Lecture 31 Flashcards
Translation: Initiation
small subunit binds mRNA
first codon (AUG) on mRNA moves to P site on ribosome
large subunit binds, forming E,P,A sites for translation
translation
components: mRNA, tRNA, ribosome
stages: initiation, elongation, termination
Translation: Elongation
- elongation factor (EF-Tu) binds to charged tRNA and to GTP and brings them to A site of ribosome
- peptide bond forms between AA in P site and AA in A (peptide = bond between AA) catalyzed by peptidyl transferase on ribosome
- tRNA in P site is empty and tRNa in A site has growing AA chain
- ribosome translocates(moves to next codon on mRNA)
- empty tRNA moves to e site, tRna with AA chain –> P site, A site ready to accept next charged tRNA: cycle repeats until the end
- eventually tRNAs in the E site are ejected
Translation: termination
- stop codon enters A site (UAA, UGA, UAG)
- stop codons do not bind tRNA, bind release factors
- dissociate entire complex, releases new protein
Messenger RNA (mRNA)
made up of codons, uses bases U, A, C, G
codon
- a block of information on mRNA, made of a set of 3 bases; specifies an amino acid
- 64 possible codons for only 20 amino acids
Transfer RNA (tRNA)
- 2D structure: clover leaf
- 3D structure: L-shape
- 2 functional ends: acceptor stem that binds amino acid (3’) and anti-codon loop of 3 sequential nucleotides that are complimentary to 1 codon on mRNA
initiator tRNA
charged with special amino acid (formylmethionine aka fmet)
ribosome
site of protein synthesis (where translation occurs) composed of protiens, enzymes (peptidyl transferase), ribosomal RNA (rRNA) when large and small subunits come together, they form 3 binding sites (P, A, and E)
stop codons
UAA, UGA, UAG
start codon
AUG
formylmethionine
charges initiator tRNA
elongation factor (EF-Tu)
binds to charged tRNA and GTP and brings them to A site of ribosome
genetic code
sequences of nucleotides that make each strand of DNA unique
Degenerate
some amino acids are specified by multiple codons
peptide bond
forms between amino acid in P site and amino acid in A site catalyzed by peptidyl transferase on ribosome
cloverleaf
2D structure due to complementary binding in molecule
acceptor stem
3’ end binds amino acid (one end of the 3D structure)
release factor
stop codons bind with these in step 2 of termination, then in step 3 they dissociate the entire complex, releasing new proteins
anticodon loop
on tRNA is amino acid, tRNA binds to mRNA at the UUU codon
charging reaction
- happens on enzyme called aminoacyl tRNA synthase active site, specific amino acid will react with ATP and attach AMP to carboxyl end of amino acid
- specific tRNA with appropriate anticodon binds to ezyme
- amino acid transferred to acceptor stem of tRNA with energy from AMP (energy from AMP is used to drive reaction)
- charged tRNA leaves enzyme and goes to ribosome
aminoacyl tRNA synthease
where the charging reactions occur
anticodon
on tRNA is AAA it binds to the UUU codon on mRNA
ribosomal small subunit
binds mRNA
ribosomal large subunit
binds after AUG codon binds in P site forming the E P and A sites for translation
Peptidyl transferase
enzyme catalyzing translation
P site (peptidyl)
binds tRNA attached to amino acid chain
A site (aminoacyl
binds charged tRNA
E site (exit)
binds empty tRNA (no AA attached)
GTP
gets bound to charged tRNA and brought to the site A of the ribosome
amino acids
translated from DNA strand, the codons all code for a certain amino acid and they make a protein
translocation
fourth step of elongation: ribosome moves to the next codon on mRNA, empty tRNA is moved to E site, tRNA with AA chain to the P site, and A site is ready to accept next charged tRNA
L-shaped
3D structure of tRNA, clover leaf folds in on itself forming L-shaped structure has 2 functional ends: acceptor stem and anti-codon loop
