Which one of the following functions is not carried out by smooth endoplasmic reticulum?
- A.Transport of materials
- B.Synthesis of lipid
- C.Synthesis of protein
- D.Synthesis of steroid hormone
Correct answer
Explanation
The correct answer is C, Synthesis of protein. Proteins are made on ribosomes, and the smooth endoplasmic reticulum has no ribosomes on its surface.
The endoplasmic reticulum is a network of membrane tubes and sacs in the cytoplasm. Its rough part (RER) is studded with ribosomes, which is why it looks rough under the electron microscope, and it makes and folds proteins, especially those meant for secretion or for membranes. The smooth part (SER) lacks ribosomes and makes lipids, phospholipids and steroid hormones, stores calcium in muscle cells and detoxifies drugs and poisons in liver cells. Both parts form channels that carry materials through the cell.
Option A is wrong, because the SER does serve as a channel for moving materials within the cell. Option B is wrong, because lipid synthesis is the main job of the SER. Option D is wrong, because steroid hormones such as testosterone, oestrogen and cortisol are made in the SER, which is why it is abundant in the adrenal glands and gonads.
Exam tip: RER = ribosomes and proteins; SER = lipids, steroids and detoxification.
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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