Glycolysis and TCA Cycle Practice Questions
20 free Glycolysis and TCA Cycle practice questions for the Zoology. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
Which level of protein structure is stabilized mainly by hydrogen bonds between peptide backbone groups?
- A Primary structure
- B Secondary structure
- C Tertiary structure
- D Quaternary structure
Correct answer: Secondary structure
Secondary structure includes alpha-helices and beta-sheets stabilized by hydrogen bonds between the backbone carbonyl oxygen and amide hydrogen. These interactions do not involve side chains.
Which amino acid side chain can both donate and accept protons at physiological pH, making it common in enzyme active sites?
- A Aspartate
- B Lysine
- C Histidine
- D Cysteine
Correct answer: Histidine
Histidine's imidazole side chain has a pKa near 6, so at pH 7.4 it sits close to its titration midpoint and can pick up or release a proton with equal ease — ideal for general acid-base catalysis. Aspartate (pKa about 3.9) is fully deprotonated at this pH, while lysine (about 10.5) and cysteine (about 8.3) are largely protonated, so none of them can shuttle protons both ways under physiological conditions.
The Michaelis constant (Km) of an enzyme reflects the:
- A The maximum attainable reaction velocity of the enzyme
- B Enzyme concentration
- C Substrate level at half-maximal velocity
- D Rate constant of product formation
Correct answer: Substrate level at half-maximal velocity
Km is the substrate concentration at which the reaction rate is half of Vmax. It provides an inverse measure of enzyme–substrate affinity.
Which type of inhibition increases the apparent Km without changing Vmax?
- A Noncompetitive inhibition
- B Uncompetitive inhibition
- C Competitive inhibition
- D Irreversible inhibition
Correct answer: Competitive inhibition
Competitive inhibitors compete with the substrate for the active site, requiring higher substrate concentrations to reach half-maximal velocity. Vmax remains unchanged because inhibition can be overcome by excess substrate.
Which molecule acts as the universal energy currency of the cell?
- A NADH
- B FADH2
- C ATP
- D GTP
Correct answer: ATP
ATP stores energy in its phosphoanhydride bonds and transfers it to drive cellular processes. It is used universally across metabolic pathways.
In glycolysis, which step is considered the first committed step?
- A Conversion of glucose to glucose-6-phosphate
- B Conversion of fructose-6-phosphate to fructose-1,6-bisphosphate
- C Cleavage of fructose-1,6-bisphosphate
- D Conversion of phosphoenolpyruvate to pyruvate
Correct answer: Conversion of fructose-6-phosphate to fructose-1,6-bisphosphate
The phosphofructokinase-1 reaction commits glucose to glycolysis. It is highly regulated and essentially irreversible under cellular conditions.
Which coenzyme carries two-carbon units in metabolic reactions?
- A Biotin
- B Thiamine pyrophosphate
- C Coenzyme A
- D Pyridoxal phosphate
Correct answer: Coenzyme A
Coenzyme A carries acetyl and other acyl groups via a thioester linkage. It is central to fatty acid metabolism and the citric acid cycle.
The citric acid cycle primarily occurs in which cellular compartment in eukaryotes?
- A Cytosol
- B Nucleus
- C Mitochondrial matrix
- D Inner mitochondrial membrane
Correct answer: Mitochondrial matrix
The enzymes of the citric acid cycle are located in the mitochondrial matrix. This location facilitates integration with oxidative phosphorylation.
Which lipid class is a major structural component of biological membranes?
- A Triacylglycerols
- B Steroids
- C Phospholipids
- D Waxes
Correct answer: Phospholipids
Phospholipids form bilayers due to their amphipathic nature. This bilayer provides the basic structural framework of cell membranes.
Which bond links monosaccharide units in polysaccharides?
- A Peptide bond
- B Ester bond
- C Glycosidic bond
- D Phosphodiester bond
Correct answer: Glycosidic bond
Glycosidic bonds join monosaccharides through a covalent linkage formed between hydroxyl groups. These bonds determine polysaccharide structure and properties.
Which nitrogenous base is found only in RNA and not in DNA?
- A Adenine
- B Guanine
- C Cytosine
- D Uracil
Correct answer: Uracil
RNA contains uracil instead of thymine. Uracil pairs with adenine during RNA base pairing.
What is the primary role of NAD+ in metabolic pathways?
- A Donating phosphate groups to substrates
- B Acting as a structural protein
- C Accepting and donating electrons
- D Transporting amino acids
Correct answer: Accepting and donating electrons
NAD+ functions as an electron carrier in redox reactions. It alternates between oxidized (NAD+) and reduced (NADH) forms.
Which enzyme catalyzes the formation of peptide bonds during protein synthesis?
- A RNA polymerase
- B DNA polymerase
- C Peptidyl transferase
- D Aminoacyl-tRNA synthetase
Correct answer: Peptidyl transferase
Peptidyl transferase activity of the ribosome catalyzes peptide bond formation. This activity resides in the rRNA component of the ribosome.
Which metabolic pathway directly produces NADPH for biosynthetic reactions?
- A Glycolysis in the cytosol
- B Citric acid cycle in the matrix
- C Pentose phosphate pathway
- D Beta-oxidation of fatty acids
Correct answer: Pentose phosphate pathway
The pentose phosphate pathway generates NADPH, which is essential for reductive biosynthesis. It also produces ribose-5-phosphate for nucleotide synthesis.
Which amino acid contains a sulfur atom in its side chain?
- A Serine
- B Threonine
- C Cysteine
- D Tyrosine
Correct answer: Cysteine
Cysteine contains a thiol (-SH) group that includes sulfur. This group can form disulfide bonds important for protein stability.
Oxidative phosphorylation primarily occurs at which site?
- A Cytosol
- B Outer mitochondrial membrane surface
- C Inner mitochondrial membrane
- D Mitochondrial matrix
Correct answer: Inner mitochondrial membrane
The electron transport chain and ATP synthase are embedded in the inner mitochondrial membrane. Proton gradients across this membrane drive ATP synthesis.
Which carbohydrate serves as the primary storage polysaccharide in animals?
- A Starch
- B Cellulose
- C Glycogen
- D Chitin
Correct answer: Glycogen
Glycogen is the main storage form of glucose in animals. It is highly branched, allowing rapid mobilization of glucose.
Which factor most directly affects enzyme activity by altering the ionization of amino acid side chains?
- A Temperature
- B pH
- C Substrate concentration
- D Cofactor availability
Correct answer: pH
pH affects the protonation state of amino acid side chains, especially at the active site. Changes in ionization can disrupt enzyme function.
Which macromolecule is primarily responsible for genetic information storage?
- A Proteins and enzymes
- B Structural lipids
- C Storage carbohydrates
- D Nucleic acids
Correct answer: Nucleic acids
Nucleic acids, particularly DNA, store genetic information. This information guides protein synthesis and cellular inheritance.
Which process converts pyruvate into acetyl-CoA in eukaryotic cells?
- A Glycolysis in the cytosol
- B Anaerobic fermentation
- C Pyruvate oxidation
- D Gluconeogenesis
Correct answer: Pyruvate oxidation
Pyruvate oxidation converts pyruvate to acetyl-CoA via the pyruvate dehydrogenase complex. This links glycolysis to the citric acid cycle.