Question 1

Individuals with two copies of a certain loss-of-function PMM2 allele suffer from hypotonia (weak muscle tone), and about 20 percent of these individuals will die of multiple organ failure during their first year of life.The PMM2 gene codes for an enzyme that is involved in the process of _______, which adds sugars to proteins on certain amino acid R groups on proteins.The modification of target proteins by this process is necessary for these proteins to fulfill their functional roles.

Accepted Answer

The answer of Individuals with two copies of a certain...

Question 2

The disease called branched-chain ketoaciduria is commonly known as maple syrup urine disease, as the urine of a person with the condition has a smell similar to that of maple syrup.Because the disease is rare and most often appears in children whose parents are first cousins, one can conclude that the disease is inherited as an autosomal _______ phenotype.

Accepted Answer

The answer of The disease called branched-chain ketoaciduria is commonly...

Question 3

Which statement about RNA is false?

Accepted Answer

Messenger RNAs (mRNAs) are not produced on ribosomes. They are produced by transcription in the nucleus and then transported to the cytoplasm where they are translated by ribosomes.

Question 4

The central dogma of molecular biology states that DNA is transcribed into _______, which is translated into protein

Accepted Answer

The answer of The central dogma of molecular biology states...

Question 5

Refer to the figure, which shows the genetic code.  Which single base substitution in the coding strand of DNA would result in premature termination of translation?

Accepted Answer

The codon CGA codes for the amino acid arginine, but if it is changed to UGA, it becomes a stop codon, causing premature termination of translation.

Question 6

The translation of mRNA occurs in the _______ of the eukaryotic cell.

Accepted Answer

The answer of The translation of mRNA occurs in the...

Question 7

Ribozymes are RNA molecules that have enzymatic activity.This conflicts with the belief of early molecular biologists that

Accepted Answer

Early molecular biologists believed that enzymes were proteins, specifically polypeptides, and ribozymes being RNA with enzymatic activity challenged this belief.

Question 8

Biologists often describe organisms that are easy to manipulate as _______ organisms.

Accepted Answer

The answer of Biologists often describe organisms that are easy...

Question 9

The language of mRNA (nucleotide codons) is translated into the language of protein (amino acids) through the actions of _______.

Accepted Answer

The answer of The language of mRNA (nucleotide codons) is...

Question 10

A researcher purifies numerous different eukaryotic mRNA species and carries out nucleic acid hybridization to identify the genes encoding the various mRNAs.As expected, the presence of exons within the genomic DNA creates regions in which there is no mRNA sequence to hybridize with the DNA.The researcher also notes that at the 3′ end of all of the mRNA species, there are RNA sequences that fails to anneal with the DNA.The researcher concludes that these RNA sequences must correspond to _______.

Accepted Answer

The answer of A researcher purifies numerous different eukaryotic mRNA...

Question 11

An individual has a metabolic disorder that is traced to an enzyme composed of two different subunits, one larger than the other.The patient has an allele of the smaller subunit that produces a protein that is abnormally large, and when it binds to the other subunit of the enzyme, the enzymatic activity is lost.Analysis of the mRNA sequence identifies a mutation in the 3′ region of a gene that has turned a UAA codon to UUA.Based on this modification, the clinical researcher hypothesizes that during the elongation cycle in the patient, there is a failure to recruit the _______ at the correct site in the mRNA sequence.This results in the translation of an abnormally long peptide.

Accepted Answer

The answer of An individual has a metabolic disorder that...

Question 12

A strain of Neurospora is able to grow on minimal medium.When substance A is added to the medium, however, the strain cannot grow.Supplying a small amount of substance B has no effect on the strain, but it cannot reverse the effect of substance A.Supplying a small amount of substance C, by contrast, enables the strain to grow with substance A.Which of the following statements best explains these facts?

Accepted Answer

Substance A is a toxin that the strain cannot break down, and substance C is an enzyme that breaks down substance A. Substance B has no effect on the strain and cannot reverse the effect of substance A, indicating that it is not an enzyme that breaks down substance A. Therefore, option B is the best choice. The strain's ability to grow with substance A in the presence of substance C suggests that substance C is an enzyme that can break down substance A. Option A is incorrect because substance B is not an enzyme that breaks down substance A. Option C may be plausible, but it is not supported by the information given in the question. Options D and E are incorrect because the question does not provide any indication that either substance A or C is a mutagen.

Question 13

Initiation of translation of an mRNA has begun, then suddenly ceases after about 20 _______ amino acids are detected at the N terminus.When the entire complex-mRNA and ribosome-binds to a specific signal recognition particle on the RER, translation resumes.

Accepted Answer

The answer of Initiation of translation of an mRNA has...

Question 14

A culture of cells is treated with a protease inhibitor that specifically blocks the activity of proteases in the RER.What effect would this have on proteins that contain the sequence -Pro-Pro-Lys-Lys-Lys-Arg-Lys-Val-?

Accepted Answer

The sequence -Pro-Pro-Lys-Lys-Lys-Arg-Lys-Val- is a nuclear localization signal (NLS), which directs proteins to the nucleus. Blocking proteases in the RER would not affect the transport of proteins with an NLS to the nucleus.

Question 15

When the introns are removed from pre-mRNA, the exons must be _______ together to form mRNA.

Accepted Answer

The answer of When the introns are removed from pre-mRNA,...

Question 16

If the coding region of an mRNA is 2,400 nucleotides long, how many codons does it have?

Accepted Answer

Each codon consists of 3 nucleotides, so 2,400 nucleotides divided by 3 equals 800 codons.

Question 17

Which scenario supports Garrod's one-gene, one-enzyme hypothesis of metabolic disease causation?

Accepted Answer

Garrod's one-gene, one-enzyme hypothesis proposes that genetic disorders are caused by the absence or alteration of a single enzyme catalyzing a specific metabolic pathway. PKU (phenylketonuria) is a classic example of a metabolic disease caused by a mutation in a single gene that codes for an enzyme called phenylalanine hydroxylase, which is required for the breakdown of the amino acid phenylalanine. Without this enzyme, excess phenylalanine accumulates and can lead to severe neurological damage.

Question 18

Comparison of the same gene and its product in two different animal species revealed that the amino acids are 98 percent identical but the nucleotides are only 86 percent identical.What accounts for the much higher amino acid identity than nucleotide identity?

Accepted Answer

The genetic code is redundant, meaning that different nucleotide sequences can code for the same amino acid. Therefore, changes in nucleotides may not necessarily lead to changes in amino acids, resulting in a higher level of amino acid identity compared to nucleotide identity.

Question 19

Gene X encodes an enzyme subunit.A researcher is studying an allele of gene X that does not produce a protein product.Experiments show that the pre-mRNA transcript undergoes RNA processing and is successfully transported out of the nucleus.However, in the cytoplasm, the mRNAs accumulate without binding to ribosomes.These results suggest a problem with the addition of the _______ to the pre-mRNA.

Accepted Answer

The answer of Gene X encodes an enzyme subunit.A researcher...

Question 20

An mRNA sequence is 5'-CAGUUACGA...UAAGC-3' ([…] denotes intervening sequences).What is the sequence of the template strand of DNA?

Accepted Answer

The template strand of DNA is complementary and antiparallel to the mRNA sequence. Therefore, the mRNA sequence 5'-CAGUUACGA...UAAGC-3' corresponds to a DNA template strand of 3'-GTCAATGCT...ATTCG-5', which is option D.

Quiz 14: From Dna to Protein: Gene Expression