chapter 9 Flashcards
how many different amino acids?
20
what do amino acids do?
serve as building blocks for polypeptides
what do all amino acids have?
central carbon
-amino group
-carboxyl group
what type of bond is between the carboxyl group of one amino acid and the amino group of the next?
peptide bond
what is distinct about each amino acid?
r-group
wht direction to ribosomes translate mRNA in?
the 5’ to 3’ direction
what are the two subunits of ribosomes?
large ribosomal subunit and the small ribosomal subunits
what is ribosomal subunit size measured in?
Svedberg units (S)
what dictates the resulting amino acid sequence?
the mRNA sequence
what are the boundaries of translation defined by?
the start codon at the N-terminus of the protein
the stop codon at the C-terminus
what segments of the mRNA are outside of the translated regions?
the 5’ un-translated region (5’ UTR) and the 3’ UTR
what type of polypeptide structure will we be working with most?
primary
how big is the small subunit in E.Coli?
30s
-21 proteins, on 16S rRNA molecule
how big is the large subunit in E. Coli?
50S
-31 proteins, a small 5S rRNA
=a large 23S rRNA
how big is the fully assembled E. Coli Ribosome?
70S
what are the three important sites in the ribosome?
-A-Site
-P-Site
-E-Site
A-site
Aminoacyl Site
-binds the incoming tRNA molecule that is carrying the next amino acid to be added to the growing polypeptide chain
P-Site
Peptidyl Site
-holds the tRNA to which the growing polypeptide chain is attached
E-Site
Exit Site
Provides a pathway for the exit of the tRNA after its amino acid has been added to the growing chain
what is the most fully characterized eukaryotic ribosome?
the mammalian ribosomes
how big is the small subunit is eukaryotes?
40S
-three proteins and one 18S rRNA
how big is the large subunit is eukaroytes?
60S
-45 to 50 proteins and three rRNA molecules of 5S, 5.8S, and 28S
how big is the fully assembled ribosome in eukaryotes?
80S
where does translation initiation begin?
where the small ribosomal subunit binds
where does the initiation tRNA bind to and what does it carry?
it carries the first amino acid of the polypeptide and it binds to the start codon (AUG)
what joins last in initiation?
the large subunit- it joins the small subunit to form the intact ribosome and translation begins
what do initiation factors (proteins) do?
help direct ribosome assembly and binding of the initiator tRNA
what provides the energy for translation?
GTP
what are charged tRNAs?
tRNAs carrying amino acids
what are uncharged tRNAS
tRNAs without amino acids attached
what components come together in E. Coli to initiate translation?
-mRNA
-small ribosomal subunit
-large ribosomal subunit
-initiator tRNA
-thee initiation factor proteins
-GTP
what is the 30S subunit in bacteria affiliated with for most of initiation and what does that thing do?
-an initiation factor - IF3
-IF3 prevents the 30S subunit from binding the 50S subunit
what binds near the 5’ end of the mRNA and what does it do in bacteria?
small subunit IF3 complex
-searches for the start codon
when does the preinitiation complex form in bacteria?
when the 16S rRNA base pairs with the Shine-Dalgarno sequence of the mRNA
what is the shine-dalgarno sequence?
a purine-rich (A/G) sequence of about six nucleotides
where is the shine-dalgarno sequence located?
3 to 9 nucleotides upstream of the start codon
where is the complementary sequence of the shine-dalgarno sequence located?
-it is a pyrmidine-rich (U/C) sequence
-found near the 3’ end of the 16S rRNA (part of the small subunit)
where does the initiatior tRNA bind?
to the start codon where the P-site will be once the ribosome is assembled
what is the amino acid on the inititator tRNA?
it is a modified amino acid, N-formylmethione (fMet)
what is the charged initiator tRNA called?
tRNAfMet
what forms the 30S initiation complex
-initiator factor - IF-2 and a GTP molecule are bound to the tRNA^fMet and IF-1 going the complex
what forms the intact ribosome in bacterial initiation?
when the 50S subunit joins the 30S subunit
what is the union of the two subunits driven by?
hydrolysis of GTP to GDP
what accompanies the joining of the subunits to create the 70S initation complex?
the dissociation of IF-1, IF-2, and IF3
the eukaryotic 40S ribosomal subunit complexes with what
eukaryotic initiation factor (elF) proteins
in eukarotic translation initiation, elf1A, elf2, elf3, binds the small subunit to forms what?
the preinitiation complex
what forms the preinitiation complex in eukaryotic translation initiation?
elf, elf1A, elf3 binding to the small subunit
what does the preinitiation complex go on to join in eukaryotic initiation?
it joins with the initiator tRNA and elF5
then joins a group of at least four elF4 proteins that assembles at the 5’ cap of the mRNA
what comprises the initiation complex in eukaryotes?
when the preinitiation complex joins a group of at least four eIF4 proteins that
assembles at the 5’ cap of the mRNA
what happens once the initiation complex is formed in eukaryotic initiation?
the small subunit scans along the 5’ UTR in search of the start codon
what is required for the small subunit to scan along the 5’ UTR in search of the start codon?
ATP hydrolysis
what percent of eukaryotic mRNAs use the first AUG as the start codon?
90%
what is AUG in?
the kozak sequence
after the start codon is located in eukaryotic initiation, what is recruited and how?
the 60S subunit, using the energy of GTP hydrolysis & the dissociation of the elF proteins
what is archaeal translation initiation like?
eukaryote-like
what is the common first amino acid in archaeal translation initiation?
methionine
do some archael mRNAs contain shine-dalgarno sequences?
yes
T or F: – Archaeal initiation factor proteins (aIFs) are homologous in structure and function to
eIFs
TRUE!
what tries to enter the A-site in polypeptide elongation in bacteria?
charged tRNAs affiliated with Ef-Tu and GTP
what happens when a tRNA pairs with the correct anticodon sequence elongation in bacteria?
hyrdrolysis fo GTP releases EF-Tu-GDP from tRNA
what catalyzes the peptide bond formation between amino acids at the P and A sites?
Peptidyl transferase
Using _____ hydrolysis, _____ translocates the ribosome, moving it three nucleotides toward the 3’ end of the mRNA
GTP
EF-G
what moves the tRNA from the A site to the P site and opens the A site for the next charged tRNA carrying the correct anticodon?
when the energy of GTP hydrolysis makes EF-G move around the ribosome (3 nucleotides toward the 3’ end of the mRNA)
