A2.1 Origin of Cells Flashcards
why was the Earth formed?
gravity caused dust and gas to come together
describe the pre-biotic atmosphere
only traces of oxygen because it reacted with other elements; methane concs higher bc of intense volcanic activity and meteorites; CO2 concs higher bc of volcanic emissions
why were temps higher than they are now?(4)
high concs of CO2 and CH4 which are heat-trapping greenhouse gases; comet and asteroid impacts; the ozone layer that now protects us wouldnt exist bc of lack of oxygen, without the layer more solar UV would have penetrated to earth’s surface; more lightening triggering other chemical processes
where would carbon compounds be formed?
specialized environments eg hot springs on land or hydrothermal vents in oceans
what would carbon compounds have formed?
droplets of water in the atmosphere, creating an ORGANIC AEROSOL HAZE which would have deposited into lakes/oceans creating a ‘soup’ of carbon compounds
what happened as organisms came about?
they increases oxy conc and decreased CO2 conc so ozone layer formed giving protection against UV + greenhouse effect was reduced
cells can be considered as…
the smallest units of self-sustaining life
what are the 3 components of cell theory?
all living organisms are composed of one or more cells; the cell is the most basic unit of life; all cells arise from pre-existing cells by division
what are the functions of life(Mr H Gren)
metabolism, response, homeostasis, growth, reproduction, excretion, nutrition
which developments are needed for the origin or cells?
catalysis, self-assembly(carbon compounds eg amino acids need to assemble to form polymers), compartmentalisation(membrane to enclose cell contents), self-replication
Miller-Urey experiment
passed steam through CH4, H, ammonia simulating earth’s atmo, used electricity to mimic lightening, found amino acids and carbon compounds could be formed, theorised these would then form polymers using energy from deep sea vents and trigger mechanisms for inheritance before becoming enclosed in a membrane to form a cell
strengths of miller-urey experiment
repeatable-similar experiments have shown a diversity of carbon compounds can form spontaneously in an atmosphere lacking oxygen
weaknesses of miller-urey experiment
miller and urey probs got some conditions wrong-pre-biotic Earth had more CO2 and N2 and less NH3 and CH4 and less lightning
what is a vesicle?
small droplets of fluid, enclosed in a membrane
what are exosomes?
extracellular vesicles which some cells produce
what does the membrane of vesicles consist of?
mainly phospholipids, experiments show that bilayers spontaneously form stable spherical structures
what would have happened if phospholipids were part of the ‘soup’ of carbon compounds?
they would have self-assembled into bilayers and vesicles would have likely formed but movement of pilar in and out would have been limited by hydrophobic membrane core so would have developed own internal chem(cell-like)
what can RNA do?
store info like DNA but is self-replicating and can act as a catalyst
what do some viruses use as genetic material?
RNA which supports theory that RNA could have been used before genes of DNA evolved
LUCA
last universal common ancestor, the hypothetical organism from which all life on earth is believed to have descended
what is convergent evolution?
when it’s possible for similar structures to evolve in organisms that don’t have a recent common ancestor
conditions for luca?
would have used RNA to store genetic info and catalyse chemical reactions, would have been highly resistant to extreme environments
evidence for luca?
universal genetic code in all cells, same building blocks for RNA and DNA in all cells, common molecular processes in all cells
what is an emergent property?
characteristics of an organism not evident on a cellular level created by interactions between cells
eg of minerals found in alkaline hydrothermal vents that act as catalysts to build organic molecules
iron and sulfur
what is a micelle
an aggragate created through self-assembly of amphipathic molecules;hydrophobic ends face in and hydrophilic ends fce out
what is a protocell
structures formed from the aggregation of abiotic components but has some similarities to living cells
bc Earths early atmosphere was absent of O2 this suggests luca was…
anaerobic
bc of earths hot thermal vents underwater it suggests luca was…
thermophilic bc thermal vents are v hot and autotrophic bc no organisms to take nutrition from and wouldnt use light as an energy source bc deep ocean is v dark
fossils for the 3rd part of the timeline for early life
rocks in australia contain fossilized stromatolites which are rocky mounds formed by mats of cyanobacteria in shallow seawater which trap sediments and secrete CaCO3
isotope ratios in rocks for the 2nd part of the timeline for early life
carbon originating from living organisms has a low 13C/12C ratio, banded iron rock dating from 3.8 Gya shows this, suggesting life had evolved by then
genomic info for the 1st part of the timeline for early life
the no. of differences between the genomes of 2 species is proportional to the time since they diverged from a common ancestor. LUCA and the first living cells existed 4.5 Gya
what kind of environment was it likely that LUCA lived in?
high concs of H, CO2 and iron and these conditions are found in and around hydrothermal vents in oceans
which conditions do hydrothermal vents have that are needed for the 1st cells to form?
alkaline, white smoke that comes out is fluid at temps of 60 to 90 and contains high concs of H, methane, ammonia and sulfides. These chemicals could have been used to generate energy anaerobically which protocells could have used to assemble carbon compounds into polymers. CO2 needed by evolving protocells would have been abundant in the pre-biotic ocean water
how did pasteur disprove spontaneous generation?
showed air was full of microorganisms, heated some broth in a flask to kill the microorganisms and left open to air through a swan-neck flask and nothing formed, broke the swan neck flask and saw microorganisms developed
what are the 3 atypical cells and why are they atypical?
skeletal muscle bc they’re multinucleated; aseptate fungi bc they contain hyphae(cells) but no septa(cell walls); acetabularia bc they’re large single cells
what happens as cells increase in size?
SA:V ratio decreases; reduces speed at which substances enter and exit the cell; reduces rate of both energy and heat transfer limiting rate of metabolism; this restricts the size of the cell which is why most cells are small
define differentiation
development of cells in different ways to carry out specific functions; involves the expression of certain genes in a cell’s genome and enables emergent properties
pluripotent
stem cell can differentiate to form any cell in an organism
multipotent
stem cell can differentiate to form many different cells in an organism
where can stem cells be found in humans?
embryonic(contained within embryo, pluripotent); cord blood stem cells(found in umbilical cord, multipotent); adult stem cells(found in bone marrow, multipotent)
how can stargardt’s disease be treated with stem cells?
blindness in children due to a dysfunction of retinal cells in the eye, stem cells injected into the eye and differentiate into healthy retinal cells curing the blindness
how can stem cells be used to treat leukaemia?
production of abnormal WBCs; stem cells extracted from bone marrow and chemotherapy kills the remaining cells; stem cells reintroduced and differentiate to form new healthy WBCs
what does endosymbiotic theory provide evidence for?
provides evidence for the origin of eukaryotes
which experiment disproved spontaneous generation?
Louis Pasteur
what is the endosymbiotic theory?
states that larger prokaryotes engulfed smaller prokaryotes; have their og membrane and the membrane of larger prokaryotes
what characteristic of a steroid shows it is a lipid?
it has a very low proportion for oxygen to carbon
