Phages,virology, environmental, parasitology,retrovirus

Question 1

Describe the genome and structural proteins of retroviruses.

Answer 1

Genome: Diploid (+)ssRNA with genes gag (structural proteins), pol (reverse transcriptase, integrase), env (envelope glycoproteins).

Proteins: Processed into MA (matrix), CA (capsid), NC (nucleocapsid) from gag; SU (surface) and TM (transmembrane) from env.

Question 2

Outline the steps of HIV replication.

Answer 2

Attachment: gp120 binds CD4 + CCR5/CXCR4.

Fusion: gp41 mediates membrane fusion.

Reverse transcription: RNA → DNA via reverse transcriptase.

Integration: Viral DNA inserts into host genome (provirus).

Assembly/Release: Budding from host membrane.

Question 3

Name 3 categories of AIDS-related illnesses.

Answer 3

Gastrointestinal: Chronic diarrhea (Cryptosporidia, Candida).

Neurological: AIDS dementia complex.

Respiratory: Tuberculosis, Pneumocystis pneumonia.

Question 4

What are NRTIs and how do they work?

Answer 4

Nucleoside Reverse Transcriptase Inhibitors (e.g., AZT) act as chain terminators, blocking HIV DNA synthesis.

Question 5

What is the global impact of HIV?

Answer 5

40 million people live with HIV (2023); Sub-Saharan Africa accounts for 2/3 of new infections.

Question 6

Compare protozoa and helminths.

Answer 6

Protozoa: Unicellular (e.g., Giardia), active (trophozoite), infective (cyst).

Helminths: Multicellular worms (e.g., Taenia), active (adult/larvae), infective (eggs).

Question 7

How does E. histolytica cause disease?

Answer 7

Ingestion of cysts → excystation in intestine → trophozoites invade mucosa → bloody diarrhea (amoebic dysentery).

Question 8

Describe transmission and symptoms of giardiasis.

Answer 8

Transmission: Fecal-oral (contaminated water). Symptoms: “Beaver fever,” fatty diarrhea, malabsorption.

Question 9

What is the definitive host for Taenia saginata?

Answer 9

Humans (harbor adult tapeworms; eggs shed in feces).

Question 10

What agar is used to culture V. cholerae?

Answer 10

TCBS Agar (Thiosulfate Citrate Bile Salts Sucrose): Yellow colonies (sucrose fermentation).

Question 11

List the 3 stages of water purification.

Answer 11

Coagulation (remove particles).

Filtration (sand/gravel).

Chlorination (disinfection).

Question 12

Why are coliforms used as water quality indicators?

Answer 12

Presence correlates with fecal contamination (e.g., E. coli = high risk of pathogens).

Question 13

What does MPN measure?

Answer 13

Most Probable Number estimates viable microbes in water using serial dilutions and statistical tables.

Question 14

What defines a virion’s symmetry?

Answer 14

Capsid arrangement: Icosahedral (adenovirus), helical (influenza), complex (bacteriophage).

Question 15

Classify HIV and influenza.

Answer 15

HIV: Group VI (ssRNA-RT).

Influenza: Group V (-ssRNA).

Question 16

What occurs during viral “uncoating”?

Answer 16

Capsid disassembles to release genome (e.g., HIV in cytoplasm; adenovirus in nucleus).

Question 17

How do enveloped viruses acquire their envelope?

Answer 17

Budding from host membrane (e.g., HIV) or internal membranes (e.g., herpesviruses)

Question 18

Name 3 viruses that caused recent outbreaks.

Answer 18

SARS-CoV-2 (COVID-19), Zika, Ebola.

Question 19

Compare lytic and lysogenic phage cycles.

Answer 19

Lytic: Immediate host lysis (e.g., T4 phage).

Lysogenic: Integration as prophage (e.g., lambda phage).

Question 20

Phage Therapy

Answer 20

Targets specific bacteria, self-replicating, effective against antibiotic-resistant strains.

Question 21

How do phages contribute to bacterial virulence?

Answer 21

Phage genes encode toxins (e.g., Vibrio cholerae CTXφ phage → cholera toxin).

Question 22

What is CRISPR’s role in bacterial immunity?

Answer 22

Stores phage DNA fragments to recognize and destroy future infections