L18: amino acids, equilibrium and pH

• Who is the author of the study material titled "LF130 Cellular and Molecular Biology"?

  1. Katrine Wallis
• What is the date of the formative test mentioned in the study material?

  31st of October
• Why is pH tightly regulated in biological systems?

  Changes to charge influence protein structure, enzyme function, and ion transport.
• How is pH measured?

  pH is measured on a log scale.
• What does a log scale measure?

  Orders of magnitude.
• If an earthquake has a magnitude of 6, how much stronger is it than one with a magnitude of 5?

  10 times stronger.
• What is the structure of an alpha amino acid represented by in a Fisher projection?

  Vertical lines represent groups away from you, and horizontal lines represent groups towards you.
• What are D and L amino acids?

  D and L are mirror images of each other.
• What are the invariant groups in an amino acid?

  Hydrogen, amino group, and carboxylic acid group.
• What is the physiological form of an amino acid at different pH levels?

  Amino acids exist as zwitterions at physiological pH.
• What happens to the charge of an amino acid at low pH?

  It has a positive charge.
• What happens to the charge of an amino acid at high pH?

  It has a negative charge.
• What can be said about the two forms of amino acids at certain pH levels?

  Two forms can coexist at certain pH levels.
• Can we predict which form of an amino acid will exist at a given pH?

  Yes, we can predict it.
• What does the pH scale measure in relation to hydrogen ions?

  pH measures the concentration of hydrogen ions [H⁺].
• What is the pH of a neutral solution?

  7
• What is the result of glucose burning fully in a chemical reaction?

  It produces carbon dioxide and water.
• What does the equilibrium constant (K_D) represent?

  The ratio of concentration of products to reactants at the end of a reaction.
• How do strong acids and bases behave in solution?

  They fully dissociate.
• What does the Acid Dissociation Constant (K_a) indicate?

  It describes how strong an acid is.
• How is the strength of an acid usually expressed?

  As pK_a.
• What does the Henderson-Hasselbalch equation relate to?

  It relates pH to the strength of the acid and the concentration of acid and conjugate base.
• What happens when the concentrations of acid and conjugate base are equal in the Henderson-Hasselbalch equation?

  pH equals pK_a.
• How can we predict the protonation state of amino acids?

  By knowing the pH and pK_a.
• What role do weak acids and bases play in biological systems?

  They function as buffers of pH.
• What are key biological buffers mentioned in the study material?

  Bicarbonate, phosphate, and proteins like hemoglobin.
• What is the ratio of bicarbonate to carbonic acid in blood?

  There is 10 times as much bicarbonate as carbonic acid.
• What are the key messages regarding pH in relation to proteins and macromolecules?

  • pH is fundamental to the structure and function of proteins and other macromolecules.
  • Weak acids and bases function as buffers of pH.
  • Knowledge of pH will be applied to side chains in the next lecture.