Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

BIOL253 > L16 + 17: Translation > Flashcards

L16 + 17: Translation Flashcards

1
Q

Formation of a peptide bond

A
  • AAs joined by peptide bonds; covalent bond formed between carboxyl group of one AA and amino grp of an adjacent aa
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Universal genetic code

A
  • 20 aas but 61 codons; 3 stop codons
    -> some degeneracy (all except Met and Trp are encoded by multiple codons)
  • AUG used in the initiation of protein synthesis
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

tRNA

A
  • Couples the region of ribosomes which binds mRNA codon and aa
  • Regions of self-complentarity form hairpin loops (D-loop, T, loop, anticodon loop) -> clover structure
  • Also has 3’ CCA tail, added post-transcriptionally
  • Unusual modified bases:
    e.g. Dihydrouridine (D-loop)
    e.g. Pseudouridine (T-loop)
    -> added post-transcriptionally by enzymes
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Charging

A
  • Adding tRNA to its cognate amino acid
  • Carried out by aminoacyl-tRNA synthetase (using ATP as a cofactor)
    -> produces aminoacyl-tRNA (very specific)
  • Reaction proceeds by IM using ATP as a cofactor…
    a. Activation of amino acid
    b. Transfer of amino acid to tRNA
    -> AMP
  • Amino acid added to 3’ or 2’ OH group of the 3’ terminal adenine nt of the tRNA
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Ways of achieving site specificity in tRNA synthetase enzymes

A
  • size exclusion
  • editing pre-transfer
  • editing post-transfer
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Wobble pairing

A
  • For the binding between 1st base of anticodon and 3rd base of codon, non-watson crick base pairing allowed
    -> wobbles
  • Provides part of the basis for degeneracy of the genetic code
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Which amino acid is incorporated into the protein first?

A
  • W/ rare exception, methionine is the first; may be removed later
  • tRNAfmet(prok) or tRNAimet is always used at the start and another for elongation involving methionine (tRNAmmet)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Bacterial vs Eukaryotic ribosome

A
  • Bacterial: 70S (50S large subunit w/ 2 rRNA molecules, 30S small subunit w/ 1 rRNA)
    *S is related to volume:SA so doesn’t directly add up
  • Eukaroytic: 80S (60S large subunit w/ 3 rRNA molecules, 40S small subunit w/ 1 rRNA molecule)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Shine-Dalgarno (bacteria)

A
  • Critical to identification of polycistronic mRNA
  • Polypurine sequence, AGGAGGU (E.coli)
  • Most efficiently allows binding of the ribosome
  • Binds to anti-shine-dalgrano sequence found on 16S rRNA of small subunit
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Attachment of ribosome to mRNA (Initiation) (bacteria)

A
  • Shine-Dalgarno binds to anti-Shine-Dalgarno by base-pairing (at small subunit), allowing small subunit to bind and f-met to recognise translation start site (AUG)
  • Small subunit will already have IF3 and IF1 bound (initiation factors)
  • IF2 (GTPase accessory factor) which binds and provides energy for substrate to bind
  • Large subunit binds, GTP hydrolysis, dissociation of IFs
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Role of IF1 an IF3 (bacteria)

A
  • Help guide the initiator tRNA into the right place (peptidyl site)
  • Protects the site either side of the initiator binding site
  • Also prevent large subunit from binding
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Sites in the ribosome

A
  • Aminoacyl site
  • Peptidyl site
  • Exit site
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Elongation (bacteria)

A
  • The next aminoacyl-tRNA molecule (in complex w/ EFTu and GTP) binds to the exposed codon in the A site
    -> initial selection (ensures fidelity)
  • The EFTu undergoes GTP hydrolysis and leave the site
  • Additional proofreading step (further fidelity)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Recycling of EFTu (bacteria)

A
  • ‘EFTs’ exchanges GDP for GTP on EFTu
  • Can be reused
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Peptide bond formation in ribosome (bacteria)

A
  • Catalysed on ribosome by peptidyl transferase centre
  • Nucleophilic attach followed by hyrolysis
  • Parts of ribosomal large subunit facilitate this by helping to coordinate; bring aas into proximity
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Ribozymes (bacteria)

A
  • RNA section of the 50S subunit
  • Involved in number of cellular processes including splicing of rRNA molecules and removal of introns form mRNA
16
Q

Translocation in the ribosome (bacteria)

A
  1. Ribosome moves one codon along in the 3’ direction
    - Requires EFG and GTP
    - Peptidyl RNA moves form A site to P site (uncharged tRNA moves from P site to E site)
  2. EFG is then released (requires GTP hyrolysis). Can be reused
17
Q

Structure of EFG (bacteria)

A
  • Structural mimic of EFT:tRNA
  • Binds to ribosome competitively w/ EFTu (binds to A site)
  • GTP hydrolysis is coupled to conformational change in EFG and ribosome
    -> forces movement of peptidyl-tRNA from A to P site, pushing deacetylated tRNA into exit site
18
Q

Termination (release factors) (bacteria)

A
  • When one of the 3 stop codons is reached, there is no tRNA available to enter the A site, instead a release factor binds to the stop codon
  • RF1 (UAA, UAG)
  • RF2 (UAA, UGA)
  • Enables hydrolysis of bond linking peptide chain to P site
19
Q

Recycling step in translation (bacteria)

A
  • Ribosome recycling factor (RRF) and EFG-GTP promote complex disassembly
  • IF3 binds to small subunit to stabilise it in its dissociated state
20
Q

Coupling of transcription and translation (prok vs euk)

A
  • In prokaryotes, coupling of transcription and translation can occur
    -> mutiple ribosomes loaded onto one mRNA
  • In euk, however, this can’t occur since they occur in different parts of cell
21
Q

Translation (eukaryotes - compare to bacteria)

A
  • Met is still first aa (but not formylated), special form of initiator tRNA only binds first AUG codon
  • No S-D sequence; the 7-methylG cap assists in binding of ribosome and ribosome moves along to first AUG encountered
  • Kozak sequence: preferred sequence context for start codons in mammals (RXX_AUG_G)
22
Q

Initiation factors (eukaryotes)

A
  • ‘eIFs’
  • Assist the start of translation; 12 identified
  • eIFs are numbered 1-6, each no. w/ different types further names w/ a letter
  • Numbers are associated with a different step
23
Q

Close loop complex, Pre-I complex formation (eukaryotes), binding of large subunit

A
  1. The mRNA is bound by the eIF4 family of initiation factors. eIF4E recognises the cap, eIF4G acts as scaffold between cap and polyA tail
    -> closed loop complex
    -> 40S, already bound to initiator tRNA (contrasts w/ bacteria) and several IFs is recruited via eIF4G/eIF3 interaction
  2. The Pre-I complex scans for start codon: the eIF4A/4B complex has ATP-dependent helicase activity; draws mRNA through until ‘AUG’ located
    -> since there are UTR regions at both ends to bypass
  3. Once a suitable start codon has been identified, the GTPase activity of eIF2 is activated, causing a conformational shift
    -> large subunit (60S) binds, majority of remaining IFs released
    -> closed loop complex aids further rounds of translation; enhances translatability of mRNA
24
Q

Elongation (eukaryotes) - analogues to bacteria

A
  • eEF1A ~ EFTu (binds aminoacyl tRNA and GTP)
  • eEF1B ~ EFTs (exchanges GTP for GDP; recycling of eEF1A)
  • eEF2 ~ EFG (involved in ribosome translocation)
    …process almost exactly identical
25
Q

Termination (eukaryotes)

A
  • eRF1 recognises all termination codons - mimics the structure of tRNA
  • Results in ribosome w/ one uncharged tRNA and RF w/ ABCE1 attached (w/ ATP)
  • Ribosome then recycled for future re-use; ABCE1 binds eRF1, starts hydrolysis, protein released
  • eIF1,1A and 3 recruited to protect A and E sites
26
Q

Protein synthesis inhibitors as antibiotics (7 examples w/ action)

A
  • A range of compounds found to inhibit translation on prokaryotic 70S rib.s but not euk 80S rib.s
  • They prevent growth of bacteria, shouldn’t affect human and animal protein synthesis
  • However, 70S rib.s present in mitochondria; can have detrimental side effects
    e.g….
  • kasugamycin (X initiation)
  • tetracyclin (X aminoacyl tRNA binding)
  • kirromycin (X release of EFTu)
  • aminoglycosides (cause miscoding in ribosome; incorrect tRNAs bind A site, nonfunctional proteins produced)
  • chloramphenicol (X peptidyl transfer)
  • thiostrepton (X translocation)
  • erthyromycin (sterically block exit tunnel)
27
Q

Fusidic acid

A
  • Narrow spectrum steroid antibiotic
  • Principally used to target staphylococci (e.g MRSA)
  • Also used in structural studies of rib. function
  • Inhibits elongation at the EG mediated translocation step
  • Binds to EFG-GDP and prevents its release from the ribosome
  • Blocks A site for next round of aa synthesis
28
Q

Puromycin

A
  • Wide spectrum; can even affect euk
  • Mimics an aminoacyl-tRNA; resembles an aromatic aa linked to a sugar-base
  • Treated by rib. as if it were an incoming aminoacyl-tRNA
    -> binds to A site but ONLY on large subunit; peptidyl transferase reaction occurs, product not anchored , so peptidyl-puromycin adduct is released in the form of a polypeptidyl-puromycin
  • Can’ be reused, essentially a suicide inhibitor
29
Q

Diptheria toxin

A
  • 63 KDa pp produced by Corynebacterium diptheriae
  • Catalyses the ADP-ribosylation of eEF-2 (NAD+ as a cofactor)
  • Blocks euk protein synthesis by inactivating elongation factor; specialist histidine on protein is (post-T) modified into dipthamide
  • Catalytic inactivation; one molecule can have widespread effects - could theoretically wipe out synthesis in whole cell
    ->very toxic
30
Q

Ricin

A
  • Very toxic by inhalation, injection or ingestion (LD50 is 5-10 microg/Kg via inhalation/injection, 30-40 orally
  • Type 2 ribosome inactivating protein (RIP)
  • Initially synthesised as pre-pro-polypeptide w/ A and B chains, split by proteolysis linked by disulphide bridge
  • Chain B is a lectin glycoprotein, binds galactose, enters cell through membrane and ER
  • Chain A is an RNA N-glycosidase, binds and depurinates specific adenine of 28S rRNA
    -> becomes sandwiched between 2 tyrosine rings in catalytic cleft
    -> hydrolysed
    -> completely inactivates ribosome
  • Enzymatic; one molecule has widespread effects

BIOL253 (19 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions