cycle 1 Flashcards
why are viruses sometimes considered “alive” and sometimes not? (8)
cannot reproduce on their own
lack a metabolic system to provide energy for life cycles (respiration, photosynthesis)
can reproduce/replicate with the aid of host
evolve rapidly with natural selection
does not have ribosomes and key enzymes required to replicate
not a cell
infectious biological particles rather than organisms
we know very little about viral evolution
basic features of animal viruses and how they infect cells and replicate
viral particles move by random molecular motions until they contact the surface of a host cell
for infection to occur, the virus or viral genome must enter the cell
viral genes are expressed, leading to replication of the viral genome and assembly of progeny viruses
viral genes are expressed, leading to replication of the viral genome and assembly of progeny viruses
virions (new viral particles) are released from the host cell, often rupturing the host cell and killing it
similarities and differences between main groups of cellular life and viruses
similarities: contain nucleic acid and replicate
differences: all forms of cellular life display order, harness and utilize energy, reproduce, respond to stimuli, exhibit homeostasis, grow and develop, and evolve. viruses lack many of these properties. viruses cannot complete lifecycle without invading living cells
evolutionary origins of HIV and why eradicating viral diseases is difficult
multiple spillovers of SIV to humans –> HIV/
processes resulting in the evolution of drug resistance in HIV and why the effectiveness of anti-viral drugs is likely to decrease over time
AZT treatment - after several months, HIV becomes resistant
mutations create variation in AZT resistance
passed from parent to offspring
when AZT is present, some forms (AZT-resistant) are more likely to reproduce than others (AZT-susceptible)
viral population changes over time
principles underlying evolution by natural selection
heritable variation - the variance among individuals in the heritable quantity
non-random mating - individuals prefer mates with specific characteristics. probability of mating for any two individuals is not the same for all possible pairs
non-random survival - individuals with favourable traits survive and reproduce and pass on their traits to next generation - evolutionary change
change in genotype - in a particular environment, some genotypes will be favoured, individuals with those genotypes will reproduce and pass on their genes more than those who have less favourable traits
rationale for using multiple drugs simultaneously to treat viral infections
less likely to evolve multi-drug resistance
how viral mutation rate affects the likelihood of developing a long-term effective vaccine, or developing long-term effective antiviral drugs
mutation in other viral genes change the outer structure of the virus
enables HIV to evade out immune system
difficult to generate vaccine for all potential variants
there may never be a universal HIV vaccine
relies on reducing transmission, developing antiviral drugs
natural selection/survival of the fittest, will become more resistant to anti-viral drugs
examples of “scala natura” thinking, and why this type of classification is not compatible with modern evolutionary theory
ladder-like classification of life
every organism has a defined position on the ladder from the simplest organisms to the most complex - at the top: humans, angels, God
evidence from geology and the fossil record, the geographic distribution of species, and comparative morphology, that supports the idea of descent with modification from a common ancestor
fossils suggest that species could die out/go extinct
contradicted the prior conception that each organism was specially created by God and that the number of species on Earth is fixed
Darwin found that some fossils clearly resembled living species
examples of homologous traits
five fingers and toes
forearm bones
four limbs
wingshow
how our understanding of evolution has changed since Darwin’s time
Mendelian genetics
phenotypic variation among organisms reflects underlying genetic variation in DNA sequences
why mutations are important to evolution
genetic diversity
characteristics of a scientific theory; differences between scientific theories and belief systems; how scientific theories can be tested, potentially falsified, and updated
falsification - some possible observation or experimental finding could prove the theory (or hypothesis) to be wrong
scientific theory must be testable and falsifiable. if falsified, change the theory (must be modified)
a coherent set a testable hypotheses that attempt to explain face about the natural world
major components of modern evolutionary theory
change through time
common ancestry
speciation
variational rather than transformational
gradualism
role of selection
