transcription the first step of gene expression – synthesis of rna molecule

transcription

The first step of gene expression – synthesis of RNA molecule

Some nomenclature conventions

RNAP

RNA DNA

DNARNA

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 ראקצייתהשיחבור

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 – drosophila125 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

1 18

Alternative splicing regulate pro or anti apoptotic pathways.

anti-apoptotic

pro-apoptotic

The last stage in gene expression – synthesis of proteintranslation

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 acids3 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 Commonly used to define DNA sequence changes that alter protein functionchanges that alter protein function

PolymorphismDNA sequence changes that do DNA sequence changes that do notnot alter alter

protein function (common definition, protein function (common definition, not technically not technically correctcorrect) )

Functional proteinFunctional protein Functional proteinFunctional protein

Single nucleotide polymorphisms (SNP) (in the coding sequence)

NormalNormalmRNAmRNA

ProteinProtein

A U G

Met

A A G

Lys

U U U

Phe

G G C

Gly

G C A

Ala

U U G

Leu

A A

Gln

C

Silent DNA sequence polymorphism

SequencSequence variante variant

mRNAmRNA

ProteinProteinA U G

Met

A A G

Lys

U U U

Phe

G G U

Gly

G C A

Ala

U U G

Leu

A A

Gln

C

G

Missense Mutations

MissenseMissense

Missense: changes to a codon for another amino Missense: changes to a codon for another amino acid (can be harmful mutation or neutral acid (can be harmful mutation or neutral

polymorphism)polymorphism)

mRNAmRNA

ProteinProtein

NormalNormalmRNAmRNA

ProteinProtein

A U G

Met

A A G

Lys

U U U

Phe

G G C

Gly

G C A

Ala

U U G

Leu

A U G

Met

A A G

Lys

U U U

Phe

A G C

Ser

G C A

Ala

U U G

Leu

A A

Gln

C

A A

Gln

C

Nonsense Mutations

Nonsense: change from an amino acid codon to a Nonsense: change from an amino acid codon to a stop codon, producing a shortened proteinstop codon, producing a shortened protein

NonsenseNonsense

mRNAmRNA

ProteinProtein

NormalNormalmRNAmRNA

ProteinProtein

A U G

Met

A A G

Lys

U U U

Phe

G G C

Gly

G C A

Ala

U U G

Leu

A U G

Met

U A G U U U G G C G C A U U G

A A

Gln

C

A AC

Frameshift Mutations

FrameshiftFrameshift U G C A AA U G

Met

A A G

Lys

G C G

Ala

C A UU U

U

G

Leu

Frameshift: insertion or deletion of base pairs, producing Frameshift: insertion or deletion of base pairs, producing a stop codon downstream and (usually) shortened proteina stop codon downstream and (usually) shortened protein

mRNAmRNA

ProteinProtein

NormalNormalmRNAmRNA

ProteinProtein

A U G

Met

A A G

Lys

U U 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 acidsA 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