A holoenzyme is a combination of a protein and one or more substances called
apoenzymes.
catalysts.
cofactors.
substrates.
The Correct Answer is C
A. apoenzymes: An apoenzyme is the protein portion of an enzyme that is inactive on its own. It requires the binding of a cofactor or coenzyme to form a fully functional holoenzyme. Without this non-protein component, the apoenzyme cannot catalyze reactions efficiently.
B. catalysts: Catalysts are substances that speed up chemical reactions without being consumed in the process. While enzymes themselves act as biological catalysts, the term “catalyst” does not describe the non-protein component needed to form a holoenzyme.
C. cofactors: Cofactors are non-protein chemical substances, such as metal ions (e.g., Mg²⁺, Zn²⁺) or organic molecules (coenzymes), that bind to an apoenzyme to form a holoenzyme. The holoenzyme is the active enzyme capable of binding substrate and catalyzing a reaction, making cofactors essential for enzymatic activity.
D. substrates: Substrates are the molecules upon which enzymes act. They bind to the active site of the enzyme to undergo a chemical transformation. Substrates are not part of the enzyme structure and are not required to convert an apoenzyme into a holoenzyme.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is B
Explanation
A. Nucleus: Prokaryotic cells do not possess a true nucleus. A nucleus is a membrane-bound organelle that encloses DNA in eukaryotic cells, separating transcription from cytoplasmic processes. Because prokaryotes lack membrane-bound organelles, their genetic material is not enclosed within a nuclear membrane.
B. Nucleoid region: In prokaryotic cells, DNA is concentrated in an irregularly shaped area of the cytoplasm called the nucleoid. This region contains the bacterial chromosome, which is typically a single circular DNA molecule. The nucleoid is organized by DNA-binding proteins that help compact and regulate the genetic material for replication and transcription.
C. Mitochondria: Mitochondria are membrane-bound organelles responsible for aerobic energy production in eukaryotic cells. They contain their own mitochondrial DNA, but prokaryotic cells do not have mitochondria. Instead, energy generation in bacteria occurs across the plasma membrane through processes such as oxidative phosphorylation.
D. Ribosome: Ribosomes are cellular structures responsible for protein synthesis by translating messenger RNA into polypeptide chains. In prokaryotes, ribosomes are 70S and are found freely in the cytoplasm. They do not store or contain the cell’s DNA and therefore are not the location of genetic material.
Correct Answer is C
Explanation
A. double-stranded DNA: In double-stranded DNA, Chargaff’s rules apply: adenine pairs with thymine and guanine pairs with cytosine, so the percentages of A and T should be roughly equal, as should G and C. The viral nucleic acid shows 20% adenine and only 10% thymine, and 40% guanine with 30% cytosine, which violates these pairing rules, indicating it unlikely.
B. double-stranded RNA: Double-stranded RNA also follows base-pairing rules, with adenine pairing with uracil instead of thymine, and guanine pairing with cytosine. The unequal proportions of bases in this viral genome (e.g., A ≠ U, G ≠ C) suggest that it is not double-stranded RNA.
C. single-stranded RNA: Single-stranded RNA does not require complementary base pairing between strands, allowing unequal proportions of the four nucleotides. The observed percentages of adenine, guanine, cytosine, and thymine/uracil can vary widely, consistent with the data provided. This pattern supports the conclusion that the viral nucleic acid is single-stranded RNA.
D. single-stranded DNA: While single-stranded DNA does not require base pairing, thymine would still be present rather than uracil. However, the high guanine content (40%) and low thymine (10%) are unusual; still, the presence of thymine rather than uracil suggests that if it were RNA, thymine would be replaced with uracil, making single-stranded RNA more likely.
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