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3/31/2019 Chapter-12-13_Homework

Due: 1:59pm on Monday, January 28, 2019
You will receive no credit for items you complete after the assignment is due. Grading Policy

BioFlix Activity: Mitosis -- The Cell Cycle

Can you label the phases of the cell cycle? To review a crucial phase of the cell cycle, watch this BioFlix animation: Mitosis.

Part A - The cell cycle

Drag the pink labels onto the pink targets to identify the two main phases of the cell cycle.
Then drag the blue labels onto the blue targets to identify the key stages that occur during those phases.

Hint 1. Phases of the Cycle

The "G" in G1 and G2 stand for "gap". This is where lots of molecules are produced in preparation for a major event. "S" stands for synthesis,
especially of DNA and replicative machinery. "Cyto" means "cell, and "kinesis" refers to movement or separation.


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Group 1 Interphase
Group 2

G1 1 G2 phase
Group 1

Mitotic (M ) 2
Group phase

Group 1



BioFlix Activity: Meiosis -- Chromosome Structure

Can you identify the structures of a chromosome?

To review chromosome structure, watch this BioFlix animation: Meiosis.

Part A - Homologous chromosomes

Drag the labels onto the diagram to identify the various chromosome structures.

Hint 1. Homologous Chromosomes

"Homologous" typically means "similar, but not identical". As such, homologous chromosomes are similar to one another in that they contain the
same types of genetic information, but they are also not identical; in a pair of homologous chromosomes, one comes from the mother and one from 1/7
3/31/2019 Chapter-12-13_Homework
the father.


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Pair of homologous


Sister chromatids


Video Tutor: The Lytic Cycle of Viral Replication

Watch the Video Tutor on The Lytic Cycle of Viral Replication and then answer the questions below.

Part A
Contact between a phage and its bacterial host occurs by _____.

Hint 1. Motility
Phages are nonmotile.

3/31/2019 Chapter-12-13_Homework

using phage tail fibers

using jet-style propulsion

using flagella

a random collision

Phages are incapable of movement, and thus are completely reliant on randomly colliding with a bacterium before attachment.

Part B
What portion of bacteriophage T4 enters E. coli?

Hint 1. Injection
Remember that the action of the T4 tail is similar to that of a hypodermic needle.


No portion of phage T4 actually enters the bacterial cell.

The entire phage enters into the bacterial cell.

Only the T4 genome enters the bacterial cell.

Only the tail fibers penetrate into the interior of the bacterial cell.

The capsid remains on the surface of the cell, and the genome is the only portion to enter the cell.

Part C
Once entry into the bacterial cell has been achieved, the next step in a lytic replication cycle is _____.

Hint 1. Replication

Viral components must be produced.






Once the phage has entered a cell, viral protein synthesis begins.

Part D
During a lytic replication cycle, what action does a phage take to ensure that its host bacterium does NOT continue synthesizing cellular molecules? 3/7
3/31/2019 Chapter-12-13_Homework

Hint 1. DNA

To synthesize bacterial molecules, a bacterium must have access to its own DNA.


The host DNA is released from the cell.

The phage integrates its DNA into the host cell DNA.

Phage enzymes degrade the bacterial DNA.

A phage traps the host DNA in an endosome.

By degrading the host DNA, the phage ensures that only phage proteins are synthesized.

Part E
In a lytic cycle of replication, release of phages involves _____.

Hint 1. Penetration

Phages are not able pass through the cell wall of a bacterium without damaging the wall.


the bacterial cell bursting open

exocytosis of phages across the cell wall

contact with another uninfected bacterium

keeping the host cell alive

The bacterial cell undergoes lysis, meaning that it is destroyed. Phages are then released.

Part F
A major difference between the lytic and lysogenic cycles of phage replication is that during the lysogenic phase _____.

Hint 1. Replication
The phage replicates at the same rate as the bacterium.


the host DNA is degraded

the bacterial cell is broken open, destroying the cell

attachment of the phage involves a random collision

the phage genome inserts itself into the host genome 4/7
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The phage DNA is integrated into the host DNA without destroying the cell.

Part G
What factor may induce a prophage to enter the lytic cycle?

Hint 1. Inductive Agents

Generally, the same agents that damage DNA molecules also lead to induction.


replication of the host bacterium

Infection by an additional phage

burst time

UV light

Ultraviolet radiation is known to cause the induction of prophage into the lytic cycle.

Part H
During the lysogenic cycle, it is possible for integrated phage genes to change the characteristics of the host cell. This is known as _____.

Hint 1. Change
Phage genes can lead to the production of new proteins, such as toxins.





lysogenic conversion

Lysogenic conversion involves phenotypic changes to the bacterium due to new genes from the integration of the phage genome.

Microbiology Animation: Prions: Characteristics 5/7
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Click here to complete this activity.

Then answer the questions.

Part A
The normal function of the PrP protein in mammals is believed to be:


assisting in normal synaptic development and function.

assisting in normal membrane development and function.

assisting proteins in forming beta-pleated sheets.

assisting proteins in forming alpha-helices.


Part B
How do normal prion proteins (PrP) differ from the infectious prion proteins?

Normal PrP lack nucleic acid; infectious PrP have nucleic acid.

Normal PrP are found in all mammals; infectious PrP are found in only cows.

Normal PrP are found on mammals; infectious PrP are found on reptiles.

Normal PrP have alpha-helices; infectious PrP have beta-pleated sheets.


Part C
How does the number of infectious prions increase?

Prions reproduce by binary fission.

Prions form multimers which can then form more single copies of the prion protein.

Prions reproduce by mitosis.

Prions transform normal proteins into the misfolded beta-pleated sheet configuration; therefore, prions multiply by conversion.


Part D
Why are the beta-pleated multimers of PrP potentially pathogenic?

3/31/2019 Chapter-12-13_Homework

They are found on the surface of immune cells, resulting in damage to the immune system.

They repress the immune system.

The multimers are more stable and resistant to protease.

They are not detected by other organisms.


Score Summary:
Your score on this assignment is 100%.
You received 4 out of a possible total of 4 points. 7/7