NEET Biology Biomolecules MCQs Set 24

Answer: (d) deoxyribonucleotides

Explanation:
1. DNA is a polymer of deoxyribonucleotides, each with a base, deoxyribose and phosphate.

Teacher's Note:
1. Ribonucleotides make RNA.
2. Nucleosides lack the phosphate.

Answer: (d) 480

Explanation:
1. A = T and C = G in DNA. With 120 A and 120 C, there must be 120 T and 120 G, so the total is 480 nucleotides.

Teacher's Note:
1. Chargaff's rules apply.
2. The segment has 480 bases.

Answer: (c) nitrogen base, sugar and phosphate

Explanation:
1. A nucleotide contains a nitrogenous base, a pentose sugar and a phosphate group.

Teacher's Note:
1. A nucleoside lacks the phosphate.
2. Nucleotides are joined by phosphodiester bonds.

Answer: (b) isoenzymes

Explanation:
1. Isoenzymes are enzymes with slightly different structures which catalyse the same reaction, such as LDH.

Teacher's Note:
1. Apoenzyme is the protein part.
2. Coenzymes are organic cofactors.

Answer: (d) nucleotide.

Explanation:
1. The basic unit of a nucleic acid is the nucleotide.

Teacher's Note:
1. Nucleoside is base plus sugar.
2. Nucleoid is the bacterial DNA region.

Answer: (d) uracil

Explanation:
1. In RNA, thymine of DNA is replaced by uracil.

Teacher's Note:
1. Uracil pairs with adenine.
2. RNA also has ribose instead of deoxyribose.

Answer: (d) reduction in activation energy

Explanation:
1. Enzymes reduce the activation energy of a reaction and so speed it up.

Teacher's Note:
1. They do not change the equilibrium.
2. They are not used up.

Answer: (c) Length of one helix is 45 Å in B-DNA

Explanation:
1. B-DNA has a pitch of 34 Å (3.4 nm), with 10 base pairs per turn, so the value 45 Å is wrong.

Teacher's Note:
1. Some viruses have single-stranded DNA.
2. Z-DNA has 12 bp per turn.

Answer: (a) GATCAATGC

Explanation:
1. Pyrimidines are C, T and U. In GATCAATGC there are T, C, T, C (four). The others have 3, 3 and 5.

Teacher's Note:
1. Purines are A and G.
2. Count only the pyrimidines.

Answer: (c) CHON

Explanation:
1. Carbon, hydrogen, oxygen and nitrogen form about 99% of living matter.

Teacher's Note:
1. Phosphorus and sulphur are less abundant.
2. Oxygen is the most abundant.

Answer: (d) phosphodiester bond

Explanation:
1. Two ribonucleotides are joined by a phosphodiester bond between the 3' carbon of one and the 5' carbon of the next.

Teacher's Note:
1. Peptide bonds join amino acids.
2. Hydrogen bonds link base pairs.

Answer: (a) proteins

Explanation:
1. Proteins are the most diverse macromolecules, with differences in sequence, length and shape.

Teacher's Note:
1. They have 20 amino acids.
2. Carbohydrates are less diverse.

Answer: (c) guanine

Explanation:
1. Guanine is a purine present in RNA; cytosine and uracil are pyrimidines, and thymine is absent from RNA.

Teacher's Note:
1. Adenine is the other purine.
2. Purines have a double ring.

Answer: (a) Starch, glycogen, cellulose

Explanation:
1. Starch, glycogen and cellulose are polysaccharides made of glucose units.

Teacher's Note:
1. Sucrose and maltose are disaccharides.
2. Glucose and fructose are monosaccharides.

Answer: (a) These are all proteins

Explanation:
1. Amylase, rennin and trypsin are all enzymes, so they are proteins.

Teacher's Note:
1. Amylase is a carbohydrase.
2. Trypsin acts at alkaline pH.

Answer: (c) loosely attached organic part

Explanation:
1. A coenzyme is a loosely attached organic non-protein part of the holoenzyme, such as NAD.

Teacher's Note:
1. Prosthetic groups are firmly attached.
2. Metal ions are inorganic cofactors.

Answer: (b) tRNA

Explanation:
1. tRNA picks up specific amino acids from the cytoplasm and carries them to the ribosome.

Teacher's Note:
1. mRNA carries the code.
2. rRNA is a ribosome part.

Answer: (c) thymidine

Explanation:
1. Radioactive thymidine is a specific precursor of DNA because thymine occurs only in DNA.

Teacher's Note:
1. Uracil is for RNA.
2. Adenine is in both.

Answer: (d) glucose + galactose

Explanation:
1. Lactose is a disaccharide of glucose and galactose.

Teacher's Note:
1. Sucrose is glucose plus fructose.
2. Maltose is glucose plus glucose.

Answer: (d) Phenylalanine

Explanation:
1. Phenylalanine is an essential amino acid, which the body cannot make.

Teacher's Note:
1. Serine, aspartic acid and glycine are non-essential.
2. Essential amino acids come from the diet.

Answer: (a) nucleotide

Explanation:
1. ATP is a nucleotide (adenine, ribose, three phosphates).

Teacher's Note:
1. A nucleoside would lack phosphate.
2. It is the energy currency.

Answer: (b) glycoproteins

Explanation:
1. Conjugated proteins with carbohydrates as the prosthetic group are glycoproteins.

Teacher's Note:
1. Chromoproteins have pigments.
2. Lipoproteins have lipids.

Answer: (d) viruses

Explanation:
1. Enzymes are absent in viruses, as they have no metabolism of their own.

Teacher's Note:
1. Algae, fungi and cyanobacteria are cellular.
2. Viruses use the host's enzymes.

Answer: (d) lowering the activation energy of the reaction

Explanation:
1. Enzymes speed up reactions by lowering the activation energy.

Teacher's Note:
1. They do not change equilibrium.
2. They form an enzyme-substrate complex.

Answer: (a) end product

Explanation:
1. In feedback inhibition the end product of a metabolic pathway inhibits the enzyme at an early step.

Teacher's Note:
1. It controls the product level.
2. It is allosteric.

Answer: (a) L-shaped

Explanation:
1. The tertiary structure of tRNA is L-shaped, though its 2D drawing looks like a clover leaf.

Teacher's Note:
1. The anticodon loop is at one end.
2. The amino acid binds at the other end.

Answer: (a) are polymers of nucleotides

Explanation:
1. DNA and RNA are both polymers of nucleotides.

Teacher's Note:
1. Only DNA replicates in cells.
2. The sugars and bases differ.