This set of Cell Biology Multiple Choice Questions & Answers (MCQs) focuses on “Chemical Basis of Life – Proteins”.
1. In an amino acid, the carboxyl group and amino group are separated from each other by a single ____________ atom.
Explanation: Proteins are polymers containing amino acids as monomers. There are twenty different types of amino acids, with varying functional groups. Every amino acid has a carboxyl group and an amino group separated by a single carbon atom between them.
2. Amino acids used in the synthesis of proteins on a ribosome are ________________
a) D-amino acids
b) Mutated amino acids
c) L-amino acids
d) Fluorescing amino acids
Explanation: Explanation: In most organisms including humans, the L amino acid is used to make up proteins. In some microorganisms D types are used. The conversion of D to L can take place in our body using an enzyme called racemase.
3. What protein makes up spider silk?
Explanation: Spider silk is a collagen molecule made up of 3 alpha helices wound together in a triple helix format. It is rich in hydrophobic residues as well as glycine and proline to incorporate a flexible nature to it. Collagen is also found in our bones and tendons.
4. Microorganisms use D-amino acids.
Explanation: Unlike animals, microorganism use D-amino acids in the synthesis of certain small peptides, including those present in cell walls and several antibiotics.
5. Which bonds are present in two neighboring amino acids?
a) Glycosidic bonds
b) Polypeptide bonds
c) Amide bonds
d) Hydrogen bonds
Explanation: Peptide bonds are present between two consecutive amino acids. Carboxyl group of one amino acid is bonded to the amino group of neighboring amino acid, by the elimination of water.
6. The longest known polypeptide is of the muscle protein called __________
Explanation: An average polypeptide chain consists of about 450 amino acids. The longest known polypeptide chain is found in the muscle protein called titin, consisting of over 30,000 amino acids.
7. Which of the following amino acids does not belong to polar charged group?
b) Aspartic acid
Explanation: Serine belongs to the category of polar uncharged amino acids whereas aspartic acid, lysine, glutamic acid and arginine belong to polar charged amino acids. These are fully charged at physiological pH and their side chains contain strong organic acids and bases.
8. Histidine is a polar uncharged amino acid.
Explanation: Histidine is considered a polar charged amino acid although it is not fully charged at physiological pH. The ability of Histidine to gain or lose a proton in physiological pH ranges, it is an important residue in active sites of many proteins.
9. Which residues are present in histone proteins?
a) Lysine & proline
b) Glutamic acid & aspartic acid
c) Arginine & Histidine
d) Serine & Cysteine
Explanation: DNA is a negatively charged molecule that wounds around histone proteins. They are rich in both arginine and histidine residues (both are positively charged Amino acids) which helps the negatively charged DNA bind to it. This forms a strong ionic bond formation allowing the DNA to be tightly packed into chromosomes.
10. Which of the following groups of amino acids are least soluble in water?
c) Polar charged
d) Polar uncharged
Explanation: Non-polar amino acids have side chains that are essentially hydrocarbons(sulphur in case of methionine and cysteine). This causes the amino acid water interaction to be weak and thus are sparsely soluble in water. The amino acids included in this category are alanine, valine, leucine, isoleucine, tryptophan, phenylalanine and methionine. Phenylalanine is least soluble due to its bulky aromatic side chain.
Sanfoundry Global Education & Learning Series – Cell Biology.
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