Translation pt II

Ribosome is composed of two subassemblies of _____ and _____. They are called the ____ and _____ subunits.

The large subunit contains the ______ _____ _______, which is responsible for the formations of _______ bonds. The small subunit contains the ______ _____ in which charged tRNAs read or decode the _____ units of the mRNA

By convention, the large and small subunits are named according to the _______ of their sedimentation when subjected to a centrifugal force. The unit used to this is the ______ (S)

In bacteria, the large subunit has a sedimentation velocity of ____ units and the small subunit has a sedimentation velocity of ____ units. The intact prokaryotic ribosome is referred to as the _____ ribosome

Why is the intact prokaryotic ribosome not the sum of the subunits?

The eukaryotic ribosome is somewhat _____, composed of _____ and _____ subunits, which together form an _____ ribosome.

The large and small subunits (eukaryotic) are each composed of one or more ______ and many _______ _____

For translation to be successfully initiated, what three events must occur?

Prokayotic mRNAs are initially recruited to the ______ _____ (via _____ _____ to rRNA)

The assembly of the ribosome on an mRNA occurs one ______ at a time. The ____ _____ associates with the mRNA first. In prokaryotes, the association of the _____ ____ with the mRNA is mediated by base pairing interactions between the ______ and the ____ _____.

For ideally positioned RBSs, the small subunit is positioned on the mRNA such that the start codon will be in the _____ when the _____ ____ joins the complex.

When does the large subunit join its partner. What is the consequence?

Translation initiation is the only time a tRNA binds to the P-site without previously occupying the ______. This event requries a special tRNA known as the ______ ____, which base-pairs with the _____ _____ (usually AUG or GUG)

AUG and GUG have a different meaning when they occur with an _____. Here, they are read by tRNAs for _______ and _____ respectively. Although the initiator tRNA is first charged with a _______, a _____ group is rapidly added to it by a separate enzyme called _________ ____________

Thus rather than valine or methionine, the initiator tRNA is couple to ______ _______. The charged initiator tRNA is referred to as _________

The inititation of prokaryotic translation commences with the small subunit is catalyzed by three _______ ______ _____ name them

State the role of each translation initiation factor

GTPase

The three key components IF2 interacts with

When does IF3 become associated with he small sub unit?

Initiation of translation in eukaryotes is similar to prokaryotic initiation. Name three similarities

What is the difference between the initiation of translation in eukaryotes vs prokaryotes

In eukaryotes, when is the small subunit initiated with an initiator tRNA

After association with an initiator tRNA, the small subunit then ______ along the mRNA in a ___ to ___ direction until it reaches the first 5'-AUG-3' which it recognizes as the _____ _____. Thus, in most instances, only the first AUG can be used as the _____ site of translation in eukaryotic cells

Note that the euk method of initiation is consistent with the fact that the vast majority of euk RNAs encode a _____ polypeptide (________). Recognition of an internal start  codon is generally neither ______ nor ______.

_____ cells require more auxiliary proteins to drive the initiation process than do _____.

The four steps of eukaryotic initiation

As the euk ribosome completes a cycle of translation, it ______ into free large and small subunits and four initiation factors (name them)

Together, eIF1, eIF1A, and eIF5 act in an analogous manner to the prok initiation factors ____ and _____. How so?

The initiator tRNA is escorted to the small subunit by the three subunit ____ binding protein called _____. Like IF2, _____ will bind the initiator tRNA only in the _____ bound state.

The complex between the initiator tRNA and eIF2 is called the ______ _____(TC). For eukaryotes, the initiator tRNA is charged with _______ not _____ ______. It is referred to as Met-tRNA_i^Met

eIF2 positions the initiator tRNA in the ______ of the _______ factor bound ____ subunit, resulting in the formation of the 43S preinitiation complex (43S PIC). eIF3 is almost as large as the entire 40S subunit but primarily binds the side of the small subunit near the RNA ____ and ____ sites

eIF3 interacts with every member of the 43S PIC including the _____ ____. What does this facilitate?

Not all eukaryotic polypeptides are encoded by an ORF that start with the AUG that is most ______ to the 5' terminus. An extreme example of initiating translation at sites downstream from such sites are ______ _______ ______ ______.

IRESs are RNA sequences that function like prokaryotic _____. They recruit the _____ ______ to bind and initiate even in the absence of a _____.

IRESs are often encoded in _____ mRNAs that lack a ____ end and have a need to exploit the sequences of their genome maximally. By using IRESs, a _____ mRNA can encode ______ protein(s), reducing the need for extended transcriptional regulatory sequences for each protein coding sequence. More importantly, by bypassing the requirement for one or more _____ _____, an IRES can function w/out them

Once the ribosome is assembled with the charged initiator tRNA in the ______, polypeptide synthesis can begin. Name the three key events that must occur for the correct addition of each amino acid

What is the result of the peptidyl transferase reaction in the second event?

As with the original positioning of the mRNA, the translocation of the peptidyl-tRNA to the P-site must occur precisely to maintain the correct ______ ______ of the message. Two auxiliary proteins known as ________ factors control these events. Both of these factors use the energy of GTP ______ and ______ to enhance the rate and accuracy of _______ function

Unlike the initiation of translation, the mechanism of elongation is highly _______ between prok and euk cells

Aminoacyl-tRNAs do not bind to the ribosome on their own, they are escorted to the ribosome by the elongation factor _______.

Once a tRNA is ________, EF-Tu binds to the tRNA's ____, masking the coupled ______ _____. This prevents the bound ________ tRNA from participating in _____ bond formation until it is _______ from EF-Tu

Like the initiation factor IF2, the elongation factor EF-Tu binds and hydrolyzes ______, and the type of _______ nucleotide bound governs its function. When can EF-Tu bind an aminoacyl-tRNA

EF-Tu bound to GDP, or lacking any bound nucleotide, shows _______ affinity for aminoacyl-tRNAs. Thus, when EF-Tu hydrolyzes its bound GTP, any associated aminoacyl-tRNA is _______.

On its own, EF-Tu bound to an aminoacyl-tRNA does not _______ GTP at a significant rate. Instead, the EF-Tu _____ is activated when it associates with the same domain on the ______ _______ of the ribosome that activates the IF2 ______ when the ______ ______ joins the initiation complex. This domain is known as the ______ _____ _____.

When does EF-Tu interacts with the factor binding center?

The ribosome's cycle of aminoacyl-tRNA binding, peptide bond formation, and translocation continues until on eof the three _____ _____ enters the ______. It was initially postulated that there would be one or more terminating tRNAs that would recognize these codons. However, this is not the case. Instead, _____ _____ are recognzied by proteins called _____ _____. What do they activate?