LUCA
last universal common ancestor
What domain(s) do we find prokaryotes in?
- archae and bacteria
Cell Culture
- plated on the surface of a solid substance bathed in a nutrient medium
- normal contact-inhibited, anchorage-dependant human cells are attatched to the surface of a coated culture dish as a monolayer
- anchorage-independant tumor cells attach to the surface of a coated culture dish and grow as foci
Normal Cells
- anchorage-dependant; usually attatched to the extracellular matrix and experience highly regulated growth
- dependant on growth factors provided in serum
- contact-inhibited; stop dividing because of declining growth factors or contact
- form monolayer at confluence
-have a finite lifespan to their Hayflick limit; normal HDF ~50-100 doublings
Transformed (malignant) Cell
- anchorage-independant (can grow in suspension)
- growth factor independant (do not need serum, but can grow better in it)
- not contact-inhibited
- can grow beyond a confluent monolayer (form foci, or multiple layers)
- grow indefinitely
Preparation of a Primary Culture
- use mechanical or enzymatic disruption to break down a tissue into individual cells
- place cells in a suitable environment
First Human Cell Culture
- Henrietta Lacks cervical cancer sample collected by Dr. George Gey and Margaret Gey
- HeLa cells; henrietta passed away two years later, and family did not know for decades that her cells were alive
Cryopreservation
Subjecting organisms to low temperatures - cryobiology: studying the effect of the above
Advantages of Cryopreservation
Biological backups: ensure cells of interest will always be available in the future (research, medical, commercial uses)
- allows for repetitions of the same experiment
- store cells for additional work at different stages at differentiation or after a variety of experimental treatments
- “suspended animation” stops biological time when cells are stored at < -130ºC
Cryoprotective Agents
Help to prevent danage caused by the freezing process.
- initial discovery by Polge, Smith, and Parkes (1949) using chicken spermatozoa with glycerol as the cryoprotectant
- most common cryoprotectants for eukaryotic cells DMSO (dimethylsulphoxide) at 5-15% v/v or glycerol at 5-20% (v/v) or more
Appearance of Cells (4 phases)
- Abioitic synthesis of simple organic compounds (ie. amino acids, nitrogenous bases)
- Abiotic polymerization of these monomers into macromolecules (ie. protiens, DNA)
- Generation of a macromolecule capable of storing genetic information and replication
- Encapsulation of this molecule in a membrane, forming a primitive cell
RNA Subunits as First Informational Molecule
- RNA monomer subunits as precursors to DNA monomer subunits
- riboenzymes (RNAs folding into shapes and serving as enzymes) can synthesize short pieces of RNA in presence of nucleotides
Liposomes
hollow, membrane-bound vesicles of differing sizes that form when lipids are mixed with water
- can carry out metabolic reactions in presence of enzymes and their substrates
- primordially may have trapped RNA, forming protocells
Prokaryotes
- bacteria and archaea
- non-nucleated, no membrane-bound organelles (DNA is folded into a compact structure called a nucleoid)
- small (1-5 um)
- divide via binary fision
- circular DNA, associates with protiens
- 70s ribosomes
Eukaryotes
- large (10-100um)
- divide via mitosis/meiosis
- 80S ribosomes
Archaea
one of the three domains of life (bacteria, archaea, eukarya)
- encompasses many species that live in extreme habitats on earth and have diverse metabolic strategies
- believe to be descended from a common ancestor of eukaryotes, long after it diverged from bacteria
- much more similar to eukaryotes than bacteria in DNA replication, transcription, RNA processing, and initiation of protien synthesis
- unique features are ribosomal RNA and membrane phospholipids
- DNA is tyically circular and complexed with moderate amounts of protiens that resemble eukaryotic histone
Methanogens
- type of archaea
- obtain energy from hydrogen while converting carbon dioxide to methane
Halophile
Grow in extremely salty environments
-archaea
Macidophiles
Thrive in acidic hot springs where pH is as low as 2 and temperature can exceed 100 degrees celsuis.
- archaea
Limitations on Cell Size
- the requirement for an adequate surface area/volume ratio
- rates at which molecules diffuse
- need to maintain adequate local concentrations of substances involved in cellular processes
Surface Area/ Volume Ratio Limitation
as a cell increases in size, surface area does not keep pace with volume, and so necessary exchange of substances cannot occur
Rate of Diffusion Limitation
- rate of diffusion decreases as size of molecule increase; size of cell is limited by diffusion rates of molecules it contains
- can be bypassed by active transport for ions, macromolecules, etc
- another bypass: cytoplasmic streaming/cyclosis; active movement/mixing of cytoplasmic components
Need for Adequate Concentrations of Reactants and Catalysts Limitation
- amount of reactants and catalysts must increase proportionally with cell size
- can be bypassed via compartmentalization of activities (localizing certain processes witin specific regions of the cell that need their products) in organelles
Cyanobacteria
- posess extensive internal membrane systems on which photosynthesis is carried out
- one of few types of prokaryotic cells which have internal membrane systems
