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Cellular Biochemistry and Biology > Protons and Their Impact > Flashcards

Protons and Their Impact Flashcards

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1
Q

What is pH?

A

Measure oh H+ conc

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2
Q

Define solution pH

A

-ve log10[H+] in mol/L

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3
Q

pH equation

A

pH= -log10[H]

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4
Q

pH in terms of protons

A

lower pH = higher [H+] conc

higher pH = lower [H+] conc

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5
Q

pH of pure water

A

7

- [H+] in pure water 10^-7 M

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6
Q

Neutral solutions

A

At pH 7, there are an equal number of hydronium and hydroxyl ions -> neutral solution

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7
Q

Jump between pH

A
  • At pH 7 ONE water molecule in every 55 MILLION will be protonated → At pH 1 one water molecule in every 55will be protonated
    • ([H+] at pH 1 is 10^-1 M, increase of 10^6)
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8
Q

What is a dynamic equilibrium?

A
  • A+ B < = > C+ D
  • The state of a system in which forward and reverse processes occur at equal rates
  • The amounts on each side of the system do not change with time
  • The state of a chemical process in which the forward and reverse reactions occur at equal rates
  • So that the concentration of the reactants and products does not change with time.
  • Forwards and backwards process still happening in a dynamic equilibrium, even if no net change in system.
  • Weak acids such as carboxylic acids are in dynamic equilibrium.
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9
Q

What are acids?

A
  • Acids are compounds that can lose an H+ion (proton), in the process they become negatively charged.
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10
Q

How do weak acids exist?

A
  • energy difference between the two states can be relatively small and going back and forth between the forms is possible in the physiological pH range
  • Giving a dynamic equilibrium.
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11
Q

What does a change in pH mean?

A

A change in pH = a change in [H+] so this will change the equilibrium

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12
Q

What is le chateliers principle?

A
  • LeChâtelier’s principle (or the equilibrium principle) states that: If an equilibrium is disturbed by a change of the environment (such as changing temperature, pressure, and concentration of components) the system will tend to shift its equilibrium position so as to counteract the effect of the disturbance (and get back to steady state)
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13
Q

How are acids ionised?

A

losing H+

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14
Q

How does equilibrium shift to oppose a decrease in pH?

A
  • Solution is rich in H+
  • Equilibrium shifts to the left to produce more reactant and use more H+ (product) therefore reversing the change in pH
  • Less ionisation occurs
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15
Q

How does equilibrium shift to oppose a increase in pH?

A
  • Solution is deficient in H+
  • Equilibrium shifts to the right to use more reactant to produce more H+ product to reverse the change in pH
  • More ionisation
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16
Q

How is Ka calculated?

A

Ka = ([H+][A-]) / [HA]

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17
Q

How is Kb calculated?

A

Kb = ([H+][B])/[HB+]

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18
Q

How is pKa calculated?

A

pKa= ─ log10(Ka)

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19
Q

How is pH calculated?

A

pH = −log10[H+]

20
Q

Equation linking pH and pKa

A

pH =pKa+ log ([B]/[HB+])

21
Q

What is pKa when a compound is 50% ionised?

A

pKa = pH

22
Q

What does the Henderson-Hassleback equation link?

A

Links pKa, pH and % ionisation

23
Q

What is the Henderson-Hassleback equation?

A

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

24
Q

How to calculate % compound ionisation

A
  • % compound ionised=100 / (1 + 10^(charge(pH− pKa)))

- Charge = −1 for acids (negatively ionised) and +1 for bases (positively ionised)

25
Q

How dissociated and ionised is an acid when pH < pKa -2

A

< 1% dissociated < 1% ionised

26
Q

How dissociated and ionised is an acid when pH = pKa - 1

A

~10% dissociated ~10% ionised

27
Q

How dissociated and ionised is an acid when pH = pKa

A

50% dissociated 50% ionised

28
Q

How dissociated and ionised is an acid when pH = pKa + 1

A

~90% dissociated ~90% ionised

29
Q

How dissociated and ionised is an acid when pH > pKa +2

A

> 99% dissociated >99% ionised

30
Q

Why is the Henderson-Hassleback equation useful?

A

Use Henderson─Hasselbach equation to calculate pH, pKa or [A-] or [HA] –can then compare/use these values for other calculations

31
Q

What is a conjugate base?

A
  • The deprotonated acid is termed the conjugate base and it acts as a base by accepting a proton in the reverse reaction.
32
Q

What do strong acids give?

A
  • Strong acids give WEAK conjugate bases
33
Q

What are bases?

A

Bases are compounds that can (reversibly) form covalent bonds with an H+ion to become positively charged (positively ionised):

34
Q

How dissociated and ionised is a base when pH < pKa -2

A

<1% dissociated>99% ionised

35
Q

How dissociated and ionised is a base when pH = pKa -1

A

~10% dissociated~90% ionised

36
Q

How dissociated and ionised is a base when pH = pKa

A

50% dissociated50% ionised

37
Q

How dissociated and ionised is a base when pH = pKa -1

A

~90% dissociated~10% ionised

38
Q

How dissociated and ionised is a base when pH > pKa +2

A

> 99% dissociated<1% ionised

39
Q

What is the general cellular pH?

A

~ 7.2-7.4 (but can be different locally within the cell/tissue)

40
Q

What is the pH range inside the body?

A

pH 1.5 (stomach) to pH 8.5 (duodenum)

41
Q

What is pKa a property of?

A

pKa is a property of an ionisable group

42
Q

What can we use pKa to describe?

A

can use pKa to describe ionisation properties of a single ionisable functional group

43
Q

Why can multiple pKa values exist?

A

Proteins can have as many pKa values as ionisable groups

- If multiple pKa values then can have multiple possible states with varying charge.

44
Q

What is the isoelectric point?

A

When net charge is 0, known as iso-electric point (pI) (pH will have no effect). When there is charge, proteins will move in an electric field.

45
Q

Where does ionised acid migrate to?

A

Cathode

46
Q

Where does an ionised alkali migrate to?

A

Annode

47
Q

How is base-pairing able to occur?

A
  • Occurs despite the relative hydropilicity of the nucleobases because ionic nature of phosphates overrides this and forms the shape of DNA
  • Phosphate is highly acidic (pKa 0-1) so all phosphates in the backbone are ionised at any pH>2
  • Charged phosphate residue on the surface of the helix - DNA /RNA are negatively charged (gel electrophoresis)

Cellular Biochemistry and Biology (5 decks)

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