amino acids and pH

Question 1

structural

all of the amino acids except glycine are…

Answer 1

chiral

Exist as L or D form that are enantiomers of each other

L-form found in humans and D-form in bacteria.

Question 2

at pH of 7.4 the amino acid groups have…

Answer 2

NH3+ and COO-

Question 3

at pH<pKa of carboxylic group, amino acid is…

Answer 3

A cation +

Question 4

at pH>pKa of amino group, amino acid is…

Answer 4

An anion -

Question 5

What is the pKa

Answer 5

Number that describes the acidity of the molecule - how likely it is to lose H+

Lower the pKa the more likely to donate H+.

Question 6

What is isoelectric point pI

Answer 6

The pH at which the number of cation and anion charges are equal so no net charge

Question 7

9 amino acids that can’t be formed in the body so need to be taken in by diet

Answer 7

Valine
Leucine
Isoleucine
Phenylalanine
Tryptophan
Methionine
Lysine
Histidine
Threonine

Question 8

Ketogenic amino acids can be…

Answer 8

Degraded to acetyl-CoA for ketone bodies, unable to form glucose

Question 9

Ketogenic and glucogenic is can be…

Answer 9

Degraded to both ketone bodies and glucose

Question 10

Glucogenic amino acids

Answer 10

Degraded to glucose in tca cycle or glycolysis

Question 11

What is Henderson-hasselbalch equation

Answer 11

Smaller the pKa the stronger the acid

Question 12

What are buffers

Answer 12

A solution to resist changes in pH when H+ or OH- are added

Consist of weak acid and conjugate base

Question 13

How to work out pI using amino acid titration

Answer 13

pI=pKa1 + pKa2 / 2

Question 14

Amino acids migrate based on charge and pH

Answer 14

A positively charged species (pH < pI) moves toward the negative electrode; a negatively charged species (pH > pI) moves toward the positive electrode; a species with no net charge does not migrate.

Lysine 9.7 to positive

Aspartic acid 2.8 to negative

Valine 6.0 is neutral

Question 15

What amino acids are changed in sickle cell anaemia

Answer 15

Valine is in glutamic acid’s place

Question 16

How does the body use the bicarbonate
buffer system to maintain plasma pH

Answer 16

Carbonic acid is a weak acid and acts as its own buffer. It partially dissociates to H+ and HCO3-. pKa = 6.1.

At low pH (high H+), HCO3- absorbs H+ and converts to H2CO3 then CO2.

At high pH (low H+), H2CO3 dissociate to H+ and HCO3-

CO2 levels can be regulated by the lungs

HCO3- levels can be regulated by the kidneys

Question 17

How does the body regulate plasma pH

Answer 17

Buffer system act immediately to prevent excessive fluctuations of blood pH

Respiratory system increases in acidosis and decreases in alkalosis. The respiratory center in brain responds to pH and CO2 in minutes. Hyperventilation is symptom of metabolic acidosis.

Kidneys excrete excess H+ in acidosis and excess HCO3- in alkalosis. This takes hours to days.

Question 18

Which amino acids can’t form glucose

Answer 18

Lyciene and leucine