Ch 13: The Molecular Basis of Inheritance

Question 1

What is the role of DNA primase during DNA replication?

Answer 1

To synthesize a short RNA chain called a primer. Primase starts a complementary RNA chain with a single RNA nucleotide and adds RNA nucleotides one at a time, using the parental DNA strand as a template.

Question 2

What is the role of DNA polymerase III during DNA replication?

Answer 2

DNA polymerase III adds a DNA nucleotide to the RNA primer and then continues adding DNA nucleotides, which are complementary to the parental DNA template strand, to the growing endof the new DNA strand.

Question 3

What is the role of DNA helicase during DNA replication?

Answer 3

They untwist the double helix at the replication forks, separating the two parental strands, and making them available as template strands.

Question 4

During mitosis, centromeres separate and chromatids become individual chromosomes during which phase?

Answer 4

anaphase

Question 5

Adenine can form _____ hydrogen bonds with thymine and only thymine.

Answer 5

two

Question 6

Cytosine can form _____ hydrogen bonds with guanine and only guanine.

Answer 6

three

Question 7

The leading strand is made continuously from a ______ RNA primer located at the origin of replication. DNA polymerase III adds nucleotides to the 3’ end of the leading strand so that it elongates ______ the replication fork.

Answer 7

single

toward

Question 8

In contrast, the lagging strand is made in segments, each with its own RNA primer. DNA polymerase III adds nucleotides to the 3’ end of the lagging strand so that it elongates ______ from the replication fork.

Answer 8

away

Question 9

Watson and Crick’s model predicts that when a double helix replicates, each of the daughter molecules will have one old strand (from the parental molecule) and one new strand. What is the term for this model?

Answer 9

the semiconservative model

Question 10

The 46 DNA molecules found in human nuclei contain about _ ______ nucleotide pairs.

Answer 10

6 billion

Question 11

If we were to print one-letter symbols for these bases (A, C, G, and T) the size of the type you are now reading, the 6 billion nucleotide pairs of information would fill about ____ thick biology textbooks.

Answer 11

1,400

Question 12

Synthesis of the lagging strand is accomplished through the repetition of the following steps.

Step 1: A new fragment begins with DNA polymerase III binding to the 3’ end of the most recently produced RNA primer, primer B in this case, which is closest to the replication fork. DNA pol III then adds DNA nucleotides in the 5’ to 3’ direction until it encounters the previous RNA primer, primer A.
Step 2: DNA pol III falls off and is replaced by DNA pol I. Starting at the 5’ end of primer A, DNA pol I removes each RNA nucleotide and replaces it with the corresponding DNA nucleotide. (DNA pol I adds the nucleotides to the 3’ end of fragment B.) When it encounters the 5’ end of fragment A, DNA pol I falls off, leaving a gap in the sugar-phosphate backbone between fragments A and B.
Step 3: DNA ligase closes the gap between fragments A and B.

Answer 12

Question 13

What kind of protein stabilizes the unwound parental strands, keeping them from repairing?

Answer 13

single-strand binding proteins

Question 14

The untwisting of the double helix causes tighter twisting and strain ahead of the replication fork. ____________ is an enzyme that helps relieve this strain by breaking, swiveling, and rejoining DNA strands.

Answer 14

Topoisomerase

Question 15

Enzymes called DNA polymerases catalyze the synthesis of new DNA by adding nucleotides to the __ ___ of a preexisting chain.

Answer 15

3′ end

Question 16

The only difference between the ATP of energy metabolism and dATP, the adenine nucleotide used to make DNA, is the sugar component, which is ____________ in the building block of DNA but ribose in ATP.

Answer 16

deoxyribose

Question 17

Because of their structure, DNA polymerases can add nucleotides only to the 3′ end of a primer or growing DNA strand, never to the 5′ end

Question 18

To elongate the other new strand of DNA in the mandatory 5′→3′ direction, DNA pol III must work along the other template strand in the direction away from the replication fork. The DNA strand elongating in this direction is called the lagging strand.

Question 19

Synthesis of the leading strand and synthesis of the lagging strand occur concurrently and at the ____ ____. The lagging strand is so named because its synthesis is delayed slightly relative to synthesis of the leading strand; each new fragment of the lagging strand cannot be started until enough template has been _______ at the replication fork.

Answer 19

same rate

exposed