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Applied Genetics > Introns > Flashcards

Introns Flashcards

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1
Q

what are introns

A

non-coding sequences in gene, not in mature mRNA and they interrupt coding sequence

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2
Q

what are Lariats

A

discarded bioproducts of RNA splicing

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3
Q

what are snRNPs

A

small nuclear ribonuceloproteins

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4
Q

what is a spliceosome

A

molecular machine that removes introns

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5
Q

what are endonucleases

A

enzymes that internally cut DNA

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6
Q

what are consensus sequences

A

calculated order of most frequent residues (nt, nucleotides or aa) found in a sequence alignment at each position

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7
Q

what are enhancers

A

short region (50-1500bp) of DNA that can bind to activator proteins, trigger transcription gene

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8
Q

what is alternative splicing

A

allows DNA to code for more than one protein by varying exons in mRNA

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9
Q

what are protein domains

A

regions in proteins that fold up in semi-independent way and have independent function

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10
Q

what is a transposon

A

genetic element that ‘jumps’ to different locations in genome – jumping genes

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11
Q

what is illegitimate recombination

A

when recombination happens despite little or no sequence homology presence

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12
Q

what is exon shuffling

A

molecular mechanism that allow new gene formation

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13
Q

how many different types of introns are there

A

4

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14
Q

where and what is group 1 introns splicing mechanism

A

found in nuclear, mitochondrial and chloroplast genes coding for rRNAs, mRNAs and tRNAs

  • No ATP
  • Splicing needs transesterification reaction steps
  • Introns self-splice
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15
Q

where and what is group2 introns splicing mechanism

A

found in primary transcripts of mitochondrial, chloroplast mRNAs in fungi, algae and plants. A lariat is formed before splicing occurs

  • No ATP
  • Splicing needs transesterification reaction steps
  • Introns self-splice
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16
Q

where and what is group 3 introns splicing mechanism

A 
largest class of introns. In nuclear mRNA primary transcripts. A lariat is formed and a RNA-protein complex of nuclear ribonucleoproteins (SnRNPs) is needed. RNA is called small nuclear RNA (snRNA and there are 5 units: U1-U6, no U5)
- Need ATP
17
Q

where and what is group 4 introns splicing mechanism

A

in certain tRNAs. Splicing endonuclease cleaves phosphodiester bond at both ends of intron. Two exons joined by mechanism similar to DNA ligase reaction

  • Need ATP
  • Splicing needs an endonuclease
18
Q

what is intron structure like

A

starts with GU (5’ donor) ends with AG (3’ acceptor)
Sequences next to GU and AG and also third sequence in middle (branch point) all similar in each intron (they’re consensus sequences)
- GU and AG are the recognition points
Branch point is a fixed distance from 3’ end

19
Q

what is the splicing of introns and alternative splicing like

A

spliceosome cuts introns and re-join exons in mRNA consists of several RNAs (U1, U2, U4, U5, U6) and also several proteins

20
Q

what percent does alternative splicing occur in genes

A

40% human genes

21
Q

how many proteins can a cell encode for with one gene in alternative splicing, where is spliced

A
  • cell can encode many related proteins with one gene
  • intron boundaries that are spliced decided by protein factors that bind to intron boundaries and either help or hinder spliceosome cutting
22
Q

what is the impact of alternative splicing 5UTR’

A

enhancer regulatory element

lead to altered translation and change in protein expression levels

23
Q

what must sometimes happen for proteins to become functional

A

need to be processed to become functional

  • Phosphorylation
  • Glycosylation
  • Methylation
  • Sometimes cleavage – cut bit of protein to be functional
24
Q

what is the evolution of introns

A

early evolution, proteins may have been small, simple functions
introns might have made it easier for DNA sequences encoding individual protein domains to be joined together in many different combinations

25
Q

what does exon shuffling form and what occurs during

A

molecular mechanism, form new genes
two or more exons from different genes can be brought together ectopically, or the same exon can be duplicated to create new exon-intron structure

26
Q

what are the three mechanisms for exon shuffling

A
  1. Transposons mediated exon shuffling
  2. Crossover during sexual recombination of parental genomes
  3. Illegitimate recombination
27
Q

impact of alternative splicing Protein coding sequence

A

altered protein structure and function, change in protein ratios

28
Q

impact of alternative splicing 3UTR’

A

stabilising domain

mRNA instability, change in protein expression levels

Applied Genetics (20 decks)

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