Name: ___________________________________ Date: ________ Period: ___
Student Exploration: Virus Lytic Cycle
Vocabulary: bacteriophage, capsid, host cell, lyse, lytic cycle, virus, lysogenic cycle
Prior Knowledge Questions (Do these BEFORE using the Gizmo.)
A computer virus is a program that can copy itself and infect a computer without the permission of the owner. How
do you think a computer virus compares to a real virus?
[ A computer virus compares to a real virus, as real viruses enter the body and start replicating itself off protein cells
and infect the body without permission of the owners body. ]
Have you ever been infected with a virus, such as the cold virus or flu virus? If so, how did the virus affect you?
[ Yes, COVID-19, and I had physical and neurological side effects. ]
Gizmo Warm-up
A virus is a microscopic particle that can infect a cell. Viruses are primarily composed of a protein coat, called a cap
sid, and nucleic acid. In the Virus Lytic Cycle Gizmo™, you will learn how a virus infects a cell and uses the cell to
produce more viruses.
Viruses are extremely small. A typical virus is about 100 times smaller than a single cell, such as a bacterium. Label
the virus and a bacterial cell in the image at right.
Bacteriophages are viruses that infect bacteria. Based on the diagram at left, identify the head, tail, tail fibers, and the
strand of nucleic acid in the image at right.
Activity A:
Lytic cycle
Get the Gizmo ready:
If necessary, click Reset ().
Introduction: Unlike living organisms, viruses cannot reproduce on their own. Instead, viruses infect host cells, takin
g over the cell’s machinery to produce more viruses. This process is called the lytic cycle.
Question: What are the steps of the lytic cycle?
Observe: Use the navigation arrows on the DESCRIPTION tab to read about the stages of the lytic cycle. Using your
own words, summarize each step of the cycle.
Step
Summary
1
The Virus attaches onto the cell, and prepares to enter.
↓
2
The virus releases it’s nucleic acid within the cell, and it heards towards the cell.
↓
3
The nucleic acid has now taken over the cell, and produced new proteins for the virus to reproduce.
↓
4
The proteins turned into new viruses that are ready to leave the cell.
↓
5
The cell is destroyed by the viruses, and the 4 viruses have been released to go infect more cells.
(Activity A (continued from previous page)
Analyze: The yellow ring inside the bacterial cell represents the bacterial DNA. Why does this structure disappear b
y step 3 of the lytic cycle?
[ The bacterial DNA destroys, as the virus has completely destroyed the bacterial DNA and turned it into a reproduct
ion cell for the viruses. ]
Describe: How does a virus destroy the host cell’s DNA?
[ With the nucleic acid, it destroys the DNA.
]
Describe: How are new viruses reproduced?
[ Through protein cells of the Bacteria. ]
Think and discuss: Why can’t a virus reproduce on its own?
[ A virus can not make proteins on it’s own. ]
Justify: To lyse is to burst apart or explode. Why do you think a virus’s reproduction cycle is called the “lytic cycle”
?
[ As the cells explode all over the body while exploding cells within the body as it reproducts. ]
Activity B:
Spread of infection
Get the Gizmo ready:
If necessary, click Reset.
Question: How does a viral infection spread?
Predict: Suppose that a virus infects a small population of bacteria. Predict how the numbers of viruses, infected cell
s, and uninfected cells will change as the infection progresses. On the blanks below, write increase, decrease, or stay
the same.
Viruses: [ Go up.
]
Infected cells: [ Go down.
Uninfected cells: [ Go down
]
]
Observe: Click Play (), and watch the simulation. Describe what you see.
[ The Viruses count shoots way up and the infected cells stay down and the uninfected cell count shoots way down.
]
Test: Click Reset, and Select the BAR CHART tab. Turn on Show numerical values. Click Play, and watch each bar
as the simulation runs. What do you notice, and how does this compare to your predictions?
[ The chart is constantly up and down and all over the place, never reaching a steady count. ]
Record data: Select the TABLE tab, and use the data to complete the second column of the table below. To complete
each cell in the third column, subtract the previous time value from the current time value. For example, if it took 80
minutes to reach 40 cells and 100 minutes to reach 30 cells, then the time difference is 20 minutes.
Number of
healthy cells
Time (minutes)
Amount of time to decrease population by 10
50
0 minutes
-40
69
69
30
86
17
20
112
18
10
128
16
(Activity B continued on next page)
Activity B (continued from previous page)
Analyze: What trend do you see in the third column of your data table?
[ As we get toward less healthy cells, it starts taking and average of 10 minutes.
]
Explain: How would you explain this trend?
[ It has and average of 16-18 minutes per 10 healthy cells destroyed.
]
Interpret: Select the GRAPH tab. Run the Gizmo again, and observe what happens in the SIMULATION pane when
the graph shows a decrease in the viruses’ population size.
Why does the number of viruses sometimes increase and sometimes decrease?
[ THe number goes all around, because one virus has to die for 4 more to reproduce, so it’s gone but not for very lon
g as 4 more will come from that one cell dying. ]
Sometimes when a virus enters a cell, it becomes dormant for a while.These viruses follow a cycle called Lysogenic.
Why might this make it difficult for a doctor to diagnose a viral infection?
[ It will make it hard, as he can not see what the virus is doing within the body, as it is lying dormant.
]
Extend your thinking:
Clinical and Pathologic Features of COVID-19 (SARS-CoV-2)
“As with SARS-CoV, MERS-CoV, and influenza viruses, the primary route of disease transmission in humans is via
respiratory droplets and direct contact. After a mean incubation period of 4 days, patients develop symptoms includi
ng fever, non-productive cough, sore throat, shortness of breath, headache, myalgias, and fatigue.”
Highlight evidence in the statement that supports Covid-19 as a “lytic cycle” virus.
Continue to the next page.
Study the diagram.
These droplets can land in the mouths or noses of people who are nearby or possibly be inhaled into the lungs.
11. Once the virus is inhaled, how does it enter the lung cells?
[ Membrane fusion or endocytosis. ]
12. What organelle from the host cell is used to translate the viral genome?
[ Ribosome. ]
13. Is the virus’s genome DNA or RNA based?
[ RNA ]
14. What are two other host organelles seen above that are needed by the virus to be able to contain and encapsulate
the virus’s proteins before being released?
[ Polymerase and nucleocapsid. ]