Introduction to Viruses Flashcards
1
Q
__________ include viruses that are difficult to detect or study.
A
Elusive virus
2
Q
UNDER THE SEARCH FOR THE ELUSIVE VIRUS
- He postulated/suggested that rabies was caused by a virus (1884).
A
Louis Pasteur
3
Q
UNDER THE SEARCH FOR THE ELUSIVE VIRUS
- They showed a disease in tobacco was caused by a virus (1890s).
A
Ivanovski and Beijerinck
Note:
- Dmitri Ivanovski and Martinus Beijerinck demonstrated that a disease affecting tobacco plants (later known as tobacco mosaic disease) was caused by an agent that could pass through filters fine enough to block bacteria.
4
Q
In 1950s, virology was multifaceted scientific discipline, combining biology, chemistry, and medicine to study viruses.
- _________ were defined as noncellular particles with a definite size, shape, and chemical composition.
A
Viruses
5
Q
There is ___________ on how and when viruses originated.
A
no universal agreement
ADD:
- Some theories suggest they evolved from cellular organisms, while others propose they emerged from genetic elements that escaped from cells.
6
Q
Viruses are considered the most _________ microbes on Earth.
A
abundant
ADD:
- They exist in every environment, including extreme conditions, and outnumber all other forms of life combined.
7
Q
Viruses have influenced the evolution of these 3. What are these?
A
Bacteria, Archaea, and Eukarya
ADD:
- This has contributed to genetic diversity and the development of new traits in different species.
8
Q
Viruses cannot reproduce independently and must infect a host cell to replicate.
Hence, they are called _______________.
A
Obligate intracellular parasites
9
Q
FAMILIARIZE ONLY!
“PROPERTIES OF VIRUSES”
A
- Obligate intracellular parasites of bacteria, protozoa, fungi, algae, plants, and animals
- Ultramicroscopic size, ranging from 20 nm up to 450 nm (diameter)
- Not cellular in nature; structure is very compact and economical
- Do not independently fulfill the characteristics of life
- Inactive macromolecules outside the host cell and active only inside host cells.
- Basic structure consists of protein shell (capsid) surrounding nucleic acid core.
- Nucleic acid can be either DNA or RNA but not both.
- Nucleic acid can be double-stranded DNA, single-stranded DNA, single-stranded RNA, or double-stranded RNA.
- Molecules on virus surface impart high specificity for attachment to host cell
- Multiply by taking control of host cell’s genetic material and regulating the synthesis and assembly of new viruses
- Lack enzymes for most metabolic processes
- Lack machinery for synthesizing proteins
10
Q
Viruses are extremely small, with most measuring ________ in diameter.
A
less than 0.2 (μm)
Note:
- Due to their size, they cannot be seen with a light microscope and require an electron microscope for detailed visualization.
11
Q
FAMILIARIZE ONLY!
“Viral Structure”
A
No Resemblance to Cells
- Viruses are not cellular and lack organelles like ribosomes, mitochondria, and a nucleus.
- They cannot synthesize proteins on their own, relying entirely on a host cell for replication.
Minimalist Design for Infection
Viruses contain only the essential components needed to invade and control a host cell:
- Genetic material (either DNA or RNA, but never both)
- Capsid (a protein coat that protects the genetic material)
- Some viruses also have an envelope (a lipid membrane derived from the host cell) that aids in infection.
12
Q
GENERAL STRUCTURE OF VIRUSES:
- All viruses have a ________, this is their protein coat that enclose and protect their nucleic acid (DNA or RNA).
A
capsid
13
Q
GENERAL STRUCTURE OF VIRUSES:
- The capsid + nucleic acid together form the _________.
A
nucleocapsid
14
Q
GENERAL STRUCTURE OF VIRUSES:
- Some viruses have an __________, an external lipid membrane derived from the host cell.
A
envelope
15
Q
GENERAL STRUCTURE OF VIRUSES:
- Viruses without an envelope are called ___________.
A
naked viruses
16
Q
GENERAL STRUCTURE OF VIRUSES:
- The capsid is made up of identical (repeating) protein subunits called ___________, which self-assemble into specific shapes.
A
capsomers
17
Q
What are the 2 Structural Capsid Types?
A
- Helical
- Icosahedral
18
Q
UNDER GENERAL STRUCTURE OF VIRUSES
- It is a continuous helix of capsomers forming a cylindrical nucleocapsid.
A
Helical or Helical capsid
19
Q
UNDER GENERAL STRUCTURE OF VIRUSES
- Has 20 triangular faces and 12 corners, forming a symmetrical geometric shape.
A
Icosahedral or Icosahedral Capsid
20
Q
UNDER GENERAL STRUCTURE OF VIRUSES
- Mostly animal viruses
- Acquired when the virus leaves the host cell
- Exposed proteins on the outside of the envelope, called spikes, are essential for attachment of the virus to the host cell.
A
Viral envelope
21
Q
The ff are the functions of _____________.
- Protects the nucleic acid when the virus is outside of the host cell.
- Helps the virus bind to a cell surface and assists the penetration of the viral DNA or RNA into a suitable host cell.
A
Capsid/Envelope
22
Q
Under GENERAL STRUCTURE OF VIRUSES – Complex Viruses
- Do not have a typical capsid structure.
- Instead, they are covered by a dense layer of lipoproteins
A
Poxviruses (Atypical Viruses)
23
Q
Under GENERAL STRUCTURE OF VIRUSES – Complex Viruses
- Have a polyhedral (icosahedral) nucleocapsid.
- Possess a helical tail and attachment fibers used to bind and inject genetic material into bacterial cells.
A
Bacteriophages (Viruses that Infect Bacteria)
24
Q
FAMILIARIZE ONLY!
“Viral Nucleic Acids”
A
Viral Genome
- A virus contains either DNA or RNA, never both.
- The genome carries essential genes for infecting a host cell and taking control of its machinery to produce new viruses.
- The number of genes varies significantly among viruses, ranging from a few to hundreds.
DNA Viruses
- Usually double-stranded (dsDNA) but can also be single-stranded (ssDNA).
- The DNA can be circular or linear.
RNA Viruses
- Usually single-stranded (ssRNA) but can also be double-stranded (dsRNA).
- Some RNA viruses have segmented genomes, meaning their genetic material is divided into separate RNA pieces.
Types of ssRNA viruses:
- Positive-sense RNA (+ssRNA): Can be directly translated into proteins.
- Negative-sense RNA (−ssRNA): Must be converted into a readable form (mRNA) before translation.
25
WHAT IS THIS?
* ssRNA genomes ready for **immediate translation** are called __________.
positive-sense RNA
26
WHAT IS THIS?
* ssRNA genomes that must be **converted into proper form** are called __________.
negative-sense RNA
27
Some viruses **carry their own enzymes** to assist in replication because they lack the cellular machinery needed for nucleic acid synthesis.
What are the (3) **Viral Enzymes** or **Pre-formed enzymes**?
* Polymerases
* Replicases
* Reverse Transcriptase
NOTE:
* These enzymes help viruses replicate inside host cells by facilitating nucleic acid synthesis and genome replication.
28
What enzyme is this?
* Enzymes that **synthesize DNA or RNA** based on the virus's genetic material.
Polymerases
29
What enzyme is this?
* Enzymes that **copy RNA** to make more viral RNA.
Replicases
30
What enzyme is this?
* An enzyme that **synthesizes DNA from an RNA template.**
* Essential for **AIDS virus** to integrate their genetic material into the host genome.
Reverse Transcriptase
31
Viruses are classified based on these **three**. What are these?
* **Structure** (capsid shape, presence of envelope)
* **Chemical composition** (type of nucleic acid: DNA or RNA)
* **Genetic makeup** (single-stranded vs. double-stranded, segmented vs. non-segmented)
32
In **Current Viral Taxonomy**, how many of the ff are currently recognized?
* (a)___ orders
* (b)___ families (end in **-viridae**)
* (c)___ genera (end in **-virus**)
Note: (There are *3* answers)
* (a) **3**
* (b) **63**
* (c) **263**
33
Under How Viruses Are Classified
* Family name ends in ________?
**-viridae**
Example: Herpesviridae
34
Under How Viruses Are Classified
* Genus name ends in _______?
**-virus**
Example: Simplexvirus
35
Under How Viruses Are Classified
* What species example is **HSV-I**?
*Herpes Simplex Virus I*
36
What are the **6 Phases in Animal Virus Multiplication Cycle**?
* **A**dsorption
* **P**enetration
* **U**ncoating
* **S**ynthesis
* **A**ssembly
* **R**elease
Remember the acronym ***APUSAR***
37
Under ANIMAL VIRUS MULTIPLICATION
* **Binding of virus** to specific molecules on the host cell.
**Adsorption**
Note:
* The virus attaches to its host cell by specific binding of its spikes to cell receptors.
38
Under ANIMAL VIRUS MULTIPLICATION
* Genome **enters** the host cell.
**Penetration**
Note:
* The virus is engulfed into a vesicle and its envelope.
39
Under ANIMAL VIRUS MULTIPLICATION
* The viral nucleic acid is **released from the capsid**.
**Uncoating**
Note:
* Freeing the viral RNA into the cell cytoplasm
40
Under ANIMAL VIRUS MULTIPLICATION
* Viral components are **produced**.
**Synthesis**
Note:
* Under the control of viral genes, the cell synthesizes the basic components of new viruses: RNA molecules, capsomers, spikes.
41
Under ANIMAL VIRUS MULTIPLICATION
* New viral particles are **constructed**.
**Assembly**
Note:
* Viral spike proteins are inserted into the cell membrane for the viral envelope; nucleocapsid is formed from RNA and capsomers.
42
Under ANIMAL VIRUS MULTIPLICATION
* Assembled viruses are released by **budding (exocytosis)** or **cell lysis**
**Release**
Note:
* Enveloped viruses bud off of the membrane, carrying away an envelope with the spikes. This complete virus or virion is ready to infect another cell.
43
WHAT IS THIS?
* A virus **randomly collides** with a **susceptible** host cell.
* It **binds specifically** to receptor sites on the **host cell membrane**.
* This interaction determines **which cells a virus can infect**.
Adsorption (Attachment)
44
What are the **3 Host Range** (Types of Cells a Virus Can Infect)?
* Narrow Host Range
* Moderate Host Range
* Broad Host Range
45
This is an example of **Narrow Host Range** where it infects only **specific cells** in a species.
* Infects ***only human liver cells***.
What is this?
Hepatitis B
46
This is an example of **Moderate Host Range** where it infects a **limited group** of species.
* Infects ***primate intestinal and nerve cells***.
What is this?
Poliovirus
47
This is an example of **Broad Host Range** where it infects **many** species.
* Infects ***various cells of many mammals***.
What is this?
Rabies virus
48
After adsorption, the virus **enters the host cell** through one of **two main methods**. What are these?
* **Endocytosis** (Engulfment)
* **Fusion** (Membrane Merging)
49
WHAT IS THIS?
* This is the process where an entire virus is **engulfed** and enclosed in a vacuole or vesicle.
Endocytosis
50
WHAT IS THIS?
* This is where an **envelope merges** directly with membrane resulting in nucleocapsid's entry into cytoplasm.
Fusion
51
Once new viruses are assembled, they **exit** the host cell in one of **two ways**. What are these?
**Budding** and **Lysis**
52
WHAT IS THIS?
* The **nucleocapsid binds** to the host **cell membrane**.
* The virus **gains an envelope** from the host's membrane as it is released.
* The **host cell remains alive longer**, releasing viruses gradually.
**Budding** (Exocytosis)
53
WHAT IS THIS?
* **Non-enveloped and complex viruses** cause the host cell to **burst** when it is full of newly assembled viruses.
* The **host cell dies immediately**.
**Lysis** (Cell Rupture)
54
WHAT IS THIS?
* These are **virus-induced damage** that alters host cells. These changes can be observed under a microscope and are often used to identify viral infections.
**Cytophathic effects (CPEs)**
55
FAMILIARIZE ONLY!
**"What are the Types of Cytopathic Effects"**
**Changes in Size and Shape**
* Infected cells may become *enlarged, shrunken, or deformed.*
**Cytoplasmic Inclusion Bodies**
* *Abnormal clusters of viral proteins* or nucleic acids appear in the cytoplasm.
**Inclusion Bodies**
* *Compact masses of viruses or damaged cell organelles* inside the cell.
**Syncytia Formation (Multinucleated Cells)**
* Infected cells *fuse together*, forming large multinucleated cells (syncytia).
**Cell Lysis (Destruction)**
* Viruses *rupture the host cell*, releasing viral particles.
**Alteration of Host DNA**
* Some viruses *insert their genetic material* into the host’s DNA, disrupting normal functions.
**Transformation into Cancerous Cells**
* Some viruses cause *uncontrolled cell growth*, leading to *tumors and cancer.*
56
Determine which **virus** is this based on the Response in Animal Cell.
* **Cell round up; inclusions appear in cytoplasm**.
Smallpox virus
57
Determine which **virus** is this based on the Response in Animal Cell.
* **Cells fuse to form multinucleated syncytia; nuclear inclusions**.
Herpes simplex
58
Determine which **virus** is this based on the Response in Animal Cell.
* **Clumping of cells; nuclear inclusions**.
Adenovirus
59
Determine which **virus** is this based on the Response in Animal Cell.
* **Cell lysis; no inclusions**.
Poliovirus
60
Determine which **virus** is this based on the Response in Animal Cell.
* **Cell enlargement; vacuoles and inclusions in cytoplasm**.
Reovirus
61
Determine which **virus** is this based on the Response in Animal Cell.
* **Cells round up; no inclusions**.
Influenza virus
62
Determine which **virus** is this based on the Response in Animal Cell.
* **No change in cell shape; cytoplasmic inclusions (Negri bodies)**.
Rabies virus
63
Determine which **virus** is this based on the Response in Animal Cell.
* **Syncytia form (multinucleate)**.
Measles virus
64
WHAT IS THIS?
* It occurs when a host cell harbors a virus **without immediate destruction**. These infections can last for **weeks, months, or even a lifetime**.
**Persistent Infection**
ADD: The **virus remains in the host cell** without causing immediate lysis.
65
WHAT IS THIS?
* This is when some viruses **reactivate periodically**, causing symptoms to return.
Chronic latent state
66
What example of Persistent Virus is this?
* Can **remain hidden in brain cells** for years.
Measles Virus
67
What example of Persistent Virus is this?
* Causes **cold sores** and **genital herpes**.
Herpes Simplex Virus
68
What example of Persistent Virus is this?
* Causes **chickenpox** in initial infection.
* Reactivates later in life as **shingles** (painful rash along nerve pathways)
Herpes zoster virus
69
WHAT IS THIS?
* Some animal viruses enter the host cell and **permanently alter its genetic material** resulting in cancer. This is called as what?
"**Transformation** of the cell"
**Characteristics of Transformed Cells:**
✔ Increased rate of growth (uncontrolled cell division).
✔ Chromosomal alterations (mutations in DNA).
✔ Indefinite cell division (loss of normal cell death, leading to tumors).
70
WHAT IS THIS?
* These are viruses that can **trigger cancer** by integrating their genes into the host's DNA.
**Oncoviruses**
Note:
* These are mammalian viruses capable of initiating tumors.
71
What type of Oncoviruses (Cancer-Causing Viruses) is this?
* Causes **cervical cancer**, as well as throat and anal cancers.
Papillomavirus
72
What type of Oncoviruses (Cancer-Causing Viruses) is this?
* Associated with **Burkitt's lymphoma** (a type of aggressive B-cell cancer.
Epstein-Barr Virus
73
WHAT IS THIS?
* These are viruses that infect bacteria (**bacterial viruses**). The most widely studied are **phages that infect Escherichia coli** (E. coli), which have **complex structures** and contain **DNA genomes.**
**Bacteriophages**
"Key Differences Between Bacteriophage & Animal Virus Multiplication:"
✔ Only the nucleic acid enters the bacterial cytoplasm (no need for uncoating).
✔ Lysis is the primary method of release, as phages break the bacterial cell open.
74
WHAT IS THIS?
* This is a process where the virus **infects, replicates, and destroys** the bacterial host.
* Release is a result of cell lysis induced by viral enzymes and accumulation of viruses.
Lytic cycle
75
Bacteriophages replicate inside bacteria through the **lytic cycle**, which results in the destruction of the host cell.
**What are the (6) Steps in Phage Replication**?
* **A**dsorption
* **P**enetration
* **R**eplication
* **A**ssembly
* **M**aturation
* **L**ysis & Release
Remember the acronym ***AP-RAM-L***
76
Under the Steps in Phage Replication
* **Binding of virus** to specific molecules on host cell.
Adsorption
77
Under the Steps in Phage Replication
* Genome **enters host** cell.
Penetration
78
Under the Steps in Phage Replication
* Viral components are **produced**.
Replication
79
Under the Steps in Phage Replication
* Viral components are **assembled**.
Assembly
80
Under the Steps in Phage Replication
* **Completion** of viral formation.
Maturation
81
Under the Steps in Phage Replication
* Virus **leave** the cell to infect other cells.
Lysis & Release
82
Comparison of the two in _________.
* Bacteriophage: **Precise attachment of special tail fibers to cell wall.**
* Animal Virus: **Attachment of capsid or envelope to cell surface receptors.**
Adsorption
83
Comparison of the two in _________.
* Bacteriophage: **Injection of nucleic acid through cell wall; no uncoating of nucleic acid**
* Animal Virus: **Whole virus is engulfed and uncoated, or virus surface fuses with cell membrane; nucleic acid is released.**
Penetration
84
Comparison of the two in _________.
**Bacteriophage:**
* Occurs in cytoplasm
* Cessation of host synthesis
* Viral DNA or RNA replicated
* Viral components synthesized
**Animal Virus:**
* Occurs in cytoplasm and nucleus
* Cessation of host synthesis
* Viral DNA or RNA replicated
* Viral components synthesized
Synthesis and Assembly
85
Comparison of the two in _________.
* Bacteriophage: **Lysogeny**
* Animal Virus: **Latency, chronic infection, cancer**
Viral Persistence
86
Comparison of the two in _________.
* Bacteriophage: **Cell lyses when viral enzymes weaken it.**
* Animal Virus: **Some cell lyse; enveloped viruses bud off host cell membrane**.
Release from Host Cell
87
Comparison of the two in _________.
* Bacteriophage: **Immediate**
* Animal Virus: **Immediate or delayed**
Cell Destruction
88
**Which of the following is a step found in animal virus
multiplication but not in bacteriophage replication?**
A. Adsorption
B. Penetration
C. Uncoating
D. Assembly
E. Release
C. Uncoating
89
This is also called as the **Silent Virus Infection**. What is this?
Lysogeny
90
FAMILIARIZE ONLY!
**"Lysogeny: The Silent Virus Infection - Explanation of Each Point"**
**Not all phages complete the lytic cycle**
*Some viruses do not immediately destroy the host cell. Instead of replicating and lysing the bacterial cell right away (as in the lytic cycle), they enter a dormant phase.
**Some DNA phages, called temperate phages, undergo adsorption and penetration but don’t replicate**
* Temperate phages attach (adsorption) and inject their genetic material (penetration) into the bacterial cell. However, instead of immediately taking over the host machinery to replicate, they stay inactive.
**The viral genome inserts into the bacterial genome and becomes an inactive prophage – the cell is not lysed**
* The viral DNA integrates into the bacterial chromosome and becomes part of its genetic material. In this inactive state, the virus is called a prophage. Since the virus does not produce new viral particles, the bacterial cell remains alive.
**Prophage is retained and copied during normal cell division, resulting in the transfer of temperate phage genome to all host cell progeny – lysogeny**
* Each time the bacterium divides, it copies its DNA—including the prophage—to its daughter cells. This means all new bacterial cells inherit the viral DNA, making the infection spread silently without destroying the host cells.
**Induction can occur, resulting in activation of lysogenic prophage followed by viral replication and cell lysis**
* Under certain conditions (e.g., UV light, chemicals, stress), the prophage "wakes up" and enters the lytic cycle. The virus then begins replicating, assembling new phages, and eventually bursts (lyses) the bacterial cell, releasing many new viruses.
**Why is Lysogeny Important, and How Does It Affect Disease Spread?**
✔ Hidden Infection: Since lysogeny does not kill the host right away, viruses can remain undetected for long periods, increasing survival chances.
✔ Silent Spreading: The viral genome spreads every time the bacterium divides, meaning hundreds or thousands of bacterial cells may carry the viral DNA without showing immediate effects.
✔ Increased Virulence (Toxin Production): Some bacterial infections only become dangerous when lysogenized by a phage carrying toxin genes.
91
WHAT IS THIS?
* Some DNA phages, called _________, undergo adsorption and penetration but don't replicate.
temperate phages
92
WHAT IS THIS?
* The viral genome inserts into bacterial Genome and becomes an inactive __________ — the cell is not lysed.
Prophage
93
WHAT IS THIS?
* Prophage is retained and copied during normal cell division resulting in the transfer of temperate phages genome to all host cell progeny — _________.
Lysogeny
94
WHAT IS THIS?
* _______ can occur resulting in activation of lysogenic prophage followed by viral replication and cell lysis.
Induction
95
WHAT IS THIS?
* ________ results in the spread of the virus without killing the host cell.
**Lysogeny**
Note:
* Unlike the **lytic cycle**, where viruses immediately replicate and destroy the host, lysogeny allows the virus to **remain hidden** inside the bacterial genome.
* Since the virus is **copied along with bacterial DNA** during cell division, it can spread silently without harming the host cells right away.
96
WHAT IS THIS?
* Some temperate phages carry extra genes that **change the behavior** of the bacteria they infect.
* What is the process where it can make harmless bacteria **dangerous** by making them produce **toxins or enzymes** that cause disease.
Lysogenic conversion
97
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**"Examples of Lysogenic Conversion in Pathogenic Bacteria"**
* **Corynebacterium diphtheriae** → Produces the diphtheria toxin, causing diphtheria (severe throat infection that can block airways).
* **Vibrio cholerae** → Produces the cholera toxin, leading to severe diarrhea and dehydration (cholera).
* **Clostridium botulinum** → Produces botulinum toxin, which causes botulism (paralysis and respiratory failure).
98
Viruses are **obligate intracellular parasites**, meaning they **cannot replicate** on their own. They **must infect a living host cell** to reproduce. Because of this, growing viruses in a laboratory setting requires _____________.
What is this?
Living cells
99
What are the (3) **Techniques in Cultivating and Identifying Animal Viruses**?
* Cell (Tissue) Cultures
* Bird Embryos (Embryonated Eggs)
* Live Animal Inoculation
100
WHAT IS THIS?
* The most **common** and **efficient** method for growing viruses.
* Cells are grown in **monolayers (sheets of cells) in petri dishes or flasks.**
* Viruses infect the cells, leading to **observable effects** (Cytophathic Effects, CPE).
* Used for Studying **viral replication, drug testing, and vaccine production**.
**Cell (Tissue) Cultures**
✅ **Advantages**:
✔ Allows **easy observation** of viral effects.
✔ **Less expensive** than live animals.
✔ Can be **scaled up** for vaccine production.
⚠ **Disadvantages:**
❌ Some viruses **do not grow well** in artificial cultures.
❌ Requires **strict sterile conditions.**
101
WHAT IS THIS?
* The egg is **incubated**, allowing the virus to multiply.
* The virus is **injected into the shell and into specific parts** of the egg (amniotic sac, yolk sac, etc).
* Used for **vaccine production** (like influenza vaccine)
**Bird Embryos** (Embryonated Eggs)
102
WHAT IS THIS?
* Used **when cell culture or eggs are not suitable**.
* Animals (mice, rabbits, monkeys, etc.) are **infected with the virus.**
* Observations are made for **disease symptoms, immune responses, and viral effects.**
**Live Animal Inoculation**
✅ **Advantages:**
✔ Useful for studying **host-virus interactions**.
✔ Necessary for studying **viruses that do not grow in culture**.
⚠ **Disadvantages:**
❌ Ethical concerns 😔
❌ Expensive and time-consuming.
103
FAMILIARIZE ONLY!
**"Medical Importance of Viruses"**
**1. Viruses are the most common cause of acute infections**
Acute infections happen suddenly and last for a short time.
Examples:
* Influenza (flu)
* Common cold (rhinovirus, coronavirus)
* Gastroenteritis (norovirus, rotavirus)
**2. Several billion viral infections per year**
**3. Some viruses have high mortality rates**
Some viruses cause severe disease and death, even though they are microscopic.
Examples of deadly viruses:
* Rabies (almost 100% fatal if untreated)
* Ebola (up to 90% fatality rate)
* HIV/AIDS (destroys the immune system)
**4. Possible connection of viruses to chronic afflictions of unknown cause**
Some chronic (long-term) diseases may be caused by viruses, even if the link is not fully understood.
104
WHAT IS THIS?
* These are **misfolded proteins** that cause disease.
* Unlike viruses, they contain **no DNA or RNA** – only protein.
* They induce normal proteins to misfold, leading to severe brain damage.
**PRIONS**
Why Are Prions Dangerous?
✅ **Extremely resistan**t to heat, radiation, and chemicals.
✅ Cannot be destroyed by **usual sterilization methods** (e.g., autoclaving).
✅ Cause **slow but fatal neurodegenerative diseases.**
105
Prion diseases are known as ___________ because they create **sponge-like holes in the brain.**
**Transmissible Spongiform Encephalopathies** (TSEs)
106
What are the (3) **Common Prion Diseases in Animals**?
* Scrapie
* Bovine Spongiform Encephalopathy (BSE)
* Chronic Wasting Disease (CWD)
107
What Prion Disease is this?
* Affects **sheep and goats**; causes itching, loss of coordination, and death.
Scrapie
108
What Prion Disease is this?
* Also called as **Mad Cow Disease**; leads to erratic behavior and motor dysfunction in **cattle.**
Bovine Spongiform Encephalopathy (BSE)
109
What Prion Disease is this?
* Found in **elk and deer**; results in weight loss, lethargy, and neurological symptoms.
Chronic Wasting Disease (CWD)
110
This is an Example of **Prion Disease in Humans** where it causes **memory loss, personality changes, muscle twitching, and eventual death.**
Creutzfeldt-Jakob Disease (CJD)
111
Aside from viruses and prions, there are **other infectious agents** that can cause diseases despite lacking a full viral structure.
There are **2**. What are these?
**Satellite viruses** and **viroids**
112
WHAT IS THIS?
* These are **incomplete viruses** that **depend on other viruses** for replication. They cannot reproduce on their own.
Satellite viruses
113
Satellite viruses have 2 examples. What are these?
* **Adeno-associated Virus** (AAV)
* **Delta Agent** (Hepatitis D Virus, HDV)
114
WHAT IS THIS?
* Can only replicate if the **adenovirus** is present. However, it **does not cause disease** and is being explored for **gene therapy.**
**Adeno-associated Virus** (AAV)
115
WHAT IS THIS?
* A small, **naked RNA virus** that **only becomes infectious in the presence of Hepatitis B Virus (HBV)**. It worsens liver disease when co-infection occurs.
**Delta Agent** (Hepatitis D Virus, HDV)
116
WHAT IS THIS?
* These are **short strands of RNA with no protein coat**. They are **smaller than viruses** and **only infect plants**.
Viroids
117
**Exposure to Nucleases that degrade DNA and RNA would damage all of the following EXCEPT**
A. Animal Viruses
B. Bacteriophage
C. Prions
D. Satellite Viruses
E. Viroids
**C. Prions**
Explanation:
* Prions are **misfolded proteins** that **do not contain nucleic acids** (DNA or RNA). Since nucleases specifically degrade **DNA and RNA**, prions would remain unaffected.
