20.6 - protein synthesis Flashcards
The process of protein synthesis is called
translation
what is translation
It involves translating the genetic information from the sequence of nucleotides into the sequence of amino acids in the primary structure of a protein.
Each mRNA has a _______ followed by the sequences that carry the information for the order of the_________ that will be produced in the process of _____.
short untranslated region
amino acids in the protein
translation
That genetic information is the
sequence of codons along the mRNA
The decoding process is carried out by
tRNA molecules
translation is carried out on
ribosomes
what are ribosomes
complexes of ribosomal RNA (rRNA) and proteins.
each ribosome is made up of two subunits:
a small and a large ribosomal subunit
In eukaryotic cells, the small ribosomal subunit contains
one rRNA molecule and thirty-three different ribosomal proteins
the large subunit contains
three rRNA molecules and about forty-nine different proteins.
Protein synthesis involves the simultaneous action of many ribosomes on a
single mRNA molecule
These complexes of many ribosomes along a single mRNA are known as
polyribosomes or polysomes
Each ribosome synthesizes what
one copy of the protein molecule encoded by the mRNA. Thus, many copies of a protein are simultaneously produced
The molecule that decodes the information in the mRNA molecule into the primary structure of a protein is
transfer RNA (tRNA).
the tRNA must ____ bind ____, and only ___, specific _____.
covalently
one one
amino acid
There is at least one transfer RNA for each
amino acid
All tRNA molecules have the sequence ____ at their 3’ ends
CCA
The CCA is the site where the amino acid will be __________
covalently attached to the tRNA molecule.
Each tRNA is specifically recognized by the active site of an enzyme called an
aminoacyl tRNA synthetase
aminoacyl tRNA synthetase also recognizes the correct amino acid and covalently links the amino acid to the
3′ end of the tRNA molecule
The resulting structure is called an
aminoacyl tRNA.
The covalently bound amino acid will be transferred from the tRNA to a
growing polypeptide chain during protein synthesis.
the tRNA must be able to recognize the
appropriate codon on the mRNA that calls for that amino acid.
Second, the tRNA must be able to recognize the appropriate codon on the mRNA that calls for that amino acid. This is mediated through a sequence of three bases called the
anticodon
where is the anticodon located
at the bottom of the tRNA cloverleaf
The anticodon sequence for each tRNA is complementary to the
codon on the mRNA that specifies a particular amino acid.
___________ will bring the correct amino acid to the site of protein synthesis.
the anticodon-codon complementary hydrogen bonding
The first stage of protein synthesis is
initiation
Proteins called ______ assist in the formation of a translation complex composed of an______________________________________-
initiation factors
mRNA molecule, the small and large ribosomal subunits, and the initiator tRNA.
This initiator tRNA recognizes the codon ____ and carries the amino acid _____.
AUG
methionine
The ribosome has two sites for binding
tRNA molecules
The first site, called the
peptidyl tRNA binding site (P-site)
what does the peptidyl tRNA binding site (P-site) hold
holds the peptidyl tRNA, the growing peptide bound to a tRNA molecule
The second site, called the
aminoacyl tRNA binding site (A-site)
what does the aminoacyl tRNA binding site (A-site) hold
holds the aminoacyl tRNA carrying the next amino acid to be added to the peptide chain.
Each of the tRNA molecules is hydrogen bonded to the
mRNA molecule by codon-anticodon complementarity.
The entire complex is further stabilized by the fact that the mRNA is also bound to the
ribosome
The second stage of translation is
chain elongation
chain elongation occurs in
three steps that are repeated until protein synthesis is complete.
We enter the action after a ______ has already been assembled, and a _______ occupies the P-site
tetrapeptide
peptidyl tRNA
The first event in elongation is the
binding of an aminoacyl-tRNA molecule to the empty A-site.
Next in elongation, ___ bond formation is catalyzed by a catalytic region of the ______.
Peptide
28S rRNA
next, peptide bond formation is catalyzed by a catalytic region of the 28S rRNA. This is another example of a ribozyme, which is called
peptidyl transferase
Now the peptide chain is shifted to the ____ that occupies the __-site
tRNA
A
Finally, the ______ falls away, and the ribosome changes positions so that the next codon on the ______ occupies the _____
tRNA in the P-site
mRNA
A-site
his movement of the ribosome is called
translocation
The process shifts the new peptidyl tRNA from the
A-site to P-site
The chain elongation stage of translation requires the hydrolysis of ____________
Several ________ factors are also involved in this process.
GTP to GDP and Pi
elongation
The last stage of translation is
termination
There are three termination codons
UAA, UAG, and UGA
UAA, UAG, and UGA have no
no corresponding tRNA molecules
When one of these “stop” codons is encountered, translation is
terminated
A_____- factor binds the empty A-site
release
The peptidyl transferase that had previously catalyzed peptide bond formation hydrolyzes the
ester bond between the peptidyl tRNA and the last amino acid of the newly synthesized protein
At this point, the tRNA, the newly synthesized peptide, and the two ribosomal subunits are
released
The peptide that is released following translation is not necessarily in its
final functional form
In some cases, the peptide is _______ cleaved before it becomes functional.
proteolytically
