transcription The first step of gene expression – synthesis of RNA molecule

Some nomenclature conventions RNAP

RNADNA

RNA Similarities and Differences Between DNA and RNA Similar strand structure Can define a 5’ and 3’ end 2’ hydroxyl in RNA: causes stability differences) Uracil in RNA takes the place of Thymine in in DNA

Secondary structure of RNA Stem & loop

Difference between DNA and RNA. –DNA – Double Helix, RNA – Single Stranded –DNA --- A-T, RNA ---A-U –DNA ---Deoxyribose Sugar, RNA---Ribose What is a similarity of DNA and RNA? –G binds with C in both DNA and RNA –Both have sugar and phosphate backbone

The pathway of gene expression

CAP

Conserved seqences Polypyrimidine tract

גן הבטא גלובין ההומני

Splice sites can be included in the exons

mRNA splicing lariat

spliceosome מעגל מחזורי של ראקציית השיחבור ספליסוזום

Systemic Lupus Erythematosus (SLE) Lupus is a type of immune system disorder known as an autoimmune disease. In autoimmune diseases, the body harms its own healthy cells and tissues. This leads to inflammation and damage of various body tissues. Lupus can affect many parts of the body, including the joints, skin, kidneys, heart, lungs, blood vessels, and brain. Although people with the disease may have many different symptoms, some of the most common ones include extreme fatigue, painful or swollen joints (arthritis), unexplained fever, skin rashes, and kidney problems. Lupus is also known as a rheumatic disease. The rheumatic diseases are a group of disorders that cause aches, pain, and stiffness in the joints, muscles, and bones.

Untreated β thalassemia 15% of the mutation leading to genetic disorders effect splicing activity

Treatment of thalassemia major

antisense

2.91 billion base pairs 24,500 genes 1.5% exons (127 nucleotides) 24% introns (~3,000 nucleotides) 75% intergenic (no genes) Average size of a gene is 27,894 bases Contains an average of 8.8 exons Titin contains 234 exons. Human genome

Gene number Arabidopsis thaliana 25,500~ Drosophila melanogaster ~13,600 C. elegans 19,000~ Rice (Oryza sativa) ~50,000 Mouse ~24,000 Homo Sapiens ~24,000

Compared to worm and fly, human has shorter exons and longer introns on the extremes of the distribution 150 nt – drosophila 125 nt – Ciona intes. 119 nt - human

5000 genes 234 introns Multi-introns genes 7.8 introns per gene

Sequences of human- mouse homologous exons are 88% conserved

Alternative splicing פוליפרימידין טראק 40% 18% 8% ? 3% Alternative splicing isoform

איזופורמים 118

Alternative splicing regulate pro or anti apoptotic pathways. anti-apoptotic pro-apoptotic

The last stage in gene expression – synthesis of protein translation

Amino acid

N C

N to C terminal 5’ to 3’

CDS

tRNA Aminoacyl

tRNA Aminoacyl-tRNA synthetase (20 diffrent) –one for each amino acid –NEEDS ENERGY!

64 combinations for 20 amino acids 3 termination codons

Met one codon LEU 6 codons, 4 of which are CUN סרט טרנסלציה ספירת מלאי

Disease-Associated Mutations A mutation is a change in the normal base pair sequence Commonly used to define DNA sequence changes that alter protein function

Polymorphism DNA sequence changes that do not alter protein function (common definition, not technically correct) Functional protein

Single nucleotide polymorphisms (SNP) (in the coding sequence) Normal mRNAProtein A UG Met A A G Lys UU U Phe G G C Gly G C A Ala U U G Leu A A Gln C Silent DNA sequence polymorphism Sequenc e variant mRNAProtein A UG Met A A G Lys UU U Phe G G U Gly G C A Ala U U G Leu A A Gln C G

Missense Mutations Missense Missense: changes to a codon for another amino acid (can be harmful mutation or neutral polymorphism) mRNAProtein Normal mRNAProtein A UG Met A A G Lys UU U Phe G G C Gly G C A Ala U U G Leu A UG Met A A G Lys UU U Phe A G C Ser G C A Ala U U G Leu A A Gln CA A C

Nonsense Mutations Nonsense: change from an amino acid codon to a stop codon, producing a shortened protein Nonsense mRNAProtein Normal mRNAProtein A UG Met A A G Lys UU U Phe G G C Gly G C A Ala U U G Leu A UG Met U A GUU U G G C G C AU U G A A Gln CA A C

Frameshift Mutations Frameshift U GC A A A UG Met A A G Lys G C G Ala C AU UU U G Leu Frameshift: insertion or deletion of base pairs, producing a stop codon downstream and (usually) shortened protein mRNAProtein Normal mRNAProtein A UG Met A A G Lys UU U Phe G G C Gly G C A Ala U U G Leu A A Gln C Pre-mature stop codon

Missense mutation mutation

A peptide – a chain of amino acids A protein – a stretch of one or more amino acid chains with biological function Translation II

+eIF3

eIF3

Translation

Life cycle of mRNA movie סרט טרנסלציה