This set of Cell Biology Multiple Choice Questions & Answers (MCQs) focuses on “Biological Molecules Structures and Functions – Bonds Types”.
1. The electron clouds around the nucleus are of ___________
a) Spherical shape
b) Spherical and Dumbbell shape
c) Spherical and Hexagonal shape
d) Cannot be determined
Explanation: Electrons swarm around the nucleus of an atom in a mostly unpredictable fashion. Erratic electron behaviour is best described by the electron cloud model. The electron cloud is an area around the nucleus of an atom where electrons are most likely to be found. The clouds are roughly defined by their boundaries which is either spherical or dumbbell shape.
2. Atoms or molecules having orbitals containing a single unpaired electron is known as ___________
c) Free radicals
Explanation: Atoms or molecules that have orbitals containing a single unpaired electron are highly unstable. They are called free radicals. Free radicals may be formed when a covalent bond is broken such that each portion keeps one-half of the shared electrons. They may also be formed when an atom or molecule accepts a single electron transferred during an oxidation-reduction reaction.
3. Which of the following is true based on the strength of the bond?
a) Ionic > Covalent > Vanderwaal > Hydrogen
b) Covalent > Ionic > Vanderwaal > Hydrogen
c) Covalent > Ionic > Hydrogen > Vanderwaal
d) Covalent > Ionic > Hydrogen = Vanderwaal
Explanation: Intramolecular bonds are called covalent bonds and are far stronger that intermolecular forces (or bonds). The latter are usually ranked as follows: ionic > Vanderwaal > hydrogen. Hydrogen bonding includes inter molecular interactions with permanent dipoles (and partial charges) between hydrogen atoms and a few other elements. Vander Waals interactions are based on random and instantaneous dipoles which last for fractions of a second in long, polarizable bonds.
4. Which of the following is a non-polar molecule?
Explanation: Polar molecules occur when two atoms do not share electrons equally in a covalent bond. A dipole is formed, with part of the molecule carrying a slight positive charge and the other part carrying a slight negative charge. This happens when there is a difference between the electronegativity of each atom. An extreme difference forms an ionic bond, while a lesser difference forms a polar covalent bond. When molecules share electrons equally in a covalent bond there is no net electrical charge across the molecule. In a nonpolar covalent bond, the electrons are evenly distributed.
5. The detailed tertiary structure of a protein is determined by the ___________ technique.
d) X-ray crystallography
Explanation: In X-ray crystallography technique, a crystal of the protein is bombarded by a thin beam of X-ray and the radiation that is scattered by the electrons of the protein’s atoms is allowed to strike a radiation sensitive plate or detector, forming an image of spots. When these diffraction patterns are subjected to complex mathematical analysis, an investigator can work backward to derive the structure responsible for producing the pattern.
6. Which of the following is not true?
a) Steroids are built around a four-ringed hydrocarbon skeleton
b) Cholesterol, testosterone, progesterone are examples of steroids
c) Steroids are found in the cell membranes of both plant and animal
d) Cannot be determined
Explanation: Cholesterol is a steroid which is found in the cell membranes of animals. Cholesterol is largely absent from plant cells, which is why vegetable oils are considered “cholesterol-free”.
7. Which of the following bond is not present in DNA?
a) Phosphate bond
b) Hydrogen bond
c) VanderWaal’s force
d) Disulphide bond
Explanation: Disulphide bond is not present in a DNA molecule. Phosphate bond is present between two deoxy-nucleotides (dNTPs) of DNA. The nitrogen bases on the two strands of DNA have hydrogen bonds between them. Adenine is connected Thymine by 2 hydrogen bonds, Guanine is bound to Cytosine by 3 hydrogen bonds. The base stacking in DNA is due to Vanderwaal’s force.
8. Which of the following amino acids may or may not be protonated at neutral pH?
Explanation: The amino acids may be negatively charged, positively charged or neutral at a neutral pH. Here, Arginine and Lysine are positively charged or protonated at neutral pH, while Glutamate is negatively charged at neutral pH. However, Histidine may or may not be protonated at normal pH. The side chain of Histidine has a pKa of 6.5, which means only 10% of Histidine is protonated.
9. Heparin is an example of ___________
a) Tertiary protein
Explanation: A more complex structures of polysaccharides is glycosaminoglycan (GAGs). Unlike other polysaccharides, they have an A-B-A-B where A and B represent two different sugars. An example of GAG is heparin, which is secreted by cells in lungs against tissue damage. Heparin prevents blood coagulation, enabling free flow of blood to heart or lungs.
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