Multiple Choice
To more accurately represent the process of photosynthesis, what must be added to the basic chemical equation: \(6\text{CO}_2 + 6\text{H}_2\text{O} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2\)?
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9. Photosynthesis
Introduction to Photosynthesis
Multiple Choice
Why is light required for photolyases during the process of DNA repair in photosynthetic organisms?
A
Light causes the denaturation of damaged DNA, allowing repair enzymes to access the site.
B
Light provides the energy needed for photolyases to cleave cyclobutane pyrimidine dimers in DNA.
C
Light is necessary for the synthesis of new DNA strands during replication.
D
Light activates chlorophyll, which then directly repairs DNA damage.
Verified step by step guidance1
Understand the role of photolyases: Photolyases are enzymes that repair DNA damage caused by ultraviolet (UV) light. Specifically, they target cyclobutane pyrimidine dimers, which are formed when UV light induces covalent bonds between adjacent pyrimidine bases (thymine or cytosine) in DNA.
Recognize the importance of light: Photolyases require light, specifically visible or near-UV light, to function. This light provides the energy needed to activate the enzyme and initiate the repair process.
Explain the mechanism: When photolyases absorb light, they use the energy to cleave the cyclobutane ring structure of the pyrimidine dimer. This restores the normal base pairing and structure of the DNA.
Clarify why other options are incorrect: Light does not denature damaged DNA, nor does it directly synthesize new DNA strands during replication. Additionally, chlorophyll is not involved in DNA repair; its role is primarily in photosynthesis.
Summarize the correct answer: Light is required because it provides the energy necessary for photolyases to cleave cyclobutane pyrimidine dimers, effectively repairing the DNA damage caused by UV light.
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