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Chapter 19 Gene Expression: Protein Synthesis
Terms in this set (50)
mRNAs encode instructions for _____, the process of assembling amino acids into a polypeptide
_______ carry out the process of polypeptide synthesis; they are the machines in polypeptide synthesis. They are particles made of _____ and _____. In eukaryotes, they are found free in ______ or bound to _____ and the outer nuclear envelope.
ribosomes, protein, rRNA, cytoplasm, ER
_______ molecules align amino acids in the correct order as they contain bases that code for amino acids that attach to mRNA (codon- anti-codon interactions).
_____-___ _____ attach amino acids to their appropriate tRNA molecules
_____ molecules encode the amino acid sequence information.
Ribosomes are built from dissociable units, the large (____) and small (_____) subunits.
Ribosomes have four important sites: ...
mRNA binding site, A (aminoacyl) site, P (peptidyl) site, E (exit) site
Which site holds the tRNA holding the growing polypeptide chain of amino acids?
P (peptidyl) site
Which site binds to the aminoacyl tRNA, which holds the new amino acid to be added to the polypeptide chain?
A site (aminoacyl/acceptor)
Which site serves as a threshold, the final transitory step before a tRNA now bereft of its amino acid is let go by the ribosome?
E site (exit)
_______ molecules bring amino acids to the ribosome.
_____ ____ is an adaptor that brings together a specific amino acid and the mRNA sequences that specify the amino acid.
Each tRNA is linked to its amino acid by what type of bond?
ester bond (O-C=O)
tRNAs attached to an amino acid are said to be _____ ____ and the tRNA is called ____.
aminoacyl tRNAs, charged
each tRNA recognizes codons in mRNA because of complementarity base pairing to its ______
Some tRNA molecules can recognize more than one codon.
______ _____ explains why multiple codons can code for a single amino acid.
It allows for _______ base pairing as mRNA and tRNA line up on the ribosome in a way that permits _____ or _____ in the pairing between the ____ base of the codon and the corresponding base of the anticodon.
The wobble position is on the _____.
This is because there are ___ potential anticodons, but the cell only contains about ____ tRNA molecules.
Wobble Hypothesis, unexpected, flexibility, wobble, third, anticodon, 61, 40
the nucleotide _____ (I) is able to pair with U, C, or A and is often found in the wobble position of the anticodon, which allows for several codons to specify one amino acid.
mRNA is the ____ and tRNA is the ____.
Cells typically have 20 different ____ ____ ____ to attach each amino acid to the appropriate tRNA; there's one aminoacyl trna synthetase for each amino acid.
______ ____ ____ catalyze the attachment of amino acids to the tRNAs through an ____ bond, using ____ ___
aminoacyl-tRNA synthetases, ester, ATP hydrolysis
Both the ____ and the ____ end of the tRNA are needed to specify the correct amino acid.
After addition of an amino acid, the ______ proofread the final product to ensure the correct amino acid was added.
It is the _____ that then recognizes the appropriate codon in mRNA.
anticodon, 3' , synthetases, tRNA
1) ___ ___ and ___ enter the active site of an enzyme, aminoacyl-trna synthetase
2) ____ is joined to the amino acid, accompanied by release and breakdown of _____
3) AMP is displaced by ____, creating an _____ _____
4) ____ ____ is released from the enzymes to serve as substrates for translation as they are charged.
ATP, amino acid, AMP, pyrophosphates, tRNA, aminoacyl tRNA, aminoacyl tRNA
____ brings polypeptide coding information to the ribosome.
The sequence of codons in mRNA directs the order of ____ ____ in the polypeptide.
mRNA must be first exported from the nucleus to the cytoplasm.
An untranslated sequence at the 5' end of the message precedes the ____ ____, the first to be translated (AUG).
mRNA, amino acids, start codon
An untranslated region at the 3' end of the mRNA follows the ____ ___, which signals the end of translation (UAA, UAG, UGA).
5' (____) and 3' (___ ___) untranslated regions vary in length and are essential for mRNA function.
stop codon, cap, poly(A) tail
most mRNAs in eukaryotes are ______, meaning they encode just one polypeptide.
In bacteria and archaea, some are _____, encoding several polypeptides, usually with related functions.
These polycistronic transcription units are called ____.
monocistronic, polycistronic, operons
Translation begins at the __ ____ of the polypeptide and adds amino acids to the growing chain until the ___ ____ is reached.
Translation is divided into 3 stages: ...
N terminus, C terminus, initiation, elongation, and termination
1) During initiation, the components of the translational apparatus come together with an _____, and a _____ carrying the first amino acid binds to the ____ ____ (AUG)
2) During elongation, amino acids are brought to the _____ by _____ and are added one by one to a growing polypeptide chain
3) During termination, a stop codon in the mRNA is recognized by a _____ ____ ____, and the translational apparatus comes apart, releasing a completed polypeptide.
mRNA, tRNA, start codon, mRNA, tRNA, protein release factor
~Initiation factors are called _______ and there are about a dozen of these that bind to 5' cap.
~_____ with GTP attached binds to the initiator tRNA(met) before the tRNA then binds the _________ _____ ____
~After initiation factors bind the small subunit, the resulting complex (___ _____ ___) then binds to the 5' end of the mRNA, recognizing the 5' cap with the assistance of ____.
~After binding the mRNA, the small ribosomal subunit (including the initiator tRNA) scans along the _____ for the start codon at the first AUG.
~____ then binds to the start codon
~ Nucleotides to either side of the start codon are involved in recognition; for example, a common start sequence is ACCAUGG, called a ____ _____
~ After the initiator tRNA is base-paired with the start codon, the _____ _____ joins the complex, facilitated by ____ ____
eIFs (eukaryotic initiation factors), eIF2, small ribosomal unit, 43s preinitiation complex, eIF4F, transcript, tRNA, kozak sequence, large subunit, GTP hydrolysis
Eukaryotic mRNAs are _______ (polyA tail).
___ ___ ___ ___ (PABP) binds the polyA stretch and can also bind eIF4G, which is involved in translational initiation
polyadenylated, poly a binding protein
1) Initiation factos bind to the _____ ____ of mRNA
2) ___ _____ _____ binds to mRNA
3) ____ hydrolyzes GTP and other eIFs dissociate
4) _____ ____ scans for AUG (start codon); ____ binds to start codon
5) ____ ____ binds, and initiation factors hydrolyze GTP
5' cap, 43s preinitiation complex, eIF2, small subunit, tRNA, large subunit
Chain elongation involves cycles of ____ ____ BINDING, ____ ____ FORMATION, and ______ (change of location).
aminoacyl tRNA, peptide bond, translocation
Once initiation has been completed, what is synthesized?
____ ____ are added in sequence to the growing chain (elongation)
polypeptide chain, amino acids
Steps of Elongation:
1) Binding of _____ ____ to the ribosome brings a new amino acid into position
2) ____ ___ ____ links this amino acid to the growing polypeptide.
It forms between the amino (N) group of the amino acid at the ___ site and the carboxyl group of the amino acid at the ____ site.
The growing peptide chain is transferred to the tRNA at the ____ site. (no GTP or ATP hydrolysis required)
3) After the peptide bond forms, the mRNA advances to bring the next codon into the proper position through ______.
The _____ _____ moves from the A site to the P site, and the empty tRNA moves to the E site. (Hydrolysis of GTP bound to ____ triggers a conformational change that completes these movements.)
The mRNA is advanced ____ nucleotides through this process.
aminoacyl tRNA, peptide bond formation, A , P, A, translocation, peptidyl tRNA, EF-G, 3
Termination of polypeptide synthesis is triggered by ____ ____ that recognize stop codons:
Codons are read on the mRNA one after the other, until a stop codon arrives at the ____ site.
Stop codons are recognized by ____ ____ _____ rather than tRNAs.
Once release factors bind to the stop codons, translation is _______ through release of the completed _____.
release factors, A, protein release factors, terminated, polypeptide
Polypeptide elongation involves hydrolysis of at least ____ high energy phosphoanhydride bonds.
Additional GTPs are used during formation of the _____ ____, the binding of incorrect ____ ____, and _____
4, initiation complex, aminoacyl tRNAs, termination
Mutations & Translations:
~ mRNAs may contain _____ codons that caused errors in the polypeptide chain synthesized.
____ ____ are point mutations that results in a change in one DNA base pair that results in the substitution of one amino acid for another in the protein made by a gene; they alter a codon.
____ ___ are point mutations that results in a change in a DNA base pair, but instead of substituting one amino acid for another, the altered DNA sequence prematurely signals the cell to stop building a protein; change an _____ codon to a ___ codon .
It results in premature _____ of translation and a ____ polypeptide than normal.
nonsense mutations, amino acid, stop, termination, shorter
____ ____ are point mutations that cause the continued translation of an mRNA strand into what should be an untranslated region as they alter a ____ codon to an ___ codon.
It results in a _____ polypeptide than normal.
nonstop mutations, stop, amino acid, longer
Besides base-pair substitutions, nonsense, nonstop, and missense codons can also arise from _____ ____ _____, ____, or a combination of these.
They cause _______ mutations.
base pair insertions, deletions, frameshift
____ ____ is a mutation that exchanges one base for another.
Since protein-coding DNA is divided into codons three bases long, _____ and _____ can alter a gene so that its message is no longer correctly parsed, resulting in mutations called ___ ___.
base-pair mutation, insertions, deletions, frameshift mutations
Sometimes a single amino acid may not affect a protein's function in a major way as substituting one amino acid for another may not affect the protein function if both amino acids are similar.
Some mutations may be ____ _____ that affect the third base of the codon and results in no change of amino acid.
_____ are insertions or deletions of bases that result in larger-scale mutations and involve longer segments of DNA
In ______, a stretch of DNA is repeated
In _____, a chromosome section is cut out and reinserted in its original position, but in reverse orientation
_____ involves movement of a segment from one position in the genome to another location
After polypeptide chains are synthesized, almost all undergo ____ ____ before they can perform their functions.
They must undergo...(2).
posttranslational modification, peptide cleavage, addition of functional groups (phosphates, lipids, sugars)
During posttranslational processing,
~Sometimes whole blocks of amino acids are removed from the polypeptide (ex: enzymes synthesized as inactive precursors).
~Proteins are activated by removal of sequences from one end of the protein.
~Transport of proteins may require removal of a _____ ____, and some have internal amino acids that must be removed
Posttranslational Processing of Insulin:
~Two subunits of mature insulin come from a single longer protein called _____
~It has the ___ terminal "pre" amino acids removed to form ____
~Then ____ linkages form between what will be the A and B subunits of the mature protein
~Finally, the intervening "___" amino acids are removed to form mature ____
preproinsulin, N, proinsulin, disulfide, pro, insulin
______ converts information in mRNAs into a chain of amino acids linked by peptide bonds.
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