3.4 translation Flashcards
rRNA aminoacyl synthetases
- enzymes that bind AA to correct tRNA molecules
- are “translators” of the code
- one enzyme for each AA
undergo base pairing with the corresponding codon
○ Directly responsible for actually translating the codon sequence in a nucleic acid to a specific amino acid in a polypeptide chain
charged tRNA
tRNA with amino acid
process to charge tRNA
- aminoacyl tRNA synthetase (enzyme) binding to a specific amino acid
- it then transfers the amino acid to the appropriate tRNA molecule
each AA has a specific aminoacyl tRNA synthetase
ribosomal subunits
large and small
○ Each composed of 1-3 types of ribsomal RNA and 20-50 types of ribosomal protein
what does rRNA do
is in ribosome!
is what catalyses the peptide bond
translation in EUKARYOTES
initiation in eukaryotes is at the 5’ cap, and the first AUG is the start codon
monocistronic mRNA (code for just one polypeptide)
translation in BACTERIA
polycistronic mRNA
Initiates at any Shine-Dalgarno sequence
can code for several polypeptide
multiple start and stop codons!!
polycistronic mRNA
multiple protein-coding genes on the same RNA
how does the ribosome bind to the 5’ cap?
through rRNA and amino acid interactions
how does the ribosome bind to the Ribosome-Binding_Site
a sequence of rRNA is complementary (Base pairs) to the sequence of RBS)
initiation factors
imitation factors recruit the small ribosomal subunit and tRNAmet and scan the mRNA for an AUG codon
initiation of translation in eukaryotes
when the complex reaches an AUG, the large ribosomal subunit joins, the imitation factors are related, and a tRNA complementary to the next codon binds to the A site
codon
set of 3 adjacent AA which code for an amino acid
reading frame
the first codon read determines how each subsequent codon is read
why do we call the genetic code redundant or degenerate?
because many AA are specified by multiple codons (wobble effect!!)
three phases of translation
- initiation - AUG recognized and Met established as the first AA
- Elongation - AA are added to the peptide
- Termination - stop codon is reached, no new aa is added, and polypeptide is released from the ribosome
how do ribosomes move in translation
- 5’ to 3’
- ribosome moves down one codon
- puts the tRNA carrying the polypeptide into the P site and the now uncharged tRNA into the E site, where it is ejected
- new tRNA complementary to the next codon binds to the A site
wobble effect
bases in the 3rd position (3’ side of the codon on the RNA) do not require as much specificity to bind
directions that proteins are built
N – C
Elongation
polypeptide transfers to the AA on the tRNA in the A site
how fast can bacteria translate
~20 a second wowwwwww
how does the ribosome recognize the correct tRNA?
- it doesn’t!!
- charged tRNAs are floating around the cytosol and diffuse in and out of the A site
- the ribosome has to “try” out each one – if the anti-codon matches the codon, it stays
- large amount of ribosomes carrying out translation at any time
large subunit of ribosome binding sites
A (aminoacyl) site
P (peptidyl) site
E (exit) site
Anticodon
three nucleotides that undergo base pairing with the corresponding codon
on tRNA
Open reading frame
uninterrupted stretch of nucleotides that make up codons that code for amino acids
elongation factors
proteins that obtain energy for Ribosome movement along the mRNA and the formation of the peptide bonds
found to GTP molecules
Break their high-energy bonds to provide energy for the elongation of the polypeptide
process of translation in eukaryotes
one group of initaiton factors binds ot the 5’ cap that is added to the mRNA during processing
○ Recruit a small subunit of the ribosome!!
○ Other initiation factors bring up tRNA charged with Met
○ Theeennnn moves along the mRNA until it find the first AUG
§ Position establishes the trnaslational reading frame
○ Large ribosomal subunit joins the complex!!
§ Initiation factors are released
§ Next tRNA is ready to join baybee
process of translation in prokaryotes
- mRNA molecules have no 5’ cap
- Initiation process is formed at one or more internal sequences present in the mNRA known as a shine-dalgarno sequence
- Ability to intitate translation internally allows projaryotic mRNAs to code for more than one protein
shine-dalgarno sequence
where initiation process is formed in the mRNA for prokaryotes
