Macromolecular Synthesis-Transcription and Translation Flashcards

1
Q

Transcription

A
  • bacteria regulate protein synthesis at level of Tc
  • mRNA in bacteria is generally unstable
  • RNA pol can initiate new strand synthesis
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2
Q

Architecture of a gene

A

Coding strand-the one that looks like the mRNA sequence (has the codon sequence)
Template strand-the one that is read

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3
Q

Tc Initiation (promoter and RNA pol)

A
  • 10 and -35 are promoter region
  • RNA pol (holoenzyme) consists of 5 subunits; alpha (2), beta, beta1, sigma, omega-6 proteins
  • core pol can synthesize RNA, core is w/o sigma factor
  • sigma helps RNA pol recognize the promoter (specificity)
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4
Q

Sigma Factors

A
  • sigma 70=housekeeping
  • alternate sigma factors recognize different promoter sequences
  • sigma54 is N related, different structure
  • sigma 32 turns on heat shock genes during stress
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5
Q

Promoter Strength

A

-closer to the consensus sequence, the stronger the promoter
-spacing b/w -10 and -35 is impt
-sequence of spacer region is sometimes impt
-control frequency and strength of pol binding
TTGACA–17–TATAAT=consensus promoter

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6
Q

Tc Initiation

A
  • polymerase binds promoter-closed complex
  • DNA unwinds to form open complex
  • holoenzyme can form open complex
  • ribonucleotides are incorporated beginning form Tc start site, not start codon
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7
Q

Elongation

A
  • sigma subunit dissociates

- DNA-RNA hybrid of 18 nt as polymerase synthesizes the mRNA–>Tc bubble

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8
Q

Termination-Intrinsic terminators (factor independent)

A
  • secondary structure in newly made message that results in pol dissociation
  • inverted repeats form hairpin
  • unfavourable for pol to bind to
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9
Q

Termination-Rho-dependent Terminators

A
  • rho binds to rut site on newly made message and moves up towards pol-DNA complex
  • pol reaches a rho-dependent termination sequence and stalls
  • rho catches up (through ATP hydrolysis) and releases RNA from elongation complex
  • rho acts together with sequence that stalls the polymerase
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10
Q

Operons

A
  • genes encoding for proteins w/ related functions are often clustered together into operons (eg. lactose operon contains genes involved in lactose metabolism)
  • one promoter is used to make a mRNA that will be translated into multiple proteins
  • polycistronic
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11
Q

Translation

A
  • ribosomes assemble on the mRNA
  • recruit charged tRNAs and from peptide bonds b/w the aa’s that the tRNAs bring
  • in bacteria Tc and TL are coupled
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12
Q

Ribosomes

A

-made of RNA and proteins
-small subunit binds mRNA
-large subunit provides enzymes needed to form peptide bonds
-binds 5’ end of mRNA, scans until it gets to 1st AUG
2 sites for charged tRNAs
-P (peptidyl) site
-A (aminoacyl) site

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13
Q

Translation Initiation

A
  • codons are paired w/ anticodon regions of tRNAs

- shine delgarno sequence (ribosome binding site) is recognized by the 16s RNA in small subunit of the ribosome (30s)

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14
Q

Degeneracy of the Genetic Code

A
  • multiple codons for the same aa
  • buffers the genome against mutations
  • changes in the 1st and 2nd position can cause mutations
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15
Q

Aminoacyl-tRNA Synthetases (AARSs)

A
  • attach the correct aa to the tRNA

- 1st aa is formulated-methionine (f-Met)

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16
Q

Translocation

A
  • peptide bond is formed b/w tRNA at A site and peptidyl-tRNA in P site
  • uncharged tRNA leaves P site
  • ribosome moves along the message to the new A site
  • need GTP
17
Q

TL Termination-release factors

A

RF 1-recognizes UAG, UAA
RF2-recognizes UGA, UAA
-release factors bind stop codons
-dislodge growing polypeptide chain, ribosome disassembles

18
Q

Common Themes in Macromolecular Synthesis

A
  1. Initiation-protein machines recruited by specific sequences in the nucleic acid
  2. Elongation
  3. Termination-specific sites on nucleic acids act to disassemble the protein machines, often by recruiting specific proteins (Tus, Rho)