All Free Biology MCQs with Answers

• A. Core enzyme
• B. U ribonucleotide
• C. 3' end
• D. Sigma factor

Explanation: The poly-A tail is a stretch of adenine nucleotides added to the 3' end of pre-messenger RNA (pre-mRNA) during mRNA processing. This modification is crucial for stabilizing the mRNA molecule and facilitating its export from the nucleus to the cytoplasm. Additionally, the poly-A tail plays a role in regulating gene expression and enhancing translation efficiency. Therefore, the poly-A tail is directly related to the 3' end of mRNA, as it is added specifically to this end during mRNA processing.

• A. U ribonucleotide
• B. Core enzyme
• C. Sigma factor
• D. GC + AT base pairs

Explanation: The transcription bubble forms during transcription, where the DNA double helix temporarily unwinds, creating a single-stranded template for RNA synthesis. Within this bubble, the exposed bases on the DNA template strand (containing both GC and AT base pairs) serve as a template for complementary base pairing with incoming ribonucleotides, ultimately determining the sequence of the newly synthesized RNA transcript.

• A. ACC
• B. Peptidyl site
• C. Phenylalanine
• D. Chromosomal aberration

Explanation: PKU is a genetic disorder that causes an inability to metabolize phenylalanine, an amino acid found in protein-containing foods. This leads to a buildup of phenylalanine in the body, which can be toxic to the brain. If left untreated, PKU can lead to intellectual disabilities, behavioral problems, and other serious health issues.

• A. Chromosomal aberration
• B. 1000 nucleotides/sec
• C. Phenylalanine
• D. Peptidyl site

Explanation: Chromosomal aberrations are abnormalities in the structure or number of chromosomes in a cell. These can occur due to errors during cell division or exposure to certain chemicals or radiation. Examples of chromosomal aberrations include deletions (loss of a portion of a chromosome), duplications (extra copies of a portion of a chromosome), inversions (reversal of a portion of a chromosome), and translocations (movement of a portion of one chromosome to another chromosome). Chromosomal aberrations can lead to genetic disorders, birth defects, or cancer.

• A. Peptidyl site
• B. Phenylalanine
• C. 1000 nucleotides/sec
• D. ACC

Explanation: DNA polymerase III is an enzyme involved in DNA replication in prokaryotes, such as bacteria. It's known for its high processivity, meaning it can add many nucleotides to a growing DNA strand before dissociating from the template. The rate of DNA synthesis by DNA polymerase III can reach up to 1000 nucleotides per second under optimal conditions. This rapid rate of nucleotide addition allows for efficient and accurate replication of the entire bacterial genome during cell division.

• A. Sex linked dominant trait
• B. Sex linked recessive trait
• C. Autosomal dominant trait
• D. Autosomal recessive trait

Explanation: Phenylketonuria (PKU) is a rare inherited disorder that causes an amino acid called phenylalanine to build up in the body. PKU is caused by a change in the phenylalanine hydroxylase (PAH) gene. This gene helps create the enzyme needed to break down phenylalanine. PKU is inherited from a person's parents. The disorder is passed down in a recessive pattern, which means that for a child to develop PKU, both parents have to contribute a mutated version of the PAH gene. So option A and C are incorrect. It is found in chromosome 12 i.e. it is autosomal, so Option B is incorrect, and option D is correct.

• A. DNA is broken up at specific sites
• B. DNA fragments are joined together
• C. DNA replication occurs
• D. DNA transcription occurs

Explanation: DNA ligases play an essential role in maintaining genomic integrity by joining breaks in the phosphodiester backbone of DNA that occur during replication and recombination, and as a consequence of DNA damage and its repair. DNA ligase sticks the DNA nucleotide backbone by forming phosphodiester linkages between two successive nucleotides as shown in the diagram below:

• A. mRNA
• B. rRNA
• C. tRNA
• D. Polysome
• E. Genes

Explanation: Option A is messenger RNA, the transcript of a segment of DNA that serves as the code which is then translated by the ribosomes. Option B is ribosomal RNA which makes up ribosomes themselves. Option C is transfer RNA, which carries amino acids from the cytoplasm to the ribosomes to add on to the growing polypeptide chain during translation. Option D describes a chain of multiple ribosomes together which enhances the efficiency of protein synthesis. Option E is a segment of DNA which codes for a specific polypeptide.

• A. Trait
• B. Centromere
• C. Genotype
• D. Locus

Explanation: A locus is a specific, fixed position on a chromosome where a particular gene or genetic marker is located. A phenotypic trait, simply trait, or character state is a distinct variant of a phenotypic characteristic of an organism. The centromere is the specialized DNA sequence of a chromosome that links a pair of sister chromatids. A genotype is an organism's complete set of genetic material. Often though, genotype is used to refer to a single gene or set of genes, such as the genotype for eye color.

• A. Deoxyribose sugar
• B. Ribose sugar
• C. Phosphate group
• D. Sequence of nitrogenous bases
• E. Sequence of phosphate group

Explanation: The genetic information of DNA is encoded as the sequence of nitrogenous bases. The specific sequence of nitrogenous bases on DNA (Adenine, Thymine, Cytosine, and Guanine) leads to the formation of specific mRNA during the transcription process. This mRNA is then converted into a specific protein corresponding to the specific sequence of nitrogenous bases.