Goldfarb D. Biophysics DeMYSTiFied

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312 Biophysics DemystifieD

upstroke

5 (2/4) weight 5 (1/2) weight (12-26)

Thus the lifting force of the upstroke 0.5 times the weight. Since the average

must equal the weight, then the lifting force of the downstroke must be 1.5

times the weight.

PROBLEM 12-5

Making all the same assumptions as in Prob. 12-4 (20 wing beats per sec-

ond, etc.) except now assuming that 75% of the lift is generated by the

downstroke and 25% of the lift is generated by the upstroke, calculate the

distance that the hummingbird moves up and down with each wing beat.

SOLUTION

This problem is almost identical to Prob. 12-4, except that some of the lift

is provided by the upstroke. This means that the force, and therefore the

acceleration, is different. On the upstroke the wing provides a lift equal to

0.5 the weight of the bird. Gravity provides a downward force equal to the

weight of the bird. Therefore the net force on the hummingbird during the

upstroke is a downward force equal to half the weight of the bird. The bird’s

mass, however, has not changed (F 5 ma); therefore since the downward

force is only half the weight of the bird (and the mass has not changed),

then the downward acceleration is only half the acceleration due to grav-

ity, (1/2)(29.807 m/s

) 5 24.903 m/s

From Eq. (12-24) we get

d 5 (0.5)(24.903 m/s

)(0.025 s)

5 20.00153 m

By providing only 25% of the upward lift during the upstroke, the hum-

mingbird has reduced its up and down motion from 3 mm to only 1.5 mm

(compared to the case where all of the upward lift is provided by the down-

stroke).

PROBLEM

Making all the same assumptions as in Prob. 12-4 (20 wing beats per sec-

ond, etc.) except now assuming that 75% of the lift is generated by the

PROBLEM

Making all the same assumptions as in Prob. 12-4 (20 wing beats per sec-

SOLUTION

This problem is almost identical to Prob. 12-4, except that some of the lift

✔

chapter 12 physiological and anatomical Biophysics 313

Quiz

Refer to the text in this chapter if necessary. Answers are in the back of the

book.

1. Which of the following is not usually considered part of physiological and ana-

tomical biophysics?

Investigation of cellular uptake of nutrients in the cells lining the small intestine

Fluid dynamics as it relates dolphins swimming in the ocean

c. calculation of the muscular forces involved in a golf swing

d. measurement of the minimal energy in sound waves necessary for hearing

2. When an animal jumps into the air, as soon as it leaves the ground there is no

longer a force pushing the animal up into the air. When this happens,

a. there is no longer any upward velocity.

its upward velocity remains constant.

c. there isn’t any acceleration.

d. its upward velocity begins to decelerate to zero.

3. The force that lifts a jumping organism into the air comes from

a. helium.

the ground pushing up on the organism.

c. the organism’s muscles pushing the organism into the air.

d. the organism’s wings.

4. Blood flow in arteries and veins is normally

a. red.

B. laminar.

c. frictionless.

d. turbulent.

5. For a person at rest, the blood pressure in the aorta is 120 torr and the velocity of the

blood is 25 cm/s. The person then goes for a brisk walk raising the blood velocity to

100 cm/s. Using Bernoulli’s equation and assuming the height of the blood remains

constant, calculate the blood pressure in the aorta during the brisk walk.

Hint: Convert everything to standard units; for example, 1 cm 5 0.01 m. The

standard unit for pressure is pascal (Pa, although blood pressure is usually re-

ported in torr). 1 torr 5 133.32 Pa (1 Pa 5 1 kg



a. 116 torr

B. 124 torr

c. 15501 torr

d. 133 pa

6. The velocity of blood is about 125 cm/s in the aorta while running. What is the

blood’s kinetic energy?

a. 125 J/m

B. 770 J/m

314 Biophysics DemystifieD

c. 828 J/m

d. 1656 J/m

7. For a hummingbird to hover, the lifting force generated by the beating of its

wings, averaged over the time of one wing cycle, must be

a. twice the weight of the bird.

B. converted to air pressure to keep the bird in the air.

c. at least 20 beats per second.

d. equal to the weight of the bird.

8. A certain species of hummingbird, while hovering, exerts 75% of its lifting force

on the downstroke of its wings and 25% of the lifting force on the upstroke. In

order to keep the up and down motion of the bird to less than 0.5 mm, how

many times per second will the bird have to beat its wings?

Hint: Use Eq. (12-24) and solve for t, the time for one beat cycle.

a. 70 times per second

B. 50 times per second

c. 35 times per second

d. 20 times per second

9. Turbulent blood flow can occur if the velocity of blood is too fast. It also

a. is proportional to the amount of laminar blood flow.

B. can lead to deposits on the walls of arteries.

c. occurs if the critical flow velocity is too large.

D. makes the heart work harder.

10. A dolphin jumps out of the water. At the moment the dolphin leaves the water,

it has an upward velocity of 7 m per second. How high above the water will the

dolphin go before it begins to descend back down to the water?

Hint: Use Eq. (12-9).

a. 2.5 m

B. 2.2 m

c. 2.1 m

d. 0.4 m

Quar

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315

Select the best answer for the following multiple-choice questions. The

answers are located in the next section.

1. What does it mean if the Gibbs energy change for a process is positive?

A. The process is favorable.

The process is reversible.

C. The reverse process is favorable.

D. The partition function is more difficult to calculate.

E. The entropy is decreasing.

2. What is the cell nucleus?

A. A membrane bound organelle found in eukaryotes

B. The cell’s genetic material

C. A set of nucleotides found at the center of a chromosome

D. The center of a neutron star

E. A membrane that surrounds the nuclear envelope

3. DNA is a

A. heteropolymer.

B. homopolymer.

C. peptide polymer.

D. ribonucleotide polymer.

E. hydrocarbon polymer.

Final Exam

316 Biophysics DemystifieD

4. An instrument that characterizes molecules according to their molecular

weight by ionizing them and passing them through a magnetic field in a

vacuum is called

A. an ionization magneto spectrometer.

B. a molecular scale.

C. molecular tweezers.

D. a mass calorimeter.

E. a mass spectrometer.

5. How many distributions are possible for given a Boltzmann distribution

for a given number of molecules and a specified amount of energy?

A. Infinite number,

B. 1.

C. 2.

D. 10

E. It depends on how much energy is available.

6. In biophysics, when the molecules making up a specific quaternary

structure are all that is required to build that structure and there is no

need for energy input or catalysis, we call this

A. prefab construction.

B. quaternary binding.

C. self-assembly.

D. self-aggregation.

E. energy-free assembly.

7. Biomechanics includes

A. electrophysiology.

B. sensory biophysics.

C. animal motion and forces.

D. anatomical steric forces.

E. allosterics.

8. Which of the following is not true about proteins?

A. Proteins are polymers of amino acids.

B. Polypeptide chains fold up into a specific shape necessary for the

protein’s function.

F inal Exam 317

C. Transfer RNAs carry amino acids to where they are needed for protein

production.

D. Peptide bonds hold base pairs together.

E. In eukaryotes, most protein synthesis takes place on ribosomes,

whereas in prokaryotes most protein synthesis takes place in the

cytoplasm, near the cell membrane.

9. Scanning differential calorimetry

A. measures heat capacity as a function of temperature.

B. can be used to obtain direct thermodynamic data for phase transitions

or temperature-induced conformational changes.

C. provides structural information from heat capacity data.

D. A and B

E. B and C

10. Passive transport refers to

S1. cells floating passively in solution.

S2. small molecules diffusing through a membrane.

S3. transport through a membrane that does not require a transport

protein.

S4. ions passing through a tunnel created by a transport protein.

A. S1 and S2

B. S2 and S3

C. S3 and S4

D. S1 and S3

E. S2 and S4

11. Given the following two expressions for the partition function

Ze Ze

=+ =

−

∆

∑

ωω

MAXMAX

and

∑∑

which of the following statements is true?

A. The partition function Z

contains a greater amount degeneracy than Z

B. The partition function Z

contains a greater amount degeneracy than Z

C. The partition function Z

is expressed relative to a reference state E

with a relative probability of 1/Z

318 Biophysics De mystifieD

D. The partition function Z

is expressed relative to a reference state E

with a relative probability of 1/Z

E. Z

is not the correct expression for a partition function; Z

is.

12. Which of the following are true regarding X-ray crystallography?

S1. X-ray crystallography provides very precise, high-resolution structural

information for molecules.

S2. X-ray crystallography is also called X-ray diffraction.

S3. For X-ray crystallography to work, the molecules must be in a regular,

repeating arrangement (also known as a crystal ).

S4. X-ray diffraction images were used to determine that DNA is a double

helix.

A. S1, S2, and S3

B. S2, S3, and S4

C. S1, S3, and S4

D. S1, S2, and S4

E. S1, S2, S3, and S4

13. A ligand is

A. connective tissue that holds bones together.

B. connective tissue that ties muscles to bones.

C. an element in the periodic table.

D. a smaller molecule or atom that binds to a larger molecule.

E. a cell structure that produces the enzyme called ligase.

14. A biophysicist wants to use a two-state approximation to model the

conformational state of a solution of lipids. That is, we assume that the

lipids can exist in only two energy states: Assuming a Boltzmann distri-

bution and using E

5 2.5 3 10

220

J and E

5 3.0 3 10

220

J, what is the

percentage of lipids in each energy level at 310 K?

A. F

5 77.4% and F

5 22.6%.

B. F

5 76.3% and F

5 73.7%.

C. F

5 77.8% and F

5 22.2%.

D. F

5 76.3% and F

5 23.7%.

E. The answer cannot be determined from the information given.

F inal Exam 319

15. A molecule made from only carbon, hydrogen, and oxygen is called

what?

A. Carbonated water

B. Hydrocarbon

C. Lipid

D. Carbohydrate

E. Carboxylic acid

16. In which of the following interactions is the internal energy propor-

tional to 1/r, where r is the distance between the entities?

A. Charge-dipole interactions

B. Dipole-induced dipole interactions

C. Charge-charge interactions

D. A and B

E. B and C

17. Decreasing temperature will make a process more likely to occur if the

process

S1. releases energy while decreasing entropy.

S2. releases energy while increasing entropy.

S3. absorbs energy while decreasing entropy.

S4. absorbs energy while increasing entropy.

A. S1 and S2

B. S1 and S3

C. S1 and S4

D. S2 and S3

E. S3 and S4

18. If the superhelix density is defined as the absolute value of the writhe

divided by 1/10 the number of base pairs, what is the superhelix den-

sity of a 6000-base-pair closed duplex DNA with linking number of

565 and a twist of 595?

A. 0.05

B. 0.99

C. 0.09

320 Biophysics De mystifieD

D. 0.10

E. 0.30

19. In the gel state

A. small holes in the lipid bilayer are easily repaired.

B. the fluid mosaic is decrystallized.

C. the fluid mosaic contains cholesterol.

D. small holes in the lipid bilayer are filled with gel.

E. lipid movement is restricted by dispersion forces.

20. Use the following table to calculate the length of a 5000-base-pair DNA

molecule in the A-DNA conformation and in the B-DNA conformation.

Geometric Parameter B-DNA A-DNA Z-DNA

Pitch of helix (length of one turn) 33.2 Å 24.6 Å 45.6 Å

Width of helix 23.7 Å 25.5 Å 18.4 Å

Average base pairs per turn of helix 10.0 10.7 12

A. A-DNA length

1.15

Å, B-DNA length

1.66

Å.

B. A-DNA length

1.66

Å, B-DNA length

1.15

Å.

C. A-DNA length

1.27

Å, B-DNA length

1.66

Å.

D. A-DNA length

8.66

Å, B-DNA length

6.11

Å.

E. The length cannot be calculated from the information provided.

21. Statistical mechanics falls into which division of biophysics?

A. Molecular and subcellular biophysics

B. Physiological biophysics

C. Environmental biophysics

D. All of the above

E. None of the above

22. What is a nucleic acid palindrome?

A. A nucleotide sequence that can form a stem-and-loop or cruciform

structure

A nucleotide sequence that reads the same forward or backward

A protein that binds to certain DNA sequences

F inal Exam 321

A dome-shaped DNA secondary structure

None of the above

23.

Fill in the blanks: Two-chain phospholipids tend to form _______

whereas single-chain phospholipids form _________.

micelles, liposomes

lysozomes, micelles

liposomes, cholesterol

liposomes, micelles

membranes, vesicles

24.

Which of the following statements is most true?

A voltage clamp is a technique used in electrophysiology to measure

and characterize voltage differences in cells, particularly in excitable

tissue cells such as neurons (nerve cells).

A voltage clamp is a technique used in electrophysiology to measure

and characterize electrical currents in cells, particularly in excitable

tissue cells such as neurons (nerve cells).

A voltage clamp is a technique used in conjunction with electrophore-

sis, to measure and characterize voltage differences among molecules.

The current clamp technique is similar to the voltage clamp, except

that the electrode feedback mechanism allows the current across the

membrane to vary while keeping a constant voltage.

None of the above

25.

DNA owes its helical shape to

Watson and Crick.

Rosalind Franklin.

hydrogen bonds between base pairs.

aromatic base stacking.

the helical phosphate backbone.

26.

The Boltzmann distribution

is the most probable distribution for any significant number of molecules.

is not the only distribution that occurs.

has units of joules per molecule.