A2.1 Origin of Cells Flashcards
early earth, cell theory, miller-urey, RNA, LUCA, hydrothermal vents
what was the atmosphere of early earth first theorized to be like and by who?
oparin and haldane suggested had N, CO2, H2S, water vapour, NH3, and traces of methane and H; no O2/O3
what hypothesized conditions allowed organic compounds to be formed?
first O2 from photosynthesis, high levels UV light from lack of ozone, high temperatures from high concentrations CO2, combined with lightning and volcanic activity
when and how was earth formed?
4.5 billion years ago from smaller particles colliding to form big particles, which attracted more particles
what are the principles of the cell theory?
- cells are the basic unit of life
- all organisms are made of one or more cells
- all cells come from pre-existing cells
how did the cell theory come to be?
- 1665: Robert Hooke sees 1st cells in cork
- few years later, Antonie van Leeuwenhoek saw 1st living cells, coined “animalcules”
- 1838: Matthias Schleiden said plants made of “separate beings” called cells; same with animals 1839
- 1880s: Louis Pasteur boiled chicken broth, sterilizing it, and confirmed life couldn’t appear without pre-existing cells
what are the characteristics of living things?
made of cells, metabolism, homeostasis, response to stimuli, growth, DNA, reproduction, excretion, need for nutrition
define paradigm shift
when theories are completely abandoned due to conflicting evidence (radical change in orthodox beliefs)
how was the first cell theorized to have developed?
- synthesis of small carbon compounds from abiotic matter
- compounds form polymers through condensation reactions catalyzed by hot sand/clay/rock
- membranes contain polymers
- create self-replicating molecules so inheritance and control occurs
who conducted the miller-urey experiment and when?
stanley miller and harold urey in 1953
what was the purpose of the miller-urey experiment?
to determine whether the hypothesized reducing environment of pre-biotic earth could have formed organic compounds
what is a reducing environment?
lacking oxidizing gases, mostly reducing gases like H, H2S
describe the procedure used in the miller-urey experiment
- upper apparatus with NH3, CH4, H2, representing reducing environment
- lower chamber of water, heated to form vapour that travels to apparatus
- 2 electrodes produce 7500 V at 30 A, simulating lightning in apparatus
- water continues to condenser to allow gas compounds to condense
- sample collected to see molecules in it after 1 week, when water is brown-black
what was discovered/concluded through the miller-urey experiment?
organic molecules like fatty and amino acids were identified; suggests life originated from primordial soup
what were the strengths of the miller-urey experiment and primordial soup theory?
- modelled pre-biotic earth
- demonstrated spontaneous generation of organic molecules
- could be replicated
what were the weaknesses of the miller-urey experiment and primordial soup theory?
- debate of actual pre-biotic atmosphere
- didn’t produce all molecules needed for life
- proteins dissolve in water, so amino acids could not have combined to form polypeptides
- couldn’t account for all conditions
what are other theories about the origins of life?
asteroids/comets, volcanoes, hydrothermal vents
how could life have come from volcanoes?
inorganic gases produced by volcanoes (water vapour, CO2, SO2, traces of CO and H2S) would result in non-reducing environment
what is a non-reducing environment?
lacking reducing gases, mostly oxidizing gases; wouldn’t form carbon compounds because lacking H for H bonds
what is a hydrothermal vent?
crack beneath ocean floor that water heated by magma-heated rocks rises out of, picks up lots of dark minerals and appears black
when were hydrothermal vents first observed?
1977
what is the evidence for hydrothermal vents being the origin of life?
- oldest fossils/precipitates found nearby
- commonality of genetic sequences in organisms nearby
- mineral-rich, acidic and basic fluids necessary for reactions
- H and C form reducing environment
how are vesicles formed?
when fatty acids placed in water, form themselves into vesicles
what is another name for a vesicle?
liposome
what are some functions of vesicles?
engulf other molecules, grow, replicate
what is the difference between a protocell membrane and a modern cell membrane?
protocell membranes only had fatty acids; modern membranes have proteins, etc. embedded
define compartmentalization
development of vesicle
what is the evidence for RNA being the first genetic material?
- assembles spontaneously from nucleotides
- self-replication; genetic material
- enzymatic
what is an example of an enzymatic RNA molecule?
ribozyme; catalyzes things like peptide bond formation
why could DNA not have been the first genetic material?
needs proteins and other molecules to replicate/grow/survive; RNA is the molecule that delivers and replicates code
what is the evidence of a LUCA?
- universal genetic code using nucleotides
- 300 genes in every animals’ cells
- common molecular processes and transport mechanisms
was the LUCA the only life form that existed during its time?
other life forms evolved but couldn’t compete
what traces of life get fossilized?
shell, bone, footprints, impressions of soft body parts
when did the LUCA form and what type of organism was it?
cyanobacteria 3.5 billion years ago
which two types of cells did the LUCA branch into?
simple (bacteria/archaea) and complex cells (plants/animals)
define half-life
time it takes for half of radioactive isotope to become stable element
what is absolute/radioactive dating?
organisms accumulate isotopes at constant rates, which start decaying after death; using half-lives and amount of isotope left in fossil, can find age
what is relative dating?
sediment strata layer from oldest at the bottom to youngest at the top; age of fossil approximated from age of strata
why is relative dating less accurate than absolute dating?
approximate, geological procceses could disturb layers
what is an index fossil?
similarly aged fossils found in different places, means strata are same age
what is genomic/genetic analysis?
compares amount of genetic difference, based on rates of genetic mutation (number of mutations between species tells when they diverged); used to estimate the LUCA’s age
why is genomic/genetic analysis sometimes unfavourable?
hard to find DNA in older fossils
