Transcript Exons and Introns - Northeastern University

Exons and Introns
Chesley Leslin
Steps in Production Proteins
• exons: the sequences in the DNA molecule that code for
the amino acid sequences of corresponding proteins.
• intron: the DNA sequence in a eukaryotic gene that is
not translated into a protein.
• Transcription
– DNA – preRNA - mRNA
• Translation
– mRNA - Proteins
What do we need for transcription?
1.DNA
In eukaryotes, the genome is divided into :
•Non-coding areas... between genes.
•Genes : Each gene is divided into several exons, separated by non coding
sequences,
•Introns (not coding)
•Exons (coding)
•Promoters, and regulation sequences.
2.RNA polymerases
RNA polymerases are enzymes that will synthesize different kinds of RNA.
3.Other factors
E.g. factor sigma: this stabilizes the polymerase at its specific site, to help
polymerization to start. These other factors may be proteins or other kinds of molecules
Translation
mRNA
UUUCUCAUUACUUAUUGUCGA
now becomes
Phe Leu Ile Thr Tyr Cys Arg
Degenerate genetic code*….what?
T
C
A
G
TTT
TTC
TTA
TTG
Phe
Phe
Leu
Leu
(F)
(F)
(L)
(L)
TCT
TCC
TCA
TCG
Ser
Ser
Ser
Ser
(S)
(S)
(S)
(S)
TAT
TAC
TAA
TAG
Tyr (Y)
Tyr (Y)
Ter
Ter
TGT Cys (C)
TGC Cys (C)
TGA Ter
TGG Trp (W)
C
CTT
CTC
CTA
CTG
Leu
Leu
Leu
Leu
(L)
(L)
(L)
(L)
CCT
CCC
CCA
CCG
Pro
Pro
Pro
Pro
(P)
(P)
(P)
(P)
CAT
CAC
CAA
CAG
His
His
Gln
Gln
(H)
(H)
(Q)
(Q)
CGT
CGC
CGA
CGG
Arg
Arg
Arg
Arg
(R)
(R)
(R)
(R)
A
ATT
ATC
ATA
ATG
Ile
Ile
Ile
Met
(I)
(I)
(I)
(M)
ACT
ACC
ACA
ACG
Thr
Thr
Thr
Thr
(T)
(T)
(T)
(T)
AAT
AAC
AAA
AAG
Asn
Asn
Lys
Lys
(N)
(N)
(K)
(K)
AGT
AGC
AGA
AGG
Ser
Ser
Arg
Arg
(S)
(S)
(R)
(R)
G
GTT
GTC
GTA
GTG
Val
Val
Val
Val
(V)
(V)
(V)
(V)
GCT
GCC
GCA
GCG
Ala
Ala
Ala
Ala
(A)
(A)
(A)
(A)
GAT
GAC
GAA
GAG
Asp
Asp
Glu
Glu
(D)
(D)
(E)
(E)
GGT
GGC
GGA
GGG
Gly
Gly
Gly
Gly
(G)
(G)
(G)
(G)
T
mRNA
1). Initiation
Codon
Anti –
Condon
2). Elongation
Amino Acid
tRNA
3). Termination
RESEARCH………
We are interested in the evolution of the intron/exon
structure of genes. Are the introns ancient structures,
used to assemble the first genes four billion years ago?
Or are they more recent acquisitions, used for exon
shuffling in recently evolved proteins? Our work ranges
from theoretical estimates for the size of the universe of
exons to theoretical arguments that the introns are very
old and that exons are related to folding subunits of
proteins. We are studying the assembling of protein
shapes from modular substructures.
Protein Encoding Exon Containing
Genes
• Based on current GenBank release 133
• 128,000 proteins – lots of info
– Have positions of Introns boundaries in
proteins
– Have structural data from PDB
– Have ability to visualize structure
•
•
•
•
Can we correlate boundaries to structure?
Are boundaries conserved b/t species?
Were there ancient exons?
Alternative Splicing?