Lecture 30 Flashcards
The molecular machine that performs translation? What are these structure mades up of?
the ribosome!!
-made up of RNA strands (rRNA), and dotted with protein chains
When synthesizing a new protein…the large and small subunit come together with what in between? The ribosome then walks down the mRNA ______ nucleotides at a time, building a new protein.
mRNA trapped in the space between
3 nucleotides at a time
Transcription produces a bunch of different RNAs, but only which one gets translated?
mRNA gets translated
At the transcript level, the mRNA has a ____________ and the information in the
middle (the protein coding sequence) is what actual gets translated into protein. The leader
and trailer sections are not translated.
leader section @ 5’ and a trailer section @ 3’
RNA triplet of three bases is called what? Which encodes what?
a codon, which encodes each specific amino acid
AUG codes for…which is always the first amino acid in bacterial proteins. Although AUG at the beginning of a coding region encodes
N-forymylmethionine, AUG within the coding region encodes what?
N-formylmethionine (or F-Met)
encodes methionine
the language of mRNA is in the form of what? Each codon “codes” for a particular amino acid. This is the _______ code.
codons, groups of three nucleotides
genetic code
There are ______ possible codons, but only ______ amino acids. This means that most amino acids are signaled by several
alternative codons, a situation referred to as the _______ of the code. What does this allow for?
64, but only 20 amino acids
degeneracy – This allows for a certain amount of
change, or mutation, in the DNA without affecting the protein produced.
Of the 64 codons, 61 are _______ codons which code for an amino acid, and 3 are ________
codons (also called stop codons) which do not code for an amino acid. They signal the end
of the protein molecule’s synthesis.
- sense
- 3 are nonsense
A codon is recognized by specific base pairing with a complementary sequence of three
bases called the _________, a sequence found on ________.
anticodon found on tRNA
what does tRNA also do?
Each tRNA can also carry on its other end the amino acid
encoded by the codon that the tRNA recognizes.
what is a wobble position?
base pairing is more flexible for 3rd base of codon than first two
Prokaryotic ribosome parts – describe the large and small subunits? Big picture here
small subunit 30s, large subunit 50s – the complete ribosome is 70s
What is the 50s subunit made of?
31 proteins, and 2 rRNA molecules the 5s rRNA and the 23S rRNA
what is the 50s large subunit involved in? In addition ______ binding proteins can interact with the subunit to aid in what?
involved in peptide bond formation through peptidyl transferase activity.
-GTP binding proteins aid in translational processes such as initiation, elongation, and termination
The 5s rRNA molecule appears to act as what?
a seventh domain in the large ribosomal subunit in conferring stability to the entire 3-D structure
The 23s rRNA is involved in? The most important feature of the 23S rRNA is the __________ center. What happens here?
translocation and peptide bond formation
-peptidyl transferase center, the site where peptide bonds are formed.
The 30S or small subunit is
composed?
of 16S rRNA and 21 ribosomal proteins
The 16s rRNA of the small subunit makes up the bulk of the subunit. It is important for what?
subunit association and translational accuracy
-on the 30S, the anticodon of an aminoacyl-tRNA is matched by base-paired
interactions to a codon on the mRNA. A key function of the small subunit is to
discriminate against aminoacyl-tRNAs that do not match the codon on the message.
There are three important stages to protein synthesis:
Initiation, elongation and
termination
In bacteria, initiation of protein synthesis always begins with what?
a free 30s ribosomal subunit
An initiation complex forms consisting of the 30S, plus mRNA, and formylmethioninetRNA
(F-Met tRNA), and several initiator proteins (IF1, 2, 3) and energy is required.
See slide for order of initiation
??
Just preceding the start codon on the mRNA is a sequence of three to nine nucleotides called the what? What does it help with, and where is this located?
Shine-Dalgarno sequence (aka ribosome binding site or leader sequence) that helps bind the mRNA to the ribosome. Ribosome binding site is at the 5’ end of the mRNA and is complementary to the base sequence in the 3’ end of the 16s rRNA (this complementary base pairing aids in holding down the ribosome to the correct reading frame on the mRNA)
The mRNA threads through the ribosome primarily bonds to ______ subunit?
30s subunit
The 50s ribosome has 3 important sites what are they?
A site, P site, E site
A site
the acceptor site, where on the ribosome the new charged tRNA ( a charged tRNA has its cognate amino acid) first attaches
The charged initiator tRNA carrying _________ (f-Met) recognizes the codon ______ on the mRNA and binds in a complementary fashion at the part of the _______ site on the 30s subunit.
N-formylmethionine
AUG
P-site
Note: the F-Met-tRNA is only tRNA that can bind to the part of the P-site on 30S subunit to initiate protein synthesis.
Usually at the P-site, the growing polypeptide is held by a tRNA
The second codon of the mRNA pairs with a tRNA carrying the second amino acid at the ______ site. The first amino acid joins to the second by a ______ bond. This attaches the polypeptide to the tRNA in the P site. The ribosome moves along the mRNA until the second tRNA is in the _____. The next codon to be translated is brought into the _______ site. The first tRNA now occupies the E site.
A site, by a peptide bond
- P site
- A site
- E site
Initiation requires what proteins?
IF-1,2 and 3
The ribosome moves along the mRNA in the _______ direction.
5’ to 3’ direction
Translation: Elongation
what protein is used to catalyze the formation of a new peptide bond
see slide
peptidyl transferase
aminoacyl tRNA
tRNA to which its cognated amino acid is chemically bonded (charged)
ribosome must advance 3 nucleotides down mRNA during ________
translocation
see slide
The last step is ______,the ribosome reaches a _______ codon (stop codon like UGA). No _____ binds here. Instead, _______ proteins bind in the vacant _______ site and cleave the attached polypeptide from the final tRNA, releasing the finished polypeptide.
- termination
- nonsense
- tRNA
- Release factor proteins (RF)
- A site
In Bacteria, the process of transcription and translation are
simultaneous.
Several ribosomes can simultaneously translate a single mRNA molecule, forming a complex called? What does this do?
polyribosome
Polyribosomes increase the speed and efficiency of translation, and because
the activity of each ribosome is independent of that of its neighbors, each ribosome in a
polyribosome complex makes a complete polypeptide.
Advantages to coupling transcription and translation
One advantage involves the energy required for
transcription and translation; specifically, the energy needed to drive the process of
transcription could be provided by the large-scale expenditure of unstable nucleotide
triphosphates during the process of translation. Another advantage to coupled transcription
and translation is that it provides a novel mechanism for gene regulation.
