Another important class of compounds in the human body is proteins. Many proteins carry out catalyti — Biochemistry Chemistry Question
Hemoglobin
Another important class of compounds in the human body is proteins. Many proteins carry out catalytic functions. Hemoglobin, on the other hand, transports oxygen from the lung to remote parts of the body.
The molecular mass of hemoglobin is about 67000 g mol–1. The average mass of hemoglobin in erythrocytes in 100 cm3 of blood is 15 g. Calculate the concentration of hemoglobin in blood (in mol dm–3).
Model Answer
150 g haemoglobin in 1 dm3
n(haemoglobin ) = 150 g / 67,000 g mol–1 = 0.0022 mol
concentration: 0.0022 mol dm–3
Estimate the average distance between two oxygen molecules in the air we breathe. Assume frigid air at 0 °C in which 21 vol. % of air is oxygen.
Model Answer
Volume of 1 mol of air = 22.4×10–3 m3
Number of oxygen molecules in the above volume =
= (6.02×1023) (0.21) = 1.26×1023
Volume of air per oxygen molecule = (22.4×10–3 m3)/(1.26×1023) = 1.78×10–25 m3
Average distance between oxygen molecules = 5.6×10–9 m
According to Henry’s law
solubility = kH × partial pressure
(kH = Henry’s constant)
Henry’s constant for oxygen is 1.3×10–3 mol dm–3 atm–1. Estimate the average distance between two oxygen molecules in water in equilibrium with air.
Model Answer
Solubility = (1.3×10–3 mol dm–3 atm–1) (0.21 atm) = 2.7×10–4 mol dm–3
Number of oxygen molecules in a liter of water
= (6×1023 mol–1) ( 2.7×10–4 mol ) = 1.6×1020
Volume of water per oxygen molecule
= (1×10–3 m3) / (1.6×1020) = 6.3×10–24 m3
Average distance between oxygen molecules = 1.8×10–8 m
A hemoglobin molecule can bind up to four oxygen molecules. Estimate the average distance between two oxygen molecules in blood when hemoglobin is saturated with oxygen. Compare your result with answers in 25.2 and 25.3 and note how efficiently hemoglobin concentrates and transports oxygen to tissues where the partial pressure of oxygen is low.
Model Answer
Number of oxygen molecules in 1 dm3 of blood = 4 × 0.0022 × 6×1023 = 5.3×1021
Volume of blood per oxygen molecule = 1.0×10–3 m3 / 5.3×1021 = 1.9×10–25 m3
Distance between oxygen molecules = 5.7×10–9 m
There are about ( ) amino acids in hemoglobin. (Fill in the number in the bracket.) Estimate using average molecular mass of amino acids and check against literature values.
Model Answer
The average relative molecular mass of amino acids is about 130. Water is removed upon peptide bond formation. 67,000 / (130 – 18) = 600 amino acid residues. Actually hemoglobin has two alpha and two beta chains, each of which consists of 141 residues.
There are about ( ) different kinds of amino acids in hemoglobin.
Model Answer
All life–forms on earth use 20 common amino acids.
Trypsin hydrolyzes peptide bonds at the carboxyl group of arginine and lysine. Consider, for example, the following peptide.
H3N +–gly–phe–arg–ala–ala–tyr–leu–phe–his–pro–lys –gly–trp–glu–ile–asp–phe–COO–
Upon complete hydrolysis by trypsin, the following set of peptides will result.
H3N +–gly–phe–arg–COO–
H3N +–ala–ala–tyr–leu–phe–his–pro–lys –COO–
H3N +–gly–trp–glu–ile–asp–phe–COO–
Upon complete hydrolysis of hemoglobin after reduction of the disulfide bonds and alkylation, you expect to find on the average about ( ) amino acids in a tryptic peptide (peptide resulting from hydrolysis by trypsin).
Model Answer
Trypsin hydrolyzes after 2 amino acid residues (arginine and lysine) out of 20 different kinds of amino acids. So, on average the enzyme breaks every tenth peptide bond. The number of amino acid residues in an average tryptic peptide = 20 / 2 = 10
The average molecular mass of the tryptic peptides is about ( ).
Model Answer
When considering the removal of water in the peptide bond formation:
(130 – 8) × 10 + 18 = 1,140 = about 1,000