amino acids and pH Flashcards
structural
all of the amino acids except glycine are…
chiral
Exist as L or D form that are enantiomers of each other
L-form found in humans and D-form in bacteria.
at pH of 7.4 the amino acid groups have…
NH3+ and COO-
at pH<pKa of carboxylic group, amino acid is…
A cation +
at pH>pKa of amino group, amino acid is…
An anion -
What is the pKa
Number that describes the acidity of the molecule - how likely it is to lose H+
Lower the pKa the more likely to donate H+.
What is isoelectric point pI
The pH at which the number of cation and anion charges are equal so no net charge
9 amino acids that can’t be formed in the body so need to be taken in by diet
Valine
Leucine
Isoleucine
Phenylalanine
Tryptophan
Methionine
Lysine
Histidine
Threonine
Ketogenic amino acids can be…
Degraded to acetyl-CoA for ketone bodies, unable to form glucose
Ketogenic and glucogenic is can be…
Degraded to both ketone bodies and glucose
Glucogenic amino acids
Degraded to glucose in tca cycle or glycolysis
What is Henderson-hasselbalch equation
Smaller the pKa the stronger the acid
What are buffers
A solution to resist changes in pH when H+ or OH- are added
Consist of weak acid and conjugate base
How to work out pI using amino acid titration
pI=pKa1 + pKa2 / 2
Amino acids migrate based on charge and pH
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
What amino acids are changed in sickle cell anaemia
Valine is in glutamic acid’s place
How does the body use the bicarbonate
buffer system to maintain plasma pH
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
How does the body regulate plasma pH
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.
Which amino acids can’t form glucose
Lyciene and leucine
