Characteristics of Life and Viruses

Lesson 3
Viruses

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I can describe the general structure of a virus.

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Poll

I can compare and contrast the lytic cycle, the lysogenic cycle, and retroviral replication?

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Poll

I can explain the relationship between a prion's structure, replication, and action to cause a disease.

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Viruses and Prions
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Viruses

• A virus is a nonliving strand of genetic material

within a protein coat.

• Scientist do not consider viruses alive because:

• No organelles to take in nutrients or use energy

• Cannot make proteins

• Cannot move

• Cannot replicate on their own

Multiple Choice

Is a virus considered living or non-living?

• Living

• Non-Living

• Neither

Multiple Choice

Reasons that viruses are considered to be nonliving is because

• They are not cellular

• They cannot reproduce on their own

• They cannot make proteins

• all of the above

Viruses and Prions
Copyright © McGraw-Hill Education

Viruses

Virus size

• Some of the smallest disease-causing structures.

• Range from 5-300 nanometers

Virus origin

• Most likely came from parts of cells

• Viral DNA similar to cellular genes

Viruses and Prions
Copyright © McGraw-Hill Education

Viruses

Virus structure

• The outside layer of all viruses is made of proteins

and called the capsid.

• Inside the capsid is the genetic material, either

DNA or RNA (never both).

Multiple Choice

What is the basic structure of a virus?

• DNA or RNA surrounded by a protein coat.

• a capsid surrounded by a protein coat.

• a tail sheath surrounded by tail

• a tiny cell surrounded by a cell.

Multiple Choice

A capsid is

• a structure that directly causes cell lysis

• the type of virus that attacks bacteria

• the genetic material of a virus

• the protein coat of a virus

Viruses and Prions
Copyright © McGraw-Hill Education

Viral Infection

• In order to replicate, a virus must enter a host cell.

• The virus attaches to the host cell using specific

receptors on the plasma membrane.

• After the genetic material is inside the host cell, the

virus uses the cell to replicate by either the lytic or
lysogenic cycle.

Multiple Choice

What do all viruses need to reproduce?

• They need host genetic material

• They need a host cell

• They need bacteria

• They need insulin

Viruses and Prions
Copyright © McGraw-Hill Education

Viral Infection
Lytic Cycle
• In the lytic cycle, the

host cell makes many
copies of the viral RNA
or DNA.

• The viral genes instruct

the host cells to make
more viral protein
capsids and enzymes.

• Viruses leave the cell

by exocytosis or by
causing the cell to
burst.

Viruses and Prions
Copyright © McGraw-Hill Education

Viral Infection
Lysogenic Cycle
• In the lysogenic

cycle, viral DNA
integrates into a
chromosome in a
host cell.

• Viral genes may

remain dormant for
some time.

• Activated viral genes

result in the lytic
cycle.

Multiple Choice

Which occurs during the lysogenic cycle of a virus infection?

• Viral genes instruct the host cell to make more viral protein capsids and enzymes needed for viral replication.

• The virus produces active, immediate infections.

• The virus takes over the cell, makes copies of itself, and usually kills the host cell.

• The viral genes become a part of the host cell DNA, so the cell continually makes more copies of the virus.

Multiple Choice

When a virus invades a living cell, its _______
takes over the cell's functions.

• outer coat

• genetic material

• core

• cytoplasm

Multiple Choice

Identify the properties of plasma.

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Viruses and Prions
Copyright © McGraw-Hill Education

Retroviruses
• Retroviruses have RNA instead

of DNA for their genetic
material.

• Have a lipid envelope

surrounding the capsid obtained
from the plasma membrane of a
host cell

• In the host cytoplasm, reverse

transcriptase synthesizes DNA
from RNA template, DNA
integrates into host
chromosome until activated

Multiple Choice

Discuss how temperature affects particle arrangement.

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Viruses and Prions
Copyright © McGraw-Hill Education

Prions
• A protein that can cause

infection or disease is
called a proteinaceous
infectious particle, or prion.

• Prions normally exist in

cells, but their function is
poorly understood.
• Normally spiral shaped
• Mutations cause

incorrect folding,
mutated prions cause
diseases

Multiple Choice

Interpret a heating curve to identify how phase changes are related to energy.

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Multiple Choice

What do viruses have in common with living cells? They both

• store genetic information

• have chloroplasts

• use glucose for cellular respiration

• have endoplasmic reticula

Multiple Choice

Describe what happens to a gas that is heated.

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Viruses and Prions
Copyright © McGraw-Hill Education

Prions

Prion infection

• Prions can cause normal proteins to mutate.

• Cause nerve cells to burst, creating space in the

brain

• Prions may be communicated between species, but

scientists are not unified on this thought.

Multiple Choice

The genetic material of a virus is in the form of

• RNA

• DNA

• either RNA or DNA

Multiple Choice

Viruses are...

• prokaryotic

• eukaryotic

• non-living

• endospores

Poll

I can describe the general structure of a virus.

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  Never Heard of it

• 1

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  Need some tutoring

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Poll

I can compare and contrast the lytic cycle, the lysogenic cycle, and retroviral replication?

• 0

  Clueless

  Never Heard of it

• 1

  Basic Knowledge

  Need some tutoring

• 2

  Advanced Knowledge

  Can apply it

• 3

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Poll

I can explain the relationship between a prion's structure, replication, and action to cause a disease.

• 0

  Clueless

  Never Heard of it

• 1

  Basic Knowledge

  Need some tutoring

• 2

  Advanced Knowledge

  Can apply it

• 3

  Expert

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