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Biochemistry MBS > Protein Synthesis > Flashcards

Protein Synthesis Flashcards

1
Q

common structure of all peptides

A
  • R group
  • amino group
  • carboxyl group
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2
Q

ribosomes

human subunits

A

sites of polypeptide assembly
-60s and 40s make a 80s subunit
found either free in cytoplasm or bound to ER

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3
Q

when is RNA to be made into a protein exported into the cytoplasm?

A

after it has been processed
-capped,
poly a tail
spliced

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4
Q

composition of mRNA from 5’ to 3’

A

cap, 5’UTR, coding region, 3’UTR, poly A tail

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5
Q

codon

-degenrative nature of mRNA

A
  • a group of 3 bases
  • there are more than one codon per amino acid
  • code is universal
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6
Q

tRNA structure

  • length
  • secondary structure
  • acceptor and anticodon location and relation
  • acceptor sequence
  • processing
A
  • 76-80 bases
  • have a high content of unusual bases
  • can be written in a clover leaf secondary struct
  • acceptor end and anticodon are opposite each other
  • 3’ end holds CCA-OH which binds the aa
  • highly processed
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7
Q

post transcriptional modifications of tRNA

A
  • addition of 3’ CCA

- modification of bases at specific locations to create unusual bases

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8
Q

purpose of attaching an aa to the 3’ end of a tRNA prior to forming the peptide bond

A
  • covalently links an aa to a tRNA with the appropriate anticodon
  • attachment to the tRNA activates the AA, generating a high energy linkage at its carboxyl end
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9
Q

aminoacyl-tRNA synthetase

A
  • responsible to binding the correct aa to the correct tRNA by recognizing the correct anticodon
  • there is a unique synthetase for every AA
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10
Q

activation of an aa

A
  • AMP is first added to the aa creating aminoacyl-adenylate
  • this molecule it then bound to tRNA which kicks off the AMP and forms aminoacyl-tRNA
  • facilitated by aminoacyl tRNA synthetase
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11
Q

wobble hypothesis

A
  • more relaxed bonding takes place between the 3’ base of the codon and the 5’ base of the anticodon
  • this allows a single tRNA to recognize several codons
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12
Q

initiation

-mechanism and factors involved

A
  • mRNA is recognized by the 5’cap
  • eIF2-GTP-Met-tRNA complex interact with the 40S ribosomal subunit before mRNA is even introduced
  • this comlex goes forth and finds the 5’cap (with the help of eIF4)
  • once recognized, the complex moves 5’ to 3’ to the AUG site
  • eIF2-GDP and other initiation factors are then booted off the mRNA as the 60S subunit is recruited to form the full ribosome and begin translation
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13
Q

elongtation

  • 3 sites
  • broad overview of what it is
A
  • there are three sites on ribosome P, A, and E
  • P: containts the peptidyl tRNA complex
  • A: accomodates the incoming aminoacyl-tRNA
  • E: exit site for lonely tRNA’s
  • elongation factors are required to position subsequent aminoacyl tRNAs on the ribosome this is called translocation
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14
Q

EF1
-job
-what does it regulate
abundance

A

elongation factor 1

  • catalyzyes the GTP-dependent binding of aminoacyl tRNA to ribosomes in the A site
  • this regulates the fidelity and the rate of polypeptideelongation during translation
  • one of the more abundant proteins in euks
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15
Q

EF2

A

elongation factor 2

  • this protein is necessary for translocation
  • translocation is the process by which the ribosome moves in the 5’to3’ direction, opening up the A site for new aminoacyl-tRNA’s
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16
Q

peptide bond formation

-catalyst

A

this is the linkage between peptides during elongation

  • happens between the amino and carboxyl group of the aa
  • catalyzed by peptidyl-transferase
17
Q

stop codons

-temrination

A

once one these is reached during elongation, temination begins

  • a termination factor binds to the stop codon causing termination
  • stop codons are UAA, UAG =, and UGA
18
Q

termination

A
  • the peptidyl-tRNA is bound to the ribosome in the P site with the stop codon exposed in the A site
  • RF1 or RF2 recognizes the stop codon, catalyzed by RF3, and promotes hydrolysis of the ester bond between the polypeptide and the tRNA, releasing the polypeptide
19
Q

monocistronic

A

this is observed in euk mRNA, we only have one stop and one start codon within a given mRNA

20
Q

polyribosomes

A

multiple sequential initiation events will take place on a single strand of mRNA allowing many proteins to be synthesized from one strand of mRNA

21
Q

missense mutation

-cryptic splice site

A
  • this is when one nucleotide is switched for another causing a single aa change in the polypeptide
  • they may also cause cryptic splice sites: this is when a the splicing of a pre-mRNA sequence is altered
22
Q

nonsense mutation

A
  • a point mutation which causes a premature stop codon

- this can make the protein much shorter than origiinally intended

23
Q

frame shift mutation

A
  • this is when a mutation -causes the reading frame of an mRNA strand to be altered and usually causes significant changes in the polypeptide composition
  • this is generally due to a deletion that has occured in the DNA sequence
24
Q

regulation of translation

-primary mechnism

A

during periods of stress (starvation, dsRNA), a key control mechanism is the phosphorylation of eIF2, inactivating eIF2

25
Q

micro RNA

A

play an important role in the regulation of translation

  • 21nt long, noncoding
  • usually target the 3’UTR and they recruit the RISC complex and either cause stalling of translation or degradation of the mRNA
26
Q

internal ribosome entry sites

A

sequences used by viruses to recruit the pre-initiation complex in a manner that does not involve the initial scanning process

27
Q

learning and memory

A

protein synthesis is very important for learning and memory

28
Q

clinical context, glioblastoma

-what protein are they looking for specifically

A

physicians are now sequencing patients total mRNA to find every mutation in that persons genome.

  • this allows them to make specialized therapy decisions
  • specifically they look for the methylation of the MGMT protein which is responsible for reapir
  • if this gene is silenced, then they will give Temozolamide

Biochemistry MBS (36 decks)

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