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ANSWER KEYfor

“Take Two and Call Me in the Morning: A Case Study inCell Structure and Function”

by

Peggy Brickman, Department of Plant Biology, University of Georgia, Athens, GA

HandoutTable 1: Differences Between Organisms (complete before class)

CHARACTERISTIC Virus Bacteria Protozoa

What differences exist in

the type and shape of the

genetic material?

RNA or DNA Circular DNA DNA in linear chromosomes


the structure that provides

an outer protective barrier?

Proteins with

or without

lipids

Phospholipids

with or without

cell wall

Phospholipids without cell wall


reproduction?

Only

reproduces

inside other

cells

Independent

reproduction but

asexual

Independent reproduction both

sexual and asexual


size?

nanometer About 1 µm size 5–100 µm

What drugs can treat

infections?

Enzyme

inhibitors

Anti-

peptidoglycans

Drugs that affect organelles only

protists have, or enzymes only

protists use (pyrimethamine) to

make folic acid which our cells

get through diet

Answer Key for “Take Two and Call Me in the Morning” - Case Study ... http://www.sciencecases.org/lock/cell_structure_key.asp

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Table 2: Mechanism of Action of Antibiotics (complete in class)

Drug Name Mechanism Why It Does Not Harm

Human Cells

Prokaryotes Amoxicillin,

penicillin, and

other betalactams

Blocks enzyme that normally

creates links in peptidoglycans

No cell peptidoglycan cell

walls

Streptomycin Blocks prokaryotic ribosomes Different ribosomal proteins

Ciprofloxin

hydrochloride

Blocks bacterial gyrase enzyme

needed to counteract excessive

twisting of DNA that occurs

when circles of DNA areunwound to be copied into

DNA or RNA

No circular DNA, DNA is

linear.

Eukaryotes Pyrimethamineand sulfonamides

Interfere with enzymes used tomake the folic acid needed to

make thymine and uracil

nucleotides; without

nucleotides, the cells have

trouble making RNA or DNA.

Human cells are affected, sodoctors often co-prescribe

folinic acid that can be

converted to folic acid in

human cells without relying

on these enzymes

Antifungal

polyenes

Combine with ergosterol

(component of fungal and

some bacterial membranes) &

disrupt and break membranes.

Ergosterol not found in

human cells; we use

cholesterol

Inhibitors of beta

glucan

Interfere with enzymes used to

create the beta glucan found in

fungal cell walls

No beta glucan cell walls

Viruses Tamiflu Blocks neuraminidase enzyme

made by all influenza A strains

(cause the “flu” and avian flu);viruses are unable to remove

sticky sialic acid can’t escape

No neuraminidase enzyme


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Table 3: Similarities between Mitochondria and Bacteria (complete in class)

ORGANISM Circular

DNA

Size

(µm)

rDNA

sequence

Phospholipids

similarityprokaryote or

eukaryote

Ribosomes

similarityprokaryote

or eukaryote

Divide to

makeclones

Bacteria yes 1 similar yes yes yes

Mitochondria yes 1 similar yes yes yes

Clicker Questions

To view individual slides and refer to individual images, hover over or click the appropriate CQ# at

the start of the question.

CQ1: “That’s great,” Becky said. “My Mom sent me 3 different antibiotics to kill bacteria.” Given the

description of Ellie’s test results, which antibiotic will definitely NOT work:

A: Amoxicillin, Penicillin, and other β-lactams—Blocks the enzyme that normally creates links in

peptidoglycan molecules.

B: Streptomycin—Blocks prokaryotic ribosomes.

C: Ciprofloxacin hydrochloride (Cipro)—Blocks bacterial DNA gyrase enzyme needed tocounteract excessive twisting of DNA that occurs when circles of DNA are unwound to be copied

into DNA or RNA.

The correct answer is: A

CQ2: “Wait a minute!” Ann said. “The doctor said the blobs in Ellie’s blood were 1/10th the size of hercells. Could they be Coxiella?”

A: Yes

B: No

The correct answer is: B

CQ3: “Well,” Becky admitted, “there should be differences between Ellie’s cells and the little blobs

they saw. Otherwise, it might mean one of my other suspects is the cause. These are some of the

structures normally found in all cells.”

“No,” Ann answered, “one isn’t.”

Which structure is NOT found in all cells?

A: Cytoplasm

B: DNA

C: Outer phospholipid membraneD: Ribosomes

E: Membrane-bound organelles

The correct answer is: E

CQ4: Becky’s Anti-Eukaryotic Medicines:

Pyrimethamine, Sulfonamides: Interfere with enzymes used to make the folic acid needed to

make thymine and uracil nucleotides.Polyenes combine with a component of fungal and some bacterial membranes, disrupt and

break them.

One of these drugs specifically affects one of the two eukaryotic suspects. Which test of Ellie’s bloodwould help you tell which eukaryotic suspect she was infected with?


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A: Presence of DNA.

B: Presence of β-glucan-containing cell walls.

C: Presence of cellulose.

D: Presence of peptidoglycan cell walls.


CQ5: Match the description with the suspect. Use your responses to Table 1 to identify the row belowthat best describes West Nile Virus [see slide].

The correct answer is: D

CQ6: Foreign DNA sequence isolated from Ellie: ACGTGGTCGTT.

Which sequence is the best match with this foreign DNA?

A: Ellie’s nucleus ATGGTCTCAATG

B: Ellie’s mitochondria TTGGTCCGTCAG

C: Coxiella bacteria TTGGTCGGTCAG

D: Toxoplasma nucleus AACGTGGTAGTT

E: Cryptococcus nucleus ATGGTGGCAATG


CQ7: Which letter best defines the place mitochondria would take next to their closest relatives on this

family tree of living organisms [see slide]?


Pre- and Post-Case Questions

The following pre- and post-case questions are available in a PowerPoint presentation for instructors

who wish to use them in class.

PQ1: To distinguish between prokaryotes and eukaryotes, we need to consider:

A: The specific types of lipids present in the outer plasma membrane.

B: The type of molecule used as its genetic information.C: Whether the genetic information is enclosed in a protective layer of phospholipid membrane

bilayer.

D: Whether the organism is harmful to the cell.

The correct answer is: C

Rationale: This is a factual question. It expects students to know the differences in structure between

prokaryotes and eukaryotes. The correct answer is whether or not the genetic information is enclosed

in a protective layer of phospholipids bilayer. Both prokaryotes and eukaryotes contain phospholipids

in their membrane bilayers, and both use DNA as their genetic information. Measures ability to

differentiate between prokaryotes and eukaryotes using factors such as presence of uniquestructures. The mean pre-test score was 46% and the post-test score was 79%.

PQ2: In which way are cells and viruses different in how they reproduce? Viruses:

A: Only reproduce sexually, by fusing with another virus, cells can reproduce both sexually and

asexually.

B: Make a duplicate copy of their genetic material before they can divide in two, cells can wait

until after they have divided to copy genes.C: Only reproduce after entering a host cell, cells can reproduce alone.

D: Invade a cell after they have reproduced, cells can invade other cells without reproducing

first.


Rationale: This is a factual question. It expects students to know basic viral biology. The correct

answer is C because viruses can only reproduce after entering a host cells, some cells can only

reproduce inside other cells, but most can reproduce on their own. A is incorrect because viruses do

not undergo sexual reproduction. B is incorrect because both cells and viruses must duplicate their

genetic information before producing more of themselves. D is incorrect because viruses invade a


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cell and then reproduce before going on to invade more cells, and not all cells can invade other cells.

The mean pre-test score was 76% and the mean post-test score was 96%.

PQ3: An organism has the following: proteins, DNA, ribosomes, plasma membrane, and mitochondria

(among other structures.) Select the most inclusive answer for what type of organism it could be.

A: A prokaryotic cell.

B: A eukaryotic cell, but not a plant cell.

C: An animal cell, but not a protist cell.

D: Any eukaryotic cell.

E: A virus or a prokaryotic cell.


Rationale: This is an application question. It expects students to apply their understanding of cell

structure to determine what the cell type could be. The correct answer is D – any eukaryotic cell—

because the organism has mitochondria, a membrane bound organelle not found in prokaryotes (A)or viruses (E) but is found in plants (B) and protists (C). Measures ability to differentiate between

prokaryotes, eukaryotes, and viruses using factors such as size or the presence of unique structures.

The mean pre-test score was 22% and the mean post-test score was 36%.

PQ4: You have an infection caused by a prokaryotic pathogen. Which of the following would make a

good choice for killing off the prokaryote without harming your cells?

A: A drug that prevents duplication of long strands of DNA.B: A drug that tangles up DNA circles and prevents their duplication.

C: A filtration system that rids the body of organisms under 0.5µm in size.

D: A drug that prevents phospholipids from being deposited into new cell membranes.

E: A drug that prevents mitochondria from functioning.


Rationale: This is an application question. Students need to recognize that prokaryotes have circular

DNA whereas eukaryotes do not, and that the safe drug would be the one that only affects

prokaryotes. The correct answer is D, any eukaryotic cell because the organism has mitochondria, a

membrane bound organelle not found in prokaryotes (A) or viruses (E) but is found in plants (B) andprotists (C). Measures ability to differentiate between prokaryotes, eukaryotes, and viruses using

factors such as size or the presence of unique structures. The mean pre-test score was 22% and the

mean post-test score was 36%. Measures ability to apply knowledge of the differences between

viruses, prokaryotes and eukaryotes to understand why various treatment methods work to

specifically kill one class of organisms while remaining harmless to the human cells or other

organisms. The mean pre-test score was 17% and the post-test score was 53%.

PQ5: Which of the following would you not expect to find in a Toxoplasma cell?

A: Rough endoplasmic reticulum

B: Lysosomes

C: Plastids

D: Mitochondria

E: Golgi


Rationale: This is an application question. Students need to understand cell components of the

organism.

Transfer Question

TQ1: The following photomicrograph shows several human cells stained as large light purple

structures with purple nuclei (stars) infected with a pathogenic organism shown as small dark purple

circles (arrowhead). These pathogens are most likely a(n):


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A: Eukaryote

B: Prokaryote

C: Virus


Image credit: Diff-Quik Stain of Ehrlichia chaffeensis in DH82 cells, 1000X. Image courtesy of

Centers for Disease Control and Prevention, http://www.cdc.gov/ncidod/dvrd/ehrlichia/Laboratory

/Laboratory.htm.

Multiple-Choice Pre-Class Preparation Questions Key

1: a, i ; b, ii; c, iii

2 a;

3 a, prokaryotic cell; b, eukaryotic cell; c, eukaryotic cell; d, eukaryotic cell; e, eukaryotic cell; f,

prokaryotic cell; g, eukaryotic cell; h, both; i, both; j, both; k, both; l, eukaryotic cell; m,

prokaryotic cell; n, eukaryotic cell; o, prokaryotic cell

4: a, i; b: ii, c, iii; d, iv; e, v

5: a, i; b: ii, c, iii; d, iv; e, v

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