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Integrated Systems 1 > RNA > Flashcards

RNA Flashcards

1
Q

Biological roles of RNA

A

Transmission of genetic info Storage of genetic info (retroviruses) Catalysis and structural components of large macromolecules (ex rRNA and snRNA) Gene regulation (miRNA/siRNA)

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2
Q

What is the mRNA sequence for this gene

5’ACGTCGTCC3’

3’TGCAGCAGG3’

A

5’ACGTCGTCC3’ the gene, coding strand, sense strand

3’TGCAGCAGG3’ non-coding, antisense, template strand

ACGUCGUCC mRNA

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3
Q

mRNA

A
  • Selected regions are transcribed from DNA to mRNA
  • Nucleotide triplets in mRNA (codons) pair with tRNA to code for specific AA
  • Prokaryotic mRNA is polycistronic (contains infor for more than one polypeptide chain)
  • Eukaryotic mRNA is monocistronic (info for only one polypeptide chain)
  • 3’ poly A tail
  • 5’ cap of methyl guanosine
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4
Q

tRNA

A
  • 73-93 nucleotides
  • Functions in translation of genetic info from mRNA into proteins
  • Highly structured
    • Acceptor Stem: site where specific AA is linked
    • Anticodon loop: Base pairs with codon on mRNA
    • Unique nucleotide bases: dihydrouridine, ribothymine, inosine, pseudouridine
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5
Q

rRNA

A
  • Ribosome is 65% protein and 35% protein
  • rRNA: 5s, 16s, 23s prokaryotes
  • rRNA is the catalytic site of the ribosome
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6
Q

Gene definition and its transcription

A

A gene is a segment of DNA that functions to generate RNA

Transcribed region of a gene contains the template for RNA synthesis

For mRNA the transcribed region contains the protein coding sequence

Transcription of a gene can proceed in either direction depending on which strand is the template strand

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7
Q

Prokaryotic RNA polymerases

A
  • Synthesize RNA using the template strand of DNA
  • Synthesize RNA 5’–>3’ and DONT require a primer
  • DO NOT have exonuclease activity
  • Core enzyme consis of alpha2betabeta’
  • Holoenzyme is core enzyme (RNA Poly) plus sigma
  • Different sigma subunits confer promoter specificity
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8
Q

Promoters definition

A
  • Binding sites in DNA where transcription begins
  • Regulatory region of DNA generally located upstream of coding sequence (5’ to start of gene)
  • Contains DNA consensus (-35 and -10 elements) sequences that are recognized by RNA polymerase
  • Consensus sequence is a sequence that is most commonly found in a given region when multiple sequences are aligned
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9
Q

Initiation

A
  • RNA Poly cannot initiate transcription on its own
  • Sigma subunit must first bind to the prokaryotic DNA promoter
  • Sigma and RNA poly together form a holoenzyme
  • Sigma works as a regulatory protein guiding RNA polymerase to specific promoter sequences on the DNA template strand
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10
Q

Initiation continues

A

Sigma opens the DNA helix, transcription begins

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11
Q

Initiation is complete and the next 3 steps

A

Sigma releases, mRNA synthesis continues

Elongation

Hairpin forms

Termination

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12
Q

Eukaryotic Transcription more complex because

A
  • Transcription factors instead of sigma factors
  • Complex promoters and regulatory regions
  • 3 RNA polymerases
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13
Q

Eukaryotic RNA polymerases

A
  • RNA poly I
    • preribosomal RNAs (pre-rRNAs): 18s rRNA, 5.8 rRNA, 28 rRNA
  • RNA poly II
    • mRNAs
  • RNA poly III
    • tRNAs and 5s rRNA
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14
Q

Eukaryotic RNA processing

A
  • Eukaryotic rRNAs tRNAs and mRNAs are processed (prokaryotic mRNAs arent)
  • Primary transcript is the linear, unprocessed RNA
  • Eukaryotic mRNA processing takes place in the nucleus prior to mRNA translation in the cytoplasm
  • Processing includes
    • 5’ capping
    • intron splicing
    • 3’ polyadenylation
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15
Q

rRNA processing

A

Preribosomal RNAs are cleaved by ribonucleases to give intermediate sized pieces of rRNA

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16
Q

tRNA processing

A
  • 3’ urasil residues replaced by the CCA sequence found in all mature tRNA
  • A 16 nucleotide sequence at the 5’ end is cleaved by RNase P
  • A 14 nucleotide intron in the anticodon loop is removed
  • Many bases are converted to characteristic modified bases
17
Q

mRNA processing 3 events

A
  • 5’ capping
  • 3’ adenylation
  • Intron splicing
18
Q

5’ mRNA capping

A
  • 5’ capping with a modified guanosine is important for
    • Stability of message (protection from ribonucleases)
    • Exit from nucleus
    • Promoting efficient translation of mRNA to protein
19
Q

Polyadenylation

A
  • Addition of A’s to 3’ end
  • Important for transcription termination
    • translation
    • mRNA stability
    • Nuclear export mRNA
  • Requires endonuclease and polyadenylate polymerase
  • Pol II synthesizes RNA beyond a cleavage site
  • Cleavage signal sequence (AAUAAA) is 20-30 nucletides upstream of cleavage site and is bound by an ezyme complex
20
Q

Intron Splicing

A
  • Pre-mRNA is spliced to remove introns
  • Introns are non-coding intervening sequences
  • Zero to dozens of introns in a eukaryotic mRNA
  • Range in size 50-20,000 nucleotides
  • More DNA devoted to introns than to protein coding exons
21
Q

Intron Splicing steps

A
  • Occurs in spliceosome
  • Spliceosome functions to recognize intron/exon boundaries and cuts/pastes exons
  • Splieosome composed of assembled
    • small nuclear RNAs (snRNA)
    • Small nuclear ribonucleoproteins (snRNP):
      • snRNAs complexed with proteins
22
Q

Alternative Splicing

A
  • Production of two or more distinct proteins from a single protein
  • Individual genes express multiple mRNAs (multiple proteins)
  • Up to 59% of gene generate multiple mRNAs
  • 80% of alternatively spliced mRNAs produce proteins that vary in amino acid sequence
23
Q

RNA dependent synthesis of RNA and DNA

A
  • Reverse transcriptase
    • Synthesizes DNA from viral RNA
    • Synthesizes complementary DNA resulting in dsDNA
    • Extremely error prone and mutations arise at a high rate, leading to drug resistance

Integrated Systems 1 (7 decks)

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