Session 1: Water and hydrogen ions

Question 1

List the 4 consequences of water having a dipolar nature.

Answer 1

1. Allows interactions between water molecules
2. Forms hydration shells (acts as a solvent)
3. Provides an aqueous medium for the chemical
   reactions
4. Determines biomolecule properties:
   * higher order structure of macromolecules
   * formation of supramolecular aggregates

Question 2

Explain the polarised bonds in water molecules.

Answer 2

• The two H atoms are bonded to the O atom at an
  angle of 105 degrees
• The H atoms share its electrons with the unshared
  electrons of the O atom
• The O atom has a high electron affinity
• The H atoms has have partial positive and the O
  atom has partial negative charge
• Thus a water atom forms a dipole

Question 3

Express the relationship between pH and H+ as a formula.

Answer 3

pH = log ( 1/[H+] )

Question 4

Give the normal blood plasma values of [H+] and pH.

Answer 4

[H+] = 40 nmol/L
pH = 7.4

Question 5

Define acidosis.

Answer 5

Excess concentration of the hydrogen ion (excess acid)

Question 6

Define alkalosis.

Answer 6

Low hydrogen ion concentration (excess base)

Question 7

Give the intracellular pH.

Answer 7

7.0

Question 8

Give the range of the pH range.

Answer 8

6.0 - 7.5

Question 9

Give the pH range of gastric acid.

Answer 9

1.5 - 3.5

Question 10

Give the average plasma pH range and its average.

Answer 10

7.37 - 7.43, average 7.4

Question 11

Give the venous and arterial blood hydrogen ion concentration.

Answer 11

Venous blood = 43 nmol/L (7.37)

Arterial blood = 37 nmol/L (7.43)

Question 12

List 5 acids produced in the body.

Answer 12

1. Acetoacetic acid
2. B-hydroxybutyric
3. Lactic acid
4. Carbonic acid
5. Phosphates

Question 13

Define and explain the meaning of an acid.

Answer 13

A compound that donates protons to a solution.

Question 14

Define and explain the meaning of a base.

Answer 14

A compound that accepts protons.

Question 15

Define and explain what a buffer is.

Answer 15

A combination of of two compounds (a weak acid and its conjugate base) that minimises pH changes when H+ is produced and added to a body fluid compartment.

Question 16

Write down and explain the Henderson- Hasselbalch equation for the bicarbonate buffer in the blood.

Answer 16

pH = pKa + log ( [HCO3-]/ [H2CO3] )

The ratio of HCO3- to H2CO3 determines the pH and therefore the acidity of blood and other body fluids.

Question 17

Write down the Henderson- Hasselbalch equation and explain it.

Answer 17

pH = pKa + log ( [A-]/ [HA] )

Question 18

What determines osmolality ?

Answer 18

The total concentration of all dissolved ions, together with organic molecules.

Question 19

What is used to express the low hydrogen ion concentration of pure water?

Answer 19

The pH notion.

Question 20

Define pH.

Answer 20

The log of the reciprocal of the hydrogen ion concentration.

Question 21

Describe the process of protein unfolding.

Answer 21

Most enzymes and proteins do not function outside the pH range of 7.37- 7.43. If the hydrogen ion concentration is increased, its high affinity for negatively charged groups on proteins leads to protein unfolding where proteins lose their 3D shape and therefore their functioning as well.

Question 22

What is a structural formula?

Answer 22

It shows the chemical bonds between atoms in a molecule.

Question 23

Define ketoacidosis.

Answer 23

A type of metabolic acidosis where the pancreas is unable to produce adequate amounts of insulin.

Question 24

Name the two factors that determine the effectiveness of a buffer.

Answer 24

1. Its pKa relative to the pH of the solution

2. Its concentration

Question 25

List in order of occurrence, the mechanisms responsible for maintaining the normal blood pH.

Answer 25

1. Extracellular buffer systems
2. Ventilatory regulation of CO2 elimination
3. Regulation of hydrogen ion excretion and
   bicarbonate ion reabsorption (kidneys and lungs)

Question 26

Explain how the bicarbonate buffer functions in the blood.

Answer 26

The acid-base pair H2C03 / HCO3- acts as a buffer. The ratio of HCO3- to H2CO3 determines the pH and therefore the acidity of the blood and other body fluids.

Question 27

Define Kussmaul respiration.

Answer 27

When high levels of carbonic acid are produced, it leads to high [H+] in the brain, stimulating chemoreceptors located in the medulla oblongata and linked to the respiratory centre in the brain stem, which leads to deeper and more frequent breathing.