All Free Biology MCQs with Answers

• A. Redundant genes
• B. Regulatory genes
• C. Polymorphic genes
• D. Operator genes

Explanation: Operator genes are a region of DNA sequence capable of interacting with a specific repressor molecule, and in doing so, they affect the activity of other genes downstream from them.The other options are incorrect because :Regulator genes code for proteins that bind to DNA and regulate the expression of other genes.Redundant genes are genes that code for the same or similar proteins.Polymorphic genes are genes that have different variants in a population.

• A. Cistron
• B. Transposons
• C. Exons
• D. Introns

Explanation: DNA elements that can switch their position are called transposons. Transposons are mobile DNA sequences that can move from one location to another in the genome. They can be short or long sequences, and they can be either coding or non-coding.The other options listed are not DNA elements that can switch their position:Cistron is a unit of heredity that codes for a single polypeptide chain.An exon is a coding region of a gene.An intron is a non-coding region of a gene.

• A. rRNA
• B. RNA
• C. mRNA
• D. tRNA

Explanation: Transfer RNA or tRNA helps in the transfer of amino acids to the ribosomes, mRNA complex to form the polypeptide chain. It has four key regions- a carrier and recognition end, an enzyme site, and a ribosome site. This recognition end has three anticodons with the help of which amino acids are identified. rRNA forms 67% of 70S ribosomes and 50% of 80S ribosomes. mRNA carries the coded information from DNA for the synthesis of proteins. mRNA stands for messenger RNA. It is the RNA molecule that carries the genetic information from the DNA in the nucleus to the ribosome in the cytoplasm. rRNA stands for ribosomal RNA. It is the main component of the ribosome, which is the organelle where protein synthesis takes place. The rRNA molecule helps to position the mRNA molecule and the tRNAs on the ribosome.

• A. The lac operon is induce
• B. E.coli cells stop dividing
• C. The lac operon is repressed
• D. All operons are induced

Explanation: When E.coli bacteria are transferred to a medium containing lactose, the lac operon is induced. The lac operon consists of 3 structural genes (lac Z, lac Y, and lac A). It involves the synthesis of the b-­galactosidase enzyme in E.coli, which hydrolyses lactose into glucose and galactose.

• A. Depressor
• B. Controlling element
• C. Regulator
• D. Inducer

Explanation: An environmental agent that triggers transcription from an operon is an inducer. An inducer is a molecule that binds to a repressor protein and changes its shape. This prevents the repressor protein from binding to the operator region of the operon, which allows RNA polymerase to bind to the promoter region and initiate transcription. Inducers are often the substrates of the enzymes that are encoded by the operon. This means that the operon is only turned on when the inducer is present, which ensures that the cell does not produce more of the enzyme than it needs. For example, the lac operon in E. coli is turned on by the inducer lactose. The lac operon encodes the enzymes that are needed to metabolise lactose. When lactose is present in the environment, it binds to the repressor protein and changes its shape, which allows RNA polymerase to bind to the promoter region and initiate transcription of the operon.The other options listed are not environmental agents that trigger transcription from an operon:A controlling element is a general term for any element that can regulate gene expression.Depressor is a synonym for repressor.A regulator is a general term for any protein that regulates gene expression.

• A. CAT GAT GATG
• B. A non­sense mutation
• C. ATG ATG ATG
• D. CA TGA TGA TG

Explanation: A nonsense mutation is a mutation which interconverts a nonsense codon to or from a sense-­coding triplet, resulting in an abnormally shortened or elongated polypeptide chain. But in this example, cytosine is added at the beginning, so CAT GAT GATG will result.

• A. Exons
• B. Cistrons
• C. Introns
• D. Operons

Explanation: Split genes are those genes that consist of a continuous sequence of nucleotides (coding sequences) interrupted by intervening sequences. Most eukaryotic genes are split as are genes of some animal viruses. The continuous coding sequences are called exons, and the intervening noncoding sequences are called introns. These introns are not represented in mRNA transcribed from the gene and are not utilised for the synthesis of proteins.

• A. 'I' gene
• B. Promoter gene
• C. β­-galactosidase
• D. Lactose

Explanation: The lac operon in E. coli is induced by β­-galactosidase, an enzyme meant for the hydrolysis of lactose in glucose and galactose.

• A. Termination
• B. Initiation
• C. Elongation
• D. Transcription

Explanation: Transcription is the mechanism of copying the message of DNA into RNA with the help of the enzyme RNA polymerase. It is meant for taking the coded information from DNA to the site where it is required for protein synthesis. Translation or protein synthesis is a complicated process involving several steps: the activation of amino acids, the transfer of amino acids to tRNA, initiation of polypeptide synthesis, elongation of the polypeptide chain, and the termination of the polypeptide chain.

• A. H 1, H 2 A, H 2 B and H 3
• B. H 1, H 2 A, H 2 B, H 4
• C. H 1, H 2 A, H 2 B, H 3 and H 4
• D. H 2 A, H 2 B, H 3 and H 4

Explanation: The Nucleosome core or histone octamer is made up of two subunits, each of H2A, H2B, H3, and H4 histone proteins. It is about 7­10 nm in diameter, consisting of histones around which a DNA strand, about 120 base pairs long, is wrapped in chromosomes.