Cell Biology Multiple Choice Questions on “Chemical Basis of Life – Carbohydrates”.
1. Heptoses are __________
A. sugars
B. proteins
C. amino acids
D. monomers
Answer: A
Clarification: Heptoses are carbohydrates that contain 7 atoms of carbon. The sugars of importance in cellular metabolism contain 3 to 7 carbon atoms.
2. Fructose is a _____________
A. aldose sugar
B. ketose sugar
C. monosaccharide
D. polymer
Answer: B
Clarification: Fructose is a ketose sugar because the carbonyl group (C==O) is located in an internal position to form a ketone group. If the carbonyl bond is located at one end of the sugar it is called aldose sugar.
3. The compounds which have same chemical reactivity but structures which are mirror images of each other are known as ____________
A. isoforms
B. allotropes
C. enantiomers
D. isomers
Answer: C
Clarification: Enantiomers or stereoisomers are the compounds having similar chemical reactivity and their structures are mirror images of each other.
4. Which of the following conventions is used to denote the presence of carbonyl group in left/right in the chemical structure of a carbohydrate?
A. Positive/ negative
B. -1/ +1
C. L/ R
D. L/ D
Answer: D
Clarification: When carbonyl group as in ketone or aldehyde is located on the left side the molecule is represented with a prefix ‘L-‘, for example L- glyceraldehyde; if present on the right prefix ‘D-‘ is added.
5. Enzymes in a cell can distinguish between L and D forms of sugar.
A. True
B. False
Answer: A
Clarification: Enzymes present in a living cell can differentiate between the D and L forms of sugar. Therefore, a cell uses only one of the stereoisomers. For example, only D-glucose is used.
6. Which types of bonds are found in sugars?
A. amide
B. acidic
C. glycosidic
D. non-covalent
Answer: C
Clarification: Sugars are joined to one another by covalent glycosidic bonds that play a major role in the formation of large sugar moieties. In these bonds carbon of one sugar molecule bonds with the hydroxyl group of another sugar generating a –C-O-C- linkage.
7. Sucrose and lactose are _____________
A. monosaccharides
B. disaccharides
C. pentoses
D. polyssaccharides
Answer: B
Clarification: Disaccharides provide the readily available stores of energy. Sucrose is found in plant sap and has the function of carrying chemical energy from one part of the plant to another. Lactose is found in milk of mammals and has the role of nourishing the new born with fuel for growth and early development.
8. Enzyme lactase is found in ______________
A. nucleus
B. ribosome
C. plasma membrane
D. golgi complex
Answer: C
Clarification: The enzyme lactase is responsible for hydrolyzing lactose. It is found in the plasma membrane of cells lining the walls of the intestine.
9. Which type of carbohydrates lead to the formation of glycolipids and glycoproteins?
A. Oligosaccharides
B. Monosaccharides
C. Glycogen
D. Glucose
Answer: A
Clarification: Oligosaccharides are formed when sugar molecules link to form small chains (oligo means few). These form covalent bonds with lipids and proteins generating glycolipids and glycoproteins.
10. Which of the following polysaccharide is not entirely composed of glucose subunits?
A. Lactose
B. Starch
C. Glycogen
D. Cellulose
Answer: A
Clarification: Lactose is a disaccharide molecule found in milk. Glycogen, starch and cellulose are all polysaccharides composed entirely of glucose subunits. They have same constitution but different chemical and physical properties.