Amino Acids: Net Charge

At physiological pH, the peptide sequence KFGEDDRFD would have a net charge of?

At pH 8, the peptide sequence TYEKTR would have a net charge of?

At pH 7, the peptide sequence HGKRPPID would have a net charge of?

At pH 5, the peptide sequence HGKRPPID would have a net charge of?

Cation exchange columns bind cationic molecules and molecules with the largest net positive charge will have the highest affinity for the column. Which of the following peptides will have the highest affinity for a cation exchange column buffered at pH 7?

A scientist generated a variant peptide sequence with the following substitutions: F56L K67E I99D. What is the change in net charge between the original peptide and the variant peptide at physiological pH?

A scientist generated a variant peptide sequence with the following substitutions: K56L K106R F199E E564K. What is the change in net charge between the original peptide and the variant peptide at physiological pH?

Negatively charged residues decrease the pI of a peptide sequence while positively charged amino acids increase the pI of a peptide. If a scientist generated the following variant proteins which of the following correctly ranks the proteins from lowest to highest pI at physiological pH? 

Variant I: R45T, G89E, K56E
Variant II: R45K, G89R, K56R
Variant III: R45E, G89R, K56E

A scientist generated a variant peptide sequence with the following substitutions: K56L G99H F340D I564K. What is the change in net charge between the original peptide and the variant peptide at physiological pH?

A scientist generated a variant peptide sequence with the following substitutions: K56L G99H F340D I564K. What is the change in net charge between the original peptide and the variant peptide at pH 5?