All Free Biology MCQs with Answers

• A. Lactose
• B. Lactose and Galactose
• C. Glucose
• D. Galactose

Explanation: In the Lac operon, lactose is an inducer. It binds with a suppressor and inactivates it. It allows RNA polymerase to access the promoter, and transcription proceeds. The lac Z, lac Y, and lac genes in the lac operon are the structural genes that code for beta-galactosidase, which converts lactose into glucose and galactose. In the lac operon, Lactose acts as an inducer for the synthesis of protein. Lactose binds with the repressor protein, causing an allosteric shift. This altered repressor cannot bind to the operator, thereby making the promoter region accessible. As the promoter region gets activated, the RNA polymerase enzyme initiates the transcription of the lac operon. Thus, lactose is required for the expression of the lac operon.

• A. tRNA^Val
• B. tRNA^Glu
• C. tRNA^Met
• D. tRNA^Lys

Explanation: tRNA^Val is the correct answer. Sickle cell anemia is caused by a single amino acid substitution in the beta-globin chain of hemoglobin from glutamic acid to valine. Therefore, the tRNA that carries valine to the ribosome, tRNA^Val, is involved in the formation of this mutated part of the hemoglobin molecule.

• A. Double bond
• B. Phosphodiester bonds
• C. Covalent bond
• D. Hydrogen bond
• E. Single bond

Explanation: Each chain of DNA is formed by the union of many nucleotides through phosphodiester bonds. Phosphodiester bonds are covalent bonds. So option B is correct answer.

• A. Genetic code
• B. Chromosome
• C. Amino acid
• D. Helix

Explanation: The correct answer is A Genetic code. Genetic information in DNA is stored in the form of a genetic code. The genetic code is the set of rules that specifies how the sequence of nucleotides in DNA is translated into the sequence of amino acids in a protein. It is the basis for the transmission of genetic information from one generation to the next and is responsible for the diversity of life.

• A. Genes
• B. Phenotypes
• C. Karyotypes
• D. Cells

Explanation: DNA stores biological information in discrete units called genes. Genes are segments of DNA that contain the instructions for building and maintaining an organism. They provide the information needed to produce proteins, which are essential for various biological processes and traits.

• A. Double Stranded binding proteins
• B. Double-stranded binding enzymes
• C. Single-stranded binding proteins
• D. Single-stranded binding enzyme

Explanation: Single-stranded (SSBs) are proteins that bind to single-stranded DNA during processes such as DNA replication and repair. They stabilize the unwound DNA strands, preventing them from re-annealing or forming secondary structures. By keeping the strands separate, SSBs allow other enzymes, like DNA polymerases, to access the DNA for replication and repair.

• A. 3rd position
• B. 6h position
• C. 5th position
• D. 4th position

Explanation: The sixth position of the beta globin chain of the hemoglobin molecule is where glutamic acid is replaced by valine.

• A. Basic amino acid
• B. Acidic fatty acid
• C. Başic citric acid
• D. Acidic amino acid

Explanation: Basic amino acids are amino acids that have a positively charged side chain at physiological pH (around 7.4), due to the presence of an additional amino group (-NH₃⁺) in their side chains. These amino acids can accept protons (H⁺), making them basic.They are found in histones.

• A. Gene
• B. Nucleosome
• C. Centrosome
• D. Centromere

Explanation: A centromere is a region of a chromosome that plays a critical role during cell division. It is the constricted region where sister chromatids are held together.

• A. Histidine
• B. Uracil
• C. Cytosine
• D. Thymine

Explanation: According to Chargaff's base pairing rule:Adenine (A) always pairs with Thymine (T) → by two hydrogen bondsCytosine (C) always pairs with Guanine (G) → by three hydrogen bondsSo,➡ If one helix (strand) contains Adenine,➡ The opposite helix (complementary strand) will contain Thymine.