1. Histones are proteins found in eukaryotic cell nuclei, tightly bound to DNA,

Question

1. Histones are proteins found in eukaryotic cell nuclei, tightly bound to DNA, which has many negatively charged phosphate groups. The pI of histones is very high, about 10.8.

a) What type of amino acids must be present in relatively large numbers in histones? Name one such amino acid and the type of noncovalent interaction that it is likely to form.

b) What type of secondary structure element(s) is the amino acid that you named above is most likely to be found in?

c) The folding of these proteins has been studied in the laboratory using structural and mutagenesis methods. The protein has 2 cysteines present in its amino acid sequence that are disulfide bonded. What reagent would you use to break this disulfide bond? Would this completely unfold the protein? Explain your answer

Any help really appreciated, thank you!

Explanation / Answer

1) a) Isoelectric point i.e pI is the pH at which the amino acid is neutral. Since the pI of histones is high around 10.8, the amino acid involved should have a basic side chain. Example of amino acid: Argenine

For Argenine:

pKa1 (alpha-carboxyl) = 2.17

pKa2 (alpha ammonium ion) = 9.04

pKa3 (the side chain) = 12.48

pI = 1/2 (pKa2 +pKa3) = 1/2 (9.04 + 12.48) =10.76

Related Questions

Navigate

• Browse (All)
• Browse 1
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.