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Return to Biochemistry: The Molecular Basis of Life 7e Student Resources
Chapter 19 Review Quiz
Protein Synthesis
Quiz Content
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Creutzfeld-Jacob syndrome, bovine spongiform encephalitis, and scrapie all seem to be variants of disease related to inappropriate folding of proteins. It seems that some infective proteins come into contact with normal proteins and induce the normal proteins to go wrong. What are the protein infective agents called?
Hormones
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Prions
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Haptoglobins
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Cytokines
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Albumins
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The molecule possessing the anticodon and which carries amino acids to the site of protein synthesis is called:
A transposon
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The first-class carrier protein
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Ribosomal RNA
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Transfer RNA
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Messenger RNA
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Degeneracy in the genetic code seems wasteful. Of what possible value could degeneracy be, when it allows or requires more than one possible codon for most amino acids?
Degeneracy prevents mutations which might result from changing the second base of the codon
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In fact, all codons for a particular amino acid are the same
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Degeneracy provides protection against some point mutations
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Degeneracy refers to the fact that there are some codons which do not code for any amino acid
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Degeneracy helps to prevent aberrant behavior among teenage biochemists
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The genetic code is a triplet code, with four bases taken three at a time, giving 64 combinations, enough for 21 amino acids and then some. If it were a duplex code, how many amino acids could be coded for?
32
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16
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8
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4
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2
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During protein synthesis in prokaryotes, the first amino acid placed in the chain is usually N-formylmethionine. Speculate on a reason why plain methionine wouldn't work just as well.
Perhaps there is not enough non-formylated methionine available
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N-formylmethionine prevents the 30S subunit from binding prematurely to the 50S subunit
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There's really nothing special about N-formylmethionine. N-acetylmethionine could perform the same function
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Leucine zippers prevent methionine alone from performing this function
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N-formylmethionine placed at the beginning of the growing peptide chain may protect the growing chain during translation
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During periods of rapid protein synthesis, the mRNA moves rapidly through a group of protein synthesizing structures called, collectively:
Endoplasmic reticulum
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Golgi apparatus
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Flagella
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Polyribosomes
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Nuclear pores
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The anticodon on one tRNA which carries histidine to the site of protein synthesis is CAU. What was the corresponding set of bases in the gene of the DNA molecule which specified placement of histidine at that location?
AAA
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GTA
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GAU
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CAT
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CAU
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Two of the codons which have traditionally been considered stop signals are now known to specify placement of unusual amino acids. Which ones?
β-alanine and ε-phospholysine
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Glutamine and carboxyhistidine
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Asparagine and thiothreonine
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Selenocysteine and pyrolysine
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Hydroxyproline and hydroxytryptophan
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During transcription, movement of the tRNA-polypeptide from the amino acid site of the ribosome to the peptide site requires a source of energy in the form of:
GTP
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cAMP
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UTP
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CDP
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TTP
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Determination of the primary structure of a peptide was once a laborious activity, requiring weeks or months of treatment of the peptide with Sanger's reagent, hydrolysis, and paper chromatographic analysis. The lucky graduate student can now use mass spectrometry to break a peptide apart and accurately analyze the fragments. The mass spectrometer gives very accurate information concerning:
The charge on individual particles
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The identity of the amino acids present
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The number of acidic and basic amino acids present in the polypeptide
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The molecular weight of fragments of the peptide
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The ultraviolet absorption spectrum of the peptide
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Chloramphenicol is an antibiotic which is effective against many microorganisms. It interferes with translation by:
Releasing the partially-formed peptide before translation is complete
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Hydrolyzing peptides prematurely
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Preventing the peptidyl-tRNA from moving from the amino acid site to the peptide site of the ribosome
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Causing misreading of the codes on mRNA
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Interfering with aminoacyl-tRNA binding
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If you had taken a biochemistry course in the 1960s, you might have learned that 61 of the 64 possible codons actually coded for placement of amino acids, and that there were some "nonsense" codons which didn't seem to direct placement of any amino acid. Now, of course, we know that all the codons are useful. What do those three nonsense codons actually do?
These three are the start and stop codons
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These are extra codons which may be used in case of mutations
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In fact, these may be nonsense codons. Their usefulness hasn't been proved
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These three codons specify isomers of the branched chain amino acids
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These three codons direct placement of glutamine and asparagine
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Protein synthesis is more rapid in organisms in which mRNA has a shorter half life. Protein synthesis in humans is much slower than that in
E.
coli
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Our cells live in an environment where changes are rapid and dangerous
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Human cells live in relatively challenging environments
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Bacteria may need to respond rapidly to changes in their environments, so must synthesize protein more rapidly
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Bacteria may need to degrade RNA rapidly
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Bacterial cells live in relatively safe, unchallenging environments
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The triplet group of bases which says, "Put this amino acid here" is called a/an:
Codon
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Anticodon
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Operator
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Promoter
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Initiator
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Proteins may be separated by a number of techniques, including isoelectric focusing. In isoelectric focusing, an artificial pH gradient is used in an electrophoresis chamber, and proteins mixed in the gradient migrate to the regions of their isoelectric points and then stop. Suppose that you set up a gel containing a mixture of acidic and basic substances ranging in pH from 3 to 10, and that you added a mixture of proteins and allowed them to move to the regions where they stopped migrating (their isoelectric pH, or pI). If you sliced the gel and found the protein
you were purifying was present in a slice having a pH of 4, you could be pretty confident that this protein:
Contained more acidic amino acids than basic amino acids
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Contained more basic amino acids than acidic amino acids
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Contained no basic amino acids
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Contained no acidic amino acids
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Contained an equal number of acidic and basic amino acids
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The complete set of proteins which can be synthesized by the organism's genome is called the:
Proteome
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Genomic
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Proteus
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Nucleome
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Ribosome
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Zymogens are inactive precursor molecules, often of extremely active digestive enzymes which are produced in inactive form and then converted to the active enzyme by removal of a protein "keeper." The type of post-translational modification involved in this case is:
Complete hydrolysis
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Proteolytic cleavage
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Methylation
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Phosphorylation
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Formation of disulfide bonds between cysteine residues of the same or different chains
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How many high-energy phosphate bonds need be broken to power inclusion of a single amino acid in a polypeptide?
Four
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Three
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Five
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Two
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One
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What is the source of energy used by aminoacyl-tRNA synthetase to power the reaction which attaches an amino acid to its tRNA?
CTP
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cAMP
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UTP
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ADP
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ATP
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Synthesis of both DNA and RNA start at the 5' end of the growing chain, or the 3' end of the template. Synthesis of protein, however, starts at the 5' end of the mRNA template. Of what value could this be to the organism?
This protects the growing polypeptide chain from hyperthermic denaturation
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This happens only in prokaryotes; in an organism as complicated as eukaryotes, protein synthesis can start at either end
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This makes it possible for transcription to begin while replication is still occurring
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Information can feed back from protein to modify transcription
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Translation can begin while transcription is occurring. This gives the organism a quick start at protein synthesis
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EF-Tu is a motor protein which positions aminoacyl-tRNA complexes in the amino acid site of the ribosome. Its major function in translation is as:
A replication factor
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An elongation factor
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A transition factor
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A factory worker
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A termination factor
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What does prokaryotic mRNA have that eukaryotic mRNA doesn't?
ATP sequences
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Termination factors
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Initiation factors
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Shine-Dalgarno sequences
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van der Waals forces
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