Chapter 7

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Which of the following statements are correct? Explain your answers.

A. an individual ribosome can make only one type of protein.
B. All mRNAs fold into particular three-dimensional structures that are required for their translation.
C. The large and small subunits of an individual ribosome always stay together and never exchange partners.
D. Ribosomes are cytoplasmic organelles that are excapsulated by a single membrane.
E. Because the two strands of DNA are complementary, the mRNA of a given gene can be synthesized using either strand as a template.
F. An mRNA may contain the sequence ATTGACCCCGGTCAA.
G. The amount of a protein present in the cell depends on its rate of synthesis, its catalytic activity, and its rate of degradation.

The Lacheinmal protein is a hypothetical protein that causes people to smile more often so drugs. It is inactive in many chronically unhappy people like Marvin. The mRNA isolated from a number of different unhappy persons in the same family are found to lack an internal stretch of 173 nucleotides that is present in the Lacheinmal mRNA isolated from a control group of happy people. The DNA sequences of the Lacheinmal genes from the happy and the unhappy families were determined and compared. They differed by a single nucleotide substitution, which lay in an intron. What can you say about the molecular basis of unhappiness in this family?

(Hints: [1] Can you hypothesize a molecular mechanism by which a single nucleotide substitution in a gene could cause the observed deletion in the mRNA? Note that the deletion is internal to the mRNA. [2] Assuming the 173 base-pair deletion removed coding sequences from the Lacheinmal mRNA, how would the Lacheinmal protein differ between the unhappy and happy people?)

Identify the sequence that codes for the polypeptide sequence arginine-glycine-aspartate.
1. 5'-AGA-GGA-GAU-3'
2. 5'-ACA-CCC-ACU-3'
3. 5'-GGG-AAA-UUU-3'
4. 5'-CGG-GGU-GAC-3'

"The bonds that form between the anticodon of a tRNA molecule and the three nucleotides of a codon in mRNA are __." Complete this sentence with each of the following options and explain why each of the resulting statements is correct or incorrect.

A. Covalent bonds form by GTP hydrolysis.
B. Hydrogen bonds that form when the tRNA is at the A-site.
C. Broken by the translocation of the ribosomes along the mRNA.


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