DNA Polymerase can only synthesize DNA in the 5' $\rightarrow$ 3' direction.
Therefore, the template strand must be read in the 3' $\rightarrow$ 5' direction.
Step 2: Analyzing the Replication Fork:
Leading Strand: Synthesized continuously. The template strand polarity is 3' $\rightarrow$ 5' towards the replication fork opening.
Lagging Strand: Synthesized discontinuously (Okazaki fragments). The template strand polarity is 5' $\rightarrow$ 3' towards the replication fork opening.
Step 3: Evaluating the Diagram (Option 4):
In Option 4:
Top template strand has 5' $\rightarrow$ 3' polarity towards the right (fork opening). The new strand is shown growing discontinuously (short fragments) away from the fork. This is correct for the lagging strand.
Bottom template strand has 3' $\rightarrow$ 5' polarity towards the right (fork opening). The new strand is shown growing continuously into the fork. This is correct for the leading strand.
Step 4: Final Answer:
Option 4 correctly depicts the polarity and the continuous vs. discontinuous synthesis.
