Chapter 30 Flashcards
Protein is synthesized from ? to ? end
N to C
mRNA is decoded in ? to ? direction
5 to 3
linking of AA to tRNA by ? is driven by ATP
aminoacyl-tRNA synthetase
Two subunits of ribosome
30S and 50S
? AAs are incorporated / second
20
one mistake in every ? AAs
10000
base modifications stabilize ? of tRNAs and provide additional contacts to ?
tertiary structure. contacts to protein factors
common features of all tRNA
cloverleaf secondary structure. 5 regions w/o complementary base pairing. anticodon and AA acceptor site at opposite ends
activation of AAs for tRNA attachment
AA + ATP»_space; Aminoacyl adenylate + PPi. driven by PPi hydrolysis
activation and charging reactions catalyzed by ?
tRNA synthetases
class one aminoacyl-tRNA synthetases acylate ?
2’-OH
class two aminoacyl-tRNA synthetases acylate ?
3’-OH
threonyl-tRNA synthetase uses ? to coordinate with -OH group of threonine to allow it to recognize threonine with an accuracy of ?
Zn ion. 99%
? allows 99.99? accuracy by threonyl-tRNA synthetase
proofreading
tRNA synthetase two active sites
activation site for charging and editing site the hydrolyzes incorrectly charged tRNAs
crucial step in converting from a nucleic acid code to a protein one
tRNA synthetases recognizing cognate tRNAs
50S subunit composed of ?
34 proteins, 23S and 5S rRNAs
30S subunit composed of ?
21 proteins and 16S rRNA
initiation of protein synthesis
30S subuint binds mRNA and a specific initiator tRNA
elongation of protein
50S subunit attaches to complex and polypeptide syntehsis begins
termination of protein synthesis
release factors bind at stop sequences to release polypeptide and disassemble ribosomes
initiator tRNA
a methionyl-tRNA that has been formylated. fMet-tRNA. Has peptide bond
start of protein synthesis is determined by?
pairing of mRNA bases w/ 3’ end of 16S rRNA. pairing of initiator codon on mRNA w/ anticodon of an initiator tRNA
binding of fMet-tRNA
30S ribosome subunit combines with initiation factors IF1-IF3 to facilitate binding and prevent premature association with 50S subunit
formation of quaternary complex
IF1 and IF3 dissociate. IF2 hydrolyzes GTP to drive release which allows 50S to bind
EPA sites
E: uncharged site. P: peptidyl site. A: aminoacyl site
elongation cycle
aninoacyl-tRNA binding > peptide bond formation > GTP hyrolysis by EF-G drives translocation > tRNA dissociation
aminoacyl-tRNAs are delivered to A site by ?
elongation factor Tu (EF-Tu) complexed with GTP
EF-Tu*GDP is recharged with GTP by ?
guanine nucleotide exchange factor of EF-Ts
peptidyl transferase reaction is catalyzed by ?
rRNA in 50S subunit
modification of a charged tRNA leads to ?. This is used in vitro to synthesize proteins containing ?
incorrect incorporation. unnatural amino acids
wobble position
5’ end (first base) of anticodon and 3’ end (third base) of codon are less discriminating
Inosine in first base of anticodon can bind with ? on third base of codon
U, C, A
yeast ala-tRNA contains ? in the anticodon
inosine
how does the ribosome read the first two codns so accurately?
rRNA makes specific contacts on the minor groove of the codon-anticodon helix
termination of translation
protein release factors that mimic tRNAs recognize and bind stop codons to release peptide from complex
STOP codons
UAA, UAG, UGA
release factors activate a ? to hydrolyze the peptidyl-tRNA
water molecule
RF-1
pairs with UAA or UAG
RF-2
pairs with UGA
RF3
causes dissociation of ribosome, mRNA and release factors
? powers conformational change in the ribosome
GTP
? (4) are all part of the g-protein superfamily and interact with the same site on the 50S subunit
IF-2, EF-Tu, EF-G, RF-3
Polysomes
on average about 10 ribosomes are attached to each mRNA
monocistronic
circularized mRNAs that encode for only one protein. found only in eucaryotes
30S and 50S ribosome subunits combine to form a ? subunit in procaryotes
70S
40S and 60S ribosome subunits combine to form a ? subunit in eucaryotes
80S
In eucaryote initiation, ? (3) associate in a ternary complex
eIF-2, GTP, Met-tRNA
in eucaryote initiation, ternary complex binds to ? complex to from ? complex
40S ribosomal subunit/eIF complex to form 43S preinitiation complex
in eucaryote initiation, ? and ? add to 43S complex forming the 48S complex
mRNA and eIF4
in eucaryote initiation, 48S initiation complex scans for ? with the help of ?
AUG start codon with the help of helicases
in eucaryote initiation, when 48S complex meets AUG, ? is hydrolyzed and ? adds to make 80S complex
GTP. 60S
eucaryotic mRNAs are unique because?
7-methyl-G cap at 5’ end. Poly(A) tail at 3’ end
5’ cap is recognized by ?
eIF-4E
PolyA tail is recognized by ?
pabp1
eIF-4E and pabp1 both bind to ?
eIF-4G
? proteins recognize both ends of mRNA to circularize, protect, and compact
eIF-4 group
some eIF-4 group proteins and S6 are activated by ?
phosphorylation
phosphorylated eIF-2 binds so tightly to eIF-sB that ?
guanine nucleotide exchange is blocked and translation cannot initiate
IRES
internal ribosome entry sites. able to translate without 5’caps and 3’ tails. Includes polio virus and eIF-4G
why is termination simpler in eucaryotes
only one release factor that hydrolyzes GTP at stop codon
proteins are synthesized as precursors with ? sequence that is subsequently removed. Purpose?
N-terminal. Tags to send to correct place in cell.
SRP
signal recognition particle. binds weakly to all ribosomes but tightly to ribosomes translating signal peptides. stops translation by blocking elongation factor binding site. targets ribosome to ER where SRP interacts with SRP receptor. SRP and receptor hydrolyze GTP and dissociate.
streptomycin function
inhibit translation initiation and cause misreading of mRNA
puromycin function
causes premature translation chain termination by acting as aminoacyl-tRNA analog
