Exam 4: Lecture 1 Flashcards

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1
Q

Translation

A

-tasked with transferring mRNA transcript sequence into protein sequence

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2
Q

Ribosome Subunits

A
  • consists of small subunit and large subuinit
  • each subunit consists of multiple different proteins
  • both associated with non-coding RNAs (ncRNA)
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3
Q

ncRNA

A

-aids in stabilizing interactions with mRNA transcript

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4
Q

Translation Brief Process

A
  • mRNA transcript bound by small ribosomal subunit
  • initiator tRNA bound to modified Methionine (fMet) brought into contact with first AUG codon of coding sequence
  • large ribosomal subunit added to complex
  • complete ribosome reads transcript 5’ to 3’ and generates appropriate protein sequence
  • process repeated till mRNA transcript is degraded
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5
Q

Polysomes/Polyribosomes

A
  • multiple ribosomes that bind each mRNA transcript
  • increases amount of protein produced prior to degradation because multiple ribosomes are simultaneously translating mRNA
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6
Q

Increasing Protein Production

A
  • mRNA transcript organized into circular structure
  • 5’ UTR and 5’ CAP structure bound initiation factors that interact with Poly-A Binding Protein which is bound to 3’ Poly-A tail
  • circular conformation protects ends from degradation and can be translated by multiple ribosomes for longer period of time than linear mRNA (prefer to degrade single stranded DNA)
  • eventually falls apart
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7
Q

Ribosome Composition

A
  • small and large subunit

- subunits composed of many individual proteins

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8
Q

Centrifugation

A
  • used in early attempts to understand ribosome structure
  • intact ribosomes placed in sucrose solution and spun at high velocities
  • size of protein complex directly proportional to sedimentation velocity
  • i.e. intact ribosome travels faster through gradient than small or large individual subunits
  • likewise large subunit sediments at higher velocity than smaller
  • after isolated, further disrupted to yield individual proteins sequenced by Fred Sanger’s methods
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9
Q

A, P, and E sites

A
  • three channels for tRNA binding within ribosome
  • initiator tRNA recruited to P site where it interacts with first AUG within coding region of mRNA transcript
  • once initiator tRNA and AUG codon intact with P site, large subunit recruited
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10
Q

Alignment

A
  • Aligning first codon with P site automatically ensures second codon aligned with A site
  • second tRNA enters ribosome and interacts with transcript via A site
  • peptide bond forms between first two amino acids then ribosome moves to next codon.
  • moves initiator tRNA into E pocket where it’s ejected
  • second tRNA moves into P pocket leaving empty A pocket
  • each subsequent tRNA enters ribosome through A site to interact with mRNA
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11
Q

Translation Initiation Sequences

A
  • ribosome must be recruited to 5’ end of mRNA transcript
  • prokaryotes: Shine-Dalgarno sequence located 3-9 bases upstream first AUG
  • eukaryotes: Kozak sequence encompasses few bases upstream and downstream AUG
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12
Q

Binding to Initiation Sequences

A
  • after binding to sequences AUG placed in P pocket
  • non-coding ribosomal RNAs associated with small ribosomal subunit important in interacting with mRNA and for ensuring first AUG aligned with P pocket
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13
Q

Initiation of Prokaryotic Translation: Blocks on Sites

A

-initiation factors bind to E and A sites to block initiator tRNA from entering

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14
Q

Initiation of Prokaryotic Translation

A
  • steps after blocking
  • mRNA and initiator RNA recruited to small ribosomal subunit
  • contact between ribosome and mRNA mediated by RNA:RNA interactions
  • 16S ribosomal RNA base pairs with Shine-Dalgarno sequence in mRNA
  • 5-9 base sequence that allows just enough space for AUG to be in P pocket which ensures AUG’s position
  • large ribosomal subunit recruited to make complete ribosomal unit
  • anticodon of initiator tRNA makes contact with AUG codon in P pocket begins elongation
  • IF’s (1 and 3) removed from A and E pockets
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15
Q

Length of Sequence for Alignment

A
  • too long, AUG won’t line up in P pocket (may be in A pocket or completely out of ribosomal subunit)
  • too short also causes problems
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16
Q

Differences in Eukaryotic Translation

A
  • initiator tRNA recruited to small ribosomal subunit independently of mRNA transcript
  • recruitment of transcript does not ensure alignment of initiator
17
Q

Similarities between Prokaryotic and Eukaryotic Translation

A
  • number of initation factors required to displace large ribosomal subunit and to block E and A channels
  • leaves P channel only one open for tRNA
18
Q

Translation Elongation (study example in notes)

A
  • subsequent tRNAs (after initiator) enter A pocket
  • second codon enters and codes for amino acid
  • tRNA attached to that protein recruited to A pocket where anticodon pairs with the codon
  • Met transferred to tRNA containing the amino acid coded for and a peptide bond will form between the Met and other amino acid
  • ribosome moves over slightly moving AUG codon into E pocket and the subsequent is in P pocket and third is in A pocket
  • empty tRNA in E pocket expelled and A pocket is filled by tRNA that base pairs with codon
  • process repeated again and again until ribosome reaches stop codon
  • then dissociates from mRNA and nascent protein is released
19
Q

Eukaryotic Translation

A
  • ready to interact with mRNA transcript when pre-initiation complex has formed
  • 5’ end of mRNA bound by IFs that interact with IFs bound to small ribosomal subunit
  • recruitment of mRNA to small ribosomal subunit does not result in alignment of initiator AUG in P pocket (difference)
  • small ribosomal subunit moves along mRNA until it finds AUG which is recognized when anticodon of tRNA bases pairs with initiator codon
  • initiator codon:anticodon binding stabilized, large ribosomal subunit recruited to make complete ribosome
  • IF blocks expelled from E and A pockets and elongation begins