BIOL 191 Exam 2 ch. 24 - 29

Hypothetical steps in the origin of simple cells

1. abiotic synthesis of small organic molecules
2. joining of these small molecules into macromolecules
packaging of molecules into protocols, membrane-bound droplets that maintain a consistent internal chemistry
3. The packaging of these molecules into protocells, droplets with membranes that maintained an internal chemistry different from that of their surroundings
4. 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

Pteridophytes

ferns and their relatives

seed

consists of an embryo and its food supply, surrounded by a protective coat

Gymnosperms

have “naked” seeds that are not enclosed in chambers

Angiosperms

have seeds that develop inside chambers called ovaries (ovaries later become fruit)

Endosporic development

gametophytes develop within the walls of spores that are retained within tissues of the parent sporophyte

Ovule

the integument and the tissues it encloses together make up

Integument

a protective layer of sporophyte tissue

Pollen grains

which consist of an enclosed male gametophyte

Pollination

the transfer of pollen to the part of a seed plant containing the ovules

Flower

an angiosperm structure specialized for sexual reproduction

Sepals

enclose the flower

Petals

brightly colored and attract pollinators

Stamens

produce pollen
A stamen consists of a stalk called a filament, with a
sac called an anther where the pollen is produced

Carpels

produce ovules in an ovary
A carpel consists of an ovary at the base and a style leading up to a stigma, where pollen is received

Sponges

Animals in the phylum Porifera

Filter feeders

capturing food particles suspended in the water that passes through their body