Bio 121: Impacts of microbes Flashcards
Bacteria Protists Fungi Viruses
Most eukaryotes are single celled organisms
Protists are classified as eukaryotes; they are in domain Eukarya. They have a nucleus and other membrane bound organelles, which provide specific locations for cell functions. Eukaryotic cells also have a cytoskeleton, which provides structural support and be able to have irregular shapes to grow, feed and move.
Prokaryotes
Do not have a nucleus or membrane bound organelle. Much simpler than eukaryotic cells. Do not have a cytoskeleton, therefore limiting the extent in which they can maintain asymmetric forms or change shape over time.
Structural and function diversity of protists
Classified in a number of different groups. Protists are unicellular. Single celled protists are justifiably the simplest eukaryotes. But at a cellular level they are very complex. Unicellular protists carry out essential functions the same as any multicellular organism, but do this by using subcellular organelle. Organelles used include, Golgi apparatus, ER, lysosomes and nucleus. Some protists also rely on organelle not found in most other eukaryotic cells, e.g contractile vacuoles (pump excess water). Protist are diverse in their nutrition, some are photoautotrophs and contain chloroplasts. some are heterotrophs, absorbing organic molecules or ingesting larger food particles. Other protists are called mixotrophs which use both methods.
Reproduction and life cycles varies among protists; asexually or sexually (use meiosis and fertilization).
Four supergroups of Eukaryotes
All groups are shown diverging simultaneously from a common ancestor, this is not correct however, we do not know which one diverged first.
Endosymbiosis in eukaryotic evolution
Evidence suggests that much of protistan diversity has its origins in endosymbiosis, a relationship between 2 species in which one organism lives inside the cell or cells in another organism (host). Mitochondria and plastids are derived from prokaryotes that were engulfed by the ancestors of early eukaryotic cells. A defining moment in the origin of eukaryotes occurred when a host cell engulfed a bacterium that would later become an organelle- mitochondrion. To determine which prokaryotic lineage mitochondrion came from DNA was compared of mitochondrial genes to those found in major clades of bacteria and archaea.
SAR
Super group contains 3 very diverse clades: Stramenopila (photosynthetic organisms), Alveolata (photosynthetic species and important pathogens e.g plasmodium) and Rhizarian subgroup (species of amoebas, most have pseudopodia that are used in movement to capture prey).
Archaeplastida
Supergroup that includes red algae and green algae along with plants. Include unicellular species, colonial species and multicellular species e.g volvox. Protists in archaeplastida include key photosynthetic species that form the base of food webs in aquatic communities.
Unikonta
Supergroup that have lobe or tube shaped pseudopodia, as well as animals, fungi and non-amoeba protists. The unikonts were the first eukaryotic supergroup to diverge from all other eukaryotes, however this hypothesis isn’t widely accepted.
Plastid evolution
In eukaryotic history there is evidence that a lineage of heterotrophic eukaryotes acquired an additional endosymbiont (photosynthetic cyanobacterium that then evolved into plastids. This lineage gave rise to 2 lineages of photosynthetic protists or algae.
Steps
Cyanobacteria are gram negative. Plastids in red and green algae are surrounded by 2 membranes. Transport proteins in these membranes are homologous to proteins in the 2 membranes of cyanobacteria, supporting that plastids originated from a cyanobacteria endosymbiont. On different occasions red and green algae underwent secondary endosymbiosis, meaning they were ingested in the food vacuoles of heterotrophic eukaryotes and became endosymbionts.
Structural and functional adaptations contribute to success
Prokaryotic populations have been subjected to natural selection in many different environments. Most prokaryotes are unicellular, some do stay attached to each other after cell division. Typically 0.5-5 nanometres in diameter.
Most common shapes of prokaryotes or cocci (sphere), in pairs (diplococci), in chains (streptococci) and in clusters (staphylococci). Bacilli (rod shaped), usually solitary but sometimes arranged in chains (streptobacilli). Spiral prokaryotes include spirilla, which range from comma-like shapes to loose coils and spirochetes which are corkscrew shaped.
Cell-surface structures
All prokaryotic cells have a cell wall, which maintains cell shape, protects the cell and prevents it from bursting in a hypotonic environment. In a hypertonic environment most prokaryotes lose water and shrink away from the cell wall, which can inhibit cell reproduction.
The cell walls of prokaryotes differ in structure from those eukaryotes. In eukaryotes cell wall normally made of cellulose or chitin. In bacteria walls contain peptidoglycan, a polymer composed of modified sugar cross-linked by short poly peptides.
Gram positive bacteria have relatively simple walls composed of a thick layer of peptidoglycan.
Gram negative bacteria have less peptidoglycan and are more complex structurally. They have an outer membrane that contains lipopolysaccharides (normally toxic layer causes fever and shock). Gram negative bacteria are normally more resistant to antibiotics.
The cell wall of many prokaryotes is surrounded by a sticky layer of polysaccharide or protein, called the capsule or they may just have a sticky layer . Both versions allow prokaryotes to adhere to their substrate or other individuals. Some layers protect against dehydration and some shield pathogenic prokaryotes from hosts immune system.
Endospores
Resistant cells developed in some bacteria as way of withstanding harsh conditions. These are developed when they lack water or essential nutrients. The original cell produces a copy of its chromosome and surrounds that copy with a multi-layered structure, forming the endospore. Water is removed from the endospore and its metabolism halts. Original cell then lyses releasing the endospore.
Fimbriae
Some prokaryotes stick to their substrate or to one another by means of hair-like appendages, called fimbriae. The bacterium that causes gonorrhoea uses fimbriae to fasten itself to mucous membranes of its host. Usually shorter and more numerous the pili, appendages than pull two cells together prior to DNA transfer from one cell to the other.
Motility
About half of all prokaryotes are capable of taxis, a direct movement toward or away from a stimulus. Chemotaxis change their movement pattern in response to chemicals. They may move toward nutrients or oxygen (positive chemotaxis) or away from a toxic substance (negative taxis).
Motility (flagella)
Of various structures that help prokaryotes move, the most common is the flagella. They may be scattered over the entire surface or concentrated at one end. They are 1/10 in width and are typically not covered by the plasma membrane. Prokaryotic flagella differ to those found on eukaryotes, in the molecular and their mechanism of propulsion. Among prokaryotes, bacteria and archaeal flagella are similar in size and rotational mechanism, but are composed of different proteins.
