GENETIC ENGINEERING AND THE MOLECULES OF LIFE

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PAGE 12
-
1

ANSWERS TO

END
-
OF
-
CHAPTER QUESTIONS


CHAPTER 12: GENETIC
ENGINEERING AND THE
MOLECULES OF LIFE

Emphasizing Essentials


1
.

The letters DNA have been called three of the most important letters of the late 20th century.
For what is DNA an acronym?


Answer:


DNA stands for
d
eoxyribo
n
ucleic
a
cid.


2.

a.

Use Figure 12.1 to determine the percent increase in human life expectancy at birth in the
United States between 1940 and 1980 for males and females.


b.

Are these percentages the same as those calculated in Yo
ur Turn 12.2? Why or why not?


Answer:


a.
Figure 12.1 provides data beginning in 1950. The percent increases in human life
expectancy between 1950 and 1980 are:




percent increase for women

78

7
1
71







100

10%



percent increase for men

69

60
60







100

13%


b.
These are not the same percentages as those c
alculated in 12.2 Your Turn because the time
intervals were different. However, in both cases the calculations show that the life
expectancy for men is increasing at a faster rate than the life expectancy for women.


3.

Consider the structural formulas in
Figure 12.2.


a.

What functional groups are in adenine?


b.

What functional groups are in deoxyribose?


c.

Does the phosphate group have any functional groups?


Answer:


a.

The base adenine has the amine group,

NH
2
.


b.

The sugar deoxyribose has several h
ydroxyl groups,

OH.


c.

There are no functional groups
in

the phosphate, but the phosphate itself is a functional
group. Do not mistake the doubly bonded oxygen atom for a ketone, as there is no bond to a
carbon atom.


4.

Consider the structural formula o
f deoxyribose given in Figure 12.2.


a.

Why is deoxyribose classified as a monosaccharide?


b.

What is the molecular formula for deoxyribose?


c.

Why isn’t deoxyribose an acid in aqueous solution?



PAGE 12
-
2

Answer:


a.
Deoxyribose is a monosaccharide because it is
a single sugar molecule with a 5
-
member
ring containing 4 carbon atoms and 1 oxygen atom.

b.

The molecular formula for deoxyribose is C
5
H
10
O
4
.


c.

The hydrogen atoms are all covalently bonded to carbon or oxygen atoms. For deoxyribose
to act as an acid, th
ese hydrogen atoms would have to be released as hydrogen ions in
aqueous solution, and this is highly unlikely to occur.


5.

Using the structural formula of thymine in Figure 12.2, write an equation showing how
thymine could react with water to generate hy
droxide ions.
Hint:
See Sections 6.2 and 6.3.


Answer:


thymine + water


thymine ion + hydroxide ion



N
N
CH
3
H
H
H
O
O
(aq)

+ H
2
O
(l)



N
N
CH
3
H
H
H
O
O
H
+
(aq)

+ OH

(aq)


6.

a.

What three units must be present in a nucleotide?


b.

What type of bonding holds

these units together?


Answer:


a.

A nucleotide must contain a base, a deoxyribose molecule, and a phosphate group linked
together.


b.

Covalent bonding holds the units together.


7.

Table 12.1 lists the base composition of DNA for various species. The fo
ur bases are
adenine, cytosine, guanine, and thymine. What relationships exist among these bases, no
matter what the species?


Answer:


The percentages of adenine and thymine are consistently similar, as are the percentages of
cytosine and guanine. These a
re the relationships known as Chargaff’s rules.


8.

a.

What happens experimentally during X
-
ray diffraction?


b
.

The first X
-
ray diffraction patterns were of simple salts, such as sodium chloride. The X
-
ray diffraction studies of nucleic acids and proteins

did not come until much later. Suggest
reasons why.


Answer:


a.

A beam of X
-
rays is directed at an unknown substance. The atoms in the substance scatter
the X
-
rays, and a detector measures the intensity of the X
-
rays as they emerge from the
substance. If

the atoms in the substance are arranged in a regular pattern, the intensity of the
diffracted X
-
rays can be used to calculate the distance between atoms in the substance.


PAGE 12
-
3


b.

Ions in a salt like sodium chloride have a very regular structure that is easil
y determined
by X
-
ray studies. Atoms in nucleic acids and proteins do not show the same simple patterns
of crystalline regularity, making the interpretation of the X
-
ray diffraction pattern more
difficult.


9.

Figure 12.7 shows the pairing of nucleotide ba
ses in DNA.


a.

What type of
intramolecular

bonding occurs within each base?


b.

What type of
intermolecular

bonding holds the base pairs together?


Answer:


a.
Covalent bonds are the intramolecular bonds between the atoms within each base.


b.
Hydrogen bo
nds are

the intermolecular bonds that attract the base pairs to each other.


10.

Identify the base sequence that is complementary to each of these sequences.


a.

ATGGCAT

b.

TATCTAG


Answer:


a
. TACCGTA

b.
ATAGATC


11.

Given that the distance between adjace
nt bases is 0.34 nm, how many base pairs are present
in a chromosome that is 3.0 cm long?
Hint:

1 m
=
10
2

cm; 1 m
=

10
9

nm.


Answer:



3.0 cm
chromosome

1 m
10
2
cm

10
9
nm
1 m

1 base pair
0.34 nm

8
.
8

10
7
base pairs
chromosome


12.

During cell division, as many as 90,000 nucleotides per minute can be added to the growing
DNA c
hain.


a.

The shortest human chromosome contains 50 million bases. What is the minimum time
required to form a strand of this chromosome?


b.

Determine the length of this chromosome (in centimeters) that would be formed in

1 minute if the distance between

bases were 0.34 nm.
Hint
: 1 m
=

10
2

cm; 1 m
=

10
9

nm.


Answer:


a.
Time to make the chromosome:





50

10
6
bases

1 minute
90,
000 nucleotides

1
nucleotide
1
base

5
.
6

10
2
minutes




b.

Chain length after 1 minute:




90,
000 nucleotides
1 min

0.34 nm
base pair

1
base pair
1
nucleotide

1 m
10
9
nm

10
2
cm
1 m

3
.
1

10

3
cm


13.

Amino acids are the monomers used to build proteins.


a.

What is the
gen
eral

structural formula for an amino acid?


b.

What functional groups are present in all amino acids?


PAGE 12
-
4


Answer:


a.

This is the general formula for an amino acid, where R represents a side chain that is
different in each of the 20 amino acids.





b.

The f
unctional groups are

COOH, the carboxylic acid group, and

NH
2
, the amine
group.


14.

The text states that if you were to use the letters A, T, C, and G in a game of Scrabble, you
could generate 64 different three
-
letter combinations. (Your Scrabble oppon
ent would surely
challenge some of these combinations!) Nature pairs the four bases A, T, C, and G, and uses
the pairs to encode for amino acids. Write down all the possible paired combinations of A, T,
C, and G to find the maximum number of amino acids th
at can be encoded from these four
bases.
Hint:

In nature, unlike Scrabble, a letter can be used more than once in forming a pair.


Answer:


There are 16 pairs, so they can be used to encode 16 amino acids. These are the pairs.

AA, AC, AG, AT, CC, CA, CG, C
T, GG, GA, GC, GT, TT, TA, TC, TG


15.

What is a codon and what is its role in the genetic code?


Answer:


A codon is a grouping of three DNA bases. An appropriate RNA molecule transfers the order
of bases in DNA into a specific amino acid that should appe
ar in a protein sequence.
Therefore, codons are used to signal that a particular amino acid should be incorporated into
a protein.


16.

Only 61 of the possible 64 triplet codons specify certain amino acids. What is the function of
the other three codons?


Answer:


The three
-
base sequences that do not correspond to specific amino acids are used to start or
stop the synthesis of the protein chain.


17.

Describe what is meant by the primary, secondary, and tertiary structure of a protein. Is one
of these more
important than the others? Explain.


Answer:

The primary structure is the sequence of amino acids along the protein chain. The secondary
structure describes the three
-
dimensional arrangement of short segments of the protein chain.
The secondary structure i
s established by hydrogen bonding between

N
-
H and

C=O
groups of the peptide linkage at various locations along the protein chain. The tertiary
structure is the three
-
dimensional folding of the long chain into an overall three
-
dimensional
shape. This conf
ormation is established by various kinds of R group interactions, especially

PAGE 12
-
5

hydrogen bonding. One cannot say that one of these structural levels is more important than
the others, because all of them contribute to the function of the protein. Errors in pr
imary
structure cause mutations in the amino acid sequence, which is not the case for errors in
secondary or tertiary structures. Errors in any of the three structures can result in a
malfunction of the protein.


18.

Explain how an error in the primary str
ucture of a protein in hemoglobin causes sickle cell
anemia.


Answer:


Only a minor change in the amino acid composition of human hemoglobin leads to sickle cell
anemia. In hemoglobin S, two of the amino acids that should be glutamic acid are replaced
with

valine. This seemingly innocuous change in the protein’s primary structure dramatically
affects the shape of the red blood cells in people with this genetic disease.


19.

What, in relation to DNA, is a gene?


Answer:


A gene is a segment of DNA that conta
ins the code for a protein or otherwise plays a role in
the phenotype of an organism.


20.

What is meant by the genetic code?


Answer:


The genetic code is the sequence of nucleotide triplets that determines the amino acid
sequence in a protein.


21.

Whic
h bases make up DNA nucleotides?

a.

adenine, thymine, uracil, and guanine

b.

adenine, uracil, guanine, and cytosine

c.

adenine, thymine, cytosine, and guanine

d.

adenine, thymine, cytosine, and uracil


Answer:


The correct answer is c. The bases adenine, t
hymine, cytosine, and guanine make up DNA
nucleotides.


22.

There are many DNA
-
damaging agents that effectively kill bacterial cells in culture dishes.
Why are DNA
-
damaging agents not typically used as antibacterial drugs?


Answer:


The DNA
-
damaging agent
s that kill bacteria can also damage the DNA in other species,
including humans. The risks involved with such drugs outweigh any potential benefits.


23.

Circle and name the functional groups present in this nucleotide.


PAGE 12
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6



Answer:








24
.

The struc
ture for thymine is shown. Use the concept of resonance forms to explain why
neither of the nitrogen atoms is likely to accept a hydrogen ion (H
+
). In other words, use
resonance forms to explain why thymine is not a very strong base.



Answer:


Thymine ha
s a resonance form in which both nitrogen atoms form a single bond with one
adjacent carbon, a double bond with the second adjacent carbon, and a single bond with
hydrogen. In this resonance form the oxygen atoms form a single bond with carbon and carry
a
negative charge, and the nitrogen atoms carry a positive charge. Because this resonance
form contributes significantly to the structure of thymine, neither nitrogen atom is likely to
accept a hydrogen ion.


25.

a.

What is the Human Genome Project?

b.

Why i
s it a significant step in understanding the genetic basis of humans?



PAGE 12
-
7

Answer:


a.
The Human Genome Project was a massive international effort to map all 100,000 genes
in the human organism. The project was begun in 1990 and the genome was completed in
200
3.


b.
This is a significant step because the entire human genome has not been sequenced before.


26.

a.

What are stem cells?

b.

How are stem cells harvested?

c.

What aspect of stem cell research makes it controversial?


Answer:


a.
Stem cells are identi
cal, undifferentiated cells that, by successive divisions, can develop
into specialized cells. These cells can be cultured and then stimulated to form specific types
of cells.

b.

Adult stem cells can be harvested from the placenta or umbilical cord left ov
er from a
birth. Stem cells can also be harvested from embryos.


c.
Embryonic stem cells are the most controversial because collecting them involves
destroying human embryos.


Concentrating on Concepts


27.

What is meant by the term
cloning?


Answer:


Clon
ing is a technique of genetic engineering. Clones are exact replicas of collections of cells
or molecules. Cloned bacteria are used to produce mass quantities of proteins such as insulin
and human growth hormone that would otherwise be expensive to harvest

from organisms.
Cloning techniques have also been applied to mammals. The DNA of one animal is
transferred to an unfertilized, un
-
nucleated egg of another animal of the same species. The
new fused cell can then be implanted into the second animal’s uterus
, where it will develop
into an exact replica of the animal from which the DNA was taken.


28.

Life expectancy in the United States increased dramatically during the 20th century, as
shown in Figure 12.1 and surrounding text. Is a similar increase possible

during the 21st
century? Explain your answer.


Answer:


Life expectancy at birth has increased from 50 years to over 75 years during the 20th century.
This increase of 50% is primarily the result of a decrease in infant mortality rate, which has a
greater

effect on life expectancy than most other changes. It is unlikely that a similar increase
in life expectancy can be achieved during the 21st century because humans may be
approaching the theoretical life span limit.


29.

Compare the two representations of

a segment of DNA in Figure 12.4. Discuss the strengths
and weakness of each representation.




PAGE 12
-
8

Answer:


The schematic representation does not identify the specific composition of any of the
components, but does help to reinforce that the phosphates and sug
ars make up the backbone
of the nucleotide. The chemical structure shows a great deal of specific chemical
information, perhaps making it difficult to recognize the simple underlying scheme.


30.

Consider Chargaff’s discovery that there are equal percentag
es of adenine and thymine and
of cytosine and guanine in DNA. Was his discovery as important to understanding the nature
of DNA as Crick and Watson’s discovery of the double helix? Explain.


Answer:


The discovery that %A
=

%T and that %C
=

%G provided the

basis for asking
why

this
pattern was observed. Chargaff’s contribution was in finding that the bases were paired.
Crick and Watson took this information a step further to discover both
how

and
why

they
were paired, and the influence the pairing had on th
e structure of DNA.


31.

Use Figure 12.7 to help explain why stable base pairing does
not

occur between adenosine
and cytosine, thymine and guanine, adenine and guanine, and thymine and cytosine. Use
molecular structures in your explanation.


Answer:


Figu
re 12.7 gives clear evidence of the importance of “fit” for the bases as they interact
through hydrogen bonding. Adenosine and thymine line up to form two hydrogen bonds. The
first bond pairs an O from thymine with an N
-
H on adenine, and the second pairs a
n N
-
H on
thymine with an N on adenine. Cytosine and guanine line up to form three hydrogen bonds
with a different set of pairings. Cross matches (e.g., adenosine and cytosine, etc.) would not
fit efficiently because the bases are not in the right positions

to permit the hydrogen bonds to
form.


32.

One of the mechanisms by which DNA sustains damage from UV light is via the formation
of covalent bonds between two thymine bases.

a.

What are the potential consequences of cross
-
linking between two thymines on a

single
strand of DNA?

b.

What possible problems do you foresee if one thymine from each of two complementary
strands undergoes a cross
-
linking reaction?


Answer:


a.
If covalent bonds formed between two thymine bases on a single strand of DNA that are
adj
acent to one another, then those bases would not be free to form hydrogen bonds as usual.
During DNA replication, both strands are used to as templates to produce new strands and a
mutation would occur.


b.

If one thymine from each of two complementary str
ands underwent a cross
-
linking
reaction it would be impossible for the DNA strands to separate for replication. Furthermore,
the proteins coded by the portion of either DNA strand at the point of the cross
-
linking could
not be synthesized.



PAGE 12
-
9

33.

Errors some
times occur in the base sequence of a strand of DNA. But not all of these errors
result in the incorporation of an incorrect amino acid in a protein for which the DNA codes.
Explain how this happens and why it is advantageous.


Answer:


Errors in the base
sequence of a DNA strand occur during DNA replication if insertion of an
inappropriate nucleotide occurs. Because it is the base of each nucleotide that contributes to
the identification of a protein, the presence of an errant base could initiate insertion

of an
inappropriate amino acid into a protein, as is the case with the sickle cell hemoglobin
molecule. Because several triplet combinations code for the same amino acid, it is also
possible that an error in the base sequence could give one of the redunda
nt combinations,
resulting in insertion of the correct amino acid into the protein. This is part of the resilience
of the genetic code.


34.

Human insulin and human growth hormone have both been made through the use of
recombinant DNA technology. Which do
you believe is a more significant use of this
technology and why? Discuss what factors have influenced your opinion.


Answer:


Answers can vary, but many students will choose the manufacture of human insulin as a
more significant development. The reason th
ey might note is that diabetes is a life
-
threatening disease for millions of people. Prior to the advent of recombinant DNA
technology, the available supply of insulin came from the pancreas glands of cows and pigs
and not all patients responded uniformly
to insulin from this source. Use of recombinant
DNA technology has provided better quality control of the product and has reduced side
effects. Without minimizing the significant difficulties of dwarfism for those affected by
having an insufficient amount
of HGH, HGH therapy represents a very expensive treatment
for a relatively small number of children with a condition that is not life
-
threatening. A factor
that is certain to influence each student’s opinion is the extent of their personal experiences
with

someone who needs either insulin or HGH.


35.

The unusual C
-
to
-
N bond length of a peptide bond was discussed in this chapter. Using
similar reasoning, describe the relative bond length of the C
-
to
-
O bond of the carbonyl group
in a peptide bond compared to

that of a ketone.


Answer:


The C
-
to
-
O bond length of the carbonyl group in a peptide (amide) bond will be longer than
the C
-
to
-
O bond length in a ketone because a resonance structure including a C
-
to
-
O single
bond contributes to the structure of the pept
ide bond. (See Figure 12.12.)


36.

What role did Chargaff’s rules play in the discovery of the DNA double helix?


Answer:


Chargaff’s contribution was the discovery that %A = %T and that %C = %G in a variety of
species, providing the basis for asking
why

t
his pattern was observed. Crick and Watson used

PAGE 12
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10

this information to discover
how

and
why

the bases were paired, and they described the
influence this pairing has on the structure of DNA.


37.

Lou Gehrig’s disease is caused by the alteration of a single ami
no acid in the enzyme
superoxide dismutase. How many base pairs are responsible for specifying this amino acid in
the gene that codes for the protein? What is the minimum number of base pairs that would
have to be changed to produce the disease?


Answer:


Three base pairs code for each amino acid. Changing any of the three base pairs could
theoretically alter the amino acid, although many amino acids are specified by more than one
set of base pairs.


38.

Do you favor the patenting of genes? What are the adv
antages and disadvantages of this
approach?


Answer:


Patenting genes, particularly if they have been characterized as part of the Human Genome
Project, is very controversial. Critics of the idea have argued that if government sources have
paid for the res
earch, the results should belong to the public. Others have reasoned that free
exchange of information is crucial to the success of this project, and patents would inhibit
this scientific communication. The picture is clouded by differences in the patent l
aws in
different countries.


39.


Use the Web to research the concept of eugenics. How did the term come into use and
how has its meaning changed over time?


Answer:


Eugenics refers to a social philosophy supporting policies that could “strengthen” the h
uman
genetic pool by encouraging the reproduction of some people and discouraging the
reproduction of others. The term was coined in 1865 by Sir Francis Galton, a cousin of
Charles Darwin. The eugenics movement gained momentum in Western countries in the
e
arly part of the twentieth century. In the U.S., eugenics policies resulted in the forced
sterilization of tens of thousands of mentally ill citizens. In Nazi Germany, hundreds of
thousands of people deemed physically and mentally weak were forcibly steril
ized while tens
of thousands of people in mental institutions were euthanized as part of the government’s
“racial hygiene” program. The meaning of the term has not changed over time, although most
people today associate it with the programs of the early tw
entieth century.


40.

How widely available is the New Leaf potato? If you wanted to plant this in your
garden, would you be able to obtain these potato plants? For what reasons would you want to
obtain this plant?




PAGE 12
-
11

Answer:


The New Leaf potato was genet
ically engineered by the Montsanto company to be resistant
to attack by the Colorado potato beetle and was introduced in the mid 1990’s. However, at
about the same time a new insecticide was developed that killed the same beetle. Montsanto
stopped selling
the New Leaf potato seed in 2001 after capturing only 2
-
3% of the US potato
market. The
New York Times

Sunday Magazine of October 25, 1998 includes an interesting
article called “Playing God in the Garden” that will help the reader to understand the issues
.
Additional information is available at

http://www.geo
-
pie.cornell.edu/crops/potato.html
.


41.


Use the Web to gather data and create a graph showing the relative amounts of GM or
transgenic crops grown by six different countries. Include with your grap
h the source of your
data.


Answer:


The data can be represented in many formats, but here is an example.





Millions of Acres of Transgenic Crops Planted in 2000





These data were taken from

http://cls.casa.colostate.edu/TransgenicCrops/current.html
.


42.

Consider the idea of mixing genes as an improvement on nature.

a.

What are transgenic organisms?

b.

Why is the alteration of the genetic makeup of plants by genetic engineerin
g preferred to
traditional crossbreeding methods?


PAGE 12
-
12


Answer:

a.
Transgenic organisms are plants and animals whose genome contains genes from another
species.


b.
Traditional crossbreeding mechanisms take more time and the results are less predictable
than us
ing genetic engineering to alter the genetic makeup of plants.


43.

Make a list of the advantages and disadvantages of transgenic crops.


Answer:


Transgenic crops can be engineered to resist disease and pests, reducing the amount of
chemicals applied. Tra
nsgenic plants can also be engineered to increase their nutritional
value. An example is golden rice which is engineered to produce beta carotene.



Transgenic crops can out
-
compete or cross
-
breed with their un
-
engineered counterparts
ultimately reducing g
enetic diversity. An extreme example of the dangers of an undiversified
crop is the Irish Potato Famine. Transgenic crops could also trigger unexpected allergic
reactions in consumers.


44.

The cloning of Dolly in 1996 and the
would
-
be

human embryos in 20
04 are remarkable
scientific events.


a.

In what ways were the techniques used similar?


b.

In what ways were they different?


Answer:


a.
The cloning of Dolly and the reported cloning of human embryos involved the technique
of nuclear transfer. To do this

the nuclear material of one cell is placed into the nucleus of an
egg cell that has had its own nucleus removed.


b.
In the case of Dolly, the egg was implanted into another sheep’s uterus, carried full term,
and the lamb Dolly was born. In the case of th
e human clone, the scientists reported the
blastocysts were not implanted. Instead, they claimed to harvest a line of stem cells from
them.


Exploring Extensions


45.


Dolly’s birth surprised genetic engineering experts and shocked members of the media
re
sponsible for reporting the birth and the method. Locate one or two early reports about the
cloning of Dolly. Evaluate these reports for their scientific accuracy and what they reveal
about the opinion of experts at that time.


Answer:

Students will find t
hat many of the early press reports reflected considerable confusion about
the cloning process and about how the experiment with Dolly was different from earlier
cloning experiments performed from embryonic cells. Errors made by reporters untrained in
the
details of molecular biology were understandable, because the technique was new and the

PAGE 12
-
13

implications of the results were not completely understood. There also may have been a
tendency to overstate or overreact to the news of Dolly’s cloned arrival into the

world.


46.

Use this information to act as a Sceptical Chymist in checking the correctness of the claim
that the DNA in an adult human would stretch from Earth to the Moon and back more than a
million times.


Distance from Earth to the Moon
=

3.8


10
5

km


Number of DNA
-
nucleated cells in an adult human
=

1


10
13


Length of stretched human DNA strand
=
2 m


Answer:


The statement is false. Calculations show that the DNA in an adult would stretch just about
26,000 times to the moon and back.




2 m
1 DNA thread



1

10
13
cells
1 adult

=
2


10
13

m of DNA in an adult



3.8


10
5

km



1

10
3
m
1 km



2
=

7.6


10
8

m, the distance to the moon and back



The ratio of these two distances is:






2

10
13
m
7.6

10
8
m

=

26,
000
1


47.

Consider the structural formula of deoxyribose

shown in Figure 12.2. The prefix
deoxy
-

means without oxygen; the

OH group is replaced by a hydrogen atom. In the specific case
of deoxyribose, the

OH group, replaced by a hydrogen, was bonded to the only carbon in
the ring that bonds to two hydrogen at
oms in deoxyribose. The structural formula of ribose
appears in Consider This 12.4. Draw another isomer of deoxyribose, one that would still
form a nucleoside with a base and with phosphate. Compare your isomer side
-
by
-
side with
the structural formula of d
eoxyribose.


Answer:


There are two

OH groups in ribose that could be replaced to form deoxyribose. These are
the third and fourth carbons away from the oxygen atom in the ring. The deoxyribose isomer
shown in Figure 12.2 has had the

OH group on the thir
d carbon replaced. The other isomer
of
deoxyribose has the

OH group on the fourth carbon replaced by hydrogen.


48.

The text states that the more closely species are related, the more similar the DNA base
compositions are in those species. The Sceptical C
hymist is having trouble believing this,
particularly if it means a close relationship between a fruit fly and a bacterium. Use the
information in Table 12.1 to determine whether it supports the generalization about similar
base pairs in similar species.




PAGE 12
-
14

Answer:


These are the data from Table 12.1, rearranged in order of similarity to
Homo sapiens.




Table 12.1
The Base Compositions of DNA for Various Species


Species

Adenine

Thymine

Guanine

Cytosine


Homo sapiens

(human)

31.0

31.5

19.1

18.4


Bacillus
subtilis

(bacterium)

28.4

29.0

21.0

21.6


Drosophila melanogaster



(fruit fly)

27.3

27.6

22.5

22.5


Zea mays

(corn)

25.6

25.3

24.5

24.6


Escherichia coli

(bacterium)

24.6

24.3

25.5

25.6


Neurospora crassa

(mold)

23.0

23.3

27.1

26.6




Noti
ce that the species most similar to humans are
Bacillus subtillis

(a kind of bacterium) and
Drosophila melanogaster

(fruit fly), so in fact the Skeptical Chymist will need to rethink the
aversion to being related to a bacterium or a fruit fly. The species
on the list that is least
similar to humans is
Neurospora crassa

(mold), so at least the Skeptical Chymist can be
reassured that there is not a good relationship between humans and mold. An interesting
point, however, is that the two listed types of bacter
ia are, themselves, not closely related.


49.

Perhaps you have learned some memory aids (mnemonics) when taking music lessons (Every
Good Boy Does Fine), memorizing the names of the Great Lakes (HOMES), or learning
about oxidation and reduction (OIL RIG).

One of the authors learned “All
-
Together, Go
-
California” as the mnemonic to remember the correct base pairings in DNA.


a.

What is the relationship in this mnemonic to DNA base pairing?


b.

Design a different mnemonic that will help you remember such base

pairings.


Answer:


a.

Adenine pairs with Thymine; Guanine pairs with Cytosine.


b.
Just remembering the word “at” is one easy way. Another possible memory aid is to
arrange the four bases alphabetically. Then note that the first and last form a pair, and

the
second and third form a pair.




A
C
G
T
b
a
s
e

p
a
i
r
s
b
a
s
e

p
a
i
r
s



Other sayings with more personal significance can also be effective, but they have to be
simple enough that one can remember the mnemonic!


50.


Of the major players in the discovery of the structure of DNA, onl
y Rosalind Franklin
had a degree in chemistry. What was her background and experience that enabled her to
make significant contributions? Did her contributions receive adequate credit and
recognition? Write a short report, citing your sources.




PAGE 12
-
15

Answer:


R
osalind Franklin was born in 1920, the daughter of a prominent London banking family. All
of the children in the family were given encouragement to pursue an education. Both her
undergraduate and graduate degrees were from Cambridge University. During Worl
d War II,
she suspended her graduate research to contribute to the war effort by studying the properties
of coal and graphite. After the war, she completed her PhD in physical chemistry and joined
a prominent laboratory in Paris where she was introduced to

the technique of X
-
ray
crystallography. She soon became an expert in the field, moved back to London in 1951 to
work at King’s College, and in 1952 produced X
-
ray photographs of DNA. Before
publishing the images, she showed them to Maurice Wilkins, anothe
r scientist studying
DNA. Without Franklin’s knowledge, Wilkins shared the photographs with James Watson, a
molecular biologist who was working with Frances Crick to describe the structure of DNA.
The X
-
ray data changed Watson and Crick’s hypothesis about
the structure, and they
published a paper describing DNA as a double helix in 1953. Watson, Crick, and Wilkins
shared the Nobel Prize for Physiology or Medicine in 1962, but Franklin did not live to be
considered for the prize. Franklin died of ovarian can
cer in 1958. For more information, good
references are:
http://www.sdsc.edu/ScienceWomen/franklin.html

and
Chemical Achievers:
The Human Face of the Chemical Science
, a publication of the Chem
ical Heritage
Foundation, Philadelphia, PA, 1997.


51.


Gene therapy involves the use of recombinant DNA techniques. Use the Web to gather
information on this medical tool that has met with mixed results. Write a one
-

to two
-
page
report on gene therapy in
cluding specific examples of diseases that are being treated and how
the patients are faring.


Answer:


Gene therapy involves introducing normal genes into patients lacking them. The first person
treated was a four
-
year old girl suffering from severe combi
ned immunodeficiency disease
(SCID) in which a genetic defect prevents the formation of a specific enzyme necessary for
the health of white blood cells. Children with SCID have extremely weak immune systems
and often die before adulthood.


Gene therapy ha
s been used to treat malignant melanoma. According to
http://www.ornl.gov/sci/techresources/Human_Genome/medicine/genetherapy.shtml#status
,
gene therapy i
s considered experimental and has not proven very successful in clinical trials.
In January 2003 the FDA temporarily halted all gene therapy trials using retroviral vectors in
blood stem cells when a second child developed a leukemia
-
like condition (the fi
rst case of
leukemia development in a child participating in a clinical trial occurred in 2002).



Gene therapy cannot be counted on to provide treatment alternatives for all diseases. There
have been some disappointing results reported from clinical trial
s. Some diseases are not
caused by flaws in DNA. Other diseases might be amenable to treatment with gene therapy,
but developing appropriate protocols is costly, both in time and money. The Human Gene
Therapy Subcommittee of the Recombinant DNA Advisory Co
mmittee of the National
Institutes of Health must give approval to all proposed uses of gene therapy.


PAGE 12
-
16


52.


Transgenic plants have not been widely accepted in all countries. Give reasons for their
rejection in some European markets.


Answer:


Transgenic p
lants have not been as widely accepted in European countries as they have been
in the U.S. Some opposition is fueled by fears of potential health effects. People in some
areas have a generalized distrust of scientists and chemical companies and are concern
ed
about the potential for misuse of genetic engineering. Until the products of transgenic
experiments have been proven safe, some would simply rather not ingest these products.


53.


A recent focus of participants in the Human Genome Project has been to

determine the
base sequence for many different microbes (that is, bacteria and viruses). Use the Web to
document recent efforts and progress. Suggest reasons why these sequences would generate
so much interest.


Answer:

An excellent website
describing the

research being done on microbes is that of the US
Department of Energy Microbial Genome Project at
http://microbialgenome.org/
. Microbes
have survived extremes of heat, cold, radiation, pressure, salt, acidity,

and darkness for
billions of years. By studying the genetic makeup of microbes, scientists hope to learn more
about the biological basis of microbes’ durability in extreme environments. Scientists also
hope to better understand the role microorganisms pla
y in the overall processing of metals,
carbon, radionuclides, hydrogen, and nitrogen.


54.


Genetic diseases are also called inborn errors of metabolism. You may be familiar with
some of these diseases, such as hemophilia, PKU, Tay

Sachs disease, or sick
le cell anemia.
One that does not get much attention is a condition known as Niemann

Pick disease. Find
out what inborn metabolic error causes this condition, how many children are born with this
disease in the United States each year, what treatments are
available, and whether a cure is
possible. Write a report to be discussed with your classmates.


Answer:


Niemann
-
Pick disease is caused by a genetic error in DNA. There are three types of
Niemann
-
Pick disease. In types A and B, the body cannot breakdown
sphingomyelin, a lipid
which then accumulates in the liver, spleen, and brain, disrupting lipid metabolism and
causing a host of symptoms including mental retardation. People with type C cannot
breakdown cholesterol in the cells. The National Niemann
-
Pick
Disease Foundation
(
www.nnpdf.org
) estimates that 1200 people worldwide have the A and B forms of the
disease, and 500 people have the C form. A small number of people with the B form have
been treated with bone marrow

transplants with encouraging results. Generally, only
treatments to help alleviate the symptoms are possible, and many children with Niemann
-
Pick disease die at a young age. Researchers have developed gene therapy approaches to treat
the disease in mice,
but no treatments are available yet for humans.


PAGE 12
-
17


55.

One reason why science fiction is successful is that it starts with a known scientific principle
and extends, elaborates, and sometimes embroiders it. Consider how
Jurassic Park

began
with the scientifi
c principle of cloning DNA and was extended into a successful story. Now it
is your turn. Take a scientific principle from this or one of the other 11 chapters in this text.
Then write a one
-

or two
-
page outline for a story based on that principle. Be sure

to identify
the chemical concepts that you plan to include and any pseudoscience that you might
employ.


Answer:


All outlines should include the scientific principle chosen and a description of how the
principle will be embellished to create the science
fiction story. The term “pseudoscience”
refers to knowledge or practice that appears to be scientific but does not follow the scientific
method.


56.


Use the Web to create a timeline with events to account for the rapid increase and
subsequent leveling
of the adoption of transgenic crops in the United States.


Answer:

The Biotechnology Industry Organization, an advocacy group for the biotechnology industry,
maintains a timeline of biotechnology developments at

http://www.bio.org/speeches/pubs/er/timeline
.asp. A graph of U.S. acreage of transgenic
crops over time is presented at http://www.ers.usda.gov/Data/BiotechCrops/.


57.


The cloning of human embryos to produce infants is a very controversial possibility.
Try to find reports of human cloning of this

type. What evidence can you find about whether
these reports are credible? What are the U.S. regulations about cloning to produce infants?


Answer:


Members of a religion called Raëlism who claim to have received instruction in cloning
techniques from ali
ens, have claimed to have produced cloned human babies since late 2002,
but these claims have yet to be verified by independent scientists. Successes in the early
stages of human cloning have been reported, most notably by the U.S. company Advanced
Cell Te
chnology. Scientists there reported it took 71 eggs to make the first of three clones.
Two of the clones divided to form early embryos of four cells and the third formed six or
more cells before it died. According to 2003 testimony by Florida Congressman D
ave
Weldon MD, “there’s zero [successes] using embryonic stem cells, zero using embryonic
stem cells in humans, zero using [cloned cells] in humans.”


According to http://www.fda.gov/cber/genetherapy/clone.htm and
http://www.fda.gov/oc/ohrt/irbs/irbletr.html
, clinical research using cloning technology to
create a human being is subject to FDA regulation under the Public Health Service Act and
the Federal Food, Drug, and Cosmetic Act. Individuals
or organizations wishing to carry out
human cloning studies are required to submit an investigational new drug application (IND)
describing the proposed research plan to the FDA. Because the FDA believes that there are

PAGE 12
-
18

major unresolved safety questions ass
ociated with the use of cloning technology to create a
human being, permits will not be approved until those questions are appropriately addressed.


58
.


The creation of “Snuppy” the cloned canine must be of significant interest to
professional dog breede
rs and their organizations. Phil Buckley, spokesman for the Kennel
Club in England was quoted on the BBC News website as saying “
Canine cloning runs
contrary to the Kennel Club's objective to promote in every way the general improvement of
dogs," and "Clon
ing cannot be used to make improvements because the technique simply
produces genetic replicas of existing dogs.” Use the Web to find out the impact cloning has
had on similar U.S. dog organizations.


Answer:


The American Kennel Club (AKC) has not taken a
n official position. An article in the
August 4, 2005 issue of Wired magazine examines the issues. In comparison to the breeding
of race horses, which is highly regulated, the AKC has traditionally been more willing to
accept reproductive technologies such

as artificial insemination. Niki Marshall, a
spokeswoman for the AKC, said, "These issues and how they may impact our constituency
are under review by the AKC board of directors with input from scientific consultants."




But the Humane Society of the Un
ited States says dog cloning poses an animal welfare
concern because the procedure requires multiple surgeries, most of the pregnancies result in
miscarriages, and cloned animals often suffer from an array of health maladies and die at
young ages.



http:/
/www.wired.com/medtech/health/news/2005/08/68423


59
.


Advances in pet cloning has not escaped the interest of entrepreneurs, both illegal and
legit. Use the Web to find:


a.

Instances of fraud concerning the cloning of pets.


b.

Companies that offer clon
ing services legally. How much do they charge? What kinds of
guarantees are made? What locations do these companies operate?


Answer:


a.

Consumers who pay a high price for a clone of their favorite pet may be disappointed.
While the new pet and the origi
nal pet will share the same genes, the clone may not look very
much like the original, and environmental factors can influence its personality.



b.
Genetic Savings and Clone of Sausalito, CA was founded in 2000 to clone favorite pets.
They charged tens of

thousands of dollars per clone and focused on cloning cats instead of
dogs due to their more simple reproductive cycles. However, after selling only two cloned
cats, the company closed in September 2006. No other pet cloning companies have been
started.



PAGE 12
-
19

60
.


Ian Wilmut and colleagues at the Roslin Institute in Scotland

were granted a license to
clone human embryos for medical research. Has this group made any progress to date?


Answer:


Late in 2007, Ian Wilmut announced that he would no longer pursue th
erapeutic human
cloning, a decision made after research groups in Japan and the U.S. independently reported
growing embryonic stem cells from adult cells.