A2.1 origin of cells Flashcards
3 statements of basis of cell theory
cells smallest unit of life
all living things made from cells
all cells arise from pre existing cells
what are atypical cells and give examples and reasoning
cells which are exeptions to cell theory
1. cells with no nuclues
eg. phloem sieve tube elements- to allow passage of phloem sap
eg. red blood cells- has more space for haemoglobin so more oxygen
- multinucleated
eg.skeletal muscle cells- formed via fusion of multiple cells
eg. aseptate fungal hyphae.- not composed of ditinct cells
explain skeletal muscle cells
formed via fusion of multiple cells
really long as function is contraction must have many nucleuses for production of actin and myosin (proteins which make proteins)
explain aseptate fungal hyphae
not composed of distinct cells instead of roots have hyphae which move when sense resources to do this must have many nuclei to branch into differnet directions
MR MH GREN stand for
movement
reproduction
metabolism
homeostasis
growth
response to stimuli
excretion
nutrition
movement
change in position
reproduction
livign things produce fertile offspring either sexually or assexually
metabolism
web of all the enzyme catalysed reactions in a cell or organism e.g respiration
homeostasis
maintainece of regulation of internal cell conditions
growth
living things can grown or change shape
response to stimuli
living things can respond to and interact with the enviornment
exrection
the removal of metabolic waste produced by the metabolism
nutrition
feeding by either the synthesis of organic molecules (e.g photosynhteisis) or the absorption of organic matter
parts in an optical microscope
eyepiece objective
nose piece
objective lenses
stage
condenser/ diaphragm
LED light source
base
fine focusing dial
coarse focusing dial
microscope stans
eyepiece graticule
scale found in optical lens
has arbitary units (no units) even if magnification increase size of eyepice graticule does not change
stage micromenter
slide with a ruler
how light microscope works and what it allows us to see
uses light to form an image
allows observation of whole cell large organelles (e.g nucleus chloroplasts) and some bacteria
can resolve objects as close as 0.2 micrometers apart
how transmission electron microscope works and what it allows us to see
uses beam of electrons that pass through a very thin specimen
can resolve objects as close as 0.2 nm apart
provides detailed images of internal cell structures such as ribosomes, membranes and mitchondria
produces black and white mage recquiring computer processing for enhancments
how scanning electron microscope works and what it allows us to see
uses beam of electrons that scane accross the surface of the specimen
produces a 3D image of the specimens external structure
produces black and white image recquiring computer processing enhancment
advantages and disadvantages of light microscope
ad;
-can be used to observe living specimesn
-produces colour images
-relatively inexpensive, eas to use
dis;
-limited magnification (x1500)
-cannot see fine details of organelles
-limited resolution due to light wavelength
-cannot view internal strucutres
advantages and disadvantages of transmission electron microscope
ad;
-provides the highest resolutin (x 1000000)
-allows visualization of small organelles eg.ribosomes, endoplasmic reticulum and lysosomes
-provides isnites into cell structure and function
dis;
-specimens must be very thin and completely dehydrated before imaging
-recquires extensive sample prepration, may introduce artifacts
-time consuming and expensibe sample prepartion
-images produced balc and white unless artificially coloured
advantages and disadvantages of scanning electron microscope
ad;
-produces detailes 3D images of specimens
-has much higher resolution than a light microscrope
dos;
-specimes must be dead because they are placedin a vaccum
-time consuming and expensive sample preparation
-lower resolutio than transmission electron microscope but higher than light
-images are black and white unless artificially coloured
describe cryogenic electron microscopy
-uses electron microscope
-involves flash freezing solution of proteins or other biomolecules, cryogenic temp used
-image reconstructs 3d shape of molecule
-used to reveal how proteins work, how malfunction of disease and how to target them with drugs
-less intense electron bemas used, evaporation fo water no longer problem
describe freeze fracture
-biological material instantly frozen solid in liquid nitrogen, at this temp living materials do not change shape
-solidised tissue broken up in vaccum exposed surfaces allowed to lose so,e of their ice
-carbon replica of exposed surface made, coated metal, mask of surface is examined using electron microscope
-resulting elcron micrograph described being produced by freeze etching
fluorescence miscroscopy
-flurorescent dyes absorb light at 1 wavelength and emit at another longer wavelength
-some dyes bind specifically to target molecules in cells
-reveals cellular location using fluorescnece microscope
-illuminating light passed through 2 sets of filters
-1st filters light before reaches soecimen, pass only wavelengths excite specifically hosen fluorescennt dye
-2nd blocks out light and passes only those wavelengths emitted of when the dye fluoresces
cytoskeleton
complex netowrk of fibres
made of 3 proteinaceous elements
microfilaments
intermediate filaments
microtubules
microfilaments
protein subunits- actin
strucutre- two intertwined strands
functions- maintain cell shape, motility, contraction, cytokinesis
can grow or shrink as actin subunits added or taken away
intermediate filmanets
protein subunits= fibrous protein eg.keratin
strucutre- fibres wound into thicker cables
functions- maintai cell shaoe, anchor nucleus and organelles
form dense network help anchor nucleus into place
microtubules
protein subunits- a and b tubulin dimers
strucutre- hollow tubes
functions- maintain cell shape, motilit, move chromsomes, move organelles
largest cytoskeletal component, grows and shrinks as tubulin subunits added or removed
what do all components of cytoskeleton have in common
all help maintain cell shape
importance of cytoskeleton being a dynamic structure
can move and change alter cell shape meaning materials can move in and out of ell, and cell itself can move
what organlle is involved in final secretion of digestive enzymes from cell
secretory vesciels
which organelle replicates mitosis and generates spindle
centrioles
what is the sequence of sedmentation of cell components with increasing speed o centrifiguation
the smaller the organelle the highest its speed
what contains highest conc of RNA
nucleolus
LUCA
last universal common ancestor
all living organisms originated from one common ancestor
LUCA-
gave rise to
prokarayotic
eukarayotic
prokarayotic give rise to;
-eubacteria
-archae
eukarayotic give rise to;
-protist
-fungi
-plant
-animal
what are the two processes which are though to have led to the origin of eukarayotes
1- infolding of the prokarayotic cell membrane- creates internal micro-enviornments, advantage= increase efficiency
2- theory of endosymbiosis
-early eukarayotic cells engulfed aerboic bacteria but did not digest them, led to the origin of mitpchondria
-early eukarayotic cells engulfed photosynthetic bacteria, did not digest them, led to origin of chloroplast
explain infolding of the prokarayotic cell membrane
1.ancestral prokarayote (lacks internal membrane compartmentalisation)
2.given enviornmental or abiotic changes prokarayotic cells adapted their structure by forming invaginations of cell membrnae
3. this internal folding formed a vesicle that trapped dna round in the cytoplasm forming nucelar membrane
4. those primitive eukarayotic cells evolved by forming other membrnae bound organelles that originiated from the infolding of plasma membrane
describe theroy of endosymbiosis
- formation mitochondrion
eukarayotic cells engulfed ancwestor aerobic bacteria
evidence for this, it that mitochondira had an internal membrane composed of proteins found in abcteria cells + an external membrane composed of proteins found in eukarayotic cells - formation chloroplasts same thing but engulfmenet of photosyntheticn bactertia
note// fluidity of membrane allows endocytosis to occur
what is structural evidence for the engulfement of both the mitochondira and chloroplasts
- same approcimate site and shape as prokarayotes
-mitochondria and chloroplast, double membrane, inner is from prokarayotic and outer membrane from eukarayotic
-both have 70s ribosomes while eukarayotes has 80s ribosomes
genetic evidence for the engulfement of both the mitochondira and chloroplasts
-circular naked DNA like prokarayotic cells, eukarayote= linear- dna wraped histone proteins
-share common DNA sequences with bacterial cells
functional evidence for the engulfement of both the mitochondira and chloroplasts
-move independetly without support cytoskeleton, move independently with eukarayotic cell
-reproduce independetly of host cell through process similar to binar fission
-are inhibited by antibiotics as are prokarayotes
endosymbiosis
because one cell livid with the other and became increasingly interdependet until the unit could only exist as a whole
what is the cell theory statement
first cells must have arisen from non living material
what is the haldane and oparin model for origin of cells
independently proposed nearly identical hypothesis for steps of how life was created
what are the steps of cell theory
= prebiotic formation of carbon compounds
inroganic compounds -> organic compounds (condition early earth led to formation carbon compounds eg. amino acids, nitrogenous bases
-> polymer (monomers may have been able to spontaneously form polymers an early earth via anabolic reacions creating proteins and RNA strands
->self-replication (formation nucleis acid polymer (likely RNA) that can encode hereditary info, self replicate and catalyze chemical reactions
->formation of cell (protocell), (packaging molecules into membranes with an internal chemistry different from surroundings. Fatty acids can spontaneously form spherical bilayers, perhaps encapsulating the slef replicating molecules
-formation of protocells that carry out metabolic reactions within an enclosed system is the final step of oparin haldane hypothesized process for origin of life
more simplified cell theory steps
1- spontaneous formation of simple organic molecules from inorganic compounds
2-assembly of carbon compounds into polymers
3- formation of polymer that can self replicat (enabling inheritance and variation)
4-packaging of molecules into compartments with an internal chemistry different from the surroudnings
what are the challenges when explaining origin of cells
-difficult to directly test hypothesis related to origin of cells because it happened billions of years ago as a result;
-conditions on earth were very different
-its not possible to replicate with certainty the conditions that would have ecisted on early earth
-well preserved fossils are rare
-the methods used to estimate dates of the first living cells have ranges of uncertainty
what were the conditions on early earth
atmosphere- “reducing atmosphere”; with higher porportion of reactive gases such as ammonia and hydrogen, very little oxygen
temperature- significantly warmer than today due to heat from asteroid collisions and accretion (coming together/ formation of the planet)
uv radiation- no ozone layer to block radiation from the sun so intense UV radiation reached the surface
volcanic activity- volcanic eruptions released gasses (H2O and CO2) into the atmosphere
asteroid bombardment- constant bombardment by asteroids as the solar system was forming
what did the atmosphere on early earth contain
hydrogen nitrogen waper vapous methane ammonia hydrogen sulfide
these gases came from volcanic activity, did not contain oxygen only ntil plants started photosynthesising
what was the first step of the oparin haldane test
test served to test hypothesis of whether simple carbon compounds can be formed from iorganic compounds
they simulated earth conditions, earths water cycle
- heat source- simulate volcanic activity
-water- simulate primodial ocean
this water evaporised
electrodes- simulate lightning
-gas inlet with ammonia, methane, hydrogen, carbon dioxide and water vapour- simulate atmosphere
cooling jackets condensed water into a primodial soup, after resting for a week soup found to contain simple amino acids and comples oily hydrocarbons
describe the assembly of carbon compounds (organic compounds) into polymers
polymerization second step in oparin haldane hypothesis
small molecules (monomers) combine chemically to produce large molecules (polymer)
anabolic reaction, condensation reaction
what was the evidence of assembly of carbon compounds into polymers
genesadapted to organisms enviornments, genes likely to have been present in LUCA are clue about where and how LUCA lived
genes indicated LUCA;
-obligate anaerobe
-chmoautotroph , obtain eneergy from hydrogen and converting co2 and nitrogen into essential organic compounds
-able to live extreme heat
-likely to have been raised from hydrothermal vents, issue supply reduced iroganic chemicals
descirbe thrid step of oparin haldane hypothesis
formation of polymer that can self replicate
once formed small organic molecules may have been able to spontaneously form polymers on early earth
evidence of formation of polymer that can self replicate
-amino acids can spontaneously link togehter to form proteins
-fatty acids could have been concentrated sufficiently to assemble into membranes
-RNA nucleotides can link together when exposed to a catalyst found in clay or in water
RNA as first molecule of inheritance
-RNA first molecule to pass genetic info between generations
-DNA very stable and effective stroing info but not able self-replicate, enzymes recquired
-RNA can store info + self replicate, can catalyse formation of copies of itself
-RNA that function as catalyst= ribozymes
-in ribosomes RNA is found in catalytic site and plays role in peptide bond formation
RNA as a catalyst
ribosomes contain ribozyme, forms peptide bond between amino acids during translation
all cells have ribosomes, ribosome used in translation to built polypeptide from an mRNA code
evidence of self replicating polymers
evidence RNA arose before DNA found in chemical differences between them
-ribose easily produced lab to attempt to simulate conditions primative earth
-deoxyribose harder to make, produced from ribose in reaction catalyzed by protein enzyme, suggests ribose predates deoxyribose in cels
-DNA replaced RNA as more stable repository of genetic info
-deoxyribose in DNA makes it more stable than chains RNA so that much greater lengths of DNA can be maintained
-hydrogen bonds holding double helical strucutre of DNA add to stability
-use of thymine instead uracil enhances DNA stability. Thymine much less succeptible to mutation
step 4 of oparin haldane hypothesis
formation of membranes to package organic molecules
membranes can exist as vesicles, micelles or bilayers
early cell membranes may have been formed from fatty acids, structurally simpler than phospholipids
formation of an internal enviornment (due to bilayer) means optimal can be maintained
evidence of formation of fatty acid vesicle
fatty acids in watery solution, attracted to each other, will spontaneously form spherical strucutres= micelles
shape micelle tucks hydrophobic tail together, away from water solvent
under high conc, under appropriate PH conditions, can form vesicles instead of micelles
evidence of formation of phospholipid vesicle
chemist mixed glycerol+phosphate+many fatty acids
put mixture in mixture gases (earths atmoshpere), phospholipids formed spontaneously
phosphoilipids attarcted to eachother form membrane
evidence for formation of protocells
chemist included aminoa cids _ nucleic acid in mixture they were trapped inside membrane compartments spontaneously
shows molecules likely existed on early earth could spontaneously give rise to membrane spheres and could trap randomly nearby molecules inside
