Hypothetical steps in the origin of simple cells
abiotic synthesis of small organic molecules
joining of these small molecules into macromolecules packaging of molecules into protocols, membrane-bound droplets that maintain a consistent internal chemistry
The packaging of these molecules into protocells, droplets with membranes that maintained an internal chemistry different from that of their surroundings
The origin of self-replicating molecules that eventually made inheritance possible
Miller and Urey experiment
in 1953, Miller and Urey showed that the abiotic synthesis of organic molecules in a reducing atmosphere is possible, or the first organic compounds may have been synthesized near volcanoes or deep-sea vents, or organic molecules have also been found in meteorites
Proposed role of RNA in early life
The first genetic material was most likely RNA, not DNA. RNA plays a central role in protein synthesis, but it can also function as an enzyme-like catalyst. Such RNA catalysts are called ribozymes. Some ribozymes can make complementary copies of short pieces of RNA, provided that they are supplied with nucleotide building blocks.
General characteristics of prokaryotes
Most prokaryotes are unicellular, although some species form colonies; Most prokaryotic cells have diameters of 0.5–5 μm, much smaller than the 10–100 μm diameter of many eukaryotic cells; Prokaryotic cells have a variety of shapes; The three most common shapes are spheres (cocci), rods (bacilli), and spirals
Cell wall
maintains cell shape, protects the cell, and prevents it from bursting in a hypotonic environment; Eukaryote cell walls are made of other materials: Plants – cellulose, Fungi - chitin
peptidoglycan
a network of modified sugars cross-linked by polypeptides
Gram-positive bacteria
have relatively simple walls composed of a thick layer of peptidoglycan
Gram-negative bacteria
have less peptidoglycan and an outer membrane that can be toxic; Gram-negative bacteria are more likely to be antibiotic resistant
Capsule
The cell wall of many prokaryotes is surrounded by a sticky layer of polysaccharide or protein
Endospores
Some bacteria can develop resistant cells; Dormant reproductive form of the bacterium
Fimbriae
allow them to stick to their substrate or other individuals in a colony
Pili
(sex pili) longer than fimbriae and allow prokaryotes to exchange DNA
Taxis
the ability to move toward or away from a stimulus ex. Chemotaxis is the movement toward or away from a chemical stimulus (positive or negative)
Internal organization
Prokaryotic cells lack the complex compartmentalization associated with the membrane- enclosed organelles found in eukaryotic cells. However, some prokaryotic cells do have specialized membranes that perform metabolic functions. These membranes are usually infolding of the plasma membrane.
Nucleoid
unlike eukaryotes, prokaryotes lack a nucleus; their chromosome is located in the nucleoid, a region of cytoplasm that is not enclosed by a membrane
Plasmids
in addition to its single chromosome, a typical prokaryotic cell may also have much smaller rings of independently replicating DNA molecules
Nutritional modes
Photoautotrophy, chemoautotrophy, photoheterotrophy, and chemoheterotrophy
Anaerobic respiration
Substances other than O2, such as nitrate ions(NO3-) or sulfate ions(SO4 2-), accept electrons at the "downhill" end of electron transport chains
Nitrogen fixation
Some cyanobacteria and some methanogens (a group of archaea) convert atmospheric nitrogen (N2) to ammonia (NH3) Essential component of nitrogen cycles in ecosystems
Heterocysts
In the cyanobacterium Anabaena, photosynthetic cells and nitrogen-fixing cells called heterocysts (or heterocytes) exchange metabolic products
Biofilms
In some prokaryotic species, metabolic cooperation occurs in surface-coating colonies
Reproduction
Prokaryotes reproduce quickly by binary fission and can divide every 1–3 hours Key features of prokaryotic biology allow them to reproduce quickly: They are small, They can reproduce by binary fission (asexual), They have short generation times Short generation times = relatively rapid evolution
Transformation
A prokaryotic cell can take up and incorporate foreign DNA from the surrounding environment in a process
Transduction
the movement of genes between bacteria by bacteriophages (viruses that infect bacteria)
Conjugation
the process where genetic material is transferred between prokaryotic cells Ex. Via a sex pilus
Chlamydias
These parasites can survive only within animal cells, depending on their hosts for resources as basic as ATP
Spirochetes
These helical gram-negative heterotrophs spiral through their environment by means of rotating, internal, flagellum-like filaments
Cyanobacteria
These gram-negative photoautotrophs are the only prokaryotes with plantlike, oxygen-generating photosynthesis
Gram-positive bacteria
Gram-positive bacteria rival the proteobacteria in diversity
Extremophiles
The first prokaryotes assigned to domain Archaea live in environments so extreme that few other organisms can survive there
Extreme halophiles
live in highly saline environments, such as the Great Salt Lake and the Dead Sea
Extreme thermophiles
thrive in very hot environments
Methanogens
archaea that release methane as a by-product of their unique ways of obtaining energy. Many methanogens use CO2 to oxidize H2, a process that produces both energy and methane waste
Decomposers
breaking down dead organisms and waste products
Symbiosis
an ecological relationship in which two species live in close contact: a larger host and smaller symbiont
Mutualism
an ecological interaction between two species in which both benefit
Commensalism
an ecological relationship in which one species benefits while the other is not harmed nor helped in any significant way
Parasitism
an interaction in which a parasite eats the cell contents, tissues, or body fluids of its host
Pathogens
Parasites that cause disease are known as pathogens, many of which are prokaryotic.
Endosymbiosis
a symbiotic relationship in which one organism lives inside the body or cell of another organism
Endosymbiont theory
proposes that mitochondria and plastids were formerly small prokaryotes that began living within larger cells
Excavata
Some members of this supergroup have an "excavated" groove on one side of the cell body
Euglenozoa
A diverse clade that includes predatory heterotrophs, photosynthetic autotrophs, and parasites The main feature distinguishing them as a clade is a spiral or crystalline rod inside their flagella Some species can be both autotrophic and heterotrophic
SAR
The “SAR”clade is a diverse supergroup named for the first letters of its three major clades, stramenopiles, alveolates, and rhizarians
Stramenopiles
Some of the most important photosynthetic organisms on Earth
Diatoms
highly diverse, unicellular algae; have a unique two-part, glass-like wall of silicon dioxide (SiO2)
Brown algae
largest and most complex algae All are multicellular, and most are marine
Alveolates
subgroup of the SAR clade that have membrane-bounded sacs (alveoli) just under the plasma membrane ex. Dinoflagellates and ciliates
Dinoflagellates
have two flagella, and each cell is reinforced by cellulose plates
Ciliates
a large varied group of protists, are named for their use of cilia to move and feed
Rhizarians
Subgroup of SAR clade. many species of amoebas, most of which have pseudopodia that are threadlike in shape
Forams
Threadlike pseudopodia extend through the pores in the test
Tests
porous shells
Archaeplastida
the supergroup that includes red algae, green algae, and land plants
Red algae
reddish in color due to an accessory pigment called phycoerythrin, which masks the green of chlorophyll
Green algae
a structure and pigment composition much like the chloroplasts of plants
Unikonta
This supergroup of eukaryotes includes amoebas that have lobe- or tube-shaped pseudopodia, as well as animals, fungi, and non-amoeba protists that are closely related to animals or fungi
Amoebozoans
amoebas that have lobe- or tube-shaped pseudopodia
Protists
Protists can be single or multi-celled; Most are unicellular Protists are found in diverse moist environments Some protists reproduce asexually, while others reproduce sexually; All three* sexual life cycles found in protists Protists show a wide range of nutritional diversity; Can be photoautotrophs, heterotrophs, or mixotrophs
Derived traits of land plants
Alternation of generations life cycle Multicellular, dependent embryos Walled spores produced in sporangia Apical meristems
Alternation of generations life cycle
each generation gives rise to the other; this type of reproductive cycle evolved in various groups of algae but does not occur in the charophytes, the algae most closely related to plants
Embryophytes
The multicellular, dependent embryo of plants is such a significant derived trait that plants
Sporangia
multicellular organs that produce spores; Spore walls contain sporopollenin
Apical meristems
localized regions of cell division at the tips of roots and shoots
Cuticle
a waxy covering of the epidermis that functions in preventing water loss and microbial attack
Stomata
specialized pores that allow the exchange of CO2 and O2 between the outside air and the plant
Chitin
a strong but flexible polysaccharide
Yeasts
single cells
Mycelia
networks of branched hyphae
Hyphae
filaments adapted for absorption
Haustoria
allow them to extract or exchange nutrients with plant hosts
Mycorrhizae
mutually beneficial relationships between fungi and plant roots
Ectomycorrhizal fungi
form sheaths of hyphae over a root and also grow into the extracellular spaces of the root cortex
Arbuscular mycorrhizal fungi
extend hyphae through the cell walls of root cells and into tubes formed by invagination of the root cell membrane
Chytrids
found in freshwater and terrestrial habitats Chytrids have flagellated spores and are thought to have diverged early in fungal evolution
Zygomycetes
include fast-growing molds, parasites, and commensal symbionts Produce a resistant zygosporangium
Glomeromycetes
form arbuscular mycorrhizae with plant roots About 80% of plant species have mutualistic relationships with glomeromycetes
Ascomycetes
live in marine, freshwater, and terrestrial habitats Called the sac fungi Produce spores in sacs called asci
Basidiomycetes
important decomposers and ectomycorrhizal fungi Ex. mushrooms Produce spores on basidia
Lichen
a symbiotic association between a photosynthetic microorganism and a fungus
Vascular tissue
cells joined into tubes that transport water and nutrients throughout the plant body
Vascular plants
most plants have vascular tissue for the transport of water and nutrients
Bryophytes
nonvascular plants; an informal name for plants that lack an extensive transport system
Seedless vascular plants
The plants in these clades lack seeds, which is why collectively the two clades
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