6.3.2 DNA: Polymerization with Triphosphate Nucleotides

Question 1

note

Answer 1

• Meselson and Stahl demonstrated that DNA copies itself using semiconservative replication. When a cell divides, each new cell gets one original parental strandthat serves as a template for the synthesis of a new complementary strand. The synthesis of the new strand is called DNA polymerization.
  • Polymerization is an endergonic process, requiring an expenditure of ATP.
• A nucleotide, the basic subunit of DNA, consists of a base, a sugar, and phosphates. The nucleotide triphosphate contains energy in the bonds that link the second and third phosphate groups. The energy in the bonds is used to join the nucleotide to the growing strand.
• As part of the new strand, the nucleotide now contains only one phosphate group. The nucleotides are joined together by 3’, 5’ phosphodiester linkages. The 3’ and 5’ designations refer to the 3’ and 5’ carbons of the sugar molecule.
• The overall direction, or orientation, of the newly synthesized strand is denoted by its top and bottom nucleotides, respectively. The outer ends are not involved in a phospho-diester linkage, resulting in an empty 5’ and 3’ carbon.
• The overall direction of the new strand is said to be 5’–3’. Note that the orientation of the complementary strand is the opposite of the parental strand. The strands are
  antiparallel.

Question 2

The newly synthesized DNA strand is antiparallel with the parental strand. The reason is that

Answer 2

• the 5′ to 3′ orientation of the parental strand is opposite of the new strand

Question 3

True or false?

The only triphosphate nucleotide that can be found freely floating in the nucleus has an adenine base.

Answer 3

• false

Question 4

The process by which the daughter strands of DNA are formed is called

Answer 4

• polymerization

Question 5

True or false?

DNA polymerization is exergonic.

Answer 5

• false

Question 6

What molecule is released when a triphosphate nucleotide is polymerized onto a strand of DNA?

Answer 6

• pyrophosphate

Question 7

True or false?

When DNA replicates, one of the daughter strands is identical to the parent strand, and one is the exact opposite.

Answer 7

• false

Question 8

At the onset of DNA replication,

Answer 8

• the two DNA strands unwind from each other