MSQ Practice Q's

Enzyme Sensitivity to pH

  • Enzymes are highly sensitive to changes in pH due to several factors:

    • Hydrogen Bonds:

    • Disrupted by changes in pH.

    • Charges on Amino Acids:

    • The charges on acidic and basic amino acid residues in the enzyme's active site vary with pH, affecting enzyme activity.

    • Hydrophobic Residues:

    • pH changes can alter hydrophobic amino acid residues, impacting the enzyme's structure and function.

    • Disulphide Bonds:

    • Small alterations in pH can lead to the breaking of disulphide bonds, which stabilize the enzyme's 3D structure.

    • Allostery:

    • Enzymes can be allosteric, meaning their activity can change in response to binding of molecules at sites other than the active site, which can influence their response to pH changes.

Lysine pKa Values

  • Lysine has three pKa values:

    • Carboxyl group: 2.2

    • Amino group: 8.95

    • Side chain amino group: 10.53

  • Assessing the charge of lysine at various pH levels:

    • At pH 12, lysine has a negative charge.

    • At pH 1, lysine has a positive charge.

    • At pH 9.74, statements about lysine's net charge must be considered.

    • At pH 7.23, lysine has a statement about having no net charge that needs examination.

    • At pH 7, lysine also has a positive charge.

  • False statement: Lysine has no net charge at pH 9.74.

Glycolytic Enzymes and ATP Production

  • Among glycolytic enzymes, only one produces ATP during glycolysis:

    • Phosphoglycerate Kinase:

    • Responsible for a substrate-level phosphorylation that results in ATP generation.

  • Other enzymes listed do not produce ATP directly:

    • Hexokinase

    • Glucokinase

    • Phosphofructokinase-1

    • Glucose-6-phosphate isomerase

The Cori Cycle

  • Understanding the Cori Cycle involves identifying false statements:

    • True aspects:

    • Skeletal muscle utilizes anaerobic respiration during exercise.

    • Lactate produced in muscles is transported to the liver.

    • The liver contains the enzyme phosphofructokinase-1 (PFK-1) that facilitates the removal of phosphate from glucose, enabling glucose release.

    • The liver converts lactate to glucose.

    • In muscle tissue, lactate dehydrogenase catalyzes the conversion of pyruvate to lactate.

  • False statement: The liver contains phosphofructokinase-1 (PFK-1) that removes phosphates from glucose, which is misleading regarding the liver's metabolic processes.

Calculating pH Using the Henderson-Hasselbalch Equation

  • pKa of Acetic Acid: 4.76.

  • Mixing Sodium Acetate and Acetic Acid

    • When mixed in a 1:10 ratio, use the Henderson-Hasselbalch equation to find the resulting pH of the solution.

    • Possible pH outcomes:

    • A. 4.76

    • B. 3.76

    • C. 5.76

    • D. 2.76

    • E. 6.76

    • Resulting pH: The correct answer is 3.76.

TCA Cycle and Amino Acids

  • Analyst the conversion of amino acids into the TCA cycle:

    • Arginine, Histidine, Glutamine, Proline: Converted to alpha-ketoglutarate.

    • Lysine and Leucine: Converted to isocitrate.

    • Tyrosine and Phenylalanine: Converted to fumarate.

    • Aspartate and Asparagine: Converted to oxaloacetate.

    • Glycine and Serine: Converted to pyruvate.

  • False statement: Lysine and leucine are incorrectly stated as being converted to isocitrate.

Folate and DNA Synthesis

  • Conversion of dUMP to dTTP: Crucial for DNA synthesis.

  • The required form of folate for this conversion is:

    • N5, N10 methylene tetrafolate: Vital in the biochemical pathway for synthesizing nucleotides essential for DNA.