Which photosynthetic pigments are found in all prokaryotic and eukaryotic photoautotrophs?

Correct Answer: B

Rationale: The correct answer is B: carotenoids. Carotenoids are photosynthetic pigments that are found in all prokaryotic and eukaryotic photoautotrophs. They play a key role in capturing light energy for photosynthesis. Chlorophyll c, phycobilins, and phycocyanin are not found in all prokaryotic and eukaryotic photoautotrophs. Chlorophyll c is primarily found in certain algae, phycobilins are specific to cyanobacteria and red algae, and phycocyanin is a type of phycobilin found in cyanobacteria. Carotenoids are the only pigment that is universally present across all photoautotrophs.

Correct Answer: C

Rationale: The correct answer is C: Smal. Smal is a restriction endonuclease that cuts DNA at specific sequences, producing fragments with blunt ends. Smal recognizes the sequence CCCGGG and cuts between the two C's on both strands, resulting in blunt-ended fragments. Explanation for incorrect choices: A: Sacl - Sacl produces sticky ends, not blunt ends. B: EcoRI - EcoRI produces sticky ends with overhangs. D: HindIII - HindIII also produces sticky ends with overhangs. In summary, Smal is the only enzyme among the choices that generates DNA fragments with blunt ends.

Correct Answer: C

Rationale: The correct answer is C: Terminal deoxynucleotidyl transferase (TdT). TdT catalyzes the addition of deoxynucleotides to the 3'OH ends of DNA molecules. It does so by adding nucleotides in a template-independent manner, making it crucial for generating diversity in immune cell receptor genes. A: Phosphohydrolase - This enzyme is not involved in adding deoxynucleotides to DNA ends. B: T4 DNA ligase - This enzyme catalyzes the joining of DNA fragments, not the addition of deoxynucleotides. D: DNA endonuclease - This enzyme cleaves DNA internally, not involved in adding deoxynucleotides to DNA ends.

Correct Answer: A

Rationale: The correct answer is A: DNA ligase. DNA ligase catalyzes the joining of two DNA strands by forming a phosphodiester bond between the 3' hydroxyl of one nucleotide and the 5' phosphate of another. In the given reaction, the enzyme is needed to seal the nick in the DNA strands after the Okazaki fragments have been synthesized during DNA replication. Explanation of other choices: B: DNA endonuclease - Endonucleases cleave the phosphodiester bond within a polynucleotide chain, not join two DNA strands. C: None of the options are correct - This is incorrect as DNA ligase is the correct enzyme for this reaction. D: DNA polymerase 1 - DNA polymerase synthesizes new DNA strands by adding nucleotides to the 3' end of the growing chain, not joining two DNA strands.

Correct Answer: D

Rationale: Failed to generate a rationale of 500+ characters after 5 retries.