Lecture 3

Question 1

What are characteristics of viruses

Answer 1

• Non-cellular and non-living
• Able to mutate – evolve
• Infectious and able to infect specific cells
  -They are Obligate parasites – unable to metabolize outside host cell
  -They are able to remain dormant until next invasion(enter a host cell)

Question 2

Explain virus classification

Answer 2

• Virus possess either DNA or RNA
• Nucleic acid either single or double –stranded
• Classification depends on size and shape
• Classified on whether an outer envelope is present or absent

Question 3

What cells are viruses able to infect

Answer 3

• HIV infects blood cells
• Polio infects nerve cells
• Hepatitis infects liver cells

Question 4

What is the outer covering made of

Answer 4

1. Capsid ( protein )
2. Envelope ( absent in some )

Question 5

What is the inner core made of

Answer 5

1. Nucleic Acid ( DNA / RNA )
2. Proteins ( enzymes )

Question 6

Explain viruses compared to prokaryote

Answer 6

Viruses :

• No cellular structure
• No metabolism
• Unable to respond to stimuli
• Multiplies inside host cell
• Able to evolve

Prokaryote :

• Consists of cell
• Able to metabolize
• Able to respond to stimuli
• Multiplies independently
• Able to evolve

Question 7

Explain the bacteriophage cycle

Answer 7

1) Lytic cycle:
During the lytic cycle, the host cell breaks open (lysis); releases viral component – host cell dies

2) Lysogenic cycle:
There is no destruction of host DNA; The virus becomes part of host DNA – it forms prophage

Question 8

Explain the lytic cycle fully

Answer 8

1. Attachment - capsid combines with receptor
2. Penetration - viral DNA enter host
3. Biosynthesis - viral components are synthesised
4. Maturation - assembly of viral components
5. Release - new viruses leave host cell

Question 9

Explain the Lysogenic cycle fully

Answer 9

1. Integration - viral DNA is integrated into bacterial DNA andd then is passed on when bacteria reproduce

Question 10

Explain animal viral reproduction - HIV in detail

Answer 10

1. Attachment and penetration :
   • Virus binds receptors on cell membrane and enters cell. Viral protein coat is removed
   • Reverse transcriptase transcribes viral DNA to double stranded DNA
   • Double stranded DNA is incorporated into host cell genome
2. Synthesis :

• Viral genes are transcribed to RNA
• Some RNA is packed into new viruses
• Other RNA is translated into HIV proteins at ribosomes in cytoplasm.

3. Assembly:

• Protein coats surround viral RNA and enzymes . Envelope proteins migrate to cell membrane

4. Release:

• New viruses bud from host cell

Question 11

What are the parts of the HIV lifecycle

Answer 11

1. Attachment
2. Fusion
3. Uncoating
4. Reverse transcription
5. Replication
6. Integration
7. Biosynthesis
8. Maturation
9. Release

Question 12

Explain Avian Influenza fully

Answer 12

• Wild birds are normally carriers
• Contagious when transmitted to domestic poultry

There are two forms:

1. Low pathogenic form –birds display ruffled feathers; reduced egg production
2. High pathogenic form – causes multiple internal organ failure – mortality 90-100% in 2 days

• Human infections since 1997 –is caused by contact with diseased birds or contaminated surfaces
• Normally single infections

Question 13

Explain viriods and prions

Answer 13

1. Are naked RNA strands that cause crop diseases
2. Misshaped protein molecules and it causes BSE (mad cow disease), Creutzfeldt-Jakob disease

Question 14

List the virus and what it causes

Answer 14

• Herpes, hepatitis, adenovirus (HVP in cervical cancer; others cause colds & sore throats)
• Varicella zoster –causes small pox
• Paramyxovirus – cause measles and mumps
• Orthomyxovirus – influenza
• N1H1 – swine flu
• Monkey pox-infectious disease caused by the monkeypox virus. Symptoms: painful rash, enlarged lymph nodes and fever

Question 15

Explain congo fever

Answer 15

Congo Crimean haemorrhagic fever – caused by a RNA based Nairovirus complex

Question 16

Explain Marburg haemorrhagic fever

Answer 16

One of the most virulent pathogens of humans - > 80% mortality in Angola in 2004

Question 17

Explain Bunyaviridae

Answer 17

Isolated from cattle, sheep, goats, hares and hedgehogs

Question 18

Explain Ebola virus

Answer 18

• African haemorrhagic fever)
• 4 distinct subtypes , 3 affect humans
  causing fatalities 50-90% of cases – mostly in central Africa since 1976 in Congo
• In 2014: June/July > 759 cases with > 460 fatalities. Where? Guinea, Liberia & Sierra Leone,

Question 19

What domain do prokaryota consist of

Answer 19

Bacteria
Archea

Question 20

What are the phylums of prokaryota

Answer 20

• Proteobacteria
• Cyanobacteria
• Spirochaetes
• Firmicutes
• Actinobacteria
• Chlamydiae

Question 21

Explain bacteria fully

Answer 21

• Characteristics of Bacteria :

1. They are Prokaryotic
2. Reproduce asexually

• They are Metabolically diverse :

1. Heterotrophic: Ingests biomass as energy source
2. Autotrophic: Produces its own energy
   
   • Chemosynthesis (Chemical) or photosynthesis (Light)

• The motile forms move by flagella (eg tail)
• Various shapes identified:

1. Bacillus - rod
2. Spirillum - spiral or helical
3. Cocci - round or spherical - own diversity

Clusters – staphylococci
Chains – streptococci
Short rods – coccobacillus
Long filament - fusiform

Question 22

Similarities between bacteria and archea

Answer 22

• Both are Prokaryotic cells-no nucleus or membrane bound organelles
• They have circular chromosomes
• Predominantly unicellular
• Some can fix nitrogen and grow at temperatures above 80 degrees

Question 23

What are the 3 types of archea

Answer 23

1. Phylum: Crenarchaeota
2. Phylum: Euryarchaeota
3. Phylum: Korarchaeota

Question 24

Expalin phylum : crenarchaeota of archea

Answer 24

Ability to withstand extremes in temperature and acidity
Phylum: Euryarchaeota – methane-producers and high saline-tolerant taxa- they are referred to as methanogens are methane producers and halophiles live in high salt concentrations
Phylum: Korarchaeota – lesser known archaea, found in hot springs or deep ocean floors
Main types divided into sub-types- thermoacidophiles

Question 25

Expalin phylum : Euryarchaeota of archea

Answer 25

Methane-producers and high saline-tolerant taxa- they are referred to as methanogens are methane producers and halophiles live in high salt concentrations

Question 26

Expalin phylum : Korarchaeota of archea

Answer 26

Lesser known archaea, found in hot springs or deep ocean floors Main types divided into sub-types- thermoacidophiles

Question 27

Explain domain Archae fully

Answer 27

- Able to withstand extreme conditions - They possess unique lipids in plasma membrane - Lipids: glycerol + hydrocarbons - They have no peptidoglycan – they have polysaccharides and proteins instead. - No photosynthesis - No parasites – some mutualists, commensalists - Archaea are biochemically different from Bacteria and Eukaryadifferent - Archaea rRNA is from Bacteria rRNA - Archaea ribosomal proteins & transcription is similar to Eukarya

Question 28

Explain cynobacteria fully

Answer 28

- They are Gram negative - They are able to Photosynthesize - Large organisms: They are unicellular/colonial/ filamentous - Non-motile - Thick-walled cell – with no nucleus - They are nitrogen fixing organisms - Cyanobacterium + fungus = lichen - Cyanobacteria form symbiotic relationships with liverworts, ferns, corals - They may cause eutrophication

Question 29

Explain bacteria fully

Answer 29

- Cell wall contains peptidoglycans - Gram-stain procedures distinguishes bacteria on the basis of cell wall structure - Gram-positive: thick peptidoglycan cell wall surrounded by outer membrane. After staining procedure cells appear purple. - Gram-negative: thin layer of peptidoglycan cell wall surrounded by outer membrane. Cells appear pink after staining procedure

Question 30

Explain the reproduction and nutrition of bacteria

Answer 30

1. Reproduction : - Asexual by binary fission - Transformation – acquisition of free strands of DNA (E.g. Plasmids) - Conjugation-transfer of genetic material - Endospore formation (survival strategy) –seen bacteria such as botulism, anthrax 2. Nutrition - Obligate anaerobes (bound by one mode) - O2 absent - Facultative anaerobes (more than one mode: can live in the presence or absence of oxygen) - Photoautotrophs – produces O2 or S2 - Chemoautotrophs: CO2 + 2H2S (CH2O)n + 2S or CO2 + H2O (CH2O)n + O2 or nitrate and nitrite formation - Heterotrophs: get organic material from the environment.