Which one of the following statements regarding Penicillin is correct ?
- A.Penicillin resistant bacteria can store this antibiotic in vacuole
- B.Penicillin resistant bacteria can degrade this antibiotic by an enzyme called β-lactamase
- C.Penicillin resistant bacteria can degrade this antibiotic by an enzyme called lactic acid dehydrogenase
- D.Penicillin is not absorbed by bacteria; so most bacteria are resistant
Correct answer
Explanation
The correct answer is B, Penicillin resistant bacteria can degrade this antibiotic by an enzyme called β-lactamase. The enzyme breaks the β-lactam ring that gives penicillin its power.
Penicillin was discovered by Alexander Fleming in 1928 from the mould Penicillium notatum. It kills bacteria by blocking the enzymes that build peptidoglycan, the material of the bacterial cell wall, so growing cells burst. Some bacteria, such as resistant strains of Staphylococcus aureus, make β-lactamase, also called penicillinase, which splits the β-lactam ring and makes the drug useless. Doctors sometimes give penicillin with a β-lactamase inhibitor such as clavulanic acid to overcome this.
A is wrong: bacteria do not resist penicillin by storing it in a vacuole. C is wrong: lactic acid dehydrogenase is an enzyme of energy metabolism that turns pyruvate into lactate; it does not destroy antibiotics. D is wrong: penicillin acts on many bacteria, so most bacteria are not naturally resistant to it.
Exam tip: Penicillin, Fleming, 1928; it attacks the cell wall, and β-lactamase is the enzyme of resistance.
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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