Translation Initiation in Prokaryotes
Summary
TLDRThis video explores the translation initiation process in prokaryotes, focusing on the unique role of the initiation codon, AUG, which codes for methionine in eukaryotes but formylated methionine in prokaryotes. The video explains the formation of initiator aminoacyl-tRNA, the binding of mRNA to the 30S ribosomal subunit, and the role of initiation factors in assembling the translation initiation complex. It also highlights the importance of the Shine-Dalgarno sequence and the subsequent steps leading to the formation of the complete translation initiation complex, setting the stage for the next video on elongation and peptide bond formation.
Takeaways
- đ The video discusses translation initiation in prokaryotes, focusing on the specific codon on mRNA known as the initiation codon, which is 'AUG'.
- đ In prokaryotes, the initiating 'AUG' codon codes for fMet (formylmethionine) instead of methionine, which is the usual amino acid coded by 'AUG' in eukaryotes.
- đ The video script mentions tRNA charging, where methionine is attached to tRNA by methionyl-tRNA synthetase enzyme, forming Met-tRNAfMet.
- đ ïž The formation of fMet-tRNAfMet involves a reaction with tetrahydrofolate and the enzyme transformylase, resulting in the initiator aminoacyl-tRNA.
- 𧏠The initiator tRNA, fMet-tRNAfMet, enters the ribosome at the P site, while other aminoacyl-tRNAs enter at the A site.
- đ The 30S subunit of the ribosome contains binding sites known as A, P, and E sites, which are crucial for the process of translation initiation.
- đŹ The 16S rRNA within the 30S subunit is complementary to the Shine-Dalgarno sequence of mRNA, facilitating the correct positioning of the mRNA for translation.
- đ Initiation factor 3 (IF3) binds to the 30S subunit to prevent premature binding of the 50S subunit, ensuring proper initiation.
- đ GTP-bound initiation factor 2 (IF2) recruits the initiating aminoacyl-tRNA (fMet-tRNAfMet) to the ribosome, where it enters the P site.
- đ After the recruitment and binding of the initiating tRNA, GTP is hydrolyzed to GDP, signaling the next steps in the translation process.
- 𧏠The video concludes with the formation of the complete translation initiation complex upon the joining of the 50S subunit, setting the stage for elongation and peptide bond formation.
Q & A
What is the main topic discussed in the video?
-The main topic discussed in the video is the translation initiation in prokaryotes, focusing on how the process begins with a specific codon on mRNA known as the initiation codon.
What is the role of the initiation codon in mRNA during translation initiation in prokaryotes?
-The initiation codon, which is typically AUG, signals the start of translation in prokaryotes. It generally codes for methionine, but in prokaryotes, it codes for formyl-methionine (fMet) at the beginning of the polypeptide chain.
What is the difference between the initiating and internal AUG codons in prokaryotes?
-The initiating AUG codon is the start codon for translation and codes for formyl-methionine (fMet) in prokaryotes. In contrast, internal AUG codons within the mRNA code for methionine as usual.
What is the purpose of tRNAfmet in translation initiation?
-tRNAfmet is the initiator aminoacyl-tRNA that carries formyl-methionine to the P site of the ribosome during translation initiation in prokaryotes.
How is methionine-tRNAfmet formed?
-Methionine-tRNAfmet is formed by the action of methionyl-tRNA synthetase enzyme in the presence of ATP, resulting in methionine-tRNAfmet and other byproducts such as PPi.
What is the role of the enzyme transaminase in the formation of fMet-tRNAfmet?
-Transaminase is involved in the reaction where formyl-tetrahydrofolate reacts with methionine-tRNAfmet to form fMet-tRNAfmet, which is the initiator aminoacyl-tRNA.
What is the significance of the Shine-Dalgarno sequence in the binding of mRNA to the ribosome?
-The Shine-Dalgarno sequence on mRNA is complementary to a sequence on the 16S rRNA of the 30S ribosomal subunit, facilitating the correct positioning of the mRNA for translation initiation.
What are the roles of initiation factors in the translation initiation process?
-Initiation factors such as IF3, IF1, and IF2 play crucial roles in the recruitment of the mRNA and the initiator tRNAfmet to the ribosome, preventing premature binding and ensuring the correct start of translation.
How does the ribosome assemble during translation initiation?
-The ribosome assembles by first binding the 30S subunit with the mRNA and the initiator tRNAfmet at the P site. After the release of initiation factors and hydrolysis of GTP to GDP, the 50S subunit joins to complete the translation initiation complex.
What happens after the translation initiation complex is formed?
-After the translation initiation complex is formed, the process moves on to elongation, where the polypeptide chain is extended by adding amino acids to the growing chain, which will be discussed in subsequent parts of the video.
What is the significance of the P site in the ribosome during translation initiation?
-The P site in the ribosome is where the initiator aminoacyl-tRNA (fMet-tRNAfmet) enters and binds, marking the start of the polypeptide chain during translation initiation.
Outlines
đŹ Translation Initiation in Prokaryotes
This paragraph introduces the topic of translation initiation in prokaryotes, focusing on the role of the initiation codon (AUG) on mRNA. It explains how the AUG codon codes for methionine in bacteria, but initially codes for formylmethionine (FMET) in prokaryotic translation. The paragraph also outlines the distinction between tRNA for methionine (tRNAmet) and formylmethionine (tRNAfmet), and how the initiator aminoacyl-tRNA (FMET tRNAfmet) is formed through a series of enzymatic reactions involving methionyl-tRNA synthetase and transformylase. The process of translation initiation is further detailed through a diagram, explaining the role of the ribosome's 30S subunit, the binding of mRNA, and the involvement of initiation factors IF3 and IF2 in recruiting the initiator aminoacyl-tRNA to the P site of the ribosome.
Mindmap
Keywords
đĄtRNA charging
đĄaminoacylation
đĄinitiation codon
đĄmethionine
đĄformylmethionine
đĄtRNAfmet
đĄribosome
đĄShine-Dalgarno sequence
đĄinitiation factors
đĄGTP
đĄelongation
Highlights
Discussion of tRNA charging and aminoacylation in the previous video.
Introduction to translation initiation in prokaryotes and the significance of the initiation codon (AUG).
Explanation of the unique role of the initiating AUG codon in prokaryotes, coding for fMet-tRNAfMet instead of methionine.
Differentiation between the initiator aminoacyl-tRNA (fMet-tRNAfMet) and the regular methionine-tRNA (Met-tRNAMet).
Formation of fMet-tRNAfMet by methionyl-tRNA synthetase enzyme in the presence of ATP.
Reaction of fMet-tRNAfMet with tetrahydrofolate to form fMet-tRNAfMet, facilitated by the transformylase enzyme.
Mechanism of formyl group transfer from tetrahydrofolate to the amino group of the methionine residue.
Entry of the initiator aminoacyl-tRNA into the ribosome at the P site.
Description of the 30S ribosomal subunit and its components, including the 16S rRNA.
Role of the Shine-Dalgarno sequence in mRNA binding to the 16S rRNA of the 30S subunit.
Binding of initiation factor 3 (IF3) to the 30S subunit to prevent premature binding of the 50S subunit.
Association of mRNA with the 30S subunit and the interaction between the Shine-Dalgarno sequence and 16S rRNA.
Recruitment of the initiating aminoacyl-tRNA (fMet-tRNAfMet) by GTP-bound IF2 and its entry into the P site.
Hydrolysis of GTP to GDP upon recruitment and binding of the initiator tRNA.
Release of initiation factors and the joining of the 50S ribosomal subunit to complete the translation initiation complex.
Overview of the translation initiation process leading to the next steps of elongation and peptide bond formation.
Encouragement for viewers to like, support, and subscribe for more educational content.
Transcripts
Oh in the previous video we discussed
about the tRNA charging there's the
aminoacylation or tRNA if you want
toward that video first with the link is
in the description now in this video
we'll be discussing about the
translation initiation in prokaryotes
the translation bigness at a specific
codon on mRNA called the initiation
codon on mRNA which is the Aug a start
codon this start codon Aug generally
codes for methionine but in you bacteria
that's in prokaryotes the initiating Aug
codes for informal me joining FME T but
later on this Aug or internal Aug codon
codes for methionine as usual in order
to understand the internal Aug codon and
initiating Aug codon we can see in this
diagram we have the initiation codon
that's Aug where from the translation
starts and it calls for informal mutiny
and then on the right we have another
Aug codon which is the internal codon on
mRNA and this edge codon codes for
methionine so we have two different
amino acids for tRNA and formyl
methionine and me Tony for MIT ihnen we
have tRNA Amity and for informal me Tony
we have tRNA fme T let's see first how
we get the formation of a committee tRNA
first me Tony is attached to tRNA fmet e
by the Makonnen trna synthetase enzyme
in presence of ATP molecule and we get
the methionine tRNA fme T plus MP plus
PPI in the next direction the mutant in
tRNA fmet e reacts with informal
tetrahydrofolate
in presence of trans formulas enzyme and
we get the FME T tRNA fmet e that is
their formal meeting in tRNA fmet e and
also we get the tetrahydrofolate from
this reaction so what happens in this
reaction we see in this reaction
transform Alice transfers a form
grew prom Poorman tetrahydrofolate to
the amino group of MIT residue and we
get the above products now this is the
initiator aminoacyl-trna it enters the
ribosome directly at P site and rest of
the M&S a tRNA intercept a site of
ribosome
now let's get to the mechanism of
initiation through diagrams we see in
the diagram we have the 30s subunit of
the ribosome having EPA sites a site
receives the incoming aminoacyl-trna p
site holds growing polypeptide chain and
each site is where there is exit of the
isolated tRNA and we know 30s subunit of
ribosome is made up of many ribosomal
RNA and all that one is the 16s rRNA
whose sequence is shown here in the
diagram this 16s RNA sequence is
complementary to the shine-dalgarno
sequence of mRNA so the first event to
take place is the binding of if3
initiation factor 3 towards the 30s
subunit as shown in the diagram this
initiation factor 3 prevents the
premature binding of 50s subunit to the
30s subunit and then if'n also binds
which prevents premature Association of
tRNA after that the mRNA is associated
with 30s subunit of ribosome as shown in
the diagram and in that the
shine-dalgarno sequence of mRNA peers
with the 16s rRNA sequence of 30s
subunit so it acts as a binding site now
the GTP bound
if2 recruits their initiating amino acyl
tRNA that's FME T tRNA and it enters the
ribosome at P site as shown in the
diagram and here the anticodon of tRNA
base pairs with a codon of mRNA and in
that case we have Aug as
initiating codon the beauty of our codon
anticodon concept is given in the
description so often all the recruits
and bindings the GTP is hydrolyzed it
into gdp and we get the gdp-bound
i have to then in the next step all the
factors
like GDP I have to I have fun I have
three as shown in the animation once all
the vectors leave they give a romp or
50s subunit to come in and join and here
in the animation we see the 50s subunit
comes in and completes their translation
initiation complex this is the
initiation of translation and after that
elongation or poles which we will
discuss in the next part along with the
formation of peptide bond formation I
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