All Free Biology MCQs with Answers

• A. Protein structure
• B. DNA replication
• C. Protein synthesis pattern
• D. RNA transcription pattern

Explanation: After a mutation at a genetic locus, the character of an organism changes due to a change in protein structure. Mutations can occur in the DNA of an organism, which can lead to changes in the RNA that is transcribed from that DNA. This, in turn, can lead to changes in the proteins that are synthesised from that RNA. If the mutation occurs in a protein-coding region of the DNA, it can lead to a change in the amino acid sequence of the protein. This change in amino acid sequence can lead to a change in the protein's structure and function.The other options are incorrect because:DNA replication is the process of copying DNA. It is not directly involved in changing the character of an organism.The protein synthesis pattern is the way in which proteins are synthesised from RNA. It is not directly involved in changing the character of an organism.RNA transcription pattern is the way in which RNA is transcribed from DNA. It is not directly involved in changing the character of an organism.

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

Explanation: The form of RNA that has a structure resembling the cloverleaf is tRNA (transfer RNA). tRNA is a small RNA molecule that plays a key role in protein synthesis. It transfers amino acids from the cytoplasm to the ribosome, where they are incorporated into the growing polypeptide chain. R.Holly, in 1965, gave the clover leaf model of tRNA for yeast alanyl tRNA.It has four major sites: the AAbinding site, the anticodon site, the TUC loop, and the DHU loop. The cloverleaf structure of tRNA is important for its function. The anticodon loop of tRNA pairs with the codon on mRNA, and the amino acid attachment site binds to the amino acid that will be incorporated into the protein.The other options are incorrect because:rRNA (ribosomal RNA) is a component of ribosomes, which are the organelles where protein synthesis takes place. rRNA does not have a cloverleaf structure.mRNA (messenger RNA) is a type of RNA that carries the genetic code from DNA to the ribosome. mRNA does not have a cloverleaf structure.hnRNA (heterogeneous nuclear RNA) is a precursor to mRNA. It is processed into mRNA before it is exported from the nucleus to the cytoplasm. hnRNA does not have a cloverleaf structure.

• A. TATGC
• B. TCTGG
• C. UAUGC
• D. UATGC

Explanation: During transcription, the nucleotide sequence of the mRNA is complementary to the nucleotide sequence of the DNA template strand, with the exception of thymine, which is replaced by uracil in mRNA.Therefore, if the nucleotide sequence of the DNA strand that is being coded is ATACG, then the nucleotide sequence in the mRNA would be:UAUGCThis is because the complementary nucleotides of adenine (A) and thymine (T) are uracil (U) and adenine (A), respectively, and the complementary nucleotides of cytosine (C) and guanine (G) are guanine (G) and cytosine (C), respectively.

• A. Frame shift mutation
• B. Transcription
• C. Transition
• D. Transversion

Explanation: When adenine replaces guanine because of a mutation, it is called a transition. Transitions are the most common type of mutation, and they occur when one purine base (adenine or guanine) is replaced by another purine base. Other options are incorrect because:Transversions are less common, and they occur when a purine base is replaced by a pyrimidine base (cytosine or thymine), or vice versa.Frame shift mutations occur when a base is inserted or deleted from the DNA sequence. This can cause the reading frame of the DNA to shift, which can lead to the production of a non-functional protein.Transcription is the process of copying DNA into RNA. It is not a type of mutation.

• A. A + G / C + T
• B. T + C / G + A
• C. G + C / A + T
• D. A + C / T + G

Explanation: According to Chargaff's rules:A = T and G = CThe GC content (G + C) and AT content (A + T) vary between species but are constant within a species. So, the ratio (G + C) / (A + T) is generally constant for a given species, making option (c) correct.

• A. Lactose
• B. Lactase
• C. Lac insect
• D. The number 1,00,000

Explanation: In the lac operon, lac refers to lactose. The lac operator is a part of the structural genes (lac Z, lac Y, lac A, and lac I). It is responsible for the uptake and initial catabolism of lactose. Lactose ➡ b ­galactosidase ➡ Glucose + Galactose. The lac operon is a group of genes that are regulated by the presence or absence of lactose in the environment. It is found in bacteria such as E. coli. The lac operon is a classic example of gene regulation, and it has been extensively studied by scientists. It has helped us to understand how bacteria regulate their gene expression in response to their environment.

• A. UCG - start
• B. UUU - stop
• C. UGU - leucine
• D. UAC - tyrosine

Explanation: Codon UAC is correctly matched as it codes for the amino acid tyrosine. UCG codes for serine, UUU codes for phenylalanine, and UGU codes for cysteine. The start codon is AUG, and stop codons are UAA, UAG, and UGA.

• A. Promoter
• B. Regulator
• C. Receptor
• D. Enhancer

Explanation: The DNA site at which RNA polymerase binds during transcription is called the promoter. The promoter is a region of DNA that is located upstream of the gene that is being transcribed. It contains sequences that are recognised by RNA polymerase and other transcription factors. These sequences help to position RNA polymerase correctly at the start of the gene and to initiate transcription.The other options are incorrect because:A regulator is a protein that binds to DNA and regulates the transcription of genes.A receptor is a protein that binds to a ligand and triggers a cellular response.An enhancer is a regulatory sequence that can bind transcription factors and increase the expression of a nearby gene.

• A. First member of a codon
• B. Second member of codon
• C. Entire codon
• D. Third member of a codon

Explanation: Degeneration of a genetic code is attributed to the third codon member. The genetic code is a set of rules that tells the cell how to translate DNA into proteins. It is based on a triplet code, which means that each codon is made up of three nucleotides. Each codon codes for a specific amino acid. The third codon member is often referred to as the "wobble" position because it can sometimes be different without affecting the amino acid that is coded for. This is because some tRNAs can recognise multiple codons. For example, the codons GCU, GCC, GCA, and GCG all code for the amino acid alanine. This is because the third codon member (U) can be either U, C, A, or G.The degeneracy of the genetic code is important. After all, it allows for some flexibility in the way that DNA is translated into proteins. This is important for cells to be able to adapt to changing conditions.

• A. 20%
• B. 40%
• C. 30%
• D. 60%

Explanation: In a DNA, the percentage of guanine is equal to the percentage of cytosine, and the percentage of adenine is equal to the percentage of thymine. This is because the two strands of DNA are complementary, meaning that A always pairs with T, and G always pairs with C. If the percentage of thymine is 20%, then the percentage of adenine must also be 20%. This means that the percentage of guanine + cytosine must be 60%. Since the percentage of cytosine is equal to the percentage of guanine, the percentage of guanine must be 30%.