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