Cell theory 1 Flashcards
What are the possible spots for accumulation of complex C-compounds and life formation?
hot springs (terrestrial) and hydrothermal vents (ocean)
Prebiotic period vs period after the first life conditions (O2, CO2, CH4, UV radiation levels, temperature, natural disasters)
prebiotic: low, high, high, high (no ozone layer), high (greenhouse gases), intense meteorite bombardment and frequent lightning storms, after: increased, everything else decreased
Exceptions to the general definition of life
1| Mature erythrocytes (no nucleus, no DNA)
2| Aseptate fungal hyphae (continuous rows of fused cells)
3| Mule (sterile, reproduction impossible)
Steps the life (1st cell) formation
1| Inorganic into simple organic compounds, Miller-Urey experiment (primordial soup)
2| Simple organic compounds (monomers) into polymers (mixture of monomers on hot clay, rocks, sand -> polymers)
3| Spontaneous formation of plasma membrane (coalescence of phospholipids) around the cell
4| Self-replicating molecules (basis of inheritance)
Why is RNA the presumed first genetic material (benefits vs weakness)
capable of both storing genes and self-replication without enzymes (unlike DNA) – some types of RNA can act as catalysts
however has less storing capacity than DNA and is more often subject to mutations
LUCA
the most recent population from which all (eukaryotic) organisms on Earth share a common descent
What is the evidence for the existence of LUCA
1| The universality of genetic code
2| All life shares a common mechanism of transcription and translation
3| Certain genes are distributed across all organisms (e.g. instructions for DNA replication)
Approaches used to estimate the dates of the 1st cells and LUCA (because microbes don’t leave fossils)
biochemical evidence and phylogenetic comparison
Describe biochemical evidence (first evidence of life)
chemicals produced by cellular processes that provide evidence of past or present life. The earliest evidence of life dates to 3.42 billion years ago in the form of stromatolites (layers of sediment laid down by microbes, Australia) – LUCA near hydrothermal vents (genomic analysis) genes proposed to belong to LUCA are involved in the use of H2 as an E source
Describe phylogenetic comparison (LUCA)
comparing the genome (genomic sequences) of different species to develop a timeline for evolutionary divergence – the number of differences between the genomes of two species is proportional to the time since they diverged from a common ancestor. Scientists established the original LUCA genome by searching for genes present in both prokaryotic domains (bacteria and archaea) - 355 genes are proposed to have originated directly from LUCA
What is the molecular clock (example)?
the estimated time of evolutionary divergence using genomic comparisons (the mutation grade of DNA/RNA/proteins) based on the assumption that there is a direct correlation between the number of sequence differences and the time since two species diverged, e.g. if a gene mutates at 1 base pair per 100 000 years rate and 2 species have 6 differences in a gene sequence, divergence occurred 600 000 years ago
When did LUCA’s evolution into archaea and bacteria happen?
at any point between 2 to 4 billion years ago – based on phylogenetic comparisons and the molecular clock
What is magnification?
the number of times an object is magnified (how much smaller/larger is the image than the real specimen). As magnification increases, FOV decreases
How is magnification calculated?
(image size)/(actual size)
What is resolution?
the ability of a microscope to show two close objects separately, depends on the wavelength of the rays that pass through the spectrum (e- have a shorter wavelength so EM has a higher resolution)
What is the scale bar?
a line added to the micrograph to show the actual size of the structure
Compare LM and EM (what passes through the specimen, FOV, magnification, resolution, colors, type of specimen)
LM: beam of light, larger, up to 500x, 0.25 microm apart, visible, alive
EM: beam of electrons, smaller, up to 500 000x, 0.25 nanom apart, black-white, dead
What are the two types of EM?
TEM (transmission electron microscope) for the interior and SEM (scanning electron microscope) for the surface of cells
Freeze-fracture EM
physically breaking apart frozen biological samples through the weakest point of the cell – structural details exposed by the fracture plane are visualized by deposition of Pt-C to make a replica for examination in the EM
Cryogenic EM
structures of proteins, nucleic acids, and other biomolecules – studying how they move around and change as they perform their functions (alive)
Cell theory
1| Cells are the basic units of life (nothing smaller than the cell can survive independently)
2| All living things consist of cells
3| New cells come from pre-existing cells by the process of cell division
Discrepancies (exceptions) to the cell theory
1| Striated (skeletal) muscles – more than 1 nucleus per cell – long cells, around 30 mm
2| Giant algae, Actabularia – single-celled organism but up to 20 cm long
3| Aseptate Funghi – fungal hyphae (narrow thread-like structures) are made up of rows of cells usually separated with septa but some funghi lack this septa (multinucleated)
Functions of life
metabolism, response, nutrition, excretion, reproduction, growth, homeostasis, movement
How did anucleate and multinucleated adapt their structure to fit their function?
anucleate cells don’t have a nucleus (cannot transcribe DNA to make mRNA and synthesize proteins – erythrocytes to have more space for Hb to carry more O2) and multinucleate cells have multiple nuclei (more mRNA and proteins), e.g. skeletal muscle/aseptate fungi
Common features and differences in prokaryotic and eukaryotic cells
common: plasma membrane, cytoplasm, DNA and ribosomes present
differences: size (eukaryotic much larger) and complexity (eukaryotic cells are compartmentalized (many differences arise from this fact like type of cell division, DNA structure…))
All components of a prokaryotic cell
cell wall, plasma membrane, nucleoid, mesosome, thylakoids, pili, plasmoid, cytoplasm, flagellum, 70S ribosomes, capsule
All components of a eukaryotic cell
cell wall (plant), plasma membrane, nucleus, chloroplast (plants), cilia, cytoplasm, flagella, 80S ribosomes, rough and smooth endoplasmic reticulum, Golgi apparatus, vesicles (lysosomes in animal, vacuole in plant), mitochondria, microtubules and microfibrils (cytoskeleton)
Binary fission
means of asexual reproduction in prokaryotes, phospholipids get added to the existing plasma membrane, and the offspring produced is genetically identical to the parent cell, in ideal conditions happens every 20 minutes
Cell wall function
provides shape, and allows the cell to withstand turgor pressure without bursting, the principal component of prokaryotic cell wall is peptidoglycan, of fungi chitin, and of plant cells cellulose
Plasma membrane function
controls transport in/out of the cell (endocytosis and exocytosis), composed of phospholipids and proteins
Nucleoid vs plasmoid
nucleoid is the region where circular, naked prokaryotic DNA is situated and a plasmoid is additional genetic info of the cell and it promotes variation
Mesosomes
infoldings of the plasma membrane, it is the site of CR
Pilli vs flagellum
pilli used for adhesion to the surface and in bacterial conjugation (sexual reproduction by the exchange of DNA between cells) and flagellum is a thread that moves the cell by propelling it through its aqueous environment
Cytoplasm function
also called cytosol, it is a fluid substance and the site of all metabolic reactions (contains enzymes that catalyze many metabolic reactions)
How are eukaryotic cells more complex than prokaryotic?
they are compartmentalized with internal membranes, meaning that they have organelles (each is specialized for a certain function)
What are the advantages of being compartmentalized
1| pH, enzyme, and substrate levels can be kept at optimal levels for each specific process happening inside the cell (processes cannot intervene with each other)
2| Free radicals (mitochondria), peroxide, and other strong oxidizing agents cannot intoxicate/damage other parts of the cell
3| Organelles can be moved around the cell (mitochondria for example)
Nucleus structure and function
the largest and heaviest organelle (animal) that controls the process of gene expression – it is surrounded by a nuclear membrane (phospholipid bilayer) with nuclear pores, contains nucleoplasm (= nucleolus + chromatin) – nucleolus contains densely packed DNA + RNA + proteins and chromatin 46 uncoiled DNA molecules associated with histones
rER vs sER function (plus rER structure)
has a single membrane and is made out of cisternae (flattened membrane sacs) – it has bound ribosomes on cisternae – rER function is to refine proteins by giving them quaternary structure (prosthetics…) and sER function is the production of carbohydrates are lipids
Golgi apparatus structure and function
made our of cisternae shorter and more curved than those in ER and has no ribosomes bound – its function is the final modification/refinement of proteins created in ER (packed into vesicles)
Vesicles function and examples (plant and animal)
organelles with a single membrane with fluid inside which can be formed as a result of budding of GA or after endocytosis – e.g. in animals are usually non-permanent and small like lysosomes (lysozyme which is used in the internal digestion of damaged cells) and peroxisomes (catalase), and permanent and larger in plants like vacuole (largest organelle in plant cells, stores water and other juices with dissolved compounds (nicotine in tobacco)
