Incorrect Nucleotides Are Sometimes Incorporated into DNA During the Process $\begin{array}{l}3 \text { '-GAAACTGCCATG-5 ' } \\5 \text { '-CTTTGG }\end{array}$

question 22

Essay

Incorrect nucleotides are sometimes incorporated into DNA during the process of replication. In the sequences shown here, the template strand is shown on top and the replicating daughter strand at the bottom. The nucleotide shown in bold is incorrect in that its base does not undergo pairing with the base in the template strand. In the situation shown in (A) the proofreading function of DNA polymerase removes the incorrect nucleotide from the daughter strand and replaces it with the correct one, but in situation (B) the polymerase has moved on and the incorrect nucleotide cannot be repaired. Can you explain why the error in situation (B) cannot be fixed by DNA polymerase?
(A) $\begin{array}{l}3 \text { '-GAAACTGCCATG-5 ' } \\5 \text { '-CTTTGG }\end{array}$ (B) $\begin{array}{l}3 \text { '-GAAACTGCCATG-5 ' } \\5 \text { '-CTTTGGC }\end{array}$

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Definitions:

Risk Genes

Genes that increase the likelihood of developing certain diseases or disorders, though their presence does not guarantee the condition will manifest.

Schizophrenia

A chronic and severe mental disorder that affects how a person thinks, feels, and behaves, often characterized by delusions, hallucinations, and impaired functioning.

Positive Symptom

Symptoms that add abnormal thoughts, behaviors, or perceptions, such as hallucinations or delusions, especially relevant in discussing psychotic disorders.

Motor Difficulties

Challenges or impairments in the ability to perform movements or tasks that require motor coordination.