Section 2 Flashcards
Structure of eukaryotic genes
Exons
Protein coding sequence
Introns
Non-Protein coding sequence, play role in gene expression regulation and alternation? NOt present in histones. More than 90% of average human gene. INcrease w/ genomic size and complexity
Gene
Segment of DNA expressed to yield a functional product: e.i. rRNA, tRNA, polypeptide
During transcription
Gene transcribed from DNA template to make long RNA molecule, introns then removed by splicing. Only exons in mRNA
mRNA
Has Exons (introns removed during splicing)
3’ and 5’ untranslated regions (UTR’s)
Exons that are not translated into proteins
Prokaryotics
Don’t contain many introns only in rare genes.
Neated genes
proteins enocded by of a larger gene. Gene contained in the INtron of a larger gene. Encode pseudogenes or noncoding RNA’s: e.i. small nucleolar RNA’s/microRNAs
small nucleolar RNA’s
Function in ribosomal RNA processing
Intron coding
SOme encode proteins or RNAs. Others contain sequences that regulate transcription. First intron sometimes contains transcriptional regulatory sequences in genes. some sequences regulate splicing. Others Allow alternative splicing.
first 5’ UTR exon
sometimes contains transcriptional regulatory sequences in genes.
Noncoding RNA’s
rRNA’s, tRNA’s, miRNA’s, lncRNA’s. Splicing of pre-mRNA’s. Processing of ribosomal RNA.
RNA interference (RNAi)
Experimental tool. mediated by short doble-stranded RNA’s.(miRNA’s) Experimental tool used to block gene expression at translational level.
play key role in protein synthesis
play key role in protein synthesis
microRNA’s (miRNA’s)
22nucelotides L, found in introns in protein coding genes. Regulate cell prolifiration and survival (too many can cause cancer and <3) COme from longer folded RNA, cleaved by Drosha and Dicer. One strand put in RISC. RISC Targets mRNA’s. Inhibits translation and stimulates RNA degradation
RNA induced silencing complex (RISC)
Targets mRNA’s with help of miRNA
Long non-coding RNA’s (lncRNA’s)
non-coding RNA’s > 200 nucleotides. MAjor regulators of gene expression. X chromosome inactivation, Xist
X chromosome inactivation
When one of the X chromosomes genes for females gets inactivated for dosage compensation by Xist
Xist
Blocks transcription
Repetitive sequences
simple-sequence repeates, DNA transposons,Retrotransposomes (SINE,LINE,retro-virus like elements)
simple-sequence repeates
tandem arrays of thousands of copies of short sequences: e.i. alpha satellite DNA. Not transcribed, no functional genetic info.
Short interspersed elements (SINE’s)
100-300bp
Long interspersed elements (LINE’s)
4-6Kb more common
Transposable elements
SINE, LINE. capable of moving to diferent parts of DNA. played major role in genome evolution
Retrotransposome
Transposition mediatied by reverse transcription. ex: SINE is on site—>transcribed RNA—->back DNA by reverse trans in new site. (retrovirus-like elements)
DNA transposons
Move through genome by being copied and reinserted as DNA sequences
Reverse transcriptase
Encoded by Retrovirus, retrovirus-like elements, LINE’s,
Retrovirus-like elements
Retrotransposome, Reverse transcriptase, integrase
Gene duplication
Caused by duplicatino of a DNA segment oe by reverse transcription
pseudogenes
inactive gene copies of gene families, inactivated by mutation
gene families
Distinct members of a group of related genes. that may be transcribed in differet tissues or at different stages of development. Arisen by duplication of ancestral genes.
