Lecture 3 Flashcards
What are characteristics of viruses
- 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)
Explain virus classification
- 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
What cells are viruses able to infect
- HIV infects blood cells
- Polio infects nerve cells
- Hepatitis infects liver cells
What is the outer covering made of
- Capsid ( protein )
- Envelope ( absent in some )
What is the inner core made of
- Nucleic Acid ( DNA / RNA )
- Proteins ( enzymes )
Explain viruses compared to prokaryote
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
Explain the bacteriophage cycle
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
Explain the lytic cycle fully
- Attachment - capsid combines with receptor
- Penetration - viral DNA enter host
- Biosynthesis - viral components are synthesised
- Maturation - assembly of viral components
- Release - new viruses leave host cell
Explain the Lysogenic cycle fully
- Integration - viral DNA is integrated into bacterial DNA andd then is passed on when bacteria reproduce
Explain animal viral reproduction - HIV in detail
- 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
- 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.
- Assembly:
- Protein coats surround viral RNA and enzymes . Envelope proteins migrate to cell membrane
- Release:
- New viruses bud from host cell
What are the parts of the HIV lifecycle
- Attachment
- Fusion
- Uncoating
- Reverse transcription
- Replication
- Integration
- Biosynthesis
- Maturation
- Release
Explain Avian Influenza fully
- Wild birds are normally carriers
- Contagious when transmitted to domestic poultry
There are two forms:
- Low pathogenic form –birds display ruffled feathers; reduced egg production
- 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
Explain viriods and prions
- Are naked RNA strands that cause crop diseases
- Misshaped protein molecules and it causes BSE (mad cow disease), Creutzfeldt-Jakob disease
List the virus and what it causes
- 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
Explain congo fever
Congo Crimean haemorrhagic fever – caused by a RNA based Nairovirus complex
Explain Marburg haemorrhagic fever
One of the most virulent pathogens of humans - > 80% mortality in Angola in 2004
Explain Bunyaviridae
Isolated from cattle, sheep, goats, hares and hedgehogs
Explain Ebola virus
- 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,
What domain do prokaryota consist of
Bacteria
Archea
What are the phylums of prokaryota
- Proteobacteria
- Cyanobacteria
- Spirochaetes
- Firmicutes
- Actinobacteria
- Chlamydiae
Explain bacteria fully
- Characteristics of Bacteria :
- They are Prokaryotic
- Reproduce asexually
- They are Metabolically diverse :
- Heterotrophic: Ingests biomass as energy source
- Autotrophic: Produces its own energy
- Chemosynthesis (Chemical) or photosynthesis (Light)
- The motile forms move by flagella (eg tail)
- Various shapes identified:
- Bacillus - rod
- Spirillum - spiral or helical
- Cocci - round or spherical - own diversity
Clusters – staphylococci
Chains – streptococci
Short rods – coccobacillus
Long filament - fusiform
Similarities between bacteria and archea
- 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
What are the 3 types of archea
- Phylum: Crenarchaeota
- Phylum: Euryarchaeota
- Phylum: Korarchaeota
Expalin phylum : crenarchaeota of archea
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
Expalin phylum : Euryarchaeota of archea
Methane-producers and high saline-tolerant taxa- they are referred to as methanogens are methane producers and halophiles live in high salt concentrations
Expalin phylum : Korarchaeota of archea
Lesser known archaea, found in hot springs or deep ocean floors
Main types divided into sub-types- thermoacidophiles
Explain domain Archae fully
- 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
Explain cynobacteria fully
- 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
Explain bacteria fully
- 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
Explain the reproduction and nutrition of bacteria
- 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
- 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.
