topic 2 (continued) Flashcards
What are viruses?
smallest microorganism (0.02 - 0.03 um ; 50 times smaller than bacterium)
Viruses are non-living structures - they are arrangements of genetic material and protein that work by invading other living cells and taking over their biochemistry to make more viruses.
non living as they also have no mechanism or cytoplasm and can’t self-replicate.
Why are they sometimes classed as living organisms?
as they can reproduce and they change and evolve in a adaptive way.
Why can viruses be difficult to treat?
As they’re non living -so we cant kill them
Antivirals must work by inhibiting virus replication
The focus of disease control should be on preventing the spread ( eg the 2014 Ebola outbreak in West Africa)
How are viruses classified?
according to structure and nucleic acid types
Name 3 types of viruses with examples
- DNA virus ( λ (lambda) phage )
- RNA virus ( tobacco mosaic virus + Ebola )
- RNA retrovirus ( HIV - human immunodeficiency virus)
The way in which the viral genetic material is used in host cells to make new viruses depends on which type of virus it is.
How do viruses attach to host cells?
through specific protein antigens = Virus Attachment Particles (VAPs) that target proteins in host cell’s membrane.
DNA virus
- genetic material - DNA
- nucleic acid
- the viral DNA acts directly as a template for mRNA transcription + DNA replication
RNA virus
- genetic material - RNA
70% viruses have RNA genetic material
more likely to mutate than DNA viruses - majority contain single strand of RNA - ssRNA
1. Positive ssRNA have RNA which can be directly translated into proteins by ribosomes as act directly as mRNA
EG of positive ssRNA - tobacco mosaic viruses
- Negative ssRNA viruses cannot be directly translated.
The RNA strand must be transcribed to produce MRNA before its translated at ribosome
- EG of negative ssRNA - Ebola, measles, influenza
RNA retroviruses
- single strand RNA
- Have protein capsid and lipid envelope
- single strand of viral RNA directs the synthesis of a special enzyme - reverse transcriptase - which makes a DNA molecule corresponding to the viral genome.
- This (double stranded) DNA then incorporated into host cell DNA + used as template for new viral proteins + viral RNA genome
- EG of RNA retrovirus - HIV
viral structures for virus
a. envelope?
b. capsid?
c. capsomeres?
a. coat around the outside of virus - made from lipids in the host cell
b. the protein coat of a virus
c. the repeating protein units making up the capsid
Viruses reproduction?
- attach to other living organisms as can only reproduce inside cells
- attach on host cells
- bacteriophages attach to bacteria by injecting genome into it but bulk of viral material remains outside bacteria forming plasmid within bacteria
lysogenic pathway / Latency
non-virulent (not disease causing) virus injects DNA into host cell DNA as provirus.
Viral DNA replicates each time host cell divides.
Virus produces repressor proteins to inhibit transcription = MRNA not produced.
virus does not affect host cell. at this part when virus is part of the reproducing host cells = virus is latent.
latent virus enters lytic pathway when host cell is damaged or immune system weakens. amount of repressor decreases.
Lytic pathway/cycle
virulent (disease causing) virus injects genetic material (+nucleic acid) into host cell cytoplasm.
viral genetic info replicates immediately, independently of host cell DNA
Many viruses are assembled and eventually bursts host cells - releasing loads of new virus to invade other cells
- cell lysis.
how can viruses cause disease in cycle?
through the cell lysis of host cell - can cause host cells to release their own lysosomes + digest themselves from inside or by production of toxins than inhibit cell metabolism.
How can viruses spread from one organism to another?
[spread of viral disease]
- infected mucus
- droplets of saliva
- infected blood or faeces
- simple contact between infected organisms
how did Ebola spread?
Ebola virus is an animal disease.
spread to humans through faeces, urine, blood or meat of infected animals.
then spread from person to person by direct contact of skin, blood, faeces , body fluids from infected person.
How do antivirals work?
cant affect acctual virus particle itself, instead it targets virus replication.
- target receptors/antigens to stop the virus from recognising host cell and therefore prevent entry
- target the enzymes that help translate or replicate the viral DNA or RNA
Whats mortality rate?
what does it depend on?
Ebola?
measure of number of deaths caused in a given population due to specific cause ( disease )
Depends on strain of virus, health of infected person, speed that they get help from health care.
Ebola -highly infectious viral disease causing fever ad internal bleeding and death sometimes
mortality rate - around 50% (25-90%)
controlling viral infections
-vaccines
when vaccinated - become immune to disease - will not get infected if encounter it
very young and elderly and health care workers usually get vaccinated first in epidemic as theres rush to deliver vaccines
How can the spread of disease be controlled?
- nursing in isolation so they dont come in contact with other ppl that are healthy
- preventing transmission from 1 person to another through regular handwashing, before + after contact with patients, careful disposal of infected bodily wastes, and frequent disinfecting surfaces
- wear protective clothing by health workers and public, facemasks, gloves, goggles, gowns
- sterilising or disposing of equipment or bedding after use.
- identifying contacts of ppl who’s infected so they can be treated or isolated fast
The development of new medicine
Preclinical testing - done in a laboratory using cells, tissues and live animals.
[Efficacy, toxicity and dosage are tested at this stage]
Clinical trials - use healthy volunteers and then patients.
Very low doses of drug given at start of the clinical trial.
If the drug is found to be safe = further clinical trials are carried out to find the optimum dose for the drug.
In double-blind trials, some patients are given a placebo - double-blind study.
Ebola outbreak - what did they use?
outbreak in late 2013 in West Africa.
took until mid 2014 for world to recognise severity of it.
World Health Organisation (WHO) looked for ways to fast track vaccines already in development.
the vaccines has not completed human trials yet.
Factors to consider when deciding whether a drug/vaccine should be fast tracked for use in a epidemic
- severity of disease
- availability of other treatments
- effectiveness of standard disease control measure for spread of it
- informing public and getting consent
- freedom of choice
reasons against using untested drugs
- not ethical to use under any circumstances as they have not completed full human trials
- unexpected side effects which could worsen situation
- informed consent is an issue, depends on level of education to understand drug and how it works
- deciding who gets the drug/vaccine first = difficult.
local ppl v health workers
whats the cell cycle?
3 main stages?
cell cycle is a regulated process in which cells divide into two identical daughter cells.
process consists of three main stages:
interphase, mitosis and cytokinesis.
Interphase ?
interphase is split into 3 sections - what?
rest of phases of cell cycle
- interphase - the period between active cell divisions when cells increase size and mass and replicate their DNA
- New DNA produced, chromosomes replicate, new proteins, cytoplasm, cell organelles are synthesised.
- ATP production increases at times to provide extra energy needed for cell to divide.
G1 (gap 1) interphase
S interphase
G2 (gap 2) interphase
Mitosis
Cytokinesis
G1?
S?
G2?
mitosis?
cytokinesis?
G1 - time between end of previous round of mitotic cell division and start of chromosome duplication.
- grows and develops
-very short
S - stage where chromosomes replicate and become double stranded chromatids.
CHROMATIDS - one strand of the replicated chromosomes pair thats joined to other chromatid at the centromere.
G2 - time that organelles + materials needed for cell division are synthesised - need 2 for everything before cell divides.
Mitosis - when cells are actively dividing
Cytokinesis - cytoplasm and new cells split to form two identical daughter cells.
What are cyclins?
What are Cyclin-dependent Kinases (CDKs) ?
small proteins that build up during interphase and are involved in the control of the cell cycle by their attachment to cyclin-depending kinases.
Cyclin-dependent Kinases (CDKs) are enzymes involved in the control of the cell cycle. Cyclin attach to CDKs and this cyclin/CDKs complex adds phosphate to other proteins, changing their shape and bringing about the next stage in the cycle.
