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Biochem Ca1 Cram > pH And Buffers > Flashcards

pH And Buffers Flashcards

1
Q

Name 7 acids found in our body

A

HCL
Lactic acid
Keto-acids
Pyruvic acid
Fatty acids
Bile acids
Uric acid

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2
Q

Name 2 bases

A

Ammonia
Sodium bicarbonate

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3
Q

Describe Ka values for weak and strong values

A

If Ka less than 1 wear coz less acids dissociate ions to water
If Ka more than 10 almost all acid dissociate to ions

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4
Q

4 strong basic anions in body

A

HCO3- , HPO4 2- , H2PO4- and
proteins-

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5
Q

What’s an ampholyte

A

Substances which can functions both as acids and
bases are called as ampholytes

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6
Q

Example of ampholyte

A

Water

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7
Q

What is pH

A

pH is a measure of the concentration of hydrogen ions in a solution.

H+ can be expressed as mol/L – (M)

Numerically,
it is equal to the negative logarithm of the hydrogen iron concentration
pH = -log [H+]
Or
the logarithm of the reciprocal of the hydrogen ion concentration
pH = log 1 [H+]

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8
Q

wut conc. Of H+ is pH basic , water, acidic

A

Basic smaller than 110^-7
Water is 110^-7
Acidic is larger than 1*10^-7

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9
Q

pH of blood plasma

A

7.35 - 7.45

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10
Q

pH of urine

A

4.8- 8.0

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11
Q

pH of gastric juice

A

1.0 - 3.5

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12
Q

pH of cerbrospinal fluid

A

7.3 - 7.5

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13
Q

pH of pancreatic juices

A

7.5- 8.0

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14
Q

Who’s does slight change in pH affect H+

A

Slight pH changes indicate a 10-fold increase/decrease in [H+] which can have damaging effects on protein structure & function

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15
Q

Optimally active pH of pepsin

A

1-2

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16
Q

Optimally active pH of trypsin

A

6-7

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17
Q

Optimally active pH of lysozyme

A

5

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18
Q

Effect of pH on nervous system

A

Abnormal pH affects the nervous system-
H+ imbalances cause K+ imbalances because transporter proteins in kidneys move H+ and K+ in antiport fashion
– In acidosis: neurons become less excitable and CNS depression can result
– In alkalosis: hyperexcitable

pH disturbances- induced by an imbalance of H+ input/output
– Compensation by buffers, ventilation, or renal regulation
– Greatest source is CO2 level – where changes are induced by metabolic or respiratory factors

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19
Q

What is buffer

A

• Solutions that resist change in pH upon addition of small volumes of acid or base
• Buffers are the mixtures of weak acids and their salts of strong bases (and vice versa)

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20
Q

2 examples of buffer

A

• Acetic acid/Sodium acetate (CH3COONa)
• CH3COOH to CH3COO- + H+ (acetic acid )

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21
Q

What does buffer system consist of

A

–a weak acid
–and the anion released by its dissociation (conjugate base)

The anion functions as a weak base

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22
Q

Titration of acetic acid with sodium hydroxide

A

pKa = 4.76

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23
Q

What is pKa

A

The pKa value of an acid group is the pH at which the protonated and unprotonated species are present in equal concentrations

Ka = [H+]
log Ka =log [H+]
-log Ka =-log [H+]
pKa = pH

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24
Q

What is Henderson-Hasselbalch equation

A

• The quantitative relationship between
– pH,
– the buffering action of a weak acid and its conjugate base and
– the pK value of weak acid

pH=pKa+log [Salt]/ [Acid]

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25
Q

5 applications of Henderson-Hasselbalch equation

A

1.Calculation of concentrations of constituents of buffers

  1. Determination of the proportions of conjugate pairs that exist at a given pH
    …at a pH equal to the pKa of a weak acid HA, the population of unionized acid molecules is exactly balanced by the number of molecules of the conjugate base.
    …At a pH above that of the pKa, the anionic form will predominate, and at low pH, the unionized acid species is favoured.
  2. Determination of pH of buffers
  3. Calculation of the effective concentration of the permeable form of drug at its site of absorption
    - Uncharged drugs pass through membranes more easily.
  4. Predicting about renal clearance of a drug
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26
Q

Amino acid structure

A

H, R group, 2 acid groups

27
Q

COOH is stronger than NH3+

A
28
Q

What is pl

A

Isoelectruc point = pK1 + pK2 /2

29
Q

Pl in simple amino acids like glycine and alanine

A

For the case of a simple amino acid like glycine
• the pI, when calculated from the Henderson- Hasselbalch equation, is shown to be the average of the pK for the α-COOH group and the pK for the α- NH2 group
• E.g.; For alanine, the pI is an average of the pKa s of the carboxyl (2.34) and ammonium (9.69) groups.
• Thus, the pI for alanine is calculated to be: (2.34 + 9.69)/2 = 6.02.

30
Q

Pl for more complex molecules like arginine and aspartic acid

A

– the pI is the average of the pKa values that represent the boundaries of the zwitterionic form of the molecule.
– i.e.; If additional acidic or basic groups are present as side-chain functions, the pI is the average of the pKa s of the two most similar acids.

•In the case of aspartic acid, the similar acids are the alpha-carboxyl function (pKa = 2.1) and the side-chain carboxyl function (pKa = 3.9); so pI = (2.1 + 3.9)/2 = 3.0.

For arginine, the similar acids are the guanidinium species on the side-chain (pKa = 12.5) and the alpha-ammonium function (pKa = 9.0); so the calculated pI = (12.5 + 9.0)/2 = 10.75.

31
Q

Significance of pl value

A

• The pI value, like that of pK, is very informative as to the nature of different molecules.
• A molecule with a low pI would contain a predominance of acidic groups, whereas a high pI indicates predominance of basic groups.

32
Q

What is physiological buffer and 2 examples

A
  • system that controls output of acids, bases or CO2
  1. Urinary system buffers greatest quantity, takes several hours
  2. Respiratory system buffers within minutes, limited quantity
33
Q

Chemical buffer systems and 3 examples

A

– restore normal pH in fractions of a second
– bicarbonate, phosphate and protein systems bind H+ and transport H+ to an exit (kidney/lung)

34
Q

What is buffering capacity

A

The efficiency of a buffer in maintaining a constant pH on the addition of small amounts of acid or base is called as its buffering capacity.

35
Q

3 things that affect buffering capacity

A

– the pH of the solution; Buffers work best within 1 pH unit of their pKa (± 1).
– the concentration of the buffer, the stronger the buffer, the greater its buffering capacity.
– Ratio of acid to conjugate base.

36
Q

3 buffer systems in ICF

A
  1. Phosphate buffer system

Protein buffer systems = 2. Hb buffer system in RBC
3. Amino acid buffers in al proteins

37
Q

3 buffer systems in ECF

A

Protein buffer systems - 1. Amino acid buffer system in all proteins
2. Plasma protein buffers
3. Carbonic acid - bicarbonate system

38
Q

3 Important buffers in the body

A

• Urine – Phosphate and Ammonia buffers
• Blood - Bicarbonate, Protein and
Haemoglobin (in RBC) buffers
• Intracellular fluid – Proteins and Phosphates

39
Q

Chemical buffers vs resp regulation vs renal regulation

A

Chemical buffers
• React very rapidly (less than a second)

Respiratory Regulation
• Reacts rapidly (seconds to minutes)

Renal Regulation
• Reacts slowly (minutes to hours)

40
Q

3 Major Buffer Systems

A

3 Major Buffer Systems

Protein buffer systems:
– help regulate pH in ECF and ICF
– interact extensively with other buffer systems

Carbonic acid–bicarbonate buffer system:
– most important in ECF

Phosphate buffer system:
– buffers pH of ICF and urine

41
Q

What are blood buffers

A

• Molecules react to prevent dramatic changes in hydrogen ion (H+) concentrations
– Bind to H+ when pH drops
– Release H+ when pH rises

42
Q

What are protein buffer systems

A

• More concentrated than bicarbonate and phosphate systems
• Depend on ability of amino acids to respond to pH changes by accepting or releasing H+

43
Q

Explain amino acids in protein buffer systems

A

In alkaline medium amino acids act as acid and release H+
In acidic medium amino acids act as base and absorb H+

44
Q

What is The Histidine R Group Buffer System

A

• Cells and extracellular fluids contain a high concentration of proteins.
• Histidine is an amino acid that occurs in most proteins.
• R group (side-chain) of histidine has an imidazole functional group that undergoes reversible protonation .
• Because the pKa of the imidazole R group is 6.0, histidine residues in proteins help buffer the pH of the cell cytosol and extracellular fluids around neutrality.
• The cell cytosol also is buffered by phosphate, which has a pKa of 6.86.

45
Q

The Histidine R Group Buffer System if pH rises

A

• If pH rises:
– carboxyl group of amino acid dissociates
– acting as weak acid, releasing a hydrogen ion – carboxyl group becomes carboxylate ion
• At normal pH (7.35–7.45):
– carboxyl groups of most amino acids have already given up their H+

46
Q

The Histidine R Group Buffer System if pH drops

A

• If pH drops:
– carboxylate ion and amino group act as weak
bases
– accept H+
– form carboxyl group and amino ion
• Carboxyl and amino groups in peptide bonds cannot function as buffers
• Other proteins with buffering capabilities:
– plasma proteins
– proteins in interstitial fluid
– proteins in ICF

47
Q

What is the Hb buffer system

A

• Helps prevent major changes in pH when plasma PCO2 is rising or falling

• Is the only intracellular buffer system with an immediate effect on ECF pH

• CO2 diffuses across RBC membrane: – no transport mechanism required
• As carbonic acid dissociates:
– bicarbonate ions diffuse into plasma
– in exchange for chloride ions (chloride shift)

Hydrogen ions are buffered by haemoglobin molecules

CO2 in plasma to CO2 + H20 in RBC TO h2co3 ( weak acid) gives H+ & HC03- ( strong acid )

Carbonate antacids work like this to relieve heartburn after heating by absorbing H+

48
Q

What happens when OH- added to blood

A

OH- + H2CO3 gives HCO3- + H2O

– strong base traded for weaker one

49
Q

When H+ added to blood

A

H+ +HCO3-→H2CO3
–strong acid traded for weak acid

50
Q

The Carbonic Acid–Bicarbonate Buffer System

A

Bicarbonate reserve is when NaHCO3 converted to Na+ and HCO3-
And HCO3- used

51
Q

How is The Carbonic Acid–Bicarbonate Buffer System

A

• Bicarbonate to carbonic acid ratio of 20 : 1 at pH 7.4 which is referred to as the alkali reserve.
• Level of PCO2 and HCO3- are regulated efficiently by lungs and kidneys
• Open buffer system

52
Q

Respiratory System Control of Acid- Base Balance

A

• Carbon dioxide in the blood is converted to bicarbonate ion and transported in the plasma
• Increases in hydrogen ion concentration produces more carbonic acid
• Excess hydrogen ion can be put out with the release of carbon dioxide from the lungs
• Respiratory rate can rise and fall depending on changing blood pH `

53
Q

Ph for death, acidosis , alkalosis , normal

A

Normal - 7.35 go 7.45
Death is less than 6.8 or more than 8
Acidosis is 6.8 to 7.35
Alkalosis is 7.45 to 8

54
Q

Phosphate Buffer System

A

• H2PO4- reversibly to HPO42- + H+
– as in the bicarbonate system, reactions that proceed to the right release H+ and dec pH, and those to the left inc pH
• Important in the ICF and renal tubules
– where phosphates are more concentrated and
function closer to their optimum pH of 6.8
• constant production of metabolic acids creates pH values from 4.5 to 7.4 in the ICF, avg. 7.0

55
Q

4 methods of renal regulation of pH

A
  1. Bicarbonate reabsorption
  2. H+ secretion
  3. Combination of H + in the tubular fluid with phosphate and ammonia
  4. New bicarbonate generation
56
Q

Bicarbonate reabsorption and proton secretion diagram

A
57
Q

Combination of phosphates and protons diagram

A
58
Q

New bicarbonate generation diagram

A
59
Q

Buffering Mechanisms in Urine and diagram

A

NaHPO4 buffer system and ammonia buffer system
• H+ is taken up by Na2HPO4 and NaH2PO4 is formed and excreted
• NH3 takes up H+ and together with Cl-, forms NH4Cl which is excreted

60
Q

3 ways to measure pH

A

Indicators
• Weak acids or bases which change color as they change from acid or base to salt
• Usually change color over a range of about 2 pH units
2. pH paper
• Indicators or a combination of indicators
placed on a piece of paper.
• Litmus
is the classical
example.
3. pHMeter
• Measures the electrical potential caused by the difference in H+ concentration in the sample vs that inside a thin glass membrane.

61
Q

PH electrode

A

The pH electrode actually consists of two electrodes.
glass electrode
measures the potential caused by the [H+] in the sample.
• The Ag/AgCI electrode is the reference
H+
The glass electrode is very FRAGILE. Handle it carefully
Always Calibrate your pH Meter before using

62
Q

pH meters

A

pH meter consists of
• a glass electrode which produces a potential (voltage) which varies with pH.
• a reference electrode
against which this potential is measured.
• Adevice to convert this potential difference to
a pH readout. This device can be an analog device such as the classical
meter, or a digital device such as a computer or even a calculator!
NOTE
The glass bulb at the bottom of a glass electrode is very fragile. Never push the electrode down.
Always calibrate the pH meter before using.

63
Q

pH papers

A

Litmus Paper is the classical form of
pH paper. The familiarp i n k or b l u e
slips of paper give rise to the LITMUS
TEST. The familiarity and “reliability” of
the test have extended the “litmus test” concept
beyond chemistry.
pH paper is produced by soaking a piece of absorbant paper with a solution of one or more
indicators. with the proper choice of indicators you can get a range of different colors from pH 1 to pH
14.

64
Q

Indicators

A

Indicators are weak acids (or bases). The undissociated weak acid (or base) has a different color than its salt.
If the indicator is a weak acid, it will dissociate:

H I nis the weak acid indicator and I n is the anion of
its salt. We will also assume the acid H I n is red and
the anion
of the salt In- is blue.
This equilibrium is described by the equilibrium expression
Ka=[H*] [In] [HIn]

Biochem Ca1 Cram (13 decks)

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