Chapter 21 Nucleic Acids and Protein Synthesis

1. Chapter 21 Nucleic Acids and Protein Synthesis 21.4DNA Replication

2. DNA Replication DNA replication involves • unwinding the DNA • pairing the bases in each strand with new bases to form new complementary strands • producing two new DNA strands that exactly duplicate the original DNA

3. Hydrolysis Energy Energy • from the hydrolysis of each nucleoside triphosphate • is used to form a phosphodiester bond to each new nucleotide on the complementary strand

4. Direction of Replication During DNA replication, • an enzyme, helicase, unwinds the parent DNA at several sections • at each open DNA section (called a replication fork), DNA polymerase catalyzes the formation of 5′–3′ester bonds of the leading strand • the lagging strand (growing in the 3′–5′ direction) is synthesized in short sections called Okazaki fragments • DNA ligase joins the Okazaki fragments to give a single 3′–5′ DNA strand

5. Direction of Replication (continued)

6. Learning Check Match the following: 1) helicase 2) DNA polymerase 3) replication fork 4) Okazaki fragments A. short segments formed by the lagging strand B. the starting point for synthesis in unwound DNA sections C. the enzyme that unwinds the DNA double helix D. the enzyme that catalyzes the formation of phosphodiester bonds of complementary bases

7. Solution Match the following: 1) helicase 2) DNA polymerase 3) replication fork 4) Okazaki fragments 4 A. Short segments formed by the lagging strand. 3 B. The starting point for synthesis in unwound DNA sections. 1 C. The enzyme that unwinds the DNA double helix 2 D. The enzyme that catalyzes the formation of phosphodiester bonds of complementary bases