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genetics > chapter 8 part 3 > Flashcards

chapter 8 part 3 Flashcards

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Biology 101 flashcards
1
Q

what part of the mRNA transcript becomes the mature mRNA

A

exons

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2
Q

are introns in bacterial genes?

A

rarely - not really

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3
Q

are there introns in archaeal gene?

A

occasionally

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4
Q

2 methods for removing introns

A
  1. spliceosome complex
  2. self-splicing
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5
Q

how are group I and II introns removed

A

self-splicing

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6
Q

how are pre-mRNA introns removed

A

spliceosome complex

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7
Q

how are rRNA and tRNA introns removed

A

enzymatic activity

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8
Q

why does intron splicing have to be precise?

A

to remove nucleotides accurately, errors would lead to inccorect protein sequences

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9
Q

who is responsible for the discovery of “split genes”

A

Roberts and Sharp - 1993 Nobel prize

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10
Q

R-looping

A

DNA gene is isolated, denatured, and hybridized to mature mRNA from the same gene
- regions of DNA where introns are present have no complementary region within the mRNA and loop out visibly

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11
Q

intron splicing signals

A
  • 5’ splice site
  • 3’ splice site
  • branch site
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12
Q

5’ splice site

A

has consensus sequence with an invariant GU dinucleotide

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13
Q

3’ splice site

A

11 nucleotide consensus w/ pyrimidine-rich region and nearly invariant AG

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14
Q

branch site

A

20-40 nucleotides upstream of 3’ end of intron
- pyrimidine-rich
- contains invariant adenine called branch point adenine near 3’ end of consensus

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15
Q

splicing action of spliceosome

A
  • 5’ splice site cleaved first
  • variant intron structure formed when 5’ intron binds to branch point adenine
  • 3’ splice site cleaved
  • exons ligated together
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16
Q

are introns always removed by the spliceosome in order?

A

no

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17
Q

composition of spliceosome

A

small nuclear ribonucleoprotein particles (snRNPs U1-U6)

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18
Q

is the composition of spliceosome steady?

A

no, always changing through steps of splicing

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19
Q

how are spliceosome components recruited to splice sites

A

SR proteins that bind to exotic splicing enhancers to ensure accurate splicing

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20
Q

what is the function of the carboxyl terminal domain (CTD) of RNA polymerase II?

A

assembly platform and regulator pre-mRNA processing machinery

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21
Q

gene expression machines

A

proteins that carry out capping, intron splicing, and polyadenylation associate with CTD of pol II

22
Q

CTD and RNase

A

degrades residual transcript resulting from 3’ cleavage and trigger termination of transcription

23
Q

how many proteins are produced for one gene

A

can be many due to alternative mRNA processing

24
Q

3 transcription-associated mechanisms that explain more proteins than genes

A
  1. pre-mRNA spliced in alternative patterns
  2. alternative promoters can initiate transcription at different start points
  3. alternative sites for polyadenylation
25
Q

how many human genes are thought to undergo alternative splicing

A

70%

26
Q

human calcitonin/calcitonin gene-related peptide and alternative splicing

A
  • gene has 6 exons, 2 alternative polya sites
  • thyroid cells: exon 4 polya site to produce calcitonin
  • neuronal cells: splice exon 4, use exon 6 polya site to produce CGRP
27
Q

Drosophila Dscam gene

A
  • 24 exons: 4, 6, 9, and 17 have alternative sequences
  • more than 38,000 dif polypeptides can be produced
28
Q

alternative promoters

A

occur when 1+ sequence upstream of a gene can initiate transcription

29
Q

alternative polyadenylation

A

requires 1+ polyadenylation signal in a gene

30
Q

group I introns and self-splicing

A

takes place via 2 transesterification reactions that excise intron and ligate exon ends

31
Q

what are group I and group II introns?

A

large, self-splicing ribozymes that catalyze own excision
- group I: bacteria, simple eukaryotic, plants
- group II: archaea, bacteria, mitochondrial and chloroplast

32
Q

group II introns and self-splicing

A

form very complex secondary structures and their self-splicing takes place in a lariat-like manner

33
Q

how are bacteria and eukaryotic rRNAs transcribed?

A

in large precursor molecules that are cleaved into smaller molecules by the removal of spacer sequences between the rRNA genes

34
Q

what do rRNAs do after processing

A

fold into complex secondary structures and join ribosomal proteins to form ribosomal subunits

35
Q

what do all tRNAs have in common?

A

similar structure, but dif nucleotide sequences

36
Q

overview of bacterial tRNA production

A

some produced simultaneously with rRNAs, others transcribed as large pre-tRNA transcript and cleaved into ind. molecules

37
Q

overview of eukartyouic tRNA production

A

each tRNA gene individually transcribed

38
Q

how many organisms do tRNAs usually produce?

A

30-40, fewer than 61 due third-base wobble

39
Q

what do bacterial tRNAs required before assuming their function role?

A

processing

40
Q

processing of bacterial tRNAS

A
  • CLEAVAGE from large precursor molecule to small
  • TRIM nucleotides from 3’ and 5’ ends
  • CHEMICALLY MODIFY certain nucleotides
  • fold into 3D STRUCTURE
  • postranscriptional ADDITION of bases (CCA at 3’ end)
41
Q

3D structure of tRNA

A

4 double-stranded stems, 3 of which capped by single-stranded loops

42
Q

do eukaryotic tRNAs undergo processing?

A

yes, may also include small introns that are removed

43
Q

RNA editing

A

responsible for post-transcriptional modifications to nucleotide sequence and protein produced of some mRNAs

44
Q

guide RNA

A

takes part in a kind of RNA editing, and adds uracils to mRNA

45
Q

base substitution

A

replacing one base with another

46
Q

frequent base substitution

A

replacing cytosine with uracil

47
Q

example of base substitution

A

production of 2 different apolipoprotein B proteins from single gene in human liver and intestinal cells
- intestinal: produces premature stop codon, produces smaller protein than liver

48
Q

cis-splicing

A

connecting exons from single mRNA

49
Q

trans-splicing

A

connecting exons from multiple different mRNAs

50
Q

intragenic splicing

A

exons from single mRNA, often repeated exons

51
Q

intergenic splicing

A

exons from more than 1 type of mRNA

genetics (47 decks)

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