chapter 16 homework quiz

All of the following statements apply to the Watson and Crick model of DNA except:

"The two strands of the helix are held together by covalent bonds."

Which enzyme makes the primer that is required to initiate the synthesis of a new DNA strand?

primase

Which enzyme synthesizes short segments of RNA?

primase

SELECT ANY/ALL THAT APPLY For a couple of decades, biologists knew the nucleus contained DNA and proteins. The prevailing opinion was that proteins were the genetic material and not DNA. The reason for this belief was that proteins were more complex than DNA. This is because: (a) proteins have a greater variety of three-dimensional forms than does DNA. (b) proteins are made of 20 amino acids and DNA is made of four nucleotides. (c) proteins have two different levels of structural organization; DNA has four.

(a) and (b)

SELECT ANY/ALL THAT APPLY In trying to determine whether DNA or protein was the genetic material, Al Hershey and Martha Chase made use of which of the following facts? (a) DNA contains greater amounts of nitrogen than does protein. (b) DNA does not contain sulfur, but protein does. (c) DNA contains phosphorus, but protein does not.

(b) and (c)

Which of these mechanisms ensures that DNA replication is accurate? (a) Excision repair (b) Proofreading (c) Mismatch repair (d) Complementary base pairing (e) All of these are correct.

(e) all of these are correct

Cytosine makes up 38% of the nucleotides in a sample of DNA from an organism. What percent of the nucleotides in this sample will be thymine?

12%

SELECT ANY/ALL THAT APPLY What is the function of DNA ligase? (a) Unwinding of the double helix. (b) Covalent bonding of the 3' end of a new DNA fragment to the 5' end of a growing chain. (c) The addition of methyl groups to bases of DNA. (d) Elongation of new DNA at a replication fork by addition of nucleotides to the existing chain.

?????

With each replication of the DNA molecule, the DNA molecule becomes shorter. This problem is resolved by telomerase, which extends the 3' end of the DNA. This is due to the fact that thymine dimers cause DNA to buckle and interfere with DNA replication. This is not a problem because the telomere is a non-essential repeating unit. This is not a problem because DNA polymerase can only add nucleotides to a 3' end. This is true only if the organism has been exposed to excessive amounts of ultraviolet rays of sunlight.

??????

In analyzing the NUMBER of different bases in a DNA sample, which result would be consistent with the base pairing rules?

A + G = C + T

Which enzyme catalyzes the elongation of a DNA strand in the 5' to 3' direction?

DNA polymerase

Which enzyme catalyzes synthesis of a new strand of DNA?

DNA polymerase III

The primer that initiates synthesis of a new DNA strand is usually made of

RNA

E. coli cells grown on 15N medium are transferred to 14N medium and allowed to grow for two generations (two rounds of DNA replication). DNA extracted from these cells is then centrifuged. What density distribution of DNA would you expect in this experiment?

One low-density and one intermediate-density band.

Which of the following help to hold the DNA strands apart while they are being replicated?

Single-strand binding proteins

Which of the following is analogous to telomeres?

aglets

In DNA, the designations 3' and 5' refer to the

carbon atoms of deoxyribose to which phosphate groups may bond.

Any eukaryotic cell lacking telomerase, regardless of age, would

eventually be unable to replicate

Which enzyme enhances separation of DNA strands during replication?

helicase

What kind of chemical bonds are found between paired bases of the DNA double helix?

hydrogen

A biochemist isolates and purifies various molecules needed for DNA replication. When she adds some DNA, replication occurs, but the DNA molecules formed are defective. Each consists of a normal DNA strand paired with numerous segments of DNA a few hundred nucleotides long. What has she probably left out of the mixture?

ligase

Which enzyme connects Okazaki fragments of DNA?

ligase

Which enzyme cuts DNA in repairing damage?

nuclease

It became apparent to Watson and Crick after completion of their model that the DNA molecule could carry a vast amount of hereditary information in its

sequence of bases

All of the following elements are present in DNA except

sulfur

All of the following elements are present in DNA except phosphorus. nitrogen. oxygen. carbon. sulfur.

sulfur

The strands that make up DNA are antiparallel. This means that

the 5' to 3' direction of one strand runs counter to the 5' to 3' direction of the other strand.