Even a single normal allele is able to code for sufficient gene
product for normal function.

Comparative Account
Tumor Suppressor Gene & Proto-oncogene Mutations

Cell cycle : Check points
A series of protein complexes of 2 sub-units : Cyclin
dependent protein kinase (Cdks) and Cyclin determine
the progression of cell cycle from one phase to the
next.
Cell cycle G1 First Gap phase
S Synthesis phase
G2 Second Gap phase
G0 Optional

 Cdks catalyzes the phosphorylation of specific serine /
threonine residues of specific target proteins.
 Cyclins hold the target proteins so that Cdks can
phosphorylate it.
Proteins encoded by TSG that regulate the cell cycle include :
 Rb – responsible for a rare childhood tumor of eye called
retinoblastoma.
 P53 – ensures apoptosis.

p53 is associated with about 50% of all cancers
 It is normally required for cell division.
 Inactivation of both alleles of p53 gene (recessive) results in non-
production of p53 proteins.
Death due to
mitotic failure
Increase in overall frequency of gene
mutations
Chromosomal rearrangements, aneuploidy
Continuous proliferations with damaged
chromosomes
Genetic instability
Malignant growth, tumors

Loss of DNA Repair

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