Welcome

Presented by:

Sanya Yaseen4010

Presented to:

Sir Danish Riaz

RNA Processing(in cellular Differenciation)

Topic

IntroductionOverview of Gene ExpressionRNA processing in EukaryotesRNA SelectionRNA splicingFamilies of Proteins Sex determination in Drosophilla

Contents

What is Cellular Differenciation?

“Embryonic differentiation is the process of development during which embryonic cells specialize and diverse tissue structures arise.”

What is RNA Processing?

“ The process of gene expression to form a specific protein at a specific place by the process of Translation”.

AN OVERVIEW OF GENE EXPRESSION

The Different Cell Types of a Multicellular Organism Contain the Same DNA.

Different Cell Types Produce Different Sets of Proteins.

A Cell Can Change the Expression of Its Genes in Response to External Signals.

Gene Expression Can Be Regulated at Many of the Steps in the Pathway from DNA to RNA to Protein.

AN OVERVIEW OF GENE EXPRESSION

The Different Cell Types of a Multicellular Organism Contain the Same DNA.

Different Cell Types Produce Different Sets of Proteins.

A Cell Can Change the Expression of Its Genes in Response to External Signals.

Gene Expression Can Be Regulated at Many of the Steps in the Pathway from DNA to RNA to Protein.

cells have ability to change genes expression without altering the nucleotide sequence of their DNA.

If DNA were altered irreversibly during development, differentiated cell would be incapable of guiding the development of the whole organism.

To test this idea, a nucleus from a skin cell of an adult frog was injected into a frog egg whose own nucleus had been removed.

the egg developed normally into a tadpole, showing the normal expression of genes.

AN OVERVIEW OF GENE EXPRESSION

The Different Cell Types of a Multicellular Organism Contain the Same DNA.

Different Cell Types Produce Different Sets of Proteins.

A Cell Can Change the Expression of Its Genes in Response to External Signals.

Gene Expression Can Be Regulated at Many of the Steps in the Pathway from DNA to RNA to Protein.

o many proteins are common to all the cells e.g. structural proteins of chromosomes, RNA polymerases,

DNA repair enzymes, ribosomal proteins, enzymes involved in glycolysis, cytoskelton proteins.

Diferent cell types produce specialized proteins:

e.g. Heamoglobin only produced by reticulocytes a typical differentiated human cell

expresses perhaps 5000–15,000 genes.

large variations seen in the size, shape, behavior, and function of differentiated cells.

AN OVERVIEW OF GENE EXPRESSION

The Different Cell Types of a Multicellular Organism Contain the Same DNA.

Different Cell Types Produce Different Sets of Proteins.

A Cell Can Change the Expression of Its Genes in Response to External Signals.

Gene Expression Can Be Regulated at Many of the Steps in the Pathway from DNA to RNA to Protein.

Cabability to change the Gene Expression due to External Cues.

e.g. Effect of Glucocortocoid Hormone on Liver cells.While some other cells of body do not

effected by that hormone e.g. fat cells illustrate a general feature of cell

specialization

AN OVERVIEW OF GENE EXPRESSION

The Different Cell Types of a Multicellular Organism Contain the Same DNA.

Different Cell Types Produce Different Sets of Proteins.

A Cell Can Change the Expression of Its Genes in Response to External Signals.

Gene Expression Can Be Regulated at Many of the Steps in the Pathway from DNA to RNA to Protein.

To become an active protein, the RNA must be:(1)processed into a messenger RNA by

the removal of introns,(2) translocated from the nucleus to the

cytoplasm,(3) translated by the protein-synthesizing

apparatus(4)must be posttranslationally modified to

become active.• Regulation can occur at any of these

steps during development

Processing in Eukaryotes

O Two Major Ways include:- censoring (RNA Selection) RNA Splicing Censoring:- Nuclear transcripts into mRNARNA Splicing:- splicing of the mRNA into different proteins by using different combinations of potential exons.

RNA Selection

۞ mRNA transcript from pre-mRNA (nuclear RNA (nRNA)

۞ Pre-mRNA is transcribed from DNA ۞ Pre-mRNA contains introns which are

spliced during its movement from nucleus to cytoplsm.

۞ Un-necessary segments are deleted ۞ More genes are transcribed in the

nucleus than are allowed to become mRNAs in the cytoplasm.

Analysis on the transcripts from the CyIIIa  genes of the sea urchin

๏ Encode calcium-binding and actin proteins, expressed only in a particular part of the ectoderm of the sea urchin larva.

๏ Trancribed not in ectoderm but also meso & endoderm but only effective in ectoderm of Sea Urchin Larva.

๏ Unprocessed genes are degraded in meso & endoderm.

RNA Splicing

nRNA contains short exons (averaging about 140 bases) & large introns.

By splicing together, different axons form different proteins.

What is an intron in one cell's nucleus may be an exon in another cell's nucleus.

Splicing of RNA is followed by these steps:

1. 5’ capping 2. polyadenyl tail3. removal of introns 4. editing

5’ Capping

Polyadenyl Tail

Removal of Introns

Editing of mRNA

Process of Translation

Families of Proteins

• Deletion of different exons in different cells forms different families of proteins.

• Instead of one gene-one polypeptide, one can have one gene-one family of proteins.

• for example:- α-tropomyosin gene to encode brain, liver, skeletal muscle, smooth muscle, and fibroblast forms of this protein.• These are called Splicing

isoforms.

Sex determination in Drosophilla