Which one of the following pairs of enzymes do not work at acidic pH?
- A.Trypsin and Pepsin
- B.Chymotrypsin and Pepsin
- C.Trypsin and Amylase
- D.Pepsin and Amylase
Correct answer
Explanation
The correct answer is C, Trypsin and Amylase. Both work in neutral to alkaline conditions, in the mouth and the small intestine, and stop working in the acid of the stomach.
Each digestive enzyme has an optimum pH. Salivary amylase starts breaking starch in the mouth at about pH 6.8 and is inactivated once the food reaches the stomach; pancreatic amylase resumes the work in the small intestine. Trypsin and chymotrypsin are protein-digesting enzymes from the pancreas that work in the alkaline medium of the small intestine, where bile and bicarbonate neutralise the acid. Pepsin, by contrast, works best in the strongly acidic stomach, at about pH 2.
A is wrong: pepsin works at acidic pH.
B is wrong: this pair also contains pepsin, an acid-loving enzyme.
D is wrong: pepsin again works in acid, so the pair does not fit.
Exam tip: pepsin in the acidic stomach; trypsin, chymotrypsin, lipase and pancreatic amylase in the alkaline small intestine.
Practice Questions
View allThe fact that the planets move around the Sun, not in circles but in ellipses, was first demonstrated by
- A.Galileo
- B.Martin Luther
- C.Johannes Kepler
- D.Copernicus
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In 1609 Kepler showed that the planets move around the Sun in elliptical orbits, with the Sun at one focus of the ellipse.
Read the full explanation →Which one of the following statements is correct?
- A.Urea is produced in liver.
- B.Urea is produced in blood.
- C.Urea is produced from digestion of starch.
- D.Urea is produced in lung and kidney.
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Liver cells turn the toxic ammonia released from the breakdown of amino acids into urea through the ornithine cycle, also called the urea cycle.
Read the full explanation →Which one of the following is the correct sequence of passage of light in a compound microscope?
- A.Condenser-Objective lens-Eyepiece-Body tube
- B.Objective lens-Condenser-Body tube-Eyepiece
- C.Condenser-Objective lens-Body tube-Eyepiece
- D.Eyepiece-Objective lens-Body tube-Mirror
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Light passes through the condenser to the specimen, is picked up by the objective lens, travels up the body tube and reaches the eye through the eyepiece.
Read the full explanation →Which one of the following statements regarding haemoglobin is correct?
- A.Haemoglobin present in RBC can carry only oxygen but not carbon dioxide.
- B.Haemoglobin of RBC can carry both oxygen and carbon dioxide.
- C.Haemoglobin of RBC can carry only carbon dioxide.
- D.Haemoglobin is only used for blood clotting and not for carrying gases.
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It binds oxygen at its iron-containing haem groups and carries some carbon dioxide on its protein chains. Each haemoglobin molecule has four polypeptide chains and four haem groups, and each haem iron can hold one oxygen molecule, forming oxyhaemoglobin in the lungs.
Read the full explanation →Which one of the following statements regarding histone proteins is correct?
- A.Histones are proteins that are present in mitochondrial membrane.
- B.Histones are proteins that are present in nucleus in association with DNA.
- C.Histones are proteins associated with lipids in the cytosol.
- D.Histones are proteins associated with carbohydrates in the cytosol.
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They are the proteins around which DNA winds to form chromatin in the nucleus of eukaryotic cells. Histones are small basic proteins, rich in the positively charged amino acids lysine and arginine, which attract the negatively charged phosphate groups of DNA.
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