cycle 1 Flashcards
principles underlying evolution by natural selection
- mutation
- variation
- heredity
- non-random survival (selection)
- change in the genetic composition of the population (evolution)
prokaryotic cells
bacteria and archaea (cell surrounded by a lipid membrane with a DNA genome)
eukaryotic cells
eukaryotes (has organelles)
characteristics of viruses
not made of cells, protein shell with DNA/RNA genome inside (can be single/double-stranded), some are surrounded by a lipid envelope, obligate parasites
what type of virus is HIV?
retrovirus ssRNA
zoonotic diseases
occur due to spillover events (usually between closely related species), usually more harmful in the new host (e.g. HIV)
antiviral drugs
prevent the virus from replicating, more difficult to design than antibiotics
how does a virus integrate its genome into a host cell?
converts RNA to DNA by reverse transcription (reverse transcriptase)
integrase
inserts viral DNA into host DNA
what was the first drug to treat HIV?
AZT, nucleoside analog (almost like thymidine)
how does AZT work?
it blocks the addition of more nucleotides (fools reverse transcriptase, stops replication)
how does HIV become resistant to AZT?
reverse transcriptase undergoes a mutation that makes it resistant to AZT, mutated reverse transcriptase survives due to natural selection
principles of evolution by natural selection
- variation
- heritable (mutations are passed on to offspring)
- variants differ in reproductive success (fitness)
- some variants are more likely to reproduce
- population changes over time
why are drug cocktails more effective?
resistance to one drug is easy, resistance to many drugs is less likely (inhibits the virus life cycle at many different points)
do viruses evolve?
yes, even “non-living beings” evolve
theory
an assumption based on limited knowledge
scientific theory
a coherent set of testable hypotheses that attempt to explain facts about the natural world
falsifiable theory
- points to hypotheses that need testing, gather evidence
- test a theory by attempting to falsify it
- falsification starts a critical discussion
- revise theory
non-falsifiable statements
usually needs some sort of exhaustive search to disprove it
falsifiable statements
needs just one observation to disprove it, open to the possibility of it being wrong
fact
indisputable observation (theories can graduate to facthood)
evidence for evolution (Darwin)
- biogeography: similar species are found in far away distant places (islands vs continents)
- comparative morphology: homologous structures (similar structures but perform different functions)
- geology: geological change is slow and gradual (earth is old, so is life), fossils (evidence life on earth today is different than in the past)
vestigial structures
structures that have no function, used to be functional in ancestral species (e.g. appendix)
theory of evolution by natural selection
- natural selection is a mechanism to explain how evolution occurs
- there is variation for traits in a population
- individuals are favoured whose traits allow them to better survive and leave more offspring (higher fitness) who inherit these traits
- over time, individuals with these favourable traits become more common in the population
