ALL ABOUT GENESoncogenes-mutations-cloning-gene therapy

Maha Adel Shaheen,MDProfessor of Dermatology & Venereology

Ain Shams University

DNA Molecule

Chargaff’s Rule

Adenine always bonds with Thymine and Cytosine always bonds with Guanine.

DNA Double Helix(twisted ladder)

DNA Models

DNA is located in the nucleus in the form of chromosomes.

Chromosomes are DNA wound tightly around proteins called histones.

DNA Packing into Chromosomes

Gene ExpressionFlow of Genetic Information

Transcription copying of DNA sequences into RNA

Translationcopying of RNA sequences into protein

DNA triplet sequence - mRNA sequence - amino acid sequence

(codon) (protein)

TAC AUG MET

,

The Genetic Code

• This is the language of mRNA.

• Based on the 4 bases of mRNA.

• “Words” are 3 RNA sequences called codons.

• The strand aaacguucgccc would be separated as aaa-cgu-ucg-ccc the amino acids would then be Lysine – Arginine – Serine - Proline

Transcription:• RNA molecules are produced by

copying part of the nucleotide sequence of DNA into complementary sequence in RNA.

Translation:• The cell uses information from

messenger RNA to produce proteins.

Gene Mutation• Definition: Changes in the DNA

sequence of a cell’s genome.

• Causes: A- Spontaneous Mutations (molecular

decay)

B- Induced Mutations (mutagens)

- Chemicals

- Radiation

- Viral

Types of Mutations

• Gene mutations result from changes in a single gene.

• Chromosomal mutations involve changes in whole chromosomes.

( Point mutations - ᵝ globin gene – HbS – sickle cell anemia )

Chromosomal Mutations• Deletion: Part of a

chromosome is deleted.• Duplication: part of a

chromosome is duplicated.

• Inversion: chromosome twists and inverts the code.

• Translocation: Genetic information is traded between non-homologous chromosomes.

Effects of Gene Mutations

A- Neutral Effect (no effect)

B- Harmful Effect

• Errors in protein sequence partly or completely non-functioning proteins.

• Germ cell mutations hereditary diseases (heterozygous/homozygous)

• Somatic cell mutations cancers

C- Beneficial Effect

Oncogenes /Proto-oncogenes• Normal cell division (mitosis) is a carefully

regulated event that requires activation of a network of proteins (one protein activates another) (signal transduction pathway).

• Few 100 out of 30,000 genes of the human genome code for proteins that regulate cell proliferation.

• Mutation of those genes → uninhibited growth (carcinogenesis).

• Proto-oncogenes: normal (pre-mutation) (pre-diseased) genes that code for proteins which regulate cell growth.

• Oncogenes: mutated versions of proto-oncogenes that contribute to cancer development by disrupting a cell's ability to control its own growth (↑division, ↓differentiation, - cell death).

Oncogene Nomenclature

• ras oncogene: rat sarcoma virus• myc oncogene: myelocytosis virus

• erb oncogene: erythroblastosis virus

Genes Implicated in Cancer Development

A- Proto-oncogenes: mutation oncogenes protein products that stimulate excessive growth signaling & cell division (egfr gene ….)

B- Tumor Suppressor Genes: mutation inhibition of apoptosis (p53 gene …..)

C- DNA Repair Genes: mutation failure of repair of mutated genes

From Good to Bad: How Proto-Oncogenes Become Oncogenes

• Point mutations, deletions, or insertions that lead to a hyperactive gene product.

• Point mutations, deletions, or insertions in the promoter region of a proto-oncogene that lead to increased transcription.

• Gene amplification events leading to extra chromosomal copies of a proto-oncogene.

• Chromosomal translocations that relocate a proto-oncogene to a new chromosomal site that leads to higher expression.

• Chromosomal translocations that lead to a fusion between a proto-oncogene and a second gene, which produces a fusion protein with oncogenic activity.

Routes to the Genesis of an Oncogene

Cloning(Duplicating Biological Material)

Three types of cloning

A- Gene cloning = Molecular cloning = DNA cloning = Recombinant DNA technology.

B- Reproductive cloning = Organism cloning (sheep Dolly).

C- Therapeutic cloning = Embryo cloning.

A- DNA Cloning

B- Reproductive CloningAll the child's genes would come from a body cell of a single individual

B- Reproductive Cloning

C- Therapeutic Cloning

Therapeutic cloning• Uses the cloning procedure to produce a clonal embryo, but instead of

being implanted in a uterus and brought to term it is used to generate stem cells.

• Stem cells can be cultured in petri dishes and potentially used to generate "therapeutic tissues" or "spare organs“ that the clonal donor can use without having these tissues or organs rejected by their body's immune system.

• Most people oppose reproductive cloning.• Some people oppose reproductive cloning but support therapeutic

cloning. • Others oppose therapeutic cloning as well as reproductive cloning,

either because they are opposed to the destruction of embryos as a matter of principle, or because they feel the acceptance of therapeutic cloning will set us on a slippery slope to the acceptance of reproductive cloning and human genetic manipulation.