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CLEP Biology practice questions

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Question 1Molecular and Cellular Biology

Which molecule stores the genetic instructions that are translated into proteins in a cell?

  1. Messenger RNA
  2. Ribosomal RNA
  3. Deoxyribonucleic acid Correct answer.
  4. Transfer RNA

Explanation

DNA carries the heritable base sequence that is transcribed into mRNA and then translated into protein. The RNA types participate in converting or executing that information rather than storing it long term.

Question 2Molecular and Cellular Biology

A polypeptide is synthesized by covalently linking amino acids through which type of bond?

  1. Hydrogen bonds
  2. Peptide bonds Correct answer.
  3. Glycosidic bonds
  4. Phosphodiester bonds

Explanation

Amino acids are joined when the carboxyl group of one reacts with the amino group of the next, forming a peptide bond. This is a covalent linkage that builds the polypeptide backbone.

Question 3Molecular and Cellular Biology

Which organelle is the primary site of ATP production by oxidative phosphorylation in a eukaryotic cell?

  1. Lysosome
  2. Mitochondrion Correct answer.
  3. Golgi apparatus
  4. Smooth endoplasmic reticulum

Explanation

The inner mitochondrial membrane houses the electron transport chain and ATP synthase, which together carry out oxidative phosphorylation. Other organelles perform different specialized functions.

Question 4Molecular and Cellular Biology

During which phase of the cell cycle does DNA replication occur?

  1. M phase
  2. G1 phase
  3. S phase Correct answer.
  4. G2 phase

Explanation

Chromosomal DNA is duplicated during S phase, which lies between the two gap phases. G1 and G2 are growth phases, and M phase is when the duplicated chromosomes are separated and the cell divides.

Question 5Molecular and Cellular Biology

In a eukaryotic cell, the majority of ATP generated by aerobic respiration is produced where?

  1. In the nucleus during transcription
  2. In the lysosome during digestion
  3. In the cytosol during glycolysis
  4. On the inner mitochondrial membrane Correct answer.

Explanation

Glycolysis yields a small net amount of ATP in the cytosol, but the electron transport chain and ATP synthase on the inner mitochondrial membrane generate most of the ATP. This is why aerobic respiration yields far more ATP than glycolysis alone.

Question 6Molecular and Cellular Biology

Which of the following best describes the function of enzymes in a cell?

  1. They are consumed as reactants in reactions
  2. They lower the activation energy of reactions Correct answer.
  3. They supply energy directly to reactions
  4. They increase the activation energy of reactions

Explanation

Enzymes are catalysts that lower the activation energy required for a reaction, allowing it to proceed faster at physiological temperatures. They are not consumed and do not supply energy to the reaction.

Question 7Molecular and Cellular Biology

Which type of transport requires energy input from ATP to move substances against their concentration gradient?

  1. Facilitated diffusion
  2. Simple diffusion
  3. Active transport Correct answer.
  4. Osmosis

Explanation

Active transport uses energy, often from ATP hydrolysis, to move solutes against their concentration gradient. Diffusion and osmosis are passive processes that move substances down their gradients.

Question 8Molecular and Cellular Biology

Which of the following is a product of the light-dependent reactions of photosynthesis that is used in the Calvin cycle?

  1. Oxygen
  2. Carbon dioxide
  3. Glucose
  4. ATP and NADPH Correct answer.

Explanation

The light-dependent reactions generate ATP and NADPH, which supply energy and reducing power for carbon fixation in the Calvin cycle. Carbon dioxide is a substrate of the Calvin cycle, and oxygen is released as a byproduct.

Question 9Molecular and Cellular Biology

A single base substitution changes a codon but the encoded amino acid remains the same. What is this type of mutation called?

  1. Frameshift mutation
  2. Missense mutation
  3. Nonsense mutation
  4. Silent mutation Correct answer.

Explanation

A silent mutation alters the nucleotide sequence but not the amino acid sequence, often because of the redundancy of the genetic code. Frameshift and nonsense mutations typically change the protein product.

Question 10Molecular and Cellular Biology

An enzyme has a Km of 5 mM for its substrate. At a substrate concentration of 5 mM, what fraction of the maximum velocity is achieved?

  1. 100%
  2. 50% Correct answer.
  3. 75%
  4. 25%

Explanation

By definition, Km is the substrate concentration at which the reaction proceeds at half of maximum velocity. Therefore at a substrate concentration equal to Km, Vmax is half reached.

Question 11Molecular and Cellular Biology

A cell is placed in a hypertonic solution. What is the most likely immediate effect on the cell?

  1. It shrinks as water leaves Correct answer.
  2. It swells as water enters
  3. It remains unchanged in volume
  4. It bursts from osmotic pressure

Explanation

In a hypertonic solution, the solute concentration outside the cell is higher than inside, so water moves out by osmosis. This causes the cell to shrink.

Question 12Molecular and Cellular Biology

During glycolysis, one molecule of glucose is converted into two molecules of pyruvate. What is the net yield of ATP and NADH per glucose?

  1. 2 ATP and 4 NADH
  2. 2 ATP and 2 NADH Correct answer.
  3. 4 ATP and 4 NADH
  4. 4 ATP and 2 NADH

Explanation

Glycolysis consumes 2 ATP in its preparatory phase and produces 4 ATP in its payoff phase, giving a net of 2 ATP. Two NADH are also produced per glucose molecule.

Question 13Molecular and Cellular Biology

Which statement best explains why DNA replication is described as semiconservative?

  1. Only half of the DNA is replicated each cycle
  2. The original DNA is fully degraded and replaced
  3. Each daughter molecule contains two new strands
  4. Each daughter molecule contains one original and one new strand Correct answer.

Explanation

In semiconservative replication, the double helix separates and each original strand serves as a template for a new strand. Consequently each resulting double helix has one parental and one newly synthesized strand.

Question 14Molecular and Cellular Biology

A mRNA sequence reads 5'-AUG GCA UUU-3'. Using the standard genetic code, which amino acid sequence is produced?

  1. Leucine–Alanine–Phenylalanine
  2. Methionine–Alanine–Leucine
  3. Methionine–Glycine–Phenylalanine
  4. Methionine–Alanine–Phenylalanine Correct answer.

Explanation

AUG codes for methionine and also serves as a start codon, GCA codes for alanine, and UUU codes for phenylalanine. Reading the codons in order gives methionine–alanine–phenylalanine.

Question 15Molecular and Cellular Biology

Which process produces the genetic variation that arises from the exchange of segments between homologous chromosomes during meiosis?

  1. Cytokinesis
  2. Independent assortment
  3. DNA methylation
  4. Crossing over Correct answer.

Explanation

Crossing over occurs during prophase I when homologous chromosomes exchange corresponding segments, creating new combinations of alleles. Independent assortment shuffles whole chromosomes but does not exchange segments.

Question 16Molecular and Cellular Biology

A reaction is catalyzed by an enzyme, and a competitive inhibitor is added. Which change is expected in the kinetic parameters?

  1. Km is unchanged and Vmax decreases
  2. Km increases and Vmax is unchanged Correct answer.
  3. Both Km and Vmax decrease
  4. Both Km and Vmax increase

Explanation

A competitive inhibitor competes with substrate for the active site, so more substrate is needed to reach half-maximal velocity, raising the apparent Km. Because inhibition can be overcome at high substrate concentration, Vmax is unchanged.

Question 17Molecular and Cellular Biology

Which feature distinguishes prokaryotic cells from eukaryotic cells?

  1. Absence of a membrane-bound nucleus Correct answer.
  2. Presence of DNA
  3. Presence of a cell membrane
  4. Presence of ribosomes

Explanation

Prokaryotes lack a membrane-bound nucleus, so their DNA resides in a nucleoid region. Both cell types possess ribosomes, a plasma membrane, and DNA, so those features do not separate them.

Question 18Molecular and Cellular Biology

In the fluid mosaic model, which component primarily determines the selective permeability of the plasma membrane?

  1. The phospholipid bilayer Correct answer.
  2. Peripheral membrane proteins
  3. The glycocalyx
  4. Cholesterol molecules

Explanation

The hydrophobic core of the phospholipid bilayer restricts the passage of polar and charged molecules, giving the membrane its selective permeability. Proteins and cholesterol modulate membrane properties but the bilayer itself is the main barrier.

Question 19Molecular and Cellular Biology

A mutation deletes a single nucleotide near the beginning of a coding sequence. What is the most likely consequence for the resulting protein?

  1. A shift in the reading frame from that point onward Correct answer.
  2. Duplication of the entire gene
  3. A single amino acid substitution
  4. No change in the protein sequence

Explanation

Insertions or deletions of a number of nucleotides not divisible by three alter the reading frame downstream of the mutation. This frameshift typically changes many amino acids and often creates a premature stop codon.

Question 20Molecular and Cellular Biology

Which of the following correctly describes the role of the promoter in gene expression?

  1. It is the site where the polypeptide chain is assembled
  2. It removes introns from the mRNA transcript
  3. It is a DNA sequence where transcription machinery binds to initiate transcription Correct answer.
  4. It encodes the amino acid sequence of the protein

Explanation

A promoter is a regulatory DNA region that binds RNA polymerase and associated factors to start transcription. It does not encode protein sequence and is distinct from the ribosome and spliceosome.

Question 21Molecular and Cellular Biology

A researcher measures oxygen consumption in isolated mitochondria. Adding an uncoupling agent that makes the inner membrane permeable to protons would most likely cause which result?

  1. Both ATP synthesis and oxygen consumption remain unchanged
  2. ATP synthesis increases while oxygen consumption falls
  3. Both ATP synthesis and oxygen consumption fall
  4. ATP synthesis falls while oxygen consumption rises Correct answer.

Explanation

Uncouplers allow protons to bypass ATP synthase, so the proton gradient is dissipated and ATP synthesis decreases. The electron transport chain continues and even accelerates, so oxygen consumption increases as energy is released as heat.

Question 22Molecular and Cellular Biology

In a cell, a mutation inactivates the enzyme that converts pyruvate to acetyl-CoA. Which metabolic outcome is most directly affected?

  1. Formation of the mitotic spindle
  2. Translation of mRNA at the ribosome
  3. The light reactions of photosynthesis
  4. Entry of carbon from glucose into the citric acid cycle Correct answer.

Explanation

Pyruvate is converted to acetyl-CoA before entering the citric acid cycle, so blocking this step limits carbon flow into the cycle. The other processes are not directly dependent on this conversion.

Question 23Molecular and Cellular Biology

A diploid cell with genotype AaBb undergoes meiosis, and the two gene loci are on different chromosomes. Assuming no crossing over, what proportion of gametes is expected to carry the genotype AB?

  1. 1/4 Correct answer.
  2. 3/4
  3. 1/2
  4. 1/8

Explanation

With independent assortment of two heterozygous loci on separate chromosomes, four gamete types (AB, Ab, aB, ab) are produced in equal proportions. Each type therefore accounts for one quarter of the gametes.

Question 24Molecular and Cellular Biology

A tRNA molecule has an anticodon that pairs with the mRNA codon 5'-GCA-3'. Which anticodon sequence on the tRNA is complementary and antiparallel to this codon?

  1. 5'-UGC-3' Correct answer.
  2. 5'-ACG-3'
  3. 5'-CGU-3'
  4. 5'-GCA-3'

Explanation

The anticodon is antiparallel and complementary to the codon, so it pairs G with C and C with G. Reading the complement of 5'-GCA-3' antiparallel gives 5'-UGC-3'.

Question 25Molecular and Cellular Biology

Two enzymes catalyze the same reaction but have different Km values. Which statement best predicts their behavior at a low substrate concentration well below either Km?

  1. The enzyme with the higher Km will have the higher fractional saturation
  2. The enzyme with the lower Km will have the higher fractional saturation Correct answer.
  3. Both enzymes will be fully saturated
  4. Neither enzyme will bind substrate

Explanation

A lower Km indicates a higher affinity for substrate, so at a given low substrate concentration that enzyme binds a larger fraction of its active sites. Fractional saturation rises toward one only when substrate greatly exceeds Km.

Question 26Molecular and Cellular Biology

Which molecule serves as the primary energy currency of the cell, directly powering most cellular processes?

  1. Glucose
  2. ATP Correct answer.
  3. FADH2
  4. NADPH

Explanation

ATP is the universal energy currency because its terminal phosphate bond can be hydrolyzed to release free energy that drives endergonic reactions. While NADPH and FADH2 carry electrons, they are not the direct energy currency for most processes.

Question 27Molecular and Cellular Biology

Which of the following is a major function of the smooth endoplasmic reticulum?

  1. Generation of ATP through oxidative phosphorylation
  2. Translation of mRNA into proteins
  3. Modification and packaging of proteins for secretion
  4. Synthesis of lipids and detoxification of drugs Correct answer.

Explanation

The smooth ER lacks ribosomes and is specialized for lipid synthesis, detoxification, and calcium storage. Protein modification and packaging occur in the Golgi apparatus, ATP generation in mitochondria, and translation on ribosomes.

Question 28Molecular and Cellular Biology

In the context of the cell cycle, what is the primary role of cyclin-dependent kinases (CDKs)?

  1. They activate DNA repair mechanisms exclusively during G1 phase.
  2. They degrade cyclins to exit mitosis.
  3. They phosphorylate target proteins to drive cell cycle progression when bound to cyclins. Correct answer.
  4. They condense chromosomes during prophase.

Explanation

CDKs are enzymes that, when activated by binding to cyclins, phosphorylate specific target proteins to trigger transitions between cell cycle phases. Cyclin degradation leads to CDK inactivation, but CDKs themselves do not degrade cyclins.

Question 29Molecular and Cellular Biology

Which of the following best describes the role of the electron transport chain in oxidative phosphorylation?

  1. It establishes a proton gradient that drives ATP synthesis. Correct answer.
  2. It converts pyruvate to acetyl-CoA.
  3. It produces NADH and FADH2.
  4. It directly phosphorylates ADP to form ATP.

Explanation

The electron transport chain transfers electrons from NADH and FADH2 to oxygen, pumping protons across the inner mitochondrial membrane to create a proton motive force. ATP synthase then uses this gradient to phosphorylate ADP, but the chain itself does not directly phosphorylate ADP.

Question 30Molecular and Cellular Biology

Which of the following statements about the citric acid cycle is correct?

  1. It produces a net gain of two ATP molecules per glucose molecule.
  2. It oxidizes acetyl-CoA and produces NADH, FADH2, and GTP/ATP. Correct answer.
  3. It occurs in the cytoplasm of eukaryotic cells.
  4. It directly uses oxygen as a substrate to oxidize acetyl-CoA.

Explanation

The citric acid cycle oxidizes acetyl-CoA, generating reduced electron carriers (NADH and FADH2) and one GTP (or ATP) per turn. In eukaryotes, it takes place in the mitochondrial matrix, not the cytoplasm, and oxygen is not directly consumed in the cycle.

Question 31Molecular and Cellular Biology

Which of the following is a key difference between DNA and RNA?

  1. DNA contains deoxyribose and thymine, while RNA contains ribose and uracil. Correct answer.
  2. DNA is usually single-stranded, while RNA is double-stranded.
  3. DNA contains uracil, while RNA contains thymine.
  4. DNA is found only in the nucleus, while RNA is found only in the cytoplasm.

Explanation

DNA has deoxyribose sugar and the base thymine, whereas RNA has ribose and uracil. DNA is typically double-stranded, and both DNA and RNA can be found in multiple cellular compartments.

Question 32Molecular and Cellular Biology

Which of the following correctly describes the function of the Golgi apparatus?

  1. It contains hydrolytic enzymes for intracellular digestion.
  2. It modifies, sorts, and packages proteins and lipids for transport. Correct answer.
  3. It serves as the site of ribosomal RNA synthesis.
  4. It synthesizes ATP through oxidative phosphorylation.

Explanation

The Golgi apparatus modifies proteins and lipids received from the ER and packages them into vesicles for transport to their final destinations. ATP synthesis occurs in mitochondria, digestion in lysosomes, and rRNA synthesis in the nucleolus.

Question 33Molecular and Cellular Biology

Which of the following is a difference between facilitated diffusion and active transport?

  1. Facilitated diffusion requires ATP, while active transport uses ion gradients only.
  2. Facilitated diffusion moves substances against their concentration gradient, while active transport moves them down their gradient.
  3. Facilitated diffusion is used only for ions, while active transport is used only for large molecules.
  4. Facilitated diffusion does not require energy input, while active transport does. Correct answer.

Explanation

Facilitated diffusion is a passive process that uses membrane proteins to move substances down their concentration gradient without energy input. Active transport requires energy, often from ATP, to move substances against their gradient.

Question 34Molecular and Cellular Biology

A cell is placed in a hypotonic solution. What is the most likely immediate effect on the cell?

  1. The cell loses its membrane potential.
  2. The cell undergoes plasmolysis.
  3. Water leaves the cell, causing it to shrink.
  4. Water enters the cell, causing it to swell. Correct answer.

Explanation

In a hypotonic solution, the solute concentration outside the cell is lower than inside, so water moves into the cell by osmosis, causing it to swell. Shrinking and plasmolysis occur in hypertonic solutions.

Question 35Molecular and Cellular Biology

Which of the following best describes the role of the enzyme helicase during DNA replication?

  1. It joins Okazaki fragments on the lagging strand.
  2. It adds nucleotides to the growing DNA strand.
  3. It unwinds the DNA double helix by breaking hydrogen bonds between base pairs. Correct answer.
  4. It synthesizes RNA primers for DNA polymerase.

Explanation

Helicase unwinds the DNA double helix by disrupting the hydrogen bonds between complementary bases, creating replication forks. Primase synthesizes RNA primers, ligase joins Okazaki fragments, and DNA polymerase adds nucleotides.

Question 36Molecular and Cellular Biology

Which of the following is true regarding the genetic code?

  1. It is overlapping, so each nucleotide is part of only one codon.
  2. It is degenerate, meaning multiple codons can specify the same amino acid. Correct answer.
  3. It is universal, with no exceptions across all organisms.
  4. It is ambiguous, so a single codon can specify multiple amino acids.

Explanation

The genetic code is degenerate because most amino acids are encoded by more than one codon. It is non-overlapping, unambiguous, and nearly universal, though some exceptions exist in mitochondria and certain organisms.

Question 37Molecular and Cellular Biology

During translation, what is the function of the release factor?

  1. It brings amino acids to the ribosome.
  2. It initiates translation by binding to the small ribosomal subunit.
  3. It catalyzes the formation of peptide bonds.
  4. It recognizes a stop codon and promotes termination of translation. Correct answer.

Explanation

Release factors recognize stop codons (UAA, UAG, UGA) in the A site and trigger the hydrolysis of the peptidyl-tRNA bond, releasing the completed polypeptide. Aminoacyl-tRNAs bring amino acids, peptidyl transferase forms peptide bonds, and initiation factors promote initiation.

Question 38Molecular and Cellular Biology

Which of the following is an example of post-translational modification?

  1. Addition of a 5' cap to mRNA
  2. Transcription of DNA into RNA
  3. Splicing of introns from pre-mRNA
  4. Phosphorylation of a protein by a kinase Correct answer.

Explanation

Post-translational modifications occur after the polypeptide is synthesized and include phosphorylation, glycosylation, and cleavage. Capping and splicing are co-transcriptional or post-transcriptional RNA processing events, and transcription is the synthesis of RNA.

Question 39Molecular and Cellular Biology

Which of the following correctly describes the difference between prokaryotic and eukaryotic ribosomes?

  1. Eukaryotic ribosomes are found only in the nucleus.
  2. Prokaryotic ribosomes are larger and have more rRNA.
  3. Prokaryotic ribosomes are 70S, while eukaryotic cytosolic ribosomes are 80S. Correct answer.
  4. Prokaryotic ribosomes lack a small subunit.

Explanation

Prokaryotic ribosomes are 70S (composed of 50S and 30S subunits), whereas eukaryotic cytosolic ribosomes are 80S (60S and 40S subunits). Both have small and large subunits, and eukaryotic ribosomes are in the cytoplasm, not the nucleus.

Question 40Molecular and Cellular Biology

Which of the following best describes the function of the enzyme DNA ligase?

  1. It joins Okazaki fragments by forming phosphodiester bonds. Correct answer.
  2. It unwinds the DNA double helix.
  3. It proofreads newly synthesized DNA.
  4. It synthesizes RNA primers.

Explanation

DNA ligase catalyzes the formation of phosphodiester bonds between adjacent DNA fragments, such as Okazaki fragments on the lagging strand. Helicase unwinds DNA, primase synthesizes primers, and DNA polymerase proofreads.

Question 41Molecular and Cellular Biology

A mutation changes a codon from UAC to UAA. What type of mutation is this?

  1. Frameshift mutation
  2. Nonsense mutation Correct answer.
  3. Silent mutation
  4. Missense mutation

Explanation

UAA is a stop codon, so a change from UAC (tyrosine) to UAA introduces a premature stop codon, which is a nonsense mutation. A missense mutation changes the amino acid, a silent mutation does not change the amino acid, and a frameshift alters the reading frame.

Question 42Molecular and Cellular Biology

Which of the following is a difference between mitosis and meiosis?

  1. Mitosis occurs only in gametes, while meiosis occurs in somatic cells.
  2. Mitosis reduces the chromosome number by half, while meiosis maintains it.
  3. Mitosis produces two genetically identical diploid cells, while meiosis produces four genetically diverse haploid cells. Correct answer.
  4. Mitosis involves crossing over, while meiosis does not.

Explanation

Mitosis produces two identical diploid daughter cells for growth and repair, whereas meiosis produces four haploid gametes with genetic variation due to crossing over and independent assortment. Mitosis occurs in somatic cells, and meiosis reduces chromosome number.

Question 43Molecular and Cellular Biology

Which of the following best explains how ATP synthase produces ATP in mitochondria?

  1. ATP synthase uses the energy of GTP hydrolysis to synthesize ATP.
  2. ATP synthase directly transfers a phosphate from a substrate to ADP.
  3. Protons flow through ATP synthase down their electrochemical gradient, driving rotation and catalysis. Correct answer.
  4. Electrons are transferred from NADH to ATP synthase, which uses the energy to phosphorylate ADP.

Explanation

ATP synthase is a rotary motor enzyme that uses the proton motive force generated by the electron transport chain. Protons flow through the enzyme, causing conformational changes that drive the phosphorylation of ADP. It does not directly receive electrons or use GTP hydrolysis.

Question 44Molecular and Cellular Biology

In the lac operon, what happens when lactose is present and glucose is absent?

  1. The repressor is inactivated and CAP activates transcription, leading to high expression. Correct answer.
  2. The operon is fully repressed due to catabolite repression.
  3. CAP is inactive, and transcription occurs at a low basal level.
  4. The repressor binds to the operator, blocking transcription.

Explanation

When lactose is present, it binds to the lac repressor, causing it to release from the operator. When glucose is absent, cAMP levels rise, and CAP-cAMP binds to the promoter to strongly activate transcription. Thus, the operon is highly expressed.

Question 45Molecular and Cellular Biology

A researcher adds a drug that inhibits the enzyme that adds the 5' cap to mRNA. Which step of gene expression is most directly affected?

  1. Transcription elongation
  2. Translation initiation Correct answer.
  3. DNA replication
  4. RNA splicing

Explanation

The 5' cap is essential for ribosome recognition and translation initiation. Inhibiting capping would impair the binding of initiation factors and ribosomes, reducing translation. Capping is not directly involved in transcription elongation, splicing, or DNA replication.

Question 46Molecular and Cellular Biology

Which of the following correctly describes the role of the signal recognition particle (SRP) in protein targeting?

  1. It unfolds proteins for degradation by the proteasome.
  2. It binds to a signal peptide on a nascent polypeptide and directs the ribosome to the ER. Correct answer.
  3. It adds mannose-6-phosphate tags to lysosomal enzymes.
  4. It transports proteins from the Golgi to lysosomes.

Explanation

The SRP recognizes the signal peptide on a growing polypeptide chain, pauses translation, and docks the ribosome to the SRP receptor on the ER membrane. This allows co-translational translocation into the ER. Mannose-6-phosphate tagging occurs in the Golgi, not by SRP.

Question 47Molecular and Cellular Biology

If a cell is treated with a drug that inhibits the sodium-potassium pump (Na+/K+ ATPase), what is the most likely immediate effect?

  1. Intracellular sodium concentration will decrease.
  2. The resting membrane potential will gradually depolarize. Correct answer.
  3. The cell will swell due to water influx.
  4. Potassium will accumulate inside the cell.

Explanation

The Na+/K+ ATPase maintains the resting membrane potential by pumping three Na+ out and two K+ in, creating a negative interior. Inhibiting it would cause ion gradients to dissipate, leading to depolarization. It would not directly cause swelling or decrease intracellular sodium.

Question 48Molecular and Cellular Biology

Which of the following statements about competitive inhibition is correct?

  1. A competitive inhibitor increases the apparent Km of the enzyme. Correct answer.
  2. A competitive inhibitor binds irreversibly to the enzyme.
  3. A competitive inhibitor decreases the Vmax of the enzyme.
  4. A competitive inhibitor binds to the enzyme-substrate complex.

Explanation

A competitive inhibitor competes with the substrate for the active site, so higher substrate concentrations are needed to reach half-maximal velocity, increasing the apparent Km. Vmax remains unchanged because inhibition can be overcome by high substrate concentration. Competitive inhibitors are typically reversible and bind to the free enzyme, not the ES complex.

Question 49Molecular and Cellular Biology

Which of the following is a key feature of the fluid mosaic model of the plasma membrane?

  1. Membrane proteins can move laterally within the lipid bilayer. Correct answer.
  2. The membrane is composed entirely of phospholipids with no proteins.
  3. Lipids are covalently linked to proteins to form a solid sheet.
  4. The membrane is a rigid, static structure.

Explanation

The fluid mosaic model describes the membrane as a fluid bilayer in which proteins and lipids can move laterally. The membrane is not rigid, and it contains both lipids and proteins.

Question 50Molecular and Cellular Biology

Which of the following correctly pairs a cytoskeletal element with its primary function?

  1. Intermediate filaments – serve as tracks for vesicle transport
  2. Microfilaments – cell movement and shape changes Correct answer.
  3. Microfilaments – form the spindle apparatus during mitosis
  4. Microtubules – provide tensile strength to resist stretching

Explanation

Microfilaments (actin filaments) are involved in cell movement, shape changes, and cytokinesis. Microtubules form the spindle and serve as tracks for transport, while intermediate filaments provide mechanical strength.