Unit 1 Review, pages 112–119
Knowledge
1. a
2. c
3. c
4. d
5. a
6. b
7. d
8. b
9. c
10. b
11. a
12. c
13. d
14. b
15. d
16. a
17. c
18. c
19. b
20. d
21. c
22. d
23. False. Isotopes are different forms of the same element with different numbers of neutrons.
24. True
25. True
26. False. When polar molecules dissolve in solution, the surrounding water reduces the
electrostatic interactions between them.
27. True
28. True
29. False. Carbon atoms form the backbone of biological molecules.
30. True
31. False. Osmosis is the diffusion of water molecules across a membrane.
32. False. A disaccharide consists of two single sugar subunits.
33. False. All proteins are polymers that are composed of amino acid monomers.
34. True
35. False. Animal cells do not contain plastids. Only plants and some protists contain plastids.
36. False. Compared with integral membrane proteins, peripheral membrane proteins are less
likely to be recognition proteins.
37. True
38. False. Membrane proteins have four specific functions.
39. True
40. False. Endocytosis moves aggregate molecules into the cell.
41. True
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42. (a) v
(b) vi
(c) iii
(d) i
(e) iv
(f) ii
43. (a) iii
(b) vi
(c) v
(d) iv
(e) ii
(f) i
44. (a) Ionic bonds form between ions with opposite charges. Unlike covalent bonds, sharing of
electrons does not occur. Ionic bonds also tend to dissociate in water.
(b) Sodium chloride crystals are held together by ionic bonds. Ionic bonds between amino acids
that make up the backbone of a protein contribute to the protein’s tertiary structure. Ionic bonds
also contribute to holding peripheral membrane proteins to membrane surfaces.
45. Tritium has two neutrons.
46. Answers may vary. Sample answer: Water has an unusually high specific heat of
vaporization. This is significant for living things because it means that the evaporation of
water from our bodies has a significant cooling effect. Water also has a high specific heat
capacity, which helps organisms maintain a constant body temperature. Water forms very
strong hydrogen bonds (cohesion) resulting in surface tension. This is significant for small
organisms that can walk on the surface of ponds and significant for plants because the strong
hydrogen bonds between water and other polar molecules (adhesion) are involved in the
capillary action of water in plant veins.
47. (a) A buffer absorbs or releases hydrogen ions. If the number of H+ ions in solution
increases, the buffer combines with them, removing them from the solution. If the number of
H+ ions in solution decreases, the buffer releases H+ ions into the solution.
(b) Buffer systems control the pH of biological systems, for example the internal pH of cells and
the pH of blood. Without buffers, living things would be unable to effectively regulate pH. This
would affect structure of many proteins, causing enzymes to stop functioning, which would
result in death.
48. Answers may vary. Sample answer:
(a) Examples of four functional groups are: hydroxyl groups, which are small and polar;
carboxyl groups, which have acidic properties; amino groups, which can form hydrogen bond
and are weak bases; and phosphate, which is an ionic group that acts as an acid and can form
phosphodiester bonds.
(b) Hydroxyl groups can be found in alcohol and sugar. Carboxyl groups can be found in
proteins and acetic acid (vinegar). Amino groups can be found in nucleic acids and proteins.
Phosphate groups can be found in nucleic acids and phospholipids.
49. In a dehydration, or condensation, water is generated when two molecules combine. An OH–
is removed from one molecule and an H+ from the other molecule, and the two form water. In a
hydrolysis reaction, the reverse happens. A larger molecule is split into two smaller molecules,
using a water molecule in the process. The components of the water molecule (H+ and OH–) are
added to functional groups as molecules break into smaller subunits.
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50.
51. (a) Glycerol is a small carbon chain with three hydroxyl functional groups. A fatty acid is a
hydrocarbon chain with a carboxyl functional group. Three fatty acid molecules combine with a
single glycerol to form three molecules of water and a lipid molecule with ester linkages. The
reaction occurs between the carboxyl group of each fatty acid, which loses an OH–, and each
hydroxyl group on the glycerol, which loses an H+. The lipid formed is called a triglyceride.
The diagram above shows glycerol and fatty acids, highlighting the hydrogen and oxygen that
will be released as water when bonds form. The diagram below shows a triglyceride formed by
the molecules above.
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(b) This reaction is a condensation or dehydration reaction because it results in the formation of
water and the joining of molecules.
52. (a) glycosidic bond:
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(b) peptide bond:
(c) phosphodiester bond:
53. Answers may vary. Protein functions include: structure for cells, bones, and other tissues
(e.g., tendons, hair), defense and immunity (antibodies), enzymatic functions like starch
digestion (amylase), signaling (hormones), carrier functions (hemoglobin), recognition and
receptor functions (major histocompatibility complex), and motility functions (actin and
myosin).
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54. In reversible inhibition, the molecules binding to the enzyme are able to release those bonds,
allowing enzyme activity to return to its normal state after the inhibitor is no longer bound to the
enzyme. In irreversible inhibition, the inhibitor binds to the enzyme so strongly through the
formation of covalent bonds that the enzyme is completely and permanently disabled.
55. Four factors that affect the functions of enzymes are: enzyme concentration, substrate
concentration, temperature, and pH.
56. Two components that are assembled in the nucleolus during the production of ribosomes are
RNA and proteins.
57. Three different types of plastids found in plant and algal cells include: chloroplasts, which
create energy through photosynthesis; chromoplasts which make and store pigments that colour
fruits and other tissues; and amyloplasts which store starch in stems, tubers, and seeds.
58. (a) Lysosomes are the cell’s waste disposal system. They contain enzymes that break down
worn out cell components and unwanted material.
(b) No, animal cells could not survive without lysosomes. Without the action of lysosomes,
waste would build up within the cell and eventually interfere with cell function.
59. (a) Cystic fibrosis transmembrane conductance regulator (CFTR) is the protein affected by
the gene that causes cystic fibrosis.
(b) In properly functioning cells, CFTR acts as a membrane transport protein that moves
negatively charged chloride ions (Cl–) out of the cells that line the lungs and intestinal tract and
into the surrounding mucus lining. This creates an electrical gradient across the membrane that
leads to the movement of sodium ions (Na+) in the same direction. Water also moves into the
mucus lining, following the chloride and sodium by osmosis. This keeps the mucus healthy and
less viscous.
(c) In people with cystic fibrosis, when the CFTR malfunctions, movement of the ions and water
into the mucus in the lungs does not occur. This makes the mucus very thick, so that it is
difficult for the lungs to breathe properly. The thick mucus is also a breeding ground for
bacteria.
60. (a) The energy source that is used by secondary active transport pumps is the concentration
gradient of an ion.
(b) The ion concentration gradient is established by primary active transport pumps using ATP
as their energy source.
Understanding
61. As carbon-14 decays, it gives off particles. One of its eight neutrons transforms into an
electron and a proton. The isotope then has a total of seven neutrons, seven electrons, and seven
protons. This is a normal atom of nitrogen. Therefore, when carbon-14 decays, it changes into an
atom of nitrogen.
62. Table 1
Electrons
Protons
Neutrons
Symbol
12
6
6
6
C
23
11
11
12
Na
35
17
17
18
Cl
1
1
1
0
H
63. Water is ubiquitous in all living systems. The small size and polar nature of water molecules
means that more substances dissolve in water than in any other liquid.
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64. Answers may vary. Sample answer: A strong acid completely ionizes when dissolved in
water, releasing all its H+ ions, which combine with water molecules to form H3O+. A weak acid
releases only some of its H+ ions. Since pH is a measure of the concentration of H3O+ ions in a
solution, you can measure the strength of an acid by dissolving a known quantity of the acid in
water and then measuring the resulting pH.
65. Carbon has four valence electrons that are unpaired, hence it is able to form four covalent
bonds. It can form two double bonds, one double and two single bonds, one single and one triple
bond, or four single bonds. This allows millions of possible structures, including rings, chains,
polymers, and smaller molecules as well. The molecule below has single carbon bonds, double
carbon bonds, and one triple carbon bond.
66. Fat is an important energy source and an essential component of plasma membranes,
hormones, and nerve fibre insulation.
67. Answers may vary. Sample Answer: Not necessarily. Enzymes are very specific, so the
mirror image of table sugar may not be able to bind to the enzyme’s active site. (In fact, the
human body cannot digest levo-sugar).
68. (a) Unsaturated fatty acid chains contain kinks.
(b) Kinks in fatty acid chains occur where the chain contains a double carbon bond created by
the removal of two hydrogen atoms.
(c) This bend in the chain means that this unsaturated fatty acid does not pack together as tightly
as a saturated fatty acid would, making the molecules more fluid, which allows them to be
liquids at room temperature. In cells, the presence of unsaturated fatty acids in plasma membrane
phospholipids allows the membrane to remain fluid over a wide temperature range.
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69. Peptide dehydration reaction:
70. Guanine and adenine are purine bases, whereas thymine and cytosine are pyrimidine bases.
Purines bond with pyrimidines because of hydrogen bonding interactions between various polar
functional groups on the bases. Guanine does not pair with thymine and cytosine does not pair
with adenine because their hydrogen bond donors and hydrogen bond acceptors do not align.
71. The antisense strand would have the following nitrogenous base sequence: CTAATTG.
72. Competitive inhibition occurs when the inhibiting molecule competes with the normal
substrate for access to the active site of the enzyme. Non-competitive inhibition occurs when
specific molecules inhibit enzyme activity, but they do not compete with substrate molecules for
binding to the active site. They bind to an enzyme at a location other than the active site to
change the conformation of the enzyme.
73. (a) During allosteric activation, (1) an allosteric activator molecule binds to a site other than
the active site of an enzyme. (2) This causes the enzyme to change its conformation, (3) which
increases the enzyme’s affinity for a substrate to bind. This allows the enzymatic reaction to
occur at the active site.
(b) During allosteric inhibition, (1) an allosteric inhibitor molecule binds to a site other than the
active site of an enzyme. (2) This causes the enzyme to change its conformation, decreasing the
ability of a substrate to bind, and the enzyme ejects the substrate.
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74. (a) A temperature above and below 37 °C will cause the activity of this enzyme to decrease.
(b) A temperature above 55 °C will cause the activity of this enzyme to be completely
eliminated.
75. The nuclear membrane is a two-layer membrane that encloses the nucleus of a eukaryotic
cell. The plasma membrane is a dynamic barrier that surrounds the cytosol of a cell. Both
membranes are lipid bilayers that allow water and gases to cross freely. The nuclear membrane
only allows other substances to enter and exit the nucleus with the help of a system of
transporters and pumps that span the nuclear envelope. The system of transporters and pumps
controls the passage of molecules between the nucleus and the cytosol. The nuclear membrane
protects the cell’s DNA. Similarly, the plasma membrane contains proteins that can transport
molecules into and out of the cell. In addition, the plasma membrane has proteins involved in
enzymatic activity, triggering signals, and attachment and recognition. Thus, the plasma
membrane allows the cell to carry out its functions.
76. (a) The organelle is the rough endoplasmic reticulum (ER).
(b) The rough ER has ribosomes attached to its surface that synthesize polypeptides. The
polypeptides are released into the ER interior where they undergo folding. The folded proteins
are then distributed to other destinations in the cell by vesicles that bud from the ER.
(c) Structure A is a mitochondrion that generates ATP for the cell.
(d) Structure B is a ribosome that is the site of peptide production.
77. (a) The organelle is a mitochondrion.
(b) Mitochondria release energy from food for the cell in the form of ATP.
(c) Biologists think that it probably evolved as a bacterial cell that was engulfed by another cell,
and then stayed to live symbiotically. Ultimately these endosymbiotic cells evolved into the
current organelle.
78. Students concept map should include the following functions:
Transport: Many substances cannot freely diffuse through the membrane. Instead, a specific
compound may be able to cross a membrane by way of a hydrophilic protein channel.
Alternatively, shape shifting allows some membrane proteins to shuttle molecules from one side
of a membrane to the other.
Enzymatic activity: Some membrane proteins are enzymes, such as those associated with
respiration and photosynthesis.
Triggering signals: Some membrane proteins bind to specific chemicals, such as hormones.
Binding to these receptors triggers changes on the inner surface of the membrane that start a
cascade of events to send a signal through the cell.
Attachment/recognition: Proteins exposed to both the internal and external membrane surfaces
act as attachment points for a range of cytoskeleton elements, as well as components involved in
cell-cell recognition and binding to the ECM.
79. A lack of moisture in the mucus lining of the lungs makes the mucus very thick and makes
breathing difficult. In the intestinal tract, thick mucus can clog pancreatic ducts, blocking
important digestive enzymes.
80. Channel proteins form hydrophilic pathways in the membrane through which water and ions
can pass. Carrier proteins also form passageways through the lipid bilayer, but each carrier
protein binds a specific single solute, such as a sugar molecule or an amino acid, and transports
it across the lipid bilayer.
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81. An ion moving through a membrane channel down its concentration gradient in one direction
gives energy to actively transport another molecule in the same direction, against its
concentration gradient.
82. (a)
The phosphate group forms phosphodiester bonds (in DNA, RNA, and phospholipids), transfers
energy (in ATP and GTP), creates hydrophilic regions on molecules due to its negative charge,
and can be attached to proteins for cellular signaling.
(b) Answers may vary. Some compounds that contain phosphate include DNA and RNA (which
store information), phospholipids (which create bilayer membranes), and ATP and GTP (which
store chemical energy).
Analysis and Application
83. Radioisotopes give off particles as they decay, so they are easy to detect in a cell.
Researchers can use radioactive tracers to follow the path of the isotope as it moves through cells
to different locations in the body.
84. Buffers prevent acidosis by absorbing excess H+ ions from the blood and extracellular fluid.
Specifically, bicarbonate ions react with H+ to produce carbonic acid. The buffer releases H+
ions if the system becomes more alkaline. This prevents large fluctuations in an organism’s pH,
helping keep it within the optimal range for cell reactions.
85. In the ice lattice, water molecules are spread farther apart than in the liquid water lattice.
Therefore the structure of ice is less dense than liquid water, so it floats on the surface instead
of sinking to the bottom of lakes, rivers, and ponds. This allows fish to live beneath the surface
of the ice.
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86. (a)
(b) Dehydration occurs when two molecules bind to form a larger molecule, producing one
water molecule from an OH– group and a H+ group. Hydrolysis is the reverse. It separates an
H2O molecule into H+ and OH– ions, which are added to the molecule, breaking the bond and
splitting the molecule into two smaller products.
87. Both are broken down by the addition of water molecules through hydrolysis. Without water,
hydrolysis could not take place.
88. (a) The primary structure of a protein is the unique linear sequence of its amino acids.
Secondary structure is the result of hydrogen bonding among molecules of the amino acid
backbone, forming patterns of folds or coils. Tertiary structure is the overall shape of a protein
due to a range of bonding interactions among the amino acid R groups. These include ionic
bonds, hydrogen bonds, disulphide bridges, and hydrophobic interactions. Hydrophobic
interactions are the interaction of nonpolar side groups that cluster together as a result of other
amino acid R groups interacting with water. Quaternary structure is the combination of multiple
protein molecules or polypeptide chains with the same bonding forces that hold the tertiary
structure together.
(b) (i) secondary
(ii) primary
(iii) tertiary
(iv) secondary
(v) primary
89. A straight protein is not likely to be an enzyme because enzymes have highly specific, threedimensional pockets that bind the specific molecules upon which they act.
90. At high concentrations, isoleucine attaches to the allosteric site of threonine deaminase,
blocking the production of intermediary molecules, thus preventing the production of any more
isoleucine.
91. Factors that should be measured include pH and temperature, to make sure they are within
the optimal range for these enzymes. As well, check that the enzymes were not exposed to too
much thermal energy before using them, since too much thermal energy can denature a protein.
92. These minerals are cofactors that specific enzymes in our body need in order to catalyze
reactions and are important components of essential compounds in the body.
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93. Answers may vary. Sample answer: The experiment will need to test a range of temperatures
and pH levels. For example:
Temp
pH (1) pH (2) pH (3)
20 °C
5
7
9
50 °C
5
7
9
80 °C
5
7
9
You will then need to measure the breakdown product of starch, for example, by using
Benedict’s reagent.
94. The ideal temperature will be 37 °C and the ideal pH will be 1–2. The human body
temperature is 37 °C, and most human enzymes have adapted so they are optimally active at that
temperature. Also, since the stomach is an acidic environment, you can expect stomach enzymes
to perform optimally at a very low pH.
95. The mitochondrial membranes are responsible for the electron transport process to make
energy in the form of ATP. This requires a large array of transport proteins. The myelin sheath
exists mainly to insulate nerve cells, and lipids are a good choice for that function.
96. (a) Cholesterol stabilizes the membrane in animal cells. It increases membrane fluidity at
low temperatures and reduces fluidity at high temperatures.
(b) Carbohydrates act as recognition markers in the lipid membrane and are involved in cell–cell
interactions.
(c) Proteins can be integral (transmembrane) proteins or peripheral (surface) proteins. If a
protein were formed incorrectly (mutated), it would not perform its function properly. This could
lead to disease or death or the cell could be only slightly affected, depending on the protein and
the specific effect of the mutation. For example, cystic fibrosis is caused by mutations in the
gene for the cystic fibrosis transmembrane conductance regulator (CFTR) protein.
97. No, plasma membranes are asymmetrical. On the external surface, hormones and growth
factors bind to receptor proteins. Glycolipids and carbohydrate groups also bind to proteins on
the external surface. On the inside of the membrane are proteins to which the cytoskeleton
attaches.
98. (a) The production of a concentrated salt solution is an active process because it requires
energy to work against a concentration gradient.
(b) Sodium-potassium pumps would be involved in the process.
(c) If the albatross were unable to remove the excess salt the result would be a lack of
homeostasis and death, since cells and tissues need a proper balance of salt and water to function
normally.
99. (a) Exocytosis carries secretory proteins and waste materials from the cytosol to the cell
exterior. Endocytosis carries proteins, larger aggregates of molecules, and even whole cells from
outside the cell into the cytosol. More simply, exocytosis carries material out of a cell, and
endocytosis carries material in. Their functions are basically opposite.
(b) (i) Flower cells involved in nectar production undergo exocytosis in order to secrete the
nectar produced within the internal environment of the cell.
(ii) The cells in the small intestine undergo endocytosis to absorb nutrients from the food in the
small intestine. Those nutrients may then be transported out of the cell via exocytosis to provide
nutrients for the rest of the body.
(iii) Cells of the mammary gland undergo large amounts of exocytosis to release proteins into
milk.
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100. No. Only hydrophobic molecules and small, uncharged polar molecules can pass through a
membrane via simple diffusion. Since starch is a complex carbohydrate, it is too large a
molecule to diffuse through the membrane.
Evaluation
101. (a) Answers may vary. Students could comment that it would be good to have all 20 amino
acids but these would not be in the ideal ratio, which would mean that we would not have an
ideal balance. Also, we don’t know if our digestive enzymes would be able to break this protein
down.
(b) Answers may vary. Students might be willing to eat the protein but they might prefer
something they know is natural and safe.
102. (a) Currently, lactose-intolerant people can avoid milk products that contain lactose, they
can drink milk that has been pre-treated with lactase to break down lactose, or they can directly
consume commercial lactase supplements when they eat dairy products.
(b) Answers may vary. Sample answer: Scientists could try to find a way to deliver lactase
directly into the small intestine or to modify the cells to produce their own lactase.
103. It would be very difficult, and may be virtually impossible depending on the protein.
Chemical synthesis of long polypeptides in the lab is not very efficient. Proteins may also need
to undergo folding and other modifications to function correctly, processes which normally
occur in the rough ER and Golgi body and may be difficult to accomplish in the lab. Instead,
when scientists want a particular enzyme they use biotechnology to get cells to mass-produce it
and then it is purified. Even that is very challenging.
104. Answers may vary. Students should be able to explain their choices, and should pick
something that moves and is porous in some way. They may choose a gelatinous substance or
make
a static model.
105. Answers may vary. One example might be the “floating iceberg” model. This reflects the
fact that proteins float within a sea of phospholipids, free to move around. Their tips protrude
from the membrane while the rest of the protein lies in the membrane.
106. Answers may vary. An example of a possible nanobot challenge would be developing a
way to power such small machines, or predicting how they will react once inside the body.
107. Yes, there is a limit on how big a cell can be. Cells depend on diffusion to acquire many of
the molecules they need. They also depend on diffusion to get rid of certain waste products. As a
cell gets bigger, however, the surface-to-volume ratio gets smaller. That means there is less
surface area available where diffusion can occur compared to the volume of the cell. If a cell
gets too big, the rate of diffusion through the plasma membrane cannot meet the needs of the
cell.
Reflect on Your Learning
108. Answers may vary. Students’ answers should include an understanding of the fact that
genetics, cellular biology, and many other areas depend on knowledge of chemistry and the
molecular scale to be properly understood.
109. Answers may vary. Students should make the connection that the regulation of acids and
bases is necessary for homeostasis to occur in various parts of the body in order for cells, tissues,
and organs to function properly (for example, in the stomach, pancreas, liver, kidneys, lungs,
vagina, and taste buds).
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110. (a) Answers may vary.
(b) Answers may vary.
(c) Answers may vary.
111. Answers may vary.
112. (a) Answers may vary.
(b) Answers may vary.
Research
113. (a) Answers may vary. Students should record an entry on a KWL chart.
(b) Answers may vary. Key information about carbon bonding includes: Carbon bonding occurs
when electrons are shared between carbon and the bonded atoms. Carbon can adapt to bonds
with different geometries, which allows it to take part in various crystal structures, such as the
crystals in diamonds and in graphite. Carbon can form single, double, or triple bonds. Students
might be surprised about the shape of the orbitals, the way they connect, or the variety of
properties that different substances composed mainly of carbon display because of their different
bonding configurations.
114. Answers may vary. Answers may include the following:
• Cryosurgery uses extreme cold to freeze and destroy abnormal or diseased tissue, such as
tumours. This is most commonly accomplished using liquid nitrogen. Other substances such as
carbon dioxide “snow”, argon gas, and a dimethyl ether/propane mixture are less commonly
used.
• Cryosurgery destroys tissues by freezing cells. The drop in temperature disrupts plasma
membrane fluidity, denatures proteins, and destroys cell structure. Ice formation causes cells to
rupture and blocks blood vessels, preventing circulation in the affected tissue. Liquid nitrogen is
frequently used as the cooling solution. It can be applied with a cotton swab, sprayed on, or
circulated inside a probe which is applied to the tumour.
• Cryosurgery is currently used to treat skin conditions and some cancers.
• Advantages of cryosurgery are that it is safe and less invasive than traditional surgery, which
requires an incision. This means that cryosurgery is accompanied by reduced pain and fewer
complications. It is also easier to perform and less expensive than traditional surgery.
Cryosurgery may be an option for otherwise inoperable conditions, and can be repeated and
combined with other treatments. Disadvantages include that long-term effectiveness is uncertain.
In addition, cryosurgery as a cancer treatment is only suitable for treating a localized area, and
not effective if the cancer spreads to other parts of the body.
115. Answers may vary. Students answer should include discussions of the following:
• Forensic anthropology involves recovering, analyzing, and identifying human remains.
Examining skeletal remains can determine characteristics such as stature, sex, race, and age,
which can help in identifying the deceased individual. Bones may also reveal signs of trauma
that can provide clues about the cause of death.
• Forensic botanists assist legal investigations by examining plant matter, such as seeds, wood,
and leaves. Identifying the type of pollen on a piece of evidence can help determine when and
where a crime took place, since different types of pollen are produced depending on the season
and geographical location.
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• Forensic entomology can aid investigations involving suspicious deaths by observing the
colonies of insects that colonized the remains and using those observations to estimate the time
of death. For example, observing the stage of growth of a maggot can help determine the time of
death based on how quickly that species is known to develop. In addition, different types of
insects colonize the body depending on the stage of decomposition, so identifying the species
can also help determine when death occurred.
• Forensic odontologists examine dental evidence, such as bite marks or the remains of teeth. For
example, human remains can be identified by examining their dental patterns and comparing
them to dental records. This is especially useful because teeth can endure even after the rest of
the body has decomposed or been destroyed.
• Biological molecules such as DNA and proteins can provide information useful to law
enforcement. One aspect of protein biology that is being explored in forensics is whether the
extent of degradation of certain proteins in dead tissues can help determine the time of death.
Evidence based on DNA analysis is especially powerful. DNA evidence can be recovered from
hair, tissues, and body fluids at the crime scene. Scientists can analyze the DNA to create a DNA
fingerprint profile that can be used to identify suspects or victims. Both nuclear and
mitochondrial DNA can be analyzed. Mitochondrial DNA is especially useful when analyzing
old or degraded samples, since many more copies of it exist in the cell and some can be
recovered even if nuclear DNA has degraded.
116. (a) Answers may vary. Students may organize the information they gather into categories
based on types of synthetic bilayer membranes that have been created, such as painted lipid
bilayers, supported lipid bilayers, and tethered lipid bilayers. Alternatively, they may organize
information into a timeline to show the development of synthetic lipid bilayer technology has
developed.
(b) Answers may vary. Students’ answer may be similar to the following:
• Scientists have been using synthetic and naturally derived lipids to make synthetic bilayers.
• They have succeeded in creating planar as well as spherical bilayers. Planar bilayers attached
via polymer cushions to a solid support can be stable at least for several weeks
• Applications of synthetic lipid bilayers include studying membrane properties such as
permeability and determining the structure and function of membrane proteins.
117. (a) The eight essential amino acids are tryptophan, phenylalanine, isoleucine, leucine,
lysine, methionine, threonine, and valine. Students should present the results of their research in
table format, with information similar to that given for tryptophan below:
Amino acid Role
Food
Results of
source
deficiency
tryptophan
production of serotonin (a
meat,
reduced
neurotransmitter) and
eggs,
production of
melatonin ( a hormone),
dairy,
serotonin and
which affect mood and
nuts, soy, melatonin,
sleep; production of niacin chocolate pellagra (niacin
(a vitamin)
deficiency)
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(b) Answers may vary. Sample answer: No, I cannot make a general recommendation for intake
of the eight amino acids for several reasons. Some of the amino acids can be synthesized in our
bodies, so if we take in enough building blocks to synthesize them we do not need to consume
the amino acid directly. Also, as with any nutrient, dietary recommendations would depend on
age and body size. In addition, since amino acids are building blocks for protein, dietary
recommendations would differ for people who lifted weights or engaged in other musclebuilding activities.
118. Answers will vary. Examples of artificial sweeteners students might research are: saccharin
(300–500 times sweeter than sugar), aspartame (200 times sweeter than sugar), acesulfame-K
(200 times sweeter than sugar), and sucralose (600 times sweeter than sugar). Differences from
sugar may include amount of energy provided, where in the body they are metabolized, side
effects, and the source of the sweetener. Students should justify their opinions about which
sweetener is better using evidence from the data they have gathered.
119. Answers may vary. Reports should include the following information:
• Fat substitutes imitate the properties of fats but provide few or no calories.
• They can be made from carbohydrates, proteins, or fats.
• Natural fats include triglycerides, which consist of three fatty acids linked to a glycerol
backbone.
On the other hand, a molecule of olestra consists of a sucrose backbone joined to six, seven, or
eight fatty acids. The resulting molecule tastes like fat but is too large to be digested or absorbed.
It passes through the gastrointestinal tract and is excreted without contributing calories or fat to
the diet. However, olestra consumption may cause side effects such as more frequent bowel
movements and reduced absorption of fat-soluble vitamins.
Possible health advantages of fat substitutes include reduced fat, calorie, and cholesterol intake.
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Unit 1: Biochemistry
U1-18