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genetics > chapter 8 part 3 > Flashcards

chapter 8 part 3 Flashcards

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Biology 101 flashcards
1
Q

do exons or introns become part of the mature mRNA?

A

exons

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2
Q

what do exons do?

A

they encode protein segments

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3
Q

are introns common in bacterial genes?

A

no, but they are common in eukaryotic genes and occasionally found in archael genes

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4
Q

what are introns most common in?

A

eukaryotes

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5
Q

what are the most common type of intron?

A

pre-mRNA transcript introns

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6
Q

what are the most common type of introns removed by?

A

the spliceosome complex

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7
Q

what are other types of introns removed by?

A

self-splicing or a different enzymatic process

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8
Q

does intron splicing require a lot of precision or not a lot of percision?

A

it requires a lot of precision since it has to remove the intron nucleotides accurately

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9
Q

what is the presence of intron sequences demonstrated by?

A

a technique called R-looping

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10
Q

do regions of the DNA where introns are present have a complementary region within the mRNA?

A

No, they loop out visibly since they dont have any complementary regions

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11
Q

what does the 5’ splice site contain?

A

a conensus sequence with an invariant GU dinucleotide at the 5’- most end of the intron

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12
Q

the 3’ splice site at the oppostite end of the intron has a how many long nucleotide consensus sequence with a what region?

A

11, pyramadine rich and a nearly invariant AG at the 3’ most end

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13
Q

where is the branch site?

A

20 ti 40 nucleotides upstream of the 3’ end of the intron

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14
Q

facts about the branch site

A

it is pyrimidine-rich and contains an invariant adenine called the branch point adenine near the 3’ end of consensus

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15
Q

what are introns removed from the pre-mRNA by?

A

an snRNP-protein complex called the spliceosome

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16
Q

what is cleaved first in introns and what is formed?

A

the 5’ splice site
lariant intron structure is formed when the 5’ intron end binds to the branch point adenine

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17
Q

what is cleaved second in intreons and what happens?

A

the 3’ splice site and the exon ends are ligated together

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18
Q

are introns removed one by one?

A

yes, but they arent really removed in order

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19
Q

composition of the spliceosome

A

a large complex of multiple snRNPs (small nucleur ribonucleoprotein particles)
-snRNPs u1 through u6
-composition is dynamic -it changes throughout the steps

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20
Q

what re the spliceosome components recruited by?

A

the SR proteins

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21
Q

what do SR proteins bind to and what do they do?

A

they bind to a sequence in exons called exonic splicing enhancers (ESEs) and ensure accurate splicing

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22
Q

what splice sites are spliceosomes recruited to?

A

5’ to 3’ sites by the SR proteins

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23
Q

what functions as an assembly platform and regulator of pre-mRNA processing machinery?

A

the carboxyl terminal domain (CTD) of RNA pol II

24
Q

what does the the carboxyl terminal domain (CTD) of RNA pol II

A

functions as an assembly platform and regulator of pre-mRNA processing machinery

25
Q

do large eukaryotic genomes express more proteins than there are genes in the genome?

A

yes

26
Q

how many polypeptides do human cells produce and how many genes are contained?

A

100,000
about 22,000 genes

27
Q

what explains the facts that eukaryotic genomes express more proteins than there are genes in the genome?

A

-pre-mRNA can be spliced in alternative patterns in different cell types
-alternative promoters can initiate transcription at distinct start points
-alternative sites for polyadenylation can produce different mature mRNAs

28
Q

what do the three transcription-associated mechanisms that explain why more proteins are expressed than genes in the genome compromise?

A

alternative pre-mrna processing

29
Q

what percent of human genes are thought to undergo alternative splicing?

A

70%

30
Q

what gene has one of the most complex patterns of alternative splicing?

A

Drosophila Dscam gene

31
Q

how many exons in the Drosophila Dscam gene?

A

24 exons

32
Q

how many different polypeptides can be produced through alternative splicing in the Drosophila Dscam gene?

A

38,000

33
Q

when do we use alternative promoters?

A

when more than one sequence upstream of a gene can initiate transcription

34
Q

what does alternative polyadenylation require?

A

more than one polyadenylation signal in a gene

35
Q

what are alternative promoters of polyadenylation controlled by?

A

variable expression of regulatory proteins in specific cell types

36
Q

what are group 1 introns

A

large, self splicing ribozymes that catalyze their own excision from some mRNAs

takes place via transesterification reactions that remove intron and ligate the exon ends together

37
Q

group II introns

A

these are also self-splicing ribozymes

form very complex secondary structures

self-splicing takes place in a lariant-like manner

38
Q

are bacteria and eukaryotes transcribed in large precursor molecules?

A

yes

39
Q

what happens to the large precursor molecules that are transcribed from bacteria and eukaryotic rRNAs?

A

they are cleaved into smaller molecules by removal of spacer sequences

40
Q

what forms the ribosome subunits?

A

the rRNAS folded up into complex secondary structures which join ribosomal proteins

41
Q

what chemical modifications occur after transcription is complete?

A

methylation

42
Q

is processing of tRNA the same in bacteria and eukaryotes?

A

no

43
Q

Some _________ tRNAs are produced
simultaneously with rRNAs, others are
transcribed as part of a large pre-tRNA
transcript and then cleaved into individual tRNA molecules

A

bacterial

44
Q

in prokaryotes or eukaryotes is each tRNA gene individually transcribed

A

in eukaryotes

45
Q

how many tRNAs do most organisms produce?

A

most produce about 30 to 40, but fewer than 61

46
Q

what happens due to a third-base wobble?

A

no more than 61 tRNAs

47
Q

do some eukaryotic genomes contain all 61 possible tRNA genes?

A

yes, some do. one for each codon

48
Q

explain bacterial tRNA Processing?

A

-bacterial trnas require processing before assuming their functional role
-many are cleaved from the large precursor transcript
-nucleotides are trimmed
=some nucleotides are chemically modified
-trans fold into a precise three-dimensional structures
-postranscriptional addition of bases

49
Q

what do eukaryotic tRNAS contain that are removed?

A

small introns

50
Q

RNA editing

A

responsible for post-transcriptional modifications to the nucleotide sequence of some mRNAS

51
Q

in one kind of RNA editing, uracils are added. what are they added with the assistance of?

A

guide RNA or gRNA

51
Q

what is a second type of RNA editing?

A

base substitution

52
Q

what is frequently replaced with base substitution?

A

cytosine with uracil

53
Q

what is base substitution seen in?

A

apolipoprotein B proteins from one gene in human liver and intestinal cells

54
Q

what does base substitution of the mRNA in intestinal cells produce?

A

a premature stop codon

55
Q

what protein multisubunit contains the TATA-binding protein

A

TFIID

genetics (23 decks)

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