Concepts in Biochemistry, Chapter 12

1. The site of protein synthesis is:
A.DNA
B.The ribosome
C.The nucleus
D.The cell membrane


2. To make protein, the cell must first transcribe the genetic code from DNA to produce mRNA. The genetic code on mRNA is in the form of codons, which are:
A.Helix-turn-helix structures
B.Positively charged bases
C.A set of three adjacent bases
D.DNA-RNA hybrids


3. Each codon on mRNA codes for one amino acid. The codons are non-overlapping, and they do not have punctuation between them. Codons are universal, meaning that the same genetic code is used for almost all organisms. Codons are also degenerate, meaning:
A.They can be read backwards.
B.A single amino acid may be specified by more than one codon.
C.They may or may not bind to ribosomes.
D.They contain radioactive carbon centers.


4. The adaptor molecule that allows the nucleic acid code of mRNA to be translated into the amino acid sequence of proteins is tRNA. Only activated tRNAs participate in protein synthesis. A tRNA is said to be activated if it contains:
A.A specific sequence at its 5' end
B.A radioactive carbonyl group
C.An anticodon
D.An ester-linked amino acid at its 3' end


5. Protein synthesis begins when mRNA, ribosomes, GTP, initiation factors and fMETtRNA come together to form the _______________. fMETtRNA sits in the ___ site and binds to the AUG codon on mRNA, leaving the ___ site open for the next activated tRNA to come into the initiation complex. Protein synthesis begins when a _______________ bond forms between the fMET of the first tRNA and the _______________ of the second tRNA. Protein synthesis continues as the ribosome complex moves toward the ___ end of mRNA. This movement is called _______________ and results in the first tRNA leaving the complex while the second tRNA containing the growing protein moves into the vacated spot. Protein synthesis proceeds in this fashion until a termination signal, called a _______________ codon, is reached on the mRNA. Finally, release factors hydrolyze the bond between the tRNA and the newly synthesized protein.

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6. After synthesis, proteins undergo different kinds of alterations, sorting, and decay. Enter "T" or "F" to indicate if each event is correctly or incorrectly matched with its proper biochemical modification category.
___ Prosthetic Group addition and Heme, FAD, and biotin attachment
___ Protein Degradation and Ubiquitin pathway
___ Proteolytic Cleavage and Conversion of zymogen to active enzyme
___ Protein Targeting and Signal sequence
___ Glycoprotein Synthesis and Carbohydrate attachment
___ Amino Acid Modification and Serine phosphorylation

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7. Protein synthesis is most often regulated at the level of gene expression. In prokaryotic cells, genes are often clustered in a group called an operon. In the blank spaces, enter the letters shown in the diagram to correctly label the descriptions of the operon parts.
-------A----------------B--------C------------------------D


___ Structural genes
___ Promoter
___ Repressor binding site (operator)
___ Activator binding site

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8. Regulation of gene expression can take different forms. __________ regulation is when an activator binds to the DNA and transcription proceeds. In __________ regulation, binding of repressor inhibits transcription. In both cases, the activator or repressor may work in concert with a molecular signal to either bind or dissociate from the DNA.

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9. Regulatory proteins all have the ability to bind DNA, primarily in the major groove. Which of the following are examples of regulatory protein structure motifs?
A.Leucine zipper
B.Inducible motif
C.Minor groove
D.Clawed motif


10. Several gene regulatory systems have been described. The __________ operon is repressed in the absence of lactose, or presence of glucose in the medium. The __________ operon is inhibited by the presence of tryptophan in the medium. The presence of heavy metals causes metal transcription factors to bind to __________ response elements. This activates the transcription of metallothionine, a protein that facilitates the removal of heavy metals from the cell. Estrogen and glucocorticoids, for example, diffuse through cell membranes to bind to specific regions on the DNA called __________ response elements.

Answer:



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