Chapter 15 Pre-Lecture

What would be the consequence(s) for DNA synthesis if primase were defective? Both leading and lagging strand synthesis would be unaffected. Lagging strand synthesis would be incomplete; leading strand synthesis would be unaffected. Leading strand synthesis would be incomplete; lagging strand synthesis would be unaffected. Both leading and lagging strand synthesis would be incomplete.

Both leading and lagging strand synthesis would be incomplete. Primase is required to synthesize the RNA primers on both the leading and lagging strands (all DNA polymerases require a primer).

The enzyme that can replicate DNA is called _____________.

DNA polymerase

What catalyzes DNA synthesis? Replication fork Primer dNTPs DNA polymerase

DNA polymerase This enzyme catalyzes DNA synthesis.

Why is the new DNA strand complementary to the 3' to 5' strands assembled in short segments? it is more efficient than assembling complete new strands DNA polymerase can assemble DNA only in the 3' to 5' direction the replication forks block the formation of longer strands DNA polymerase can assemble DNA only in the 5' to 3' direction only short DNA sequences can extend off the RNA primers

DNA polymerase can assemble DNA only in the 5' to 3' direction Since DNA polymerase can assemble DNA only in the 5' to 3' direction, the new strand complementary to the 3' to 5' strand must be assembled either in short 5' to 3' segments, which are later joined together by ligase, or be assembled continuously.

What would be the consequence(s) for DNA synthesis if DNA ligase were defective? Both leading and lagging strand synthesis would be mostly incomplete. Leading strand synthesis would be mostly incomplete; lagging strand synthesis would be unaffected. Lagging strand synthesis would be incomplete; leading strand synthesis would be largely unaffected. Both leading and lagging strand synthesis would be unaffected.

Lagging strand synthesis would be incomplete; leading strand synthesis would be largely unaffected. Without DNA ligase activity, Okazaki fragments on the lagging strand would not be joined together; leading strand synthesis would be largely unaffected.

__________________ are the short sections of DNA that are synthesized on the lagging strand of the replicating DNA.

Okazaki fragments

Which part of a deoxynucleoside triphosphate (dNTP) molecule provides the energy for DNA synthesis? Sugar Free 3' hydroxyl (-OH) group Base Phosphate groups

Phosphate groups The potential energy stored in the bonds of the phosphates provides the energy for DNA synthesis.

Which of the following enzymes creates a primer for DNA polymerase? Helicase Primase Ligase Topoisomerase

Primase This RNA polymerase synthesizes an RNA primer antiparallel to the template DNA strand.

Which of the following statements about DNA synthesis is true? DNA polymerase adds dNTP monomers in the 3' to 5' direction. As DNA polymerase moves along the template strand, each new nucleotide provides a 5' hydroxyl group for the next reaction to occur. Nucleotides are added in a random fashion to single-stranded DNA. Primers are short sequences that allow the initiation of DNA synthesis.

Primers are short sequences that allow the initiation of DNA synthesis. When a primer is added to a single strand of DNA, DNA polymerase can start adding nucleotides to synthesize a complementary strand.

The synthesis of a new strand begins with the synthesis of a(n) _____. single-strand binding protein RNA primer complementary to a preexisting DNA strand Okazaki fragment short pieces of DNA poly(A) tail

RNA primer complementary to a preexisting DNA strand The synthesis of a DNA strand begins with the formation of an RNA primer.

After replication is complete, the new DNAs, called _____________, are identical to each other.

daughter DNA

The primers used for DNA synthesis are ______. RNA polymerases short RNA sequences short amino acid sequences (peptides proteins that bind to single-stranded DNA short DNA sequences

short RNA sequences

An old DNA strand is used as a _____ for the assembly of a new DNA strand. source of nucleotides complement model template primer

template An old DNA strand is used as a template for the synthesis of a complementary new strand.

In a DNA double helix an adenine of one strand always pairs with a(n) _____ of the complementary strand, and a guanine of one strand always pairs with a(n) _____ of the complementary strand. guanine ... adenine uracil ... cytosine cytosine ... uracil cytosine ... thymine thymine ... cytosine

thymine ... cytosine This is referred to as specific base pairing.

Why does telomerase have to have a built-in template for DNA synthesis? All of leading strand synthesis requires genetic information that is not present in the parent DNA molecule. Telomerase is involved in adding DNA to the end of the lagging strand. All of lagging strand synthesis requires genetic information that is not present in the parent DNA molecule. Telomerase is involved in adding DNA to the end of the leading strand.

Telomerase is involved in adding DNA to the end of the lagging strand. At the ends of linear chromosomes (telomeres), telomerase uses its built-in RNA template to extend the parent DNA template near the end of the lagging strand, providing room for an RNA primer so that lagging strand synthesis can be completed to the end of the chromosome (Figure 15.13).

Which statement is correct concerning DNA synthesis catalyzed by DNA polymerases? The new DNA strand is synthesized in the 3—>5' direction; the template strand is read in the 3'—>5' direction. The new DNA strand is synthesized in the 5'—>3' direction; the template strand is read in the 5'—>3' direction. The new DNA strand is synthesized in the 5'—>3' direction; the template strand is read in the 3'—>5' direction. The new DNA strand is synthesized in the 3'—>5' direction; the template strand is read in the 5'—>3' direction.

The new DNA strand is synthesized in the 5'—>3' direction; the template strand is read in the 3'—>5' direction. DNA synthesis by DNA polymerases always proceeds in the 5'—>3' direction, using a complementary, antiparallel strand as template (Figure 15.6).

Which of the following statements about Okazaki fragments in E. coli is true? They are formed on the lagging strand of DNA. They are sealed together by the action of helicase. They are usually 50 to 500 bases long. They are synthesized in the 3' to 5' direction.

They are formed on the lagging strand of DNA. While DNA is synthesized continuously on the leading strand, Okazaki fragments are formed on the lagging strand because DNA synthesis always proceeds in the 5' to 3' direction.

Which of the following enzymes is important for relieving the tension in a helix as it unwinds during DNA synthesis? Helicase Topoisomerase Ligase Single-stranded binding proteins

Topoisomerase This enzyme untwists the coils that occur in the DNA as it is being unwound into a single-stranded template.

True or false? Single-stranded DNA molecules are said to be antiparallel when they are lined up next to each other but oriented in opposite directions. True False

True When the 3' end of one DNA strand points in the same direction as the 5' end of the other DNA strand, the strands are said to be antiparallel.

After DNA replication is completed, _____. one DNA double helix consists of two old strands and one DNA double helix consists of two new strands each of the four DNA strands consists of some old strand parts and some new strand parts each new DNA double helix consists of one old DNA strand and one new DNA strand each new DNA double helix consists of two new strands there are four double helices

each new DNA double helix consists of one old DNA strand and one new DNA strand DNA replication is semiconservative.

The first step in the replication of DNA is catalyzed by _____. single-strand binding protein helicase DNA polymerase primase ligase

helicase The first step of DNA replication is unwinding the DNA double helix.

The new DNA strand that grows continuously in the 5' to 3' direction is called the ______________.

leading strand

Okazaki fragments are found ______. only in front of the replication fork only at the origin of replication only on the leading strand only on the lagging strand only within primase

only on the lagging strand Okazaki fragments are found on the strand that replicates discontinuously.

Telomerase is needed to ______. prevent the loss of DNA bases at the ends of linear chromosomes allow DNA replication at the ends of chromosomes to occur in the 3' to 5' direction open the two strands of DNA in front of the replication fork create repetitive DNA sequences that allow the assembly of the kinetochore synthesize telomere proteins

prevent the loss of DNA bases at the ends of linear chromosomes Without telomerase, linear chromosomes would shorten after each replication and eventually disappear.

Topoisomerase works to ______. prevent twisting of DNA in front of the replication fork incorporate new RNA building blocks at the beginning of a chain open up the two strands of DNA at the replication fork incorporate new DNA building blocks in the growing DNA strand recognize origins of replication and open a replication bubble at these sites

prevent twisting of DNA in front of the replication fork Topoisomerase relaxes the twisting induced by helicase.

During DNA replication, an open section of DNA, in which a DNA polymerase can replicate DNA, is called a _______________.

replication fork

The action of helicase creates _____. primers and replication bubbles replication forks and replication bubbles DNA fragments and replication bubbles primers and DNA fragments DNA fragments and replication forks

replication forks and replication bubbles A replication fork is the transition region between paired and unpaired DNA strands.