translation Flashcards
what is the central dogma
transcription and translation
what is a codon
A series of three adjacent bases in an mRNA molecule codes for a specific amino acid
what three codes dont specify amino acids
stop codons, UAA, UAG, and UGA
what is the function of tRNA
molecular “bridges” that connect mRNA codons to the amino acids they encode
what is wobble pairing
when atypical base pairs—between nucleotides other than A-U and GC—can form at the third position of the codon
what is the rule of wobble pairing
G anticodon can pair with C or U but not at A or T in the third position
what is the process of covalently attaching an amino acid to the tRNA
Charging
what enzyme attaches the appropriate amino acid onto its tRNA
An aminoacyl-tRNA synthetase (aaRS or ARS), also called tRNA-ligase
what are the slots on ribosomes where tRNAs find their matching codons on mRNA
A (aminoacyl), P (peptidyl), and E (exit) sites
what is the most common initiator amino acid
methionine
during initiation of translation in bacteria, what initiation factors bind to the 30S ribosomal subunit
IF1,2,3 with 2 specifically recognizing the initiator tRNA
what does the ribosomal complex recognize when binding to the 5’ end of the mRNA
5’ cap
what direction does the complex “walk” along the mRNA
in the 3’ direction
what happens when IF3 is released from the complex
50S ribosomal subunit associate with the complex
what does the 50S binding trigger
hydrolysis of GTP bound to IF2
what happens after hydrolysis of GTP in bacterial translation
IF1 and IF2 are released
in bacteria, what brings the second tRNA to the A site
EF-Tu which then leaves the ribosome following GTP hydrolysis
what pulls the mRNA onwards by one codon
EF-G
what is required in order for translocation to continue in bacteria
active EF-Tu/GTP complex regenerated by EF-Ts
what proteins recognize stop codons during termination
release factors
what does the release factor cause addition of instead of an amino acid
a water molecule
what doe
a) RF1
b) RF2
in prokaryotic cells recognize
a) UAA or UAG
b) UAA or UGA
in eukaryotic cells the release factor recognizes two termination codons. true or false
false, it recognizes all three
what is the function of RF3
doesn’t recognize specific termination codons but act together with the other RFs
what is a polysome
A number of ribosomes can translate a single mRNA simultaneously, forming a polyribosome
what is an advantage of a polyribosome
enable a cell to make many copies of a polypeptide very quickly
what are the five mechanisms of regulation of translation
•binding of repressor proteins •repressors binding to regulatory sequences and initiation factor of 3’untranslated region and 5’ cap •mRNA localization •modulation of IF activity •small regulatory RNA (go read page 42 to 52)
how many more initiation factors do eukaryotes have then prokaryotes
6 more
what is scanning in eukaryotic cells
40S ribosomal subunit attaches at the 5’ end of the mRNA and moves downstream (i.e. in a 5’ to 3’ direction) until it finds the AUG initiation codon
what is the function of tetracycline
Blocks attachment of the aa-tRNA to the A site in the ribosome
what is the function of erythromycin
Blocks the movement of the ribosome down the mRNA
what is the function of streptomycin
Blocks formation of the initiation complex and causes miscoding
what is the function of rifamycin
Blocks transcription by blocking binding of RNA polymerase
why shouldn’t we antibiotics randomly
- prevent resistance
* avoid killing beneficial bacteria
what helps polypeptide chain coil and fold into 3D shape
chaperon proteins
what are the three ways of protein processing
- Protein Cleavage
- Glycosylation
- Attachment of Lipids
what does protein cleavage include
Removal of the initiator methionine from the amino terminus
what are the functions of glycoproteins
(1) in protein folding in the ER
(2) targeting of proteins for delivery to the appropriate intracellular compartments
(3) recognition sites in cell-cell interactions
what are the three general types of lipid additions on proteins
Nmyristoylation, prenylation, palmitoylation
what are the two major protein degradation pathways
- the ubiquitin-proteasome pathway
* lysosomal proteolysis
what is a polypeptide that is highly conserved in all eukaryotes
Ubiquitin
what degrades the polyubiquinated proteins in the UPP
proteasome
what does the lysosomal proteolysis pathway involve formation of
formation of vesicles (autophagosomes) contain proteins derived from the ER
what do the autophagosomes fuse with in the lysosomal proteolysis pathway
Lysosomes
what chaperones are required for lysosomal degradation
A member of the Hsp70 family of molecular chaperones
what proteins are susceptible to degradation the lysosomal proteolysis pathway
long-lived but dispensable proteins (usually during starvation)
what are the amino acids sequence of proteins degraded by lysosomal proteolysis pathway similar to
broad consensus sequence Lys-Phe-Glu-Arg-Gln,
