Which one of the following statements is not correct?
- A.Fischer projection represents the molecule in an eclipsed conformation.
- B.Newman projection can be represented in eclipsed, staggered and skew conformations.
- C.Fischer projection of the molecule is its most stable conformation.
- D.In Sawhorse projections, the lines are inclined at an angle of 120° to each other.
Correct answer
Explanation
The correct answer is C, Fischer projection of the molecule is its most stable conformation.. A Fischer projection draws a molecule as a cross: the horizontal bonds point towards the viewer and the vertical bonds point away. To draw it this way, the groups on neighbouring carbon atoms have to be lined up behind one another, which is the eclipsed conformation. The eclipsed form has the most torsional strain and is the least stable, while the staggered form is the most stable, so statement C is not correct. Option A is a correct statement, since a Fischer projection shows the eclipsed conformation. Option B is correct, since a Newman projection, looking straight down a carbon-carbon bond, can show the eclipsed, staggered and skew (gauche) forms. Option D is correct, since in a Sawhorse projection the three bonds on each carbon are drawn at 120° to one another, with the central carbon-carbon bond drawn at an angle. Fischer projections are mainly used to show the configuration of sugars and amino acids, not their stable shape. Exam tip: staggered is most stable, eclipsed least; Fischer always shows the eclipsed form.
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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