9.3 - 9.4 Flashcards
Transfer RNA nucleotides
74-95 nucleotides (short)
Transfer RNA
small RNA adapter moelcule that, through complementary base pairing with codons in mRNA, places a specific amino acid at the correct position in a growing polypeptide chain at the ribosome
tRNA secondary structur
cloverleaf
tRNA tertiary structure
looks compact letter L
anticodon
codon in tRNA molecules that recognize codon on the mRNA by complementary base pairing and wobble
Amino acid is attached on
3’ end of tRNA
Aminoacyl-tRNA synthetases
enzymes that catalyze the attachment of tRNAs to the amino acids that corresponds to tRNA’s anticodon, forming charged tRNAs
Only molecules that read both nucleic acid and protein language
Aminoacyl-tRNA synthetases
One Aminoacyl-tRNA synthetases exists for
each of the 20 common amino aicds
Charged tRNA
a tRNA molecule to which the corresponding amino acid has been attached y an aminoacyl-tRNA synthetase (uses ATP)
Bond between the amino acid and tRNA contains substantial energy that is later used to form
peptide bonds
Amino acid attached to tRNA treated with nickel hydride
changes amino acid
Treatment with nickel hydride on anticodon
leaves anticodon unchanged
Specific interaction between a tRNA’s anticodon and mRNA’s codon determines
which amino acid is added to growing polypeptide chain
Wobble
the ability of the 5’-most base of an anticodon to pair with more than one type of base at the 3’ ends of codons
possible codon triplets in genetic code
61 possible codons
E. Coli makes tRNAs containing 42 different anticodon
61-42 =19 of potential anticodons are not represented
Do cells carry tRNA with anticodons complementary to all possible codons
no
How can an organism construct proper polypeptides if some of the codon in its mRNAs cannot locate tRNAs with complementary anticodons?
Some tRNAs can recognize more than one codon for the amino acid with which they are charged
U in the 5’ end of tRNA can bind
A or G in the codon 3’ end
G in the 5’ end of the tRNA can
U or C in the codon’s 3’ end
I (inosine) in the 5’ end pf tRNA can bind
A, U or C in the codon’s 3’ end
Ribosome in eukaryotic
80S
Ribosome in prokaryotic
70S
Small subunit of ribosome
binds to mRNA
Site of polypeptide synthesis
ribosomes
Large subunit of ribosome
has peptidy transferase activity
Parts of karge subunit of rubosome
Aminoacyl (A) site, Peptidy (P) site, Exit (E) site
in prokaryotic what is the first amino acid in the polypeptide chain
N-formyl-methionine
Translation of mRNAs on ribosomes for prokaryotes, during initiation phase what does ribosomes bind to
Shine-Dalgarno box and an AUG
Shine-Dalgarno box
5’ - AGGAGG - 3’
Translation of mRNAs on ribosomes for eukaryotes, during initiation
small ribosomal subunits binds to 5’ cap, then migrates to the first AUG codon
Elongation phase in ribosomes
addition of AA to C-terminus of polypeptide
Termination phase in ribosomes
No normal tRNAs carry anticodons for the stop codons
Release factors bind to the stop codon
Release of ribosomal subunits, mRNA, and polypeptide
Posttranslational processing
Enzymatic cleavage
Addition of chemical constituents
Enhancers can be located
upstream, downstream or within coding region
or intron of a gene
Enhancers
Stabilize RNA polymerase at promoter and enhancers clear histones from promoter
Prokaryotic translation
Multiple ribosomes binding sites and can direct synthesis of several different polypeptide and immediatiely binds to binding site of mRNA
