chapter 16: DNA test 5

Question 1

In 1953, ___ and ___ introduced an elegant double-helical model for the structure of deoxyribonucleic acid, or DNA

Answer 1

James Watson and Francis Crick

Question 2

DNA is unique in its ability to ___. (and cells can repair their DNA)​

When is DNA copied?​

​

The resemblance of offspring to parents depends upon ___ and its transmission from one generation to the next

Answer 2

direct its own replication

information encoded in DNA

Question 3

When T. H. Morgan’s group showed that genes are located ___, the two components of chromosome ___ became candidates for the genetic material​

The role of DNA in heredity was first discovered​
by studying microorganisms such as ___

Answer 3

on chromosomes

DNA and protein

bacteria and the viruses that infect them

Question 4

The discovery of the genetic role of DNA began with research by ___ in 1928​

Griffith worked with two strains of a bacterium (Streptococcus pneumoniae)​

one strain: harmless ​

one strain: pathogenic (disease causing)

Answer 4

Frederick Griffith

Question 5

(Frederick Griffith 1928 research: two strains of bacterium)

When he mixed heat-killed remains of the pathogenic strain with living cells of the harmless strain, some living cells became ___​

He called this phenomenon ___, now defined as a change in ___ due to uptake of foreign DNA​

genotype: genetic makeup​
phenotype: physical observable characteristics (traits)

Answer 5

pathogenic

transformation

genotype and phenotype

Question 6

(Evidence That Viral DNA Can Program Cells​)

A virus is ___ (sometimes RNA) enclosed by a protective coat, often simply protein​

To replicate, a virus infects a ___ and takes over the machinery.​

Viruses that specifically attack bacteria are called ___ (or phages). ​

Answer 6

DNA

cell

bacteriophages

Question 7

In 1952, Alfred Hershey and Martha Chase showed that DNA is the genetic material of a phage known as ___

They designed an experiment showing that only one of the two components of T2 (___) enters an E. coli (bacteria) cell during infection​

They concluded that the injected DNA of the phage provides the genetic information (___)​

Answer 7

T2​

DNA or protein

transfection

Question 8

(1952, Alfred Hershey and Martha Chase showed that DNA is the genetic material of a phage)

They concluded that the ___ of the phage provided the genetic information that made the infected cells produce new ___

Answer 8

injected DNA

viral DNA and proteins to assemble into new viruses.​

Question 9

(Additional Evidence That DNA Is the Genetic Material​)

It was known that DNA is a polymer of nucleotides, each consisting of a ___, a ___, and a ___

Nitrogenous Bases: ___

Answer 9

nitrogenous base, a sugar, and a phosphate group​

Adenine, Guanine, Cytosine, Thymine​

Question 10

In 1950, Erwin Chargaff reported that DNA composition ___ from one species to the next​

This evidence of diversity made DNA a more credible candidate for the genetic material​

​

Answer 10

varies

Question 11

Two findings became known as Chargaff’s rules​

1. The base composition of DNA ___
2. In any species the number of A and T bases are ___ and the number of G and C bases are ___​

The basis for these rules was not understood until the discovery of the double helix​

Answer 11

varies between species​

equal, equal

Question 12

Question 13

After DNA was accepted as the genetic material, the challenge was to determine how its three dimensional structure accounts for its role in heredity​

Maurice Wilkins and Rosalind Franklin were using a technique called ___ to study molecular structure​

Franklin produced a picture of the DNA molecule using this technique​

Answer 13

X-ray crystallography

Question 14

Franklin’s X-ray crystallographic images of DNA enabled Watson to deduce that DNA was ___ ​

The X-ray images also enabled Watson to deduce the width of the helix and the spacing of the nitrogenous bases​

The pattern in the photo suggested that the DNA molecule was made up of two strands, forming a ___

Answer 14

helical

double helix​

Question 15

Franklin had concluded that there were two outer ___ backbones, with the ___ paired in the molecule’s interior​

Watson built a model in which the backbones were parallel however their subunits run in opposite directions or are ___.

Answer 15

sugar-phosphate

nitrogenous bases

antiparallel

Question 16

Watson and Crick reasoned that the pairing was more specific, dictated by the base structures​

They determined that adenine (A) paired only with ___, and guanine (G) paired only with ___​

The Watson-Crick model explains Chargaff’s rules: in any organism the amount of A = T, and the amount of G = C​

Each gene has a unique sequence of nucleotides​

Answer 16

thymine (T)

cytosine (C)

Question 17

Since the two strands of DNA are complementary, each strand acts as a template for building a new strand in replication​

In DNA replication, the parent molecule ___, and two new daughter strands are ___ based on base-pairing rules​

Answer 17

unwinds

built

Question 18

Watson and Crick’s ___ model of replication predicts that when a double helix replicates, each daughter molecule will have ___ and ___

Answer 18

semiconservative

one old strand (derived or “conserved” from the parent molecule) and one newly made strand

Question 19

The copying of DNA is remarkable in its ___ and ___

More than a dozen enzymes and other proteins participate in DNA replication

Answer 19

speed and accuracy​

Question 20

Replication begins at particular sites called ___, where the two DNA strands are separated, opening up a replication “bubble”​

A eukaryotic chromosome may have hundreds or even thousands of origins of replication​

Replication proceeds in both directions from each origin, until the entire molecule is copied​

Answer 20

origins of replication

Question 21

At the end of each replication bubble is a ___, a Y-shaped region where​
new DNA strands are elongating​

___ are enzymes that untwist the double helix at the replication forks​

___ corrects “overwinding” ahead of replication forks by breaking, swiveling, and rejoining DNA strands​

___ bind to and stabilize single-stranded DNA​

Answer 21

replication fork

Helicases

Topoisomerase

Single-strand binding proteins

Question 22

___ cannot initiate ___; they can only add nucleotides to an existing 3′ end​

The initial nucleotide strand is a short RNA ___​

An enzyme called ___ can start an RNA chain from scratch and adds RNA nucleotides one at a time using the parental DNA as a template​

The primer is short (5–10 nucleotides long), and the 3′ end serves as the starting point for the new DNA strand​

​

Answer 22

DNA polymerases

synthesis of a polynucleotide

primer

primase

Question 23

Enzymes called ___ catalyze the elongation of new DNA at a replication fork​

Most DNA polymerases require a ___ and a ___ strand​

The rate of elongation is about 500 nucleotides per second in bacteria and 50 per second in human cells

Answer 23

DNA polymerases

primer

DNA template

Question 24

Each nucleotide that is added to a growing DNA strand is a ___ (dATP, dTTP, dCTP, dGTP)​

As each monomer of nucleoside triphosphate joins the DNA strand, it loses two phosphate groups as a molecule of pyrophosphate​

The ___ of the pyrophosphate to two inorganic phosphates drives the ___ of the nucleotide to the new strand​

Answer 24

nucleoside triphosphate

exergonic hydrolysis

addition/polymerization

Question 25

(Antiparallel Elongation​Antiparallel Elongation​)

The ___ structure of the double helix affects replication​

DNA polymerases add nucleotides only to the free 3′ end of a growing strand; therefore, a new DNA strand can elongate only in the 5′ to 3′ direction​

Answer 25

antiparallel

Question 26

Along one template strand of DNA, the DNA polymerase synthesizes a ___ strand continuously, moving toward the replication fork​

Answer 26

leading

Question 27

To elongate the other new strand, called the ___strand, DNA polymerase must work in the direction away from the replication fork​

The lagging strand is synthesized as a series of segments called ___, which are joined together by ___​

Answer 27

lagging

Okazaki fragments

DNA ligase

Question 28

Question 29

Question 30

DNA polymerases ___ newly made DNA, replacing any incorrect nucleotides​

In ___ of DNA, repair enzymes correct errors in base pairing​

DNA can be damaged by exposure to harmful chemical or physical agents such as cigarette smoke and X-rays; it can also undergo spontaneous changes​

In nucleotide excision repair, a ___ cuts out and replaces damaged stretches of DNA​

Answer 30

proofread

mismatch repair

nuclease

Question 31

Most bacteria have a ___ chromosome​

The bacterial chromosome is a double-stranded, ___ DNA molecule associated with a small amount of protein​

In a bacteria, the DNA is “supercoiled” and found in a region of the cell called the ___​

Eukaryotic chromosomes have linear DNA molecules associated with a large amount​
of protein (\_\_\_)​

Answer 31

single

circular

nucleoid

histones