pH and Buffering in Biological Systems
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Questions and Answers

What is the primary factor that acidity depends on?

  • Bound hydrogen ions
  • Free hydrogen ions (correct)
  • pKa value of the acid
  • Total hydrogen ion concentration

    • What is the normal pH range of blood?

  • 7.35-7.45 (correct)
  • 7.0-7.8
  • 7.2-7.6
  • 6.5-7.5

    • Which of the following is NOT a source of acid in the body?

  • Breakdown of proteins
  • Incomplete oxidation of fats or glucose
  • Loading and transport of oxygen in the blood (correct)
  • Incomplete oxidation of carbohydrates

    • What is the purpose of chemical buffers in the body?

    <p>To resist abrupt changes in pH</p> Signup and view all the answers

    What is the role of the kidneys in acid-base balance?

    <p>To excrete excess hydrogen ions</p> Signup and view all the answers

    What is the term for a condition where the blood pH falls below 7.35?

    <p>Acidosis</p> Signup and view all the answers

    What is the importance of pKa in biological buffering?

    <p>It determines the strength of an acid</p> Signup and view all the answers

    How do proteins act as physiological buffers?

    <p>By binding to hydrogen ions</p> Signup and view all the answers

    What is the ionic product of water?

    <p>10-14M2</p> Signup and view all the answers

    What is the pH of a solution with a hydrogen ion concentration of 10-2M?

    <p>2</p> Signup and view all the answers

    What is the concentration of hydroxide ions in a solution with a hydrogen ion concentration of 10-4M?

    <p>10-10M</p> Signup and view all the answers

    What is the definition of a strong acid?

    <p>An acid that dissociates completely in solution</p> Signup and view all the answers

    What is the pH of blood?

    <p>7.4</p> Signup and view all the answers

    What is the concentration of hydrogen ions in blood?

    <p>3.98 x 10-8M</p> Signup and view all the answers

    What is the main component of buffers?

    <p>Weak acid and strong base</p> Signup and view all the answers

    What percentage of body mass is water in a healthy young woman?

    <p>50%</p> Signup and view all the answers

    What is the significance of the pKa value?

    <p>It is the pH at which the acid is half dissociated</p> Signup and view all the answers

    What is the purpose of the Henderson-Hasselbalch equation?

    <p>To relate the pH of a solution to the pKa of a weak acid and the relative amounts of dissociated and non-dissociated forms of the acid</p> Signup and view all the answers

    What is the characteristic of a strong acid?

    <p>It has a low pKa value</p> Signup and view all the answers

    What is the significance of the buffering region?

    <p>It is the region where the pH remains constant with the addition of acid or base</p> Signup and view all the answers

    What is the relationship between the pKa and the strength of an acid?

    <p>The lower the pKa, the stronger the acid</p> Signup and view all the answers

    What is the purpose of a buffer solution?

    <p>To keep the pH of a solution constant with the addition of acid or base</p> Signup and view all the answers

    What is the significance of the equivalence point in a titration curve?

    <p>It is the point where the titration is complete</p> Signup and view all the answers

    What is the relationship between the conjugate base and acid in a buffer solution?

    <p>The conjugate base is the dissociated form of the acid</p> Signup and view all the answers

    What is the main reason why the pKa of histidine in Hb is different from that of free His?

    <p>The presence of neighbouring groups affects the pKa</p> Signup and view all the answers

    Which of the following is a better buffer for H+ produced in metabolism?

    <p>Oxyhaemoglobin</p> Signup and view all the answers

    What is the ratio of base to acid for oxyhaemoglobin at a pH of 7.4?

    <p>3.98:1</p> Signup and view all the answers

    What can be predicted about the diffusion of aspirin across biological membranes?

    <p>It diffuses more easily at pH 2 than pH 7</p> Signup and view all the answers

    What is the pH of blood at which the ratio of base to acid for oxyhaemoglobin is 1:1?

    <p>6.8</p> Signup and view all the answers

    Which of the following statements about deoxyhaemoglobin is true?

    <p>The ratio of base to acid is 1:2.51 at a pH of 7.4</p> Signup and view all the answers

    What is the primary function of a buffer in a physiological system?

    <p>To maintain a constant pH by donating or accepting protons</p> Signup and view all the answers

    At what pH does an acid buffer best?

    <p>At a pH equal to its pKa</p> Signup and view all the answers

    What is the purpose of the Henderson-Hasselbalch equation?

    <p>To calculate the pH of a buffer solution</p> Signup and view all the answers

    Why is glycine not a good physiological buffer?

    <p>It buffers best at pH 2.3 and 9.6</p> Signup and view all the answers

    What is the role of the alpha carboxyl and alpha amino groups in proteins?

    <p>They are involved in the peptide bond</p> Signup and view all the answers

    What is the characteristic of amino acid side chains that makes them poor physiological buffers?

    <p>They have pKa values outside the physiological range</p> Signup and view all the answers

    What is the primary reason why histidine residues make haemoglobin a good blood buffer?

    <p>There are a large number of histidine residues</p> Signup and view all the answers

    What is the advantage of using the Henderson-Hasselbalch equation in diagnosing acidosis?

    <p>It can distinguish between metabolic and respiratory acidosis</p> Signup and view all the answers

    Study Notes

    pH and Buffering

    • pH is a measure of hydrogen ion concentration (acidity or alkalinity of a solution)
    • Acidity depends only on free hydrogen ions, not those still bound to anions
    • Blood pH is normally maintained within a narrow range of 7.35 to 7.45, and outside this range can be fatal
    • Living range of pH: 7.0-7.8

    Acid-Base Balance

    • Acid-base balance is regulated in the body by the lungs, kidneys, and chemical buffers in the blood
    • Buffers resist abrupt and large swings in pH of body fluids by releasing H+ (acting as acids) when pH rises and binding H+ (acting as bases) when pH drops

    Buffering Mechanism

    • Buffers operate by releasing H+ when pH rises and binding H+ when pH drops
    • Strong acids are completely dissociated in solution, while weak acids are partially dissociated
    • Strong bases are more effective proton acceptors than weak bases

    Ionisation of Water

    • Pure water is a 55.6M solution that dissociates to a very small extent
    • At neutrality, [H+] = [OH-] = 10-7M
    • pH = -log[H+]

    Dissociation of Acids

    • Acids are proton (H+) donors, while bases are proton acceptors
    • Strong acids dissociate completely in solution, while weak acids dissociate partially
    • pKa is the pH at which an acid is half-dissociated, and is a measure of an acid's strength

    Henderson-Hasselbalch Equation

    • pH = pKa + log([A-] / [HA])
    • The equation relates the pH of a solution, the pKa of a weak acid, and the relative amounts of dissociated and non-dissociated forms of the acid
    • At the pKa, buffering is best, as there are equal amounts of dissociated and non-dissociated forms of the acid

    Physiologically Important Buffers

    • Physiologically important buffers include H2CO3/HCO3- (pKa 6.1), H2PO4-/HPO42- (pKa 6.8), and protein buffers
    • Haemoglobin is an important buffer in the blood, with a pKa of 6.8 for oxyhaemoglobin and 7.8 for deoxyhaemoglobin

    Haemoglobin as a Buffer

    • Haemoglobin is a good blood buffer due to the presence of histidine residues
    • The pKa of histidine in haemoglobin is different from that of free histidine, due to the effects of neighbouring groups
    • Oxyhaemoglobin is a better buffer for H+ produced in metabolism than deoxyhaemoglobin

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    Description

    This quiz covers the basics of pH and buffering in biological systems, including strong and weak acids, pKa, Henderson-Hasselbalch equation, physiological buffers, and proteins as buffers.

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