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Genetics - BIO 2306 > Ch 14 RNA Molecules & RNA Processing > Flashcards

Ch 14 RNA Molecules & RNA Processing Flashcards

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1
Q

RNA coding regions

A

exons

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2
Q

RNA noncoding regions (intervening sequences)

A

introns

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3
Q

are introns more common in eukaryotes or bacteria?

A

introns are more common in eukaryotes

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4
Q

sequence of 3 nucleotides that encode an amino acid of a protein

A

codon

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5
Q

bacterial mRNA structure

A

5’ untranslated region (5’ UTR) (w/ Shine-Dalgarno sequence)
protein-coding region
3’ untranslated region (3’ UTR)

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6
Q

sequence of nucleotides at 5’ end of mRNA that do not encode any amino acids

A

5’ untranslated region (5’ UTR)

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7
Q

consensus sequence in bacterial mRNA only within 5’ UTR
serves as ribosomal binding site

A

Shine-Dalgarno sequence

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8
Q

codons that specify protein amino acid sequence from start to stop codon

A

protein-coding region

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9
Q

sequence of nucleotides at 3’end of mRNA that do not encode any amino acid
affects mRNA stability and regulates mRNA’s protein-coding sequence translation

A

3’ untranslated region (3’ UTR)

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10
Q

three steps of pre-mRNA processing in eukaryotes

A
  • addition of 5’ cap
  • addition of 3’ poly(A) tail
  • removal of introns
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11
Q

why is there no pre-mRNA processing in prokaryotes?

A

transcription and translation occur simultaneously, and there is no pre-mRNA

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12
Q

describe the addition of 5’ cap process

A
  • one of the three phosphates at the 5’end of mRNA is removed
  • guanine nucleotide added
  • methyl groups added
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13
Q

function of the addition of 5’ cap

A
  • facilitates binding of 5’ ribosome to 5’ end of mRNA
  • increases mRNA stability
  • influences intron removal
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14
Q

describe the addition of poly(A) tail process

A
  • pre-mRNA cleaved downstream of consensus sequence AAUAAA in 3’UTR
  • adenine nucleotides (polyadenylation) added to 3’ end of pre-mRNA
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15
Q

50-250 adenine nucleotides added to 3’ end of pre-mRNA

A

poly(A) tail

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16
Q

what is the polyadenylation signal

A

consensus sequence AAUAAA located upstream of cleavage site
sequence rich in uracil located downstream of cleavage site

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17
Q

function of addition of poly(A) tail

A
  • increases stability of mRNA
  • facilitates ribosome attachment to 5’ cap
  • helps exports mRNA to cytoplasm
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18
Q

removal of introns

A

RNA splicing

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19
Q

where does splicing occur?

A

in the spliceosome in the nucleus

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20
Q

what does the spliceosome consist of

A

five snRNAs (U1, U2, U4, U5, U6) combining with proteins to form 5 snRNPs, along with hundreds of other proteins

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21
Q

what are the three sequences in an intron that are present for splicing to occur

A

5’ splice site
3’ splice site
branch point

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22
Q

5’ end of intron

A

5’ splice site

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23
Q

3’ end of intron

A

3’ splice site

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24
Q

adenine nucleotide 5’ and 3’ splice sites

A

branch point

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25
Q

what would happen if the adenine nucleotide (branch point) of an intron was deleted?

A

splicing would not occur

26
Q

describe pre-mRNA splicing

A
  1. pre-mRNA cut at 5’ splice site
    - 5’ end of intron attaches to branch point to form lariat
  2. pre-mRNA cut at 3’ splice site
    - lariat branching enzyme breaks bond at branch point and lariat is released
    - intron is degraded by nuclear enzymes
    - exons spliced together
27
Q

one pre-mRNA processed in different ways to produce different types of mRNA

A

alternative RNA processing

28
Q

what’s the purpose of alternative splicing?

A

pre-mRNA spliced in more than one way to yield different mRNAs –> diff amino acids –> diff proteins

29
Q

what’s the purpose of multiple 3’ cleavage sites?

A

3’ cleavage could occur at different locations and therefore produce different proteins

30
Q

two parts of addition of poly(a) tail

A

cleavage
polyadenylation

31
Q

coding sequence of mRNA molecule altered AFTER transcription

A

RNA editing

32
Q

RNAs that contain partly complementary sequences to unedited RNA

A

guide RNAs (gRNAs)

33
Q

describe RNA editing

A
  • unedited mRNA pairs with guide RNA
  • Guide RNA serves as template for addition, deletion, or alteration of bases
  • mature mRNA released
34
Q

carries specific amino acid to ribosome to be incorporated into growing polypeptide chain

A

tRNA

35
Q

how do modified bases arise?

A

t-RNA-modifying enzymes chemically change a nucleotide base after transcription

36
Q

describe structure of tRNA

A
  • cloverleaf structure due to complementary base pairing
  • acceptor arm
  • TΨC arm
  • anticodon arm
  • DHU arm
37
Q

what is the acceptor arm

A

stem formed from 5’ and 3’ ends base pairing, and contains CCA, which is where amino acid attaches

38
Q

what is the TΨC arm

A

contains thymine, pseudourine, and cytosine

39
Q

what is the anticodon arm

A

comprises three bases (anticodon) and interacts with codon in mRNA

40
Q

describe tRNA processing

A

tRNA may undergo cleavage, splicing, base addition, and base modification

41
Q

complex where genetic instructions of mRNA are translated into amino acid sequence of polypeptides

A

ribosomes

42
Q

structure of ribosomes

A

protein + rRNA
large ribosomal subunit and small ribosomal subunit

43
Q

describe prokaryotic rRNA processing

A

each rRNA gene transcribed into 30S rRNA precursor, which is methylated, cleaved, and trimmed

44
Q

describe eukaryotic rRNA processing

A

snoRNAs associate with proteins to form snoRNPs, which help to cleave, modify, and assemble into mature rRNA

45
Q

defense mechanism to limit invasion of foreign genes by controlling expression of their own genes

A

RNAi (RNA interference)

46
Q

what triggers RNAi?

A

double-stranded RNA molecules

47
Q

chops up double stranded RNA to produce miRNAs or siRNAs

A

dicer

48
Q

how do dsRNA arise?

A
  • inverted repeats in RNA base pair with self to form dsRNA
  • two complementary RNA pair to form dsRNA
  • infection from viruses form dsRNA
49
Q

describe miRNAs (origin, cleavage of, complementarity, action, target)

A
  • cleaved from RNA transcribed from distinct gene
  • form from cleavage of single-strand RNA that forms short hairpins
  • limited complementarity with target mRNAs
  • inhibit translation
  • target genes different than those from which they were transcribed
50
Q

describe siRNAs (origin, cleavage of, complementarity, action, target)

A
  • cleaved from mRNA, transposons, RNA viruses
  • form from cleavage of RNA duplex of 2 diff RNA or ssRNA that form long hairpins
  • exact complementarity with target RNA or DNA
  • degrade mRNA
  • target genes from which they were transcribed
51
Q

miRNAs and siRNAs combine with proteins to form

A

RNA-induced silencing complex (RISC)

52
Q

describe how miRNAs are used for RNAi

A
  • transcription of an inverted repeated produces primary miRNA, which is cleaved to produce RNA with hairpin
  • dicer chops up terminal loop of hairpin
  • miRNA + proteins = RISC
  • RISC pairs with mRNA to inhibit translation
53
Q

describe how siRNAs are used for RNAi

A
  • double stranded RNA cleaved by dicer to produce siRNAs
  • siRNAs + proteins = RISC
  • RISC pairs with and cleaves mRNA, leading to degradation
54
Q

series of palindromic sequences separated by spacers

A

CRISPR array

55
Q

what do CRISPR RNAs do?

A

combine with Cas proteins to provide defense against invasion of foreign DNA

56
Q

describe the CRISPR-Cas system

A

aquisition
expression
interference

57
Q

foreign DNA enters cell, identified, processed, and inserted into CRISPR array as a new spacer and serves as a memory

A

aquisition

58
Q

CRISPR array transcribed into long precursor RNA; cleaved by Cas proteins; processed into crRNAs (each with a foreign DNA spacer sequence)

A

expression

59
Q

crRNA + Cas protein

A

effector complex

60
Q

foreign DNA enters cell again; effector complex binds and cleaves foreign DNA

A

interference

Genetics - BIO 2306 (20 decks)

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