1Generalized eukaryotic cell test w solutions

be found in a higher concentration in the plasma membrane of eel nerve cells as compared to the plasma membrane of eel epithelial cells.. Experiment 1 Mutant cells are inoculated onto a

BIOLOGY TOPICAL:

Generalized Eukaryotic Cell

Test 1

Time: 21 Minutes*

Number of Questions: 16

* The timing restrictions for the science topical tests are optional If you are using this test for the sole purpose of content reinforcement, you may want to disregard the time limit

DIRECTIONS: Most of the questions in the following

test are organized into groups, with a descriptive passage preceding each group of questions Study the passage, then select the single best answer to each question in the group Some of the questions are not based on a descriptive passage; you must also select the best answer to these questions If you are unsure of the best answer, eliminate the choices that you know are incorrect, then select an answer from the choices that remain Indicate your selection by blackening the corresponding circle on your answer sheet A periodic table is provided below for your use with the questions

PERIODIC TABLE OF THE ELEMENTS

19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36

39.1 40.1 45.0 47.9 50.9 52.0 54.9 55.8 58.9 58.7 63.5 65.4 69.7 72.6 74.9 79.0 79.9 83.8

37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54

85.5 87.6 88.9 91.2 92.9 95.9 (98) 101.1 102.9 106.4 107.9 112.4 114.8 118.7 121.8 127.6 126.9 131.3

55 56 57 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86

Cs Ba La * Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn

132.9 137.3 138.9 178.5 180.9 183.9 186.2 190.2 192.2 195.1 197.0 200.6 204.4 207.2 209.0 (209) (210) (222)

87 88 89 104 105 106 107 108 109

Fr Ra Ac † Rf Ha Unh Uns Uno Une

(223) 226.0 227.0 (261) (262) (263) (262) (265) (267)

*

†

58 59 60 61 62 63 64 65 66 67 68 69 70 71

Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

140.1 140.9 144.2 (145) 150.4 152.0 157.3 158.9 162.5 164.9 167.3 168.9 173.0 175.0

90 91 92 93 94 95 96 97 98 99 100 101 102 103

232.0 (231) 238.0 (237) (244) (243) (247) (247) (251) (252) (257) (258) (259) (260)

Passage I (Questions 1–6)

It has been proposed that the nervous tissue of the

electric eel, Electrophorus electricus, may be useful in the

repair of damaged nerves in humans To isolate the

various subcellular structures within the nerve cells of

Electrophorus electricus, a researcher uses rate-zonal

centrifugation This technique separates the various

subcellular structures by size and density After

centrifugation, the large dense structures typically form a

pellet at the bottom of the test tube, while the lighter,

less dense structures remain suspended in the supernatant

(the fluid layer) By centrifuging at different speeds and

durations, different organelles can be isolated

The eel nerve cells are suspended in a 0.25 M

sucrose solution, which is isotonic to the cells Most of

the cells are broken open by stirring this suspension in a

high-speed blender to form a cell homogenate The

homogenate is then filtered to remove any unbroken cells

The filtered homogenate is centrifuged at increasing speeds

four times, with a pellet collected after each step, and the

supernatant transferred to each successive tube This

procedure is outlined in Figure 1

Centrifuge

Filtered

homogenate

600g x

Pour out:

15,000g x

5 min

Pour out:

100,000g x

60 min

Pour out:

300,000g x

2 hr

Pellet 1 Pellet 2 Pellet 3 Pellet 4

Supernatant Supernatant Supernatant Supernatant

Figure 1

1 Analysis of Pellet 2 showed that it possessed high

succinate cytochrome C reductase activity This enzyme oxidizes succinic acid to fumaric acid, both intermediates of the Krebs cycle Therefore, this pellet most likely contains:

A mitochondria

B plasma membrane

C endoplasmic reticulum

D cytoplasm

2 To determine the activity of the enzyme lactate

dehydrogenase, the compound DPNH is added to each sample of supernatant For every molecule of pyruvate that is reduced to lactate by lactate dehydrogenase, a molecule of DPNH is oxidized:

Pyruvate + DPNH → Lactate + DPN

In which of the following samples would you expect lactate dehydrogenase activity to be found?

I Supernatant 1

II Supernatant 2 III Supernatant 3

IV Supernatant 4

A I only

B III and IV only

C II, III, and IV only

D I, II, III, and IV

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3 Which of the following molecules would you expect 4 Which of the following structures would most likely

to find in the pellet containing the plama membrane? be found in a higher concentration in the plasma

membrane of eel nerve cells as compared to the plasma membrane of eel epithelial cells?

O

I

A Glycoproteins

N

C Acetylcholine receptors

O

-II

O

O

III

O

O H

H

H

H

N

N

O

A I only

B II only

C III only

D I and III only

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5 The enzyme DNase is added to Pellet 1 After this

enzymatic digestion, which of the following would

most likely be found within the digested pellet?

A mRNA

B Histones

C Rhodopsin

D Elongation Factor 2

6 The researcher believes that Pellet 4 contains

ribosomal subunits Which of the following

observations would most support this hypothesis?

A Pellet 4 was found to contain uncharged tRNA

B Pellet 4 was found to contain two molecules

with sedimentation coefficients of 40S and 60S

C Pellet 4 was found to contain the enzyme

peptidyl transferase

D Supernatant 4 was found to contain unprocessed

proteins

Passage II (Questions 7–12)

The yeast Schizosaccharomyces pombe divides by

fission and is thus an ideal microorganism for the study of cell division in higher eukaryotic cells A scientist

believes that she has identified the region of the S pombe

chromosome containing the DNA sequence that includes the centromere From this region she has isolated two different fragments of DNA: Fragments I and II The centromere is the region of the chromosome that maintains the attachment of sister chromatids during meiosis I and includes the site of attachment to the microtubules of the meiotic and mitotic spindles During division, the spindle must both assemble and disassemble its tubulin subunits to properly function in the segregation of chromosomes

To test which of the two fragments contains the

centromere region, the scientist takes a mutant strain of S

pombe cells that cannot grow unless adenine is provided

in the growth medium, and performs the following set of experiments

Experiment 1

Mutant cells are inoculated onto an agar plate containing minimal medium

Experiment 2

The normal gene for adenine biosynthesis (adenine+)

is inserted into a plasmid, which is then inserted into the mutant cells The cells are then inoculated onto agar plates containing minimal medium (A plasmid is a self-replicating extrachromosomal DNA fragment.)

Experiments 3A and 3B

Fragment I and Fragment II are inserted into separate plasmids containing the adenine+ gene The plasmids are then inserted into the mutant cells, which are inoculated onto separate agar plates containing minimal medium If the plasmid contains the DNA fragment with the functional centromere, it will be stably inherited by daughter cells during cell division

The experimental results are shown in Table 1

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Table 1 9 Minimal medium contains only salts and sugar The

primary reason that the cells used in Experiment 1 Expt Mutant S pombe

on minimal

medium with:

Increase in cell # after 1st round

of division

Visible colonies after 20 rounds of division

3A* cells + adenine+ +

Fragment I

3B* cells + adenine+ +

Fragment II

cannot grow on minimal medium is that these cells are NOT able to synthesize:

A protein

B essential fatty acids

C nucleic acids

D salts

*Cells with introduced plasmid

1 0 Which of the following graphs best represents the

four growth curves obtained under the experimental conditions summarized in Table 1?

7 Based on the information in the passage, it can be Key: Expt 1 Expt 3A

A Fragment I contains a centromere

C

C Fragments I and II both contain centromeres

D the mutant S pombe chromosomes do not

contain centromeres

8 The results obtained in Experiment 3B can be changed

such that they are identical to the results obtained in

# of cell divisions # of cell divisions

I a drug that inhibits microtubule assembly is

added to the growth medium used in

Experiment 3B

II a drug that inhibits microtubule disassembly is

added to the growth medium used in

Experiment 3B

III a drug that inhibits cytokinesis is added to the

D

1 20 1 # of cell divisions 20

growth medium used in Experiment 3B # of cell divisions

A I only

B II only

C I and II only

D I, II, and III

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1 1 The cells used in Experiment 2 are most likely able

to increase their cell number after one round of cell

division because:

A the replicated adenine+ plasmid binds to

microtubules and segregates to daughter cells

during mitosis

B the replicated adenine+ plasmid binds to

microtubules and segregates to daughter cells

during meiosis

C the replicated adenine+ plasmid binds to

microfilaments and segregates to daughter cells

during cell division

D the replicated adenine+ plasmid randomly

segregates to daughter cells during cell division

Questions 12 through 16 are

NOT based on a descriptive

passage

1 2 In vitro, the transcription factor SP1 binds nucleic

acids with a high affinity Radio-labeled SP1 would most likely be found in all of the following organelle preparations EXCEPT:

A nucleoli

B mitochondria

C ribosomes

D Golgi apparati

1 3 All of the following are involved in directing proteins

to their final destination within a cell EXCEPT:

A amino acid sequence of the protein

B vesicles

C lysosomes

D endoplasmic reticulum

1 4 A researcher discovered that in order for the HAP2

protein to elder the nucleus and bind to the CYC1

gene, a molecule of ATP must be consumed Which

of the following transport mechanisms must be involved in the movement of HAP2 into the nucleus?

A Active transport

B Facilitated diffusion

C Passive diffusion through the nuclear pores

D Endocytosis

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1 5 Three funnels, each containing a different

concentration of a urea solution, are covered with a

semi-permeable membrane that is impermeable to

urea The funnels are inverted and placed in a beaker

containing a different urea solution What is the

concentration of the solution?

A 2.0 M urea

B 1.5 M urea

C 1.0 M urea

D 0.0 M urea

dH20 urea urea dH20 urea urea

1 6 Which of the following would most likely play a role

in cellular adhesion and recognition?

A Carbohydrate molecules on the exterior of the

plasma membrane

B The fluidity of the plasma membrane

C Peripheral proteins on the interior of the plasma

membrane

D The hydrophobic regions of the plasma

membrane

END OF TEST

ANSWER KEY:

GENERALIZED EUKARYOTIC CELL TEST 1 EXPLANATIONS

Passage I (Questions 1-6)

1 The correct answer is choice A Although the question stem may have scared you a little bit, this question is really quite easy The only thing you needed to get out of the question stem is that Pellet 2 was found to have one of the enzymes

of the Krebs cycle So as you can see, this question is simply asking you where the Krebs cycle occurs Well from introductory biology, you should know that the Krebs cycle occurs in the mitochondria, along with electron transport and oxidative phosphorylation Therefore choice A is the correct answer Just to review briefly, in eukaryotic cells, glucose is broken down to pyruvate in the cytoplasm in a series of reactions known as glycolysis The pyruvate then enters the mitochondria, where it is converted into acetyl CoA The acetyl CoA then enters the Krebs cycle All of the NADH and FADH2 molecules generated during these processes are shuttled into the electron transport chain, which is coupled with oxidative phosphorylation to produce ATP

Anyway, back to the question As we just learned, glycolysis, not the Krebs cycle, occurs in the cytoplasm, and so choice D is incorrect The other two choices have nothing to do with the Krebs cycle at all The plamsa membrane surrounds the cell and acts as a barrier between the cell and the outside environment and regulates the passage of material into and out of the cell So choice B is incorrect Finally, the endoplasmic reticulum, choice C, is involved with protein processing and is the site of ribosomal attachment during translation Thus choice C is also wrong

2 Choice D is the correct answer In order to answer this question you need to understand the basic principle of centrifugation as explained in the passage, as well as the information provided in the question stem From the question stem you know that DPNH is used to monitor the conversion of pyruvate to lactate Although you have probably never heard of DPNH, you should recognize the reaction of pyruvate going to lactate as the fermentation step that occurs in most eukaryotic cells under anaerobic conditions Well, where in the cell does fermentation occur? Glycolysis occurs in the cytoplasm, while the Krebs cycle and electron transport/oxidative phosphorylation occur in the mitochondria

So now that we’ve deciphered the question stem, let’s see how centrifugation works From the passage you know that larger objects will form a pellet at the bottom of a tube, while lighter, less dense structures remain suspended in the supernatant You also are told in the passage and shown in Figure 1, that the supernatant from the first tube is transferred to the second, and so on and so on Therefore, cytoplasm will be present in ALL four supernatants and so choice D is the correct answer

3 The correct answer is choice B The question is essentially asking, “the plasma membrane is made up of what molecules?” The plasma membrane is composed of phospholipids, a molecule that has a glyerol backbone attached to two fatty acids and a phosphate group The phospholipids are arranged in a bilayer, which is why the cell membrane is also referred to as the “phospholipid bilayer.” Roman numeral II is a phospholipid, so must appear in the correct answer Answer choice C is the only one that includes Roman numeral II Molecule I is an RNA molecule, and III is a DNA molecule Neither RNA or DNA make up the plasma membrane Another possible molecule could be a protein, as the plasma membrane has receptors and ion channels/pumps studded throughout its length

4 Choice C is the correct answer You’re being asked to deduce what will be found in a higher concentration in the plasma membrane of an eel nerve cell as compared to the membrane of an eel epithelial cell Well, what are the normal components of a generic plamsa membrane? A eukaryotic plasma membrane consists of a phospholipid bilayer So phospholipids are a common element of all plasma membranes and therefore would not be found in a higher concentration in nerve cell membranes Thus choice D is incorrect Cholesterol molecules are embedded in the hydrophobic interior of the bilayer Therefore, cholesterol is also a common component of plasma membranes So choice B is incorrect Glycoproteins, which are proteins that contain carbohydrate components, extend out of the plasma membrane and function in cell adhesion and recognition Therefore, glycoproteins are also common plasma membrane elements, and thus choice A is incorrect So by the process of elimination, choice C is the correct answer if you think about it, this answer makes sense Acetylcholine is one of the principal neurotransmitters responsible for the transmission of a nerve impulse, and its message is transmitted when it binds to acetylcholine receptors found on the plasma membrane of its target cells Since acetylcholine is a neurotransmitter, the plasma membrane of an epithelial cell would not be expected to have a high concentration of acetylcholine receptors But you would most likely find a high concentration of acetylcholine receptors on the plasma membrane of eel nerve cells Therefore, choice C is the correct answer

5 Choice B is the correct answer Although you are not explicitly told what is in Pellet 1, you should have been able

to figure it out First of all, you’re told that DNase is added to Pellet 1 Well, you know that the only place DNA is found in