Viruses

Question 1

What are some infectious limitations of viruses?

Answer 1

-Obligate intracellular parasite meaning they can reproduce only within host cell
-Virus can infect only a limited number of host cell types

Question 2

What are the potential types of nucleic acid found in genomes?

Answer 2

Double- or single-stranded DNA or RNA

Question 3

What is a capsid?

Answer 3

A protein shell that encloses the viral genome

Question 4

What is a capsomere?

Answer 4

Built from protein subunits

Question 5

What is the structure of a tobacco mosaic virus?

Answer 5

cylindrical, made up of capsomeres and has coiled RNA inside

Question 6

What is the structure of adenovirus

Answer 6

hexagonal made up of capsomeres, with glycoproteins extending from the corners. Contains DNA

Question 7

What is the structure of Influenza virus?

Answer 7

Membranous envelope with glycoproteins extending from around the sphere. Has Capsids inside with RNA coiled within.

Question 8

what is the structure of bacteriophage T4?

Answer 8

Has a head containing DNA, has a tail sheath (like a body) and tail fibres (like legs)

Question 9

What are bacteriophages

Answer 9

Viruses that infect bacteria, have the most complex viral capsids.
elongated capsid head that encloses their DNA/RNA.
Protein tailpiece to attach to host and inject phage DNA.
Can have an envelope.
Reproduces through lytic and lysogenic cycles

Question 10

Describe the lytic cycle

Answer 10

Phage reproductive cycle that results in host cell death:
1) attachment
2) entry of phage DNA and degradation of host DNA
3) Synthesis of viral genomes and proteins
4) assembly
5) release

Virulent phages reproduce only by lytic cycle
Bacteria have defences against phages

Question 11

Describe the lysogenic cycle

Answer 11

Replicates phage genome without destroying host
Viral DNA incorporated into host cell chromosome
Integrated viral DNA = prophage
Host cell replicates invaded DNA and passes on to daughter cells
temperate phages use both lytic and lysogenic cycles
Environmental signals such as UV exposure, mutagenic chemicals and desiccation can trigger viral genome and switch to lytic mode

Question 12

What is the animal virus reproductive cycle?

Answer 12

-Viral genome entry and uncoating of cell
-Cell manufactures viral proteins via replication and transcription
-Viral DNA/RNA and capsomeres self-assemble, producing new viruses

Question 13

What are viral envelopes?

Answer 13

A membranous envelope
Some envelopes formed from host cell plasma membrane as capsids exit
help virus evade host immune system
Viral glycoproteins on envelope bind to receptor molecules on host cell surface (they do not enter the cell, attach on cell membrane at exit)

Question 14

Discuss RNA as viral genetic material

Answer 14

-Broadest variety in found in animal viruses
-Retroviruses use reverse transcriptase (RT) to copy their RNA genome into viral DNA
-Functions as both mRNA for synthesis of viral proteins and genome for new virus particles

Question 15

What is a provirus?

Answer 15

Viral DNA integrated into host genome

Question 16

Does Provirus remain permanently in the host cell

Answer 16

yes

Question 17

What does host RNA polymerase transcribe?

Answer 17

proviral DNA -> RNA

Question 18

What are the 2 major surface antigens of influenza virus

Answer 18

-hemagglutinin (HA)
-neuraminidase (NA)

Question 19

What usually causes ‘new’ outbreaks of human viral diseases?

Answer 19

Usually caused by existing viruses that expand their host territory
Viral strains that jump species can exchange genetic information with other viruses to which humans have no immunity

Question 20

What are viroids?

Answer 20

-Simple infectious agents
-Single circular RNA molecule
-A few 100s of nucleobases
-Does not encode any proteins
-Mostly infects plants and disrupt growth

Question 21

Where is Hep D thought to have originated from?

Answer 21

A viroid
Infection caused by a sub-viral satellite
-ve sense, single-stranded RNA virus
Can propagate only in presence of HBV

Question 22

What are prions?

Answer 22

slow-acting, virtually indestructible infectious proteins cause brain diseases in mammals. Spread by converting normal form of protein to prion version
Causes mad cow disease

Question 23

What are the 2 domains of prokaryotes and where do they live?

Answer 23

bacteria and archaea
Thrive almost everywhere in all conditions

Question 24

Discuss prokaryotic metabolism, (an)aerobes..

Answer 24

-Obligate aerobes require O2 for cellular respiration
-Obligate anaerobes poisoned by O2
-Facultative anaerobes can survive +- O2

Question 25

Discuss chemical cycling by prokaryotes

Answer 25

Chemoheterotrophs - decompose corpses, dead vegetation and waste products They are N-fixers, Fix N2 from air to usable NH3 (ammonia) – a fertilizer, e.g. bacterial genus Rhizobium Increase availability of N, P, & K for plant growth Can also immobilise / decrease nutrient availability

Question 26

What are the typical structures of eukaryotic cells

Answer 26

-nuclear membrane -cytoplasmic membrane -ribosomes -mitochondria -nuclear membrane -several chromosomes per cell membrane-bound organelles

Question 27

What are Anammoxosomes

Answer 27

-Membrane-bound organelle produces energy for bacteria that perform anaerobic ammonia oxidation

Question 28

What are Acidocalcisomes?

Answer 28

membrane-bound 
acidic calcium storage compartments

Question 29

What are the typical structures of bacterial cells?

Answer 29

-DNA which can be double- or single-stranded. Bacterial chromosome. Can have circular plasmids -ribosomes -cytoplasm -cell wall -flagellum -cytoplasmic membrane -Generally lacks membrane-bound organelles

Question 30

What are Gram stains and what does it mean if they are negative?

Answer 30

Gram stains test for in bacterialinfections. Coloured pink if ve = negative.

Question 31

Bacteria cell wall structures?

Answer 31

-Give bacteria shape -Protect them from osmotic lysis t-oxic substances Contain a unique polymer.. peptidoglycan -Bacteria classified into 2 groups based on 
composition of this polymer in cell wall -Differentiated by stain developed by Hans Christian Gram in 1884 An additional polysaccharide or protein layer called a capsule 
covers many prokaryotes

Question 32

Bacteria can be one of 3 shapes... what are these?

Answer 32

Coccus, Rod, Spirochete

Question 33

Bacillus anthracis is an example of what?

Answer 33

Gram-positive that causes anthracis

Question 34

What is the density of organisms in the stomach

Answer 34

10^3-10^5/g

Question 35

What is the density of organisms in the large bowel and anus?

Answer 35

>10^10/g

Question 36

What is the role of normal microbiota?

Answer 36

Protect surfaces from physical colonisation and by pathogenic bacteria from others..

Question 37

Define microbiome

Answer 37

microbes, their genomes + environmental interactions in a defined environment

Question 38

Discuss the (mostly) symbiotic relationship between gut microbiome and host

Answer 38

Human host provides food, warmth etc. Microbes prevents colonisation by pathogenic bacteria, ferment unused energy substrates, regulate gut development etc.

Question 39

What are the principles of pathogenesis

Answer 39

1) Attach to / invade host 2) Evade innate local defences & spread in the body 3) Multiply 4) Evade adaptive defences long enough to complete life cycle 5) Leave body and spread to fresh hosts

Question 40

What is an example of bacterial micro-colonies growing on tooth surface?

Answer 40

Streptococcus mutans which ferment sugar to lactic acid causing decalcification of enamel, leading to tooth decay

Question 41

How does penicillin work?

Answer 41

Prevents peptidoglycan cross-linking (which is necessary for proper cell wall assembly) and bacteria lyse under osmotic pressure

Question 43

How do anti-viral agents work?

Answer 43

Must inhibit multiplication of virus but not infected host cell