All Free Biology MCQs with Answers
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19844 questions · page 718 of 1985
7171. The gonadotropic hormones of the anterior lobe of the pituitary include:
- A. Prolactin, Thyroid Stimulating Hormone, Somatotropin Hormone
- B. Follicle Stimulating Hormone, Luteinizing Hormone, Prolactin
- C. Adrenocorticotropic Hormone, Luteinizing Hormone, Follicle Stimulating Hormone
- D. Luteinizing Hormone, Follicle Stimulating Hormone, Thyroid Stimulating Hormone
Explanation: Gonadotropins are glycoprotein hormones secreted by gonadotropic cells of the anterior pituitary gland. Luteinizing Hormone (LH), Follicle Stimulating Hormone (FSH), and prolactin are the three hormones secreted by the anterior pituitary.
Correct answer: Follicle Stimulating Hormone, Luteinizing Hormone, Prolactin7172. Which pathway will be followed by water-soluble hormones for crossing the plasmamembrane?
- A. Receptor → 2nd messenger → Activation of energy
- B. 2nd messenger → Receptor → Activation of energy
- C. Receptor → Activation of energy → 2nd messenger
- D. . Activation of energy → 2nd messenger → Receptor
Explanation: Water soluble hormones binds to the receptors on the plasma membrane which passes them.through the second messengers which results in the activation of energy producing mechanisms.
Correct answer: Receptor → 2nd messenger → Activation of energy7173. The Urey-Miller experiment determined which of the following results?
- A. DNA replicates by semiconservative replication
- B. Cyanobacteria were responsible for the oxygenation of the atmosphere
- C. The early atmosphere was composed of ammonia and methane
- D. Organic molecules can arise from inorganic precursor
Explanation: Stanley Miller and Harold Urey simulated early Earth's atmosphere (methane, ammonia, hydrogen, and water vapor) and passed electric sparks to mimic lightning. They obtained amino acids and organic molecules, proving life's building blocks can form abiotically.
Correct answer: Organic molecules can arise from inorganic precursor7174. According to the principle of semi-conservative replication the sequence of the original _ is conserved after one round of replication, the _ itself is not:
- A. Duplex, Helix
- B. Helix, Duplex
- C. Duplex, Duplex
- D. Helix, Helix
Explanation: In semi-conservative replication, each new DNA double helix (duplex) contains one parental and one new strand. Thus, the original sequence is preserved, but the parental duplex is not conserved as a whole.
Correct answer: Duplex, Duplex7175. In translation, methionine is released from its tRNA and is attached by a peptide bond to the second amino acid. This is catalyzed in :
- A. Small ribosomal subunit
- B. Initiation factor
- C. Elongation factor
- D. Large ribosomal subunit
Explanation: The large ribosomal subunit (60S in eukaryotes, 50S in prokaryotes) contains the peptidyl transferase activity that catalyzes peptide bond formation during protein synthesis.
Correct answer: Large ribosomal subunit7176. The site of ribosome where peptide bond is formed is called?
- A. Aminoacyl site
- B. Exit site
- C. Peptidyl site
- D. E site
Explanation: The P site (Peptidyl site) of the ribosome holds the tRNA carrying the growing polypeptide chain and is the site of peptide bond formation.
Correct answer: Peptidyl site7177. The sequence of amino acids in a polypeptide chain corresponds to the sequence of nucleotides on mRNA. If the reading frame of mRNA for a human protein is 993 nucleotides including a stop codon, how many amino acids would be incorporated?
- A. 331
- B. 993
- C. 93
- D. 330
Explanation: Each codon = 3 nucleotides → 993 ÷ 3 = 331 codons. One is a stop codon → 330 codons code for amino acids.
Correct answer: 3307178. In translation, the terminating codon is:
- A. GUA
- B. UAA
- C. UUG
- D. AGU
Explanation: UAA, UAG, and UGA are stop codons. They do not code for any amino acid, instead signal termination of translation.
Correct answer: UAA7179. In what direction can a DNA polymerase work when catalyzing the addition of nucleotide monomers?
- A. From the 5' toward the 3' end of the new strand
- B. From the replication centers in two directions called replication forks
- C. From the 3' to the 5' end of the strand being assembled
- D. In both directions if DNA ligase is present
Explanation: DNA polymerase adds nucleotides to the 3′-OH end, meaning the new strand grows in the 5′ → 3′ direction.
Correct answer: From the 5' toward the 3' end of the new strand7180. A synthetic mRNA uses only adenine and cytosine. How many different codons could it contain?
- A. 4
- B. 16
- C. 8
- D. 64
Explanation: Each codon = 3 bases. With 2 possible nucleotides (A and C): 2³ = 8 codons.
Correct answer: 8