OAT Cell and Molecular Biology Questions and Answers — Questions and Answers
Question 1: A cell biologist is studying a cell line that has a diminished capacity to synthesize lipids and detoxify certain drugs. Microscopic examination reveals a significant reduction in the abundance of a specific organelle. Which of the following organelles is most likely deficient in these cells?
- Golgi apparatus
- Smooth endoplasmic reticulum (Correct answer)
- Lysosome
- Rough endoplasmic reticulum
Correct answer: Smooth endoplasmic reticulum
The smooth endoplasmic reticulum (SER) is the primary site for lipid synthesis, including steroids, and is responsible for the detoxification of drugs and poisons. A deficiency in the SER would directly lead to the observed cellular dysfunctions. The rough ER is involved in protein synthesis, the Golgi apparatus modifies and packages proteins, and lysosomes are involved in waste breakdown.
Question 2: During the process of transcription in a eukaryotic cell, which enzyme is responsible for synthesizing a pre-mRNA molecule by reading the DNA template strand?
- DNA Polymerase III
- Helicase
- RNA Polymerase II (Correct answer)
- Primase
Correct answer: RNA Polymerase II
RNA Polymerase II is the key enzyme in eukaryotes that synthesizes precursors of mRNA (pre-mRNA) and most small nuclear RNAs (snRNAs) and microRNAs. DNA Polymerase III is involved in DNA replication. Helicase unwinds the DNA double helix. Primase synthesizes RNA primers for DNA replication.
Question 3: Which of the following events is a key distinguishing feature of Meiosis I when compared to Mitosis?
- Separation of sister chromatids
- Formation of a spindle apparatus
- Synapsis of homologous chromosomes (Correct answer)
- Condensation of chromatin
Correct answer: Synapsis of homologous chromosomes
Synapsis, the pairing of homologous chromosomes to form bivalents (or tetrads), occurs during Prophase I of meiosis. This event allows for crossing over and is unique to meiosis, not occurring in mitosis. Separation of sister chromatids occurs in both Mitosis (Anaphase) and Meiosis II (Anaphase II). Spindle formation and chromatin condensation occur in both mitosis and meiosis.
Question 4: A scientist develops a new drug that binds to an enzyme at a location other than the active site. This binding event changes the enzyme's three-dimensional shape, rendering it inactive. What type of inhibition does this scenario describe?
- Competitive inhibition
- Feedback inhibition
- Irreversible inhibition
- Noncompetitive inhibition (Correct answer)
Correct answer: Noncompetitive inhibition
Noncompetitive inhibition occurs when an inhibitor binds to an allosteric site (a site other than the active site) on the enzyme. This binding changes the enzyme's conformation, so its active site is no longer fully functional, regardless of the substrate concentration. Competitive inhibition involves binding directly to the active site.
Question 5: The sodium-potassium pump is a crucial protein for maintaining cellular membrane potential. It actively transports three sodium ions out of the cell for every two potassium ions it transports into the cell. This process directly requires which of the following?
- Facilitated diffusion
- Osmosis
- Hydrolysis of ATP (Correct answer)
- A hypertonic extracellular environment
Correct answer: Hydrolysis of ATP
The sodium-potassium pump is a form of primary active transport, meaning it moves ions against their electrochemical gradients. This energetically unfavorable process is powered by the hydrolysis of adenosine triphosphate (ATP) into adenosine diphosphate (ADP) and inorganic phosphate, which provides the necessary energy.
Question 6: The primary structure of a protein is ultimately determined by which of the following?
- The sequence of amino acids (Correct answer)
- Hydrogen bonding between backbone atoms
- Interactions between R-groups
- The arrangement of multiple polypeptide subunits
Correct answer: The sequence of amino acids
The primary structure of a protein is the unique linear sequence of its amino acids, linked by peptide bonds. This sequence is dictated by the genetic information in mRNA. Secondary structure (alpha-helices, beta-sheets) is formed by hydrogen bonding. Tertiary structure is the 3D shape from R-group interactions. Quaternary structure involves multiple polypeptide chains.
OAT Cell and Molecular Biology Questions and Answers
A cell biologist is studying a cell line that has a diminished capacity to synthesize lipids and detoxify certain drugs.
Microscopic examination reveals a significant reduction in the abundance of a specific organelle.
Which of the following organelles is most likely deficient in these cells?